Other heat conversion technologies

Scout intake sheet

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Challenge description

Within the heat integration cluster of the Institute for Sustainable Process Technology (ISPT), the foundation is laid for a nationally supported cross-sectoral Integrated Circular Heat Program, in which innovation and practice are actively linked. Indeed, for a large number of companies in the agro-food, paper, chemical, horticultural and food sectors, heat is the biggest energy consumer. Therefore, heat technologies need to be vastly integrated to reach a carbon neutral heat supply for all temperature levels by 2050. As this knowledge is spread through various industries and discipline, ISPT wants to present to its partners an overview of the existing technologies that are linked with the (re-)use and storage of heat. This specific scouting case will focus on all the other techniques that can be used to recover process heat and are not related to heat storage, heat exchangers, heat pumps or heat transformers. It can for instance be a technique to convert waste heat to electricity as Organic Rankine Cycles. Criteria of interest are the efficiency and the temperatures.

Scope
Discover Demonstrate Develop Deploy
Current known technique(s)
  • Organic Rankine Cycle
Ideal outcome

A list of alternative technologies to recover process heat with their requirements and suppliers

Minimum viable outcome

A list of alternative technologies to recover process heat

Objective(s)
  • Temperature
  • Efficiency
Constraint(s)
  • Capacity
Functions
Action = [recover] OR [transform ] OR [recover]

Object = [heat] OR [heat] OR [waste heat]

Environment = [heat pumps (exclude)] OR [heat transformers (exclude)] OR [heat exchangers (exclude)] OR [electricity] OR [transformation] OR [power] OR [rankine cycle] OR [cycle] OR [heat conversion] OR [electricity production] OR [review] OR [thermoelectric] OR [thermoacoustic] OR [pyroelectric] OR [kalina] OR [thermal energy] OR [CO2] OR [adsorption] OR [brayton cycle] OR [supercritical co2]
Case Confirmation
Confirmed by
Comments

Preliminary Results

Concept Technology Selection
1. 1. Cycles used in heat conversion
Different (thermodynamic) cycles are possible for the conversion of thermal energy into mechnical energy or electricity.
1.1 1.1 Steam rankine cycle

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1.2 1.2 Organic rankine cycle

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1.3 1.3 Supercritical/transcritical CO2 rankine cycles

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1.4 1.4 Kalina cycle

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1.5 1.5 Stirling cycle

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1.6 1.6 Trilateral flash cycle

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2. 2. Solid-state generators for heat conversion
Solid state thermal to electrical energy converters are heat engines, or small generators, and energy harvesters capable of transforming heat directly into electricity. The governing physical principles with solid state thermal to electrical energy converters work over several orders of magnitude and enable the utilization of previously unexplored low grade thermal energy and waste heat. With solid state heat engines, small quantities of low grade thermal energy and waste heat, at temperatures just above ambient, can be directly converted into electrical power in the microwatt to milliwatt range. The generated electrical power allows to locally power a large number of small scale electronic devices as well as autonomous and self-sustaining applications, without the need for maintenance and additional costs.
2.1 2.1 Thermoelectric generator

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2.2 2.2 Thermionic energy converter (TEC)

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2.3 2.3 Thermomagnetic generators

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2.4 2.4 Pyroelectric generator

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2.5 2.5 Thermally regenerative battery

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2.6 2.6 Piezoelectric heat conversion

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3. 3. Oher heat conversion technologies
3.1 3.1 Thermoacoustic heat engine (TAHE)

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3.2 3.2 Water desalination

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3.3 3.3 Shape-memory metals/alloys

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Published 08/10/2019

Based on the case described above we have executed the first line of queries in IGOR^AI. The goal was to obtain a broad set of heat conversion technologies that transform heat. 3 concepts are distinguished based on the results: 1. Cycles used in heat conversion 2. Solid-state generators for heat conversion 3. Oher heat conversion technologies Every concept comprises multiple heat conversion technologies (15 in total). Below the table, short descriptions, research findings and sources per heat conversion technology are listed as well. You can use this information to get a better understanding of the heat conversion technology. During the midway meeting, we would like to discuss the heat conversion technologies and concepts, determine their relevance and select the top selection that needs to be deepened in the second phase of the project.

To determine which technologies are relevant to proceed to the next scouting phase you can play the technology selection game by clicking on the button below.

Concept Technology Selection
1. 1. Cycles used in heat conversion
Different (thermodynamic) cycles are possible for the conversion of thermal energy into mechnical energy or electricity.
1.1 1.1 Steam rankine cycle

0 of 0
1.2 1.2 Organic rankine cycle

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1.3 1.3 Supercritical/transcritical CO2 rankine cycles

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1.4 1.4 Kalina cycle

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1.5 1.5 Stirling cycle

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1.6 1.6 Trilateral flash cycle

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2. 2. Solid-state generators for heat conversion
Solid state thermal to electrical energy converters are heat engines, or small generators, and energy harvesters capable of transforming heat directly into electricity. The governing physical principles with solid state thermal to electrical energy converters work over several orders of magnitude and enable the utilization of previously unexplored low grade thermal energy and waste heat. With solid state heat engines, small quantities of low grade thermal energy and waste heat, at temperatures just above ambient, can be directly converted into electrical power in the microwatt to milliwatt range. The generated electrical power allows to locally power a large number of small scale electronic devices as well as autonomous and self-sustaining applications, without the need for maintenance and additional costs.
2.1 2.1 Thermoelectric generator

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2.2 2.2 Thermionic energy converter (TEC)

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2.3 2.3 Thermomagnetic generators

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2.4 2.4 Pyroelectric generator

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2.5 2.5 Thermally regenerative battery

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2.6 2.6 Piezoelectric heat conversion

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3. 3. Oher heat conversion technologies
3.1 3.1 Thermoacoustic heat engine (TAHE)

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3.2 3.2 Water desalination

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3.3 3.3 Shape-memory metals/alloys

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1. 1. Cycles used in heat conversion

Back

Different (thermodynamic) cycles are possible for the conversion of thermal energy into mechnical energy or electricity.


1.1 1.1 Steam rankine cycle

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A Rankine cycle is a closed-cycle system where a working fluid circulates through a minimum of an evaporator, turbine, condenser and a pump to convert heat into work, see figure. The evaporator can incorporate or be followed by a superheater if the working fluid/heat source temperature allow it. The conventional working fluid for Rankine cycle plants is water. [[Source]](https://www.dieselnet.com/tech/engine_whr_rankine.php) The most commonly used system for power generation from waste heat involves using the heat to generate steam in a waste heat boiler, which then drives a steam turbine. Steam rankine cycles are not very efficient and can only use higher temperature waste streams. Art. [#ARTNUM](#article-33275-2903781546)

1.1.1 1.1 Steam rankine cycle
A review of unconventional bottoming cycles for waste heat recovery: Part I – Analysis, design, and optimization
Abstract In this paper, an extensive overview of unconventional waste heat recovery power cycles is presented. The three-unconventional waste heat recovery bottoming cycles discussed in this paper are the air bottoming cycle, carbon dioxide-based power cycles and Kalina bottoming cycle. The review paper is divided into two parts; first part is about a detailed discussion of energy, exergy, economic analysis, as well as reviewing part load analysis, component design, power augmentation and comparative studies. Whereas, the second part of the review paper demonstrate and thoroughly review the applications of the aforementioned unconventional bottoming cycles, including renewable energy sources. According to the literature, it was found that the air bottoming cycle is not as competitive when compared to the conventional bottoming cycle, such as the steam Rankine cycle. Nevertheless, air bottoming cycle can be economically competitive for low system capacities. Furthermore, CO 2 power cycles have shown better performance in terms of energetic and exergetic analyses when compared to the conventional bottoming cycles. The transcritical and supercritical CO 2 power cycles excel to recover low and medium grade waste heat, respectively. Finally, Kalina bottoming cycle was found to be competitive to recover the low-grade waste heat when compared to organic Rankine cycle. In addition, optimizing the ammonia-water concentrations at different stages of the cycle has the most notable effect in improving the cycle’s performance.
12/01/2018 00:00:00
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1.1.2 1.1 Steam rankine cycle
Investigation of a cascade waste heat recovery system based on coupling of steam Rankine cycle and NH 3 -H 2 O absorption refrigeration cycle
Abstract Cogeneration system based on cascade utilization of heat has been proved to be a promising technology to enhance energy conversion efficiency. An electricity-cooling cogeneration system (ECCS) based on coupling of a steam Rankine cycle (SRC) and an absorption refrigeration system (ARS) is proposed to recover the waste heat of marine engine to meet the electricity and cooling demand aboard. The SRC absorbed heat from the exhaust gas of engine to generate electricity, and the ARS makes use of the condensation heat of SRC to provide cooling needed on ship. Electricity output, cooling capacity, equivalent electricity output, exergy efficiency, and equivalent thermal efficiency are adopted to evaluate the performance of ECCS. The simulation results indicate that recovering the expansion work in the absorption refrigeration cycle is an effective way to increase electricity output at the cost of decreasing cooling capacity. The equivalent electricity output of the WHR system is 5223 kW, accounting for 7.61% of the rated power output of the marine engine.
06/01/2018 00:00:00
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1.2 1.2 Organic rankine cycle

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The Organic Rankine Cycle (ORC) is named for its use of an organic, high molecular mass fluid with a liquid-vapor phase change, or boiling point, occurring at a lower temperature than the water-steam phase change. The fluid allows Rankine cycle heat recovery from lower temperature sources such as biomass combustion, industrial waste heat, geothermal heat, solar ponds etc. The low-temperature heat is converted into useful work, that can itself be converted into electricity. [[Wiki]](https://en.wikipedia.org/wiki/Organic_Rankine_cycle) There are several configurations and several working fluids possible for organic rankine cycles. **Research findings:** - Organic working fluids because of the lower boiling points compared to water, make it possible to recover energy from low temperature waste heat sources. The thermal efficiency of an ORC system depends on the thermodynamic properties of the working fluid and operating conditions of heat source, sink and cycle. Generally, the range of average thermal efficiency of an ORC system is from 0.02 to 0.19, and for small systems (lower than 5 kW) has lower thermal efficiency. Waste heat recoveries/efficiencies are between 5 and 40% depending on configuration and working fluids, using waste temperatures between 50 and 280 degreesC. [#ARTNUM](#article-29721-1966156747)

1.2.1 1.2 Organic rankine cycle
A proposed coal-to-methanol process with CO2 capture combined Organic Rankine Cycle (ORC) for waste heat recovery
Abstract Coal-to-methanol (CTM) is the main methanol production process in China. Application of carbon capture and storage (CCS) technology in CTM is a possible way for CO 2 reduction. However, the increase of energy consumption caused by CCS and related increase of Green House Gas footprint has to be minimised. This paper presents a CTM combined with CO 2 capture and Organic Rankine Cycle (ORC) power generation, which improves energy efficiency simultaneously. The electricity generated from ORC is through the thermodynamic cycle converted the waste heat recovered from the CO 2 compression and water gas shift unit in CTM process. The proposed process is simulated and analysed from energy efficiency and economic viewpoints. The analysis indicates several points: (1) Heat Integration of CO 2 compression and water gas shift unit produce the heated water as the heat source of ORC; (2) With the CO 2 ratio of 60%, the energy efficiency of the proposed CTM combined ORC system is 45.5%; (3) From economic point of view, electricity generated from waste heat conversion is around 4.8 MW, and the payback period of the ORC invested in CTM with CO 2 capture process is 2.7 y.
08/01/2016 00:00:00
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1.2.2 1.2 Organic rankine cycle
A recent review of waste heat recovery by Organic Rankine Cycle
Abstract The increment of using fossil fuels has caused many perilous environmental problems such as acid precipitation, global climate change and air pollution. More than 50% of the energy that is used in the world is wasted as heat. Recovering the wasted heat could increase the system efficiency and lead to lower fuel consumption and CO2 production. Organic Rankine cycle (ORC) which is a reliable technology to efficiently convert low and medium temperature heat sources into electricity, has been known as a promising solution to recover the waste heat. There are numerous studies about ORC technology in a wide range of application and condition. The main objective of this paper is to presents a review of studies both theoretical and experimental on ORC usage for waste heat recovery and investigation on the effect of cycle configuration, working fluid selection and operating condition on the system performance, that have been developed during the last four years. Finally, the related statistics are reported and compared regarding the configuration and the employed working fluid with type of the heat source.
10/01/2018 00:00:00
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1.2.3 1.2 Organic rankine cycle
A review of thermodynamic cycles used in low temperature recovery systems over the last two years
This review explores the potential of low and medium grade heat in different thermodynamic cycles used to transform wasted heat into mechanical work. The aim of this review is to study the state of the art of the thermodynamic cycles used to recover low-grade heat. The relevance of researching low grade heat or waste heat applications is that a vast amount of heat energy is available at negligible cost within the range of medium and low temperatures, with the drawback that existing thermal cycles cannot make efficient use of such available low temperature heat due to their low efficiency. The different types of Organic Rankine Cycles have been reviewed, highlighting their relevant characteristics where Simple Organic Rankine Cycle, Regenerative Organic Rankine Cycle, Cascade Organic Rankine Cycle, Organic Flash Cycles, Other Rankine Configurations and Trilateral Cycles are included. Reviews were conducted of specific applications of the low-grade heat recovery. In contrast, there are no actual publications which summarise the current state of the art of the thermodynamic cycles used to convert wasted heat into mechanical power. This paper offers a different approach and analyses low-grade heat recovery from a thermodynamic point of view and compares their efficiency. The analysis shows that cycles using closed processes are by far the most efficient published thermal cycles for low-grade heat recovery. Rankine cycles reviewed show similar low efficiencies. In contrast, closed process cycles have a configuration, which allows efficient exploitation of low-grade heat.
01/01/2018 00:00:00
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1.2.4 1.2 Organic rankine cycle
Heat Conversion into Power Using Small Scale Organic Rankine Cycles
The world economy heavily relies on fossil fuels. Their use leads to carbon dioxide emissions responsible of global warming and fuels international tensions. Renewable energy sources and energy efficiency are alternatives. An Organic Rankine Cycle is similar to a steam cycle but uses an organic fluid instead of water. It is suitable for conversion of solar radiation, geothermal energy, biomass energy, ocean thermal gradient, and waste heat into power. Although investigated in the 1970s, it was soon abandoned after the oil crisis. With the growing concern on the environment, the interest for this technology for electricity generation was renewed. The technology for medium and large scale systems is already mature but solutions are still sought for small systems. This book presents results of investigation on micro organic Rankine cycles of less than 2 kW power output. Overview of different organic Rankine cycle applications, working fluid selection, cycle performance analysis, and economic evaluation constitute the content of the book and will be useful to energy professionals, researchers working on thermodynamics and those interested in next generation power systems.
10/24/2012 00:00:00
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1.2.5 1.2 Organic rankine cycle
Low-grade heat conversion into power using organic Rankine cycles – A review of various applications
An organic Rankine cycle (ORC) machine is similar to a conventional steam cycle energy conversion system, but uses an organic fluid such as refrigerants and hydrocarbons instead of water. In recent years, research was intensified on this device as it is being progressively adopted as premier technology to convert low-temperature heat resources into power. Available heat resources are: solar energy, geothermal energy, biomass products, surface seawater, and waste heat from various thermal processes. This paper presents existing applications and analyzes their maturity. Binary geothermal and binary biomass CHP are already mature. Provided the interest to recover waste heat rejected by thermal devices and industrial processes continue to grow, and favorable legislative conditions are adopted, waste heat recovery organic Rankine cycle systems in the near future will experience a rapid growth. Solar modular power plants are being intensely investigated at smaller scale for cogeneration applications in buildings but larger plants are also expected in tropical or Sahel regions with constant and low solar radiation intensity. OTEC power plants operating mainly on offshore installations at very low temperature have been advertised as total resource systems and interest on this technology is growing in large isolated islands.
10/01/2011 00:00:00
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1.2.6 1.2 Organic rankine cycle
Organic Rankine Cycle Working Fluid Selection and Performance Analysis for Combined Application With a 2 MW Class Industrial Gas Turbine
The selection of suitable working fluids for use in Organic Rankine Cycles (ORC) is strongly addicted to the intended application of the ORC system. The design of the ORC, the kind of heat source and the ambient condition has an influence on the performance of the Organic Rankine Cycle and on the selection of the working fluid. It can come to a discrepancy between the best candidate from the thermodynamic point of view and the transformation into a real machine design. If an axial turbine design is considered for expansion and energy conversion within the ORC, the vapor volume flow ratios within the expansion path, the pressure ratio and of course the number of stages have to be considered within the fluid selection process and for the design parameters. Furthermore, environmental aspects have to be taken into account, e.g. the global warming potential (GWP) and the flammability of the selected fluid.This paper shows the results of the design and fluid selection process for an Organic Rankine Cycle for application in a combined operation with a 2MW class industrial gas turbine.The gas turbine contains two radial compressor stages with an integrated intercooler. To further increase the thermal cycle efficiency, a recuperator has been implemented to the gas turbine cycle, which uses the exhaust gas waste heat to preheat the compressed air after the second compressor, before it enters the combustion chamber. The shaft power is generated by a three stage axial turbine, whereby the first stage is a convection cooled stage, due to a turbine inlet temperature of 1100°C.To further increase the electrical efficiency and the power output of the energy conversion cycle, a combined operation with an organic Rankine cycle is intended. Therefore the waste heat from the GT compressor intercooler is used as first heat source and the waste heat of the exhaust gas after the recuperator as second heat source for the Organic Rankine Cycle. It is intended that the ORC fluid acts as heat absorption fluid within the compressor intercooler. Due to these specifications for the ORC, a detailed thermodynamic analysis has been performed to determine the optimal design parameter and the best working fluid for the ORC, in order to obtain a maximum power output of the combined cycle.Due to the twice coupling of the ORC to the GT cycle, the heat exchange between the two cycles is bounded by each other and a detailed analysis of the coupled cycles is necessary. E.g. the ambient temperature has an enormous influence on the transferred heat from the intercooler to the ORC cycle, which itself affects the heat transfer and temperatures of the transferable heat from the second heat source. Thus, a detailed analysis by considering the ambient operation conditions has been performed, in order to provide a most efficient energy conversion system over a wide operation range.The performance analysis has shown that by application of an ORC for a combined operation with the intercooled and recuperated gas turbine, the combined cycle efficiency can be increased, for a wide ambient conditions range, by more than 3 %pts. and the electrical power output by more than 10 %, in comparison to the stand alone intercooled and recuperated gas turbine.Copyright © 2014 by ASME
06/16/2014 00:00:00
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1.2.7 1.2 Organic rankine cycle
Vapor Rankine and organic Rankine combined cycle electricity generation device
The utility model relates to a vapor Rankine and organic Rankine combined cycle electricity generation device. Organic working media in an organic Rankine cycle are used for cooling vapor in a vapor Rankine cycle, latent heat of vaporization of the vapor in the vapor Rankine cycle is recovered to be used for electricity generation of the organic Rankine cycle, and accordingly the vapor Rankine cycle and the organic Rankine cycle are compounded together to form the enforceable combined cycle device. Meanwhile, the safety difficult problem that the organic Rankine cycle recovers waste heat of exhaust gas is solved, the exhaust gas temperature is effectively reduced, low-temperature corrosion of the exhaust gas is avoided, and waste gas, waste water and waste heat of waste vapor in a vapor Rankine cycle system can be recycled effectively. The vapor Rankine and organic Rankine combined cycle electricity generation device not only can be used for energy-saving transformation of an existing set, but also can be used for design and construction of a new set, especially is suitable for new construction, extension and rebuilding of an electricity generation set in areas such as severe cold areas, water-deficient areas and electricity-deficient areas, and is significant in economic benefits, social benefits and environment protection benefits.
07/31/2013 00:00:00
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1.3 1.3 Supercritical/transcritical CO2 rankine cycles

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In supercritical Rankine cycle (Figure), a stream of the working fluid is pumped above its critical pressure (1–2), and then heated isobarically from liquid directly to supercritical vapor (2–3); the supercritical vapor is expanded in the turbine to extract mechanical work (3–4); after expansion, the fluid is condensed in the condenser by dissipating heat to a heat sink (4–1); the condensed liquid is then pumped to the high pressure again, which completes the cycle. A basic supercritical CO2 Rankine cycle consists of gas heater, expansion turbine, condenser and pump. Art. [#ARTNUM](#article-29717-1999416566) Besides CO2 there are other working fluids that could be used for a supercritical rankine cycle, but they remain largely unexplored. The temperature glide for CO2 above the critical point allows for a better matching to the heat source temperature glide than an organic working fluid working below the critical point. Therefore, the so-called pinching problem, which may occur in ORC׳s counter current heat exchanger, can be avoided by carbon dioxide transcritical power cycle. Compared to organic and steam-based Rankine Cycle systems, supercritical CO2 Rankine cycle can achieve high efficiencies (upto 30% higher) over a wide temperature range of heat sources with compact components resulting in a smaller system footprint, lower capital and operating costs. Art. [#ARTNUM](#article-29717-1999416566)

1.3.1 1.3 Supercritical/transcritical CO2 rankine cycles
A review of unconventional bottoming cycles for waste heat recovery: Part I – Analysis, design, and optimization
Abstract In this paper, an extensive overview of unconventional waste heat recovery power cycles is presented. The three-unconventional waste heat recovery bottoming cycles discussed in this paper are the air bottoming cycle, carbon dioxide-based power cycles and Kalina bottoming cycle. The review paper is divided into two parts; first part is about a detailed discussion of energy, exergy, economic analysis, as well as reviewing part load analysis, component design, power augmentation and comparative studies. Whereas, the second part of the review paper demonstrate and thoroughly review the applications of the aforementioned unconventional bottoming cycles, including renewable energy sources. According to the literature, it was found that the air bottoming cycle is not as competitive when compared to the conventional bottoming cycle, such as the steam Rankine cycle. Nevertheless, air bottoming cycle can be economically competitive for low system capacities. Furthermore, CO 2 power cycles have shown better performance in terms of energetic and exergetic analyses when compared to the conventional bottoming cycles. The transcritical and supercritical CO 2 power cycles excel to recover low and medium grade waste heat, respectively. Finally, Kalina bottoming cycle was found to be competitive to recover the low-grade waste heat when compared to organic Rankine cycle. In addition, optimizing the ammonia-water concentrations at different stages of the cycle has the most notable effect in improving the cycle’s performance.
12/01/2018 00:00:00
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1.3.2 1.3 Supercritical/transcritical CO2 rankine cycles
A thermodynamic analysis and economic assessment of a modified de-carbonization coal-fired power plant incorporating a supercritical CO2 power cycle and an absorption heat transformer
Abstract An improved de-carbonization coal-fired power plant configuration incorporating a supercritical CO 2 (S-CO 2 ) power cycle and an absorption heat transformer (AHT) was proposed. The adopted S-CO 2 power cycle efficiently absorbs the process waste heat within the CO 2 capture process to drive a S-CO 2 turbine to produce work, and the exhaust S-CO 2 is beneficially utilized to preheat the air prior to the air preheater, saving a part of the flue gas energy, which can then be absorbed by the low-temperature economizer (LTE). An AHT is employed here to recover the remaining waste heat within the CO 2 capture unit to vaporize the reboiler condensate for solvent regeneration. The mass and energy balance and the overall performance of the proposed system were determined by the developed models and process simulation. The detailed energy/exergy distributions of the reference and proposed plants were also investigated. Finally, the economics of the proposed system were assessed by the cost of electricity (COE) and the cost of CO 2 avoided (COA). Results showed that the energy/exergy efficiency could reach 34.38% and 33.36%, respectively, better than the reference plant. The COE and COA of the proposed system were $92.21/MWh and $46.27/t CO 2 , also showing an advantage over the reference one.
05/01/2019 00:00:00
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1.3.3 1.3 Supercritical/transcritical CO2 rankine cycles
An improved CO2-based transcritical Rankine cycle (CTRC) used for engine waste heat recovery
CO2-based transcritical Rankine cycle (CTRC) is a promising technology for the waste heat recovery of an engine considering its safety and environment friendly characteristics, which also matchs the high temperature of the exhaust gas and satisfies the miniaturization demand of recovery systems. But the traditional CTRC system with a basic configuration (B-CTRC) has a poor thermodynamic performance. This paper introduces an improved CTRC system containing both a preheater and regenerator (PR-CTRC), for recovering waste heat in exhaust gas and engine coolant of an engine, and compares its performance with that of the B-CTRC system and also with that of the traditional excellent Organic Rankine Cycle (ORC) systems using R123 as a working fluid. The utilization rate of waste heat, total cooling load, net power output, thermal efficiency, exergy loss, exergy efficiency and component size have been investigated. Results show that, the net power output of the PR-CTRC could reach up to 9.0kW for a 43.8kW engine, which increases by 150% compared with that of the B-CTRC (3.6kW). The PR-CTRC also improves the thermal efficiency and exergy efficiency of the B-CTRC, with increases of 184% and 227%, respectively. Compared with the ORC system, the PR-CTRC shows the significant advantage of highly recycling the exhaust gas and engine coolant simultaneously due to the special property of supercritical CO2’s specific heat capacity. The supercritical property of CO2 also generates a better heat transfer and flowing performances. Meanwhile, the PR-CTRC possesses a smaller SP (0.010–0.020m) than that of R123 systems (0.055–0.070m). Therefore, the PR-CTRC system is suitable for the waste heat recovery of an engine, especially for recovering both high-grade and low-grade waste heat.
08/01/2016 00:00:00
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1.3.4 1.3 Supercritical/transcritical CO2 rankine cycles
Configurations selection maps of CO2-based transcritical Rankine cycle (CTRC) for thermal energy management of engine waste heat
CO2-based transcritical Rankine cycle (CTRC) can be used for the waste heat recovery due to its safety and environment-friendly characteristics, and also fits for the high temperature of exhaust gas and satisfy the miniaturization demand of recovery systems. It can provide a reasonable pathway toward thermal energy management of engine. This work proposes novel configurations selection maps of four CTRC configurations for waste heat recovery of engines. Except for considering a regenerator added to traditional CTRC (basic CTRC) recovering exhaust waste heat, a preheater driven by engine coolant will be also taken into account in this paper. Thus, the four configurations include the basic CTRC (B-CTRC), the CTRC with a preheater (P-CTRC), the CTRC with a regenerator (R-CTRC) and the CTRC with both of the preheater and the regenerator (PR-CTRC). As different CTRC configurations have advantage of performance indicators under different conditions, and the focused indicators may also be various with applications, this paper focuses on proposing a kind of selection maps, which is used for the selection of the four CTRC configurations in the field of engine waste heat recovery. Comprehensive performance comparison are researched in this paper from three aspects, net power output based on the first law of thermodynamics, exergy efficiency based on the second law of thermodynamics and electricity production cost (EPC) as an indicator of the economic performance. After the comparative analysis, three selection maps separately based on the three performance indicators are proposed to give the selection reference of the CTRC configurations under different design conditions, which refer to turbine inlet pressure and temperature in this paper. It is meaningful for the design and operating of the CTRC configuration used for waste heat recovery of engines. Besides, it can also be a new method that can be expanded to other recovery system selection (e.g. ORCs) in engine field or other fields (e.g. solar, geothermal).
01/01/2017 00:00:00
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1.3.5 1.3 Supercritical/transcritical CO2 rankine cycles
Exergoeconomic analysis of utilizing the transcritical CO2 cycle and the ORC for a recompression supercritical CO2 cycle waste heat recovery: A comparative study
Two combined cogeneration cycles are examined in which the waste heat from a recompression supercritical CO2 Brayton cycle (sCO2) is recovered by either a transcritical CO2 cycle (tCO2) or an Organic Rankine Cycle (ORC) for generating electricity. An exergoeconomic analysis is performed for sCO2/tCO2 cycle performance and its comparison to the sCO2/ORC cycle. The following organic fluids are considered as the working fluids in the ORC: R123, R245fa, toluene, isobutane, isopentane and cyclohexane. Thermodynamic and exergoeconomic models are developed for the cycles on the basis of mass and energy conservations, exergy balance and exergy cost equations. Parametric investigations are conducted to evaluate the influence of decision variables on the performance of sCO2/tCO2 and sCO2/ORC cycles. The performance of these cycles is optimized and then compared. The results show that the sCO2/tCO2 cycle is preferable and performs better than the sCO2/ORC cycle at lower PRc. When the sCO2 cycle operates at a cycle maximum pressure of around 20MPa (∼2.8 of PRc), the tCO2 cycle is preferable to be integrated with the recompression sCO2 cycle considering the off-design conditions. Moreover, contrary to the sCO2/ORC system, a higher tCO2 turbine inlet temperature improves exergoeconomic performance of the sCO2/tCO2 cycle. The thermodynamic optimization study reveals that the sCO2/tCO2 cycle has comparable second law efficiency with the sCO2/ORC cycle. When the optimization is conducted based on the exergoeconomics, the total product unit cost of the sCO2/ORC is slightly lower than that of the sCO2/tCO2 cycle.
05/01/2016 00:00:00
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1.3.6 1.3 Supercritical/transcritical CO2 rankine cycles
High-Temperature Receiver Designs for Supercritical CO2 Closed-Loop Brayton Cycles
High-temperature receiver designs for solar powered supercritical CO2 Brayton cycles that can produce ∼1 MW of electricity are being investigated. Advantages of a supercritical CO2 closed-loop Brayton cycle with recuperation include high efficiency (∼50%) and a small footprint relative to equivalent systems employing steam Rankine power cycles. Heating for the supercritical CO2 system occurs in a high-temperature solar receiver that can produce temperatures of at least 700 °C. Depending on whether the CO2 is heated directly or indirectly, the receiver may need to withstand pressures up to 20 MPa (200 bar). This paper reviews several high-temperature receiver designs that have been investigated as part of the SERIIUS program. Designs for direct heating of CO2 include volumetric receivers and tubular receivers, while designs for indirect heating include volumetric air receivers, molten-salt and liquid-metal tubular receivers, and falling particle receivers. Indirect receiver designs also allow storage of thermal energy for dispatchable electricity generation. Advantages and disadvantages of alternative designs are presented. Current results show that the most viable options include tubular receiver designs for direct and indirect heating of CO2 and falling particle receiver designs for indirect heating and storage.Copyright © 2014 by ASME
06/30/2014 00:00:00
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1.3.7 1.3 Supercritical/transcritical CO2 rankine cycles
Hybrid type supercritical CO2 power generation system
The present invention relates to a hybrid power generation system, in which a supercritical carbon dioxide power generation system generating electric energy by using supercritical carbon dioxide as operation fluid and a cogeneration system generating thermal energy and electric energy by burning fuel are mixed, comprises at least one pump which circulates the operation fluid; at least one recuperator which primarily heats the operation fluid passing through the pump; at least one heat exchanger which reheats the operation fluid heated by the recuperator by using waste heat as a heat source; a plurality of turbines which are driven by the operation fluid reheated by the heat exchanger; and a complex heat exchanger which exchanges between heating water of the cogeneration system and the operation fluid to heat the heating water and to cool the operation fluid. The operation fluid passing through the turbine exchanges heat with the operation fluid passing through the pump to be cooled, and is supplied to the complex heat exchanger. The supercritical carbon dioxide power generation system and the cogeneration system share the complex heat exchanger. According to the present invention, there is an advantage of improving efficiency of electricity generation and heating heat generation by integrally operating the supercritical carbon dioxide power generation and cogeneration. In addition, heat efficiency of a power generation cycle is improved, and it is possible to actively cope with power demand since it varies seasonally.
04/12/2018 00:00:00
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1.3.8 1.3 Supercritical/transcritical CO2 rankine cycles
Performance improvement of a preheating supercritical CO2 (S-CO2) cycle based system for engine waste heat recovery
Abstract Due to the compact structure in addition to the system safety level and environmental friendly characteristics, supercritical CO 2 (S-CO 2 ) cycle has emerged as a promising method to be used in engine waste heat recovery. This paper explores the potential of using a preheating S-CO 2 cycle based system to recover the waste heat of a diesel engine. An original preheating system is presented, in which the high temperature engine exhaust gas is firstly utilized in the evaporator and then it is further cooled through preheating process together with the low temperature jacket cooling water. Though the entire heat load from these two heat sources could be entirely recovered, the high preheating temperature suppresses the heat transfer in the regenerator. An improved preheating S-CO 2 cycle based system with a regeneration branch is then presented. S-CO 2 flow from the compressor is divided into two parts, one of which is still preheated by the jacket cooling water and the cooled engine exhaust gas in series while the other is heated in a low temperature regenerator. The two flows converge and then continues to be heated in the high temperature regenerator and in the evaporator. The simulation results reveal that the improved system could achieve a deeper utilization of the regeneration heat load hence improve the system performance. The maximum net power output of the improved system reaches 68.4 kW, which is 7.4% higher than that of the original system, 63.7 kW. Adopting the improved preheating S-CO 2 cycle based system for waste heat recovery, the engine power output (996 kW) can be increased by 6.9%.
04/01/2018 00:00:00
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1.3.9 1.3 Supercritical/transcritical CO2 rankine cycles
Review and future trends of supercritical CO2 Rankine cycle for low-grade heat conversion
Due to personal and environmental safeties along with various advantages, CO2 became a potential choice as working fluid for both heat engine and heat pump cycles. Because of better temperature glide matching between heat source and working fluid during heat addition leading to no pinch limitation, CO2 has been proposed recently as working fluid for supercritical Rankine cycle with low grade heat sources. Supercritical Rankine cycle and its various working fluids, heat sources, heat sinks and analysis approaches, and performance analyses and optimization of various supercritical CO2 Rankine cycle configurations along with comparison with other working fluids, prototype development, component design and challenges are well-grouped and discussed. Supercritical CO2 Rankine cycle is superior to both steam and organic Rankine cycles, whereas yields mix results compared to other fluids in supercritical Rankine cycle with system compactness and environmental benefit as unique advantages. Future research pathways regarding to system components, experimentation, operating parameter optimizations, control strategies, etc. are discussed as well. Although, there is no supercritical CO2 Rankine cycle in operation up to now, it is becoming a future pathway due to its promising research outcomes and this review will be useful for further progress.
08/01/2015 00:00:00
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1.3.10 1.3 Supercritical/transcritical CO2 rankine cycles
Supercritical CO2 Power Cycle Developments and Commercialization: Why sCO2
The U.S. DOE estimates that 280,000 MW discharged annually in the U.S. as waste heat could be recycled as usable energy to provide 20 percent of U.S. electricity needs while slashing GHG by 20 percent and saving USD $70-150B per year on energy costs. Waste heat can be considered as the other green energy because it is a renewable energy equivalent resource that improves energy efficiency from existing fossil fuel usage, while reducing grid demand by converting the recovered heat into usable electricity, heating and/or cooling. While various sources of independent data suggest that this waste heat recovery opportunity is valued at over USD $600B for the U.S. market, similar large opportunities exist worldwide. Echogen Power Systems LLC (Akron, OH U.S.A.) is developing power generation technologies that transform heat from waste and renewable energy sources into electricity and process heat. The thermal engine technology; the Thermafficient ® Heat Engine converts waste heat to power using a breakthrough supercritical CO2-based power cycle. Compared to organic and steam-based Rankine Cycle systems, supercritical CO2 can achieve high efficiencies over a wide temperature range of heat sources with compact components resulting in a smaller system footprint, lower capital and operating costs. The Levelized Cost of Electricity (LCOE) is calculated at an average USD $0.025 per kWh for the CO2-based heat engine and averages at USD $0.065 per kWh for a complete combined cycle gas turbine system utilizing the supercritical CO2 heat engine for bottom cycling. This paper presents an exemplary trade study comparison between the CO2 and steam-based heat recovery systems. An update is also provided for the Echogen 250 kW demonstration thermal engine which completed initial testing at the American Electric Power’s research center during 2011. Also presented is current status of long term testing with this system at a commercial district heating organization, and a multi-megawatt heat engine that will be installed at a U.S. customer host site during 2013.
01/01/2012 00:00:00
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1.4 1.4 Kalina cycle

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It uses a solution of 2 fluids with different boiling points for its working fluid. Since the solution boils over a range of temperatures as in distillation, more of the heat can be extracted from the source than with a pure working fluid. The same applies on the exhaust (condensing) end. This provides efficiency comparable to a Combined cycle, with less complexity. [[Wiki]](https://en.wikipedia.org/wiki/Kalina_cycle) By appropriate choice of the ratio between the components of the solution, the boiling point of the working solution can be adjusted to suit the heat input temperature. Water and ammonia is the most widely used combination, but other combinations are feasible. In the 1980s, Kalina proposed a thermodynamic power cycle with high thermoelectric efficiency using ammonia-water as the working medium. It is suitable for using in low and medium-temperature heat sources and small-power demand. The ammonia gas is volatilized of the mixed working fluid during the heating. The reduction of residual liquid concentration increases the saturated vapor pressure, and the system is more flexible than zeotropic evaporation. The schematic diagram is shown in the figure. Art. [#ARTNUM](#article-33257-2902891177) In the second figure: The super-heated ammonia-water solution at state 1, which gains its heat from a boiler, heat recovery exchanger, or a renewable energy source, expands in a turbine for power generation. The expanded working solution then recovers some of its heat to other streams via two recuperators. At state 4, the working solution is mixed with a lean liquid (low ammonia concentration) to dilute the mixture before entering the first stage condenser at state 5. The basic solution exiting the mixer enters the condenser to cool down and then pumped by a low-pressure pump to a splitter at state 7. The splitter splits a part of the basic solution to get preheated in a heat exchanger before entering the separator at state 10. The separator separates the solution into lean liquid (low ammonia concentration) at state 12 and rich vapor (high ammonia concentration) at state 11. The lean liquid goes to the first mixer mentioned earlier to dilute the working mixture at stage 5 before it enters the first stage condenser. Whereas the rich vapor goes to the second mixer to recover back the ammonia concentration at stage 14 before entering the second stage condenser. At stage 15, the working solution gets pumped in a high-pressure pump at stage 16, which then recovers some of the heat rejected from the steam turbine at stage 17 before it gets superheated from the heat source to repeat the process again. Art. [#ARTNUM](#article-33257-2903781546)

1.4.1 1.4 Kalina cycle
A review of low-temperature heat recovery technologies for industry processes
Abstract The amount of low-temperature heat generated in industrial processes is high, but recycling is limited due to low grade and low recycling efficiency, which is one of the reasons for low energy efficiency. It implies that there is a great potential for low-temperature heat recovery and utilization. This article provided a detailed review of recent advances in the development of low-temperature thermal upgrades, power generation, refrigeration, and thermal energy storage. The detailed description will be given from the aspects of system structure improvement, work medium improvement, and thermodynamic and economic performance evaluation. It also pointed out the development bottlenecks and future development trends of various technologies. The low-temperature heat combined utilization technology can recover waste heat in an all-round and effective manner, and has great development prospects.
11/01/2018 00:00:00
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1.4.2 1.4 Kalina cycle
A review of unconventional bottoming cycles for waste heat recovery: Part I – Analysis, design, and optimization
Abstract In this paper, an extensive overview of unconventional waste heat recovery power cycles is presented. The three-unconventional waste heat recovery bottoming cycles discussed in this paper are the air bottoming cycle, carbon dioxide-based power cycles and Kalina bottoming cycle. The review paper is divided into two parts; first part is about a detailed discussion of energy, exergy, economic analysis, as well as reviewing part load analysis, component design, power augmentation and comparative studies. Whereas, the second part of the review paper demonstrate and thoroughly review the applications of the aforementioned unconventional bottoming cycles, including renewable energy sources. According to the literature, it was found that the air bottoming cycle is not as competitive when compared to the conventional bottoming cycle, such as the steam Rankine cycle. Nevertheless, air bottoming cycle can be economically competitive for low system capacities. Furthermore, CO 2 power cycles have shown better performance in terms of energetic and exergetic analyses when compared to the conventional bottoming cycles. The transcritical and supercritical CO 2 power cycles excel to recover low and medium grade waste heat, respectively. Finally, Kalina bottoming cycle was found to be competitive to recover the low-grade waste heat when compared to organic Rankine cycle. In addition, optimizing the ammonia-water concentrations at different stages of the cycle has the most notable effect in improving the cycle’s performance.
12/01/2018 00:00:00
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1.4.3 1.4 Kalina cycle
The Kalina cycle for cement kiln waste heat recovery power plants
Cement production is one of the most energy intensive industrial processes in the world. In many world regions, energy cost is 50% to 60% of the direct production cost of cement. Energy cost is incurred due to the need for large quantities of thermal heat for the kiln, calcination and drying processes and electrical energy for operation of motors for grinding mills, fans, conveyers and other motor driven process equipment. The Kalina Cycle/spl reg/ utilizes the waste heat from the cement production process to generate electrical energy with no additional fuel consumption, and reduces the cost of electric energy for cement production. The thermal efficiency improvement of the Kalina Cycle is 20% to 40% in comparison with conventional waste heat power plants that utilize the hot gases available in a cement plant. A Kalina Cycle power plant offers the best environmentally friendly alternative for power generation from low-grade waste heat. It maximizes kW-hrs generated using a closed loop system to recover heat for electricity production without hazard to the environment. The Kalina Cycle uses a mixture of ammonia and water as its working fluid; a common solution used extensively world wide for refrigeration plants. In the event of an accidental release, ammonia is considered a biodegradable fluid. It does not contribute to photochemical smog, global pollution or global warming; and will not deplete the ozone layer. Its use as an industrial fluid is well documented with a proven track record for safety in industrial plants. This paper is a summary of Kalina Cycle Technology for cement plant waste heat applications. Specific plant designs are referenced to present a summary of the power plant systems and to describe the financial advantages of the Kalina Cycle waste heat power plant to the cement plant owner.
01/01/2005 00:00:00
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1.5 1.5 Stirling cycle

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Due to the great capability of recovering low-grade heat with potentially high efficiencies, Stirling cycle engines have attracted increasing attention in recent decades. They operate with a closed regenerative thermodynamic cycle that has the same theoretical thermal efficiency of the Carnot cycle. The compressible working fluid in a Stirling cycle engine, such as air, helium, hydrogen, nitrogen, etc., experiences periodical compression and expansion at different temperature levels to convert thermal energy into mechanical work. The lack of valves and absence of periodic explosions in Stirling cycle engines enable them to be operated more quietly than other piston engines. In Stirling cycle engines, the thermal energy is externally supplied through recuperative heat exchangers. Therefore, they have a great flexibility to be powered by any kind of heat sources at any temperature levels. The Stirling cycle engines working at low and moderate temperatures with simple constructions and low costs have a wide application prospect for recovering small-scale distributed low-grade thermal energy. Art. [#ARTNUM](#article-33278-2346231020)

1.5.1 1.5 Stirling cycle
Review of low-temperature vapour power cycle engines with quasi-isothermal expansion
External combustion heat cycle engines convert thermal energy into useful work. Thermal energy resources include solar, geothermal, bioenergy, and waste heat. To harness these and maximize work output, there has been a renaissance of interest in the investigation of vapour power cycles for quasi-isothermal (near constant temperature) instead of adiabatic expansion. Quasi-isothermal expansion has the advantage of bringing the cycle efficiency closer to the ideal Carnot efficiency, but it requires heat to be transferred to the working fluid as it expands. This paper reviews various low-temperature vapour power cycle heat engines with quasi-isothermal expansion, including the methods employed to realize the heat transfer. The heat engines take the form of the Rankine cycle with continuous heat addition during the expansion process, or the Stirling cycle with a condensable vapour as working fluid. Compared to more standard Stirling engines using gas, the specific work output is higher. Cryogenic heat engines based on the Rankine cycle have also been enhanced with quasi-isothermal expansion. Liquid flooded expansion and expander surface heating are the two main heat transfer methods employed. Liquid flooded expansion has been applied mainly in rotary expanders, including scroll turbines; whereas surface heating has been applied mainly in reciprocating expanders.
06/01/2014 00:00:00
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1.5.2 1.5 Stirling cycle
Stirling cycle engines for recovering low and moderate temperature heat: A review
A review is presented for the research development of Stirling cycle engines for recovering low and moderate temperature heat. The Stirling cycle engines are categorized into four types, including kinetic, thermoacoustic, free-piston, and liquid piston types. The working characteristics, features, technological details, and performances of the related Stirling cycle engines are summarized. Upon comparing the available experimental results and the technology potentials, the research directions and the possible applications of different Stirling cycle engines are further discussed and identified. It is concluded that kinetic Stirling engines and thermoacoustic engines have the greatest application prospect in low and moderate temperature heat recoveries in terms of output power scale, conversion efficiency, and costs. In particular, kinetic Stirling engines should be oriented toward two directions for practical applications, including providing low-cost solutions for low temperatures, and moderate efficient solutions with moderate costs for medium temperatures. Thermoacoustic engines for low temperature applications are especially attractive due to their low costs, high efficiencies, superior reliabilities, and simplicities over the other mechanical Stirling engines. This work indicates that a cost effective Stirling cycle engine is practical for recovering small-scale distributed low-grade thermal energy from various sources.
09/01/2016 00:00:00
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1.6 1.6 Trilateral flash cycle

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In a TFC system, heat gain is achieved without phase change of the organic working fluid, and the expansion process therefore starts from the saturated liquid state rather than a vapor phase. With reference to the plant layout displayed and T-s diagram presented in the figure, the working fluid is pressurized, heated at constant pressure to its saturation point, expanded as a two-phase mixture and eventually condensed at constant pressure. Art. [#ARTNUM](#article-33276-2758081676) **Research findings:** - The current research tackles the energy trilemma of emissions reduction, security of supply and cost savings in industrial environments by presenting the development of a packaged, plug & play power unit for lowgrade waste heat recovery applications. The heat to power conversion system is based on the Trilateral Flash Cycle (TFC), a bottoming thermodynamic cycle particularly suitable for waste heat sources at temperatures below 100 °C which, on a European scale, account for 469 TWh in industry and are particularly concentrated in the chemical and petrochemical sectors. The industrial test case refers to a UK tire manufacturing company in which a 2 MW water stream at 85 °C involved in the rubber curing process was chosen as hot source of the TFC system while a pond was considered the heat sink. The design of the industrial scale power unit, which is presented at end of the manuscript, was carried out based on the outcomes of a theoretical modelling platform that allowed to investigate and optimize multiple design parameters using energy and exergy analyses. In particular, the model exploitation identified R1233zd(E) and R245fa as the most suitable pure working fluids for the current application, given the higher net power output and the lower ratio between pumping and expander powers. At nominal operating conditions, the designed TFC system is expected to recover 120 kWe and have an overall efficiency of 6%. Art. [#ARTNUM](#article-33276-2758081676) - The advantage of TFC over an equivalent steam ORC system is that its power recovery potential is high, twice that of ORC. It can also eliminate the requirement for an extra cooling tower/heat rejection system, where heat in the waste stream will be rejected. Art. [#ARTNUM](#article-33276-2920834504)

1.6.1 1.6 Trilateral flash cycle
Development and analysis of a packaged Trilateral Flash Cycle system for low grade heat to power conversion applications
Abstract The current research tackles the energy trilemma of emissions reduction, security of supply and cost savings in industrial environments by presenting the development of a packaged, plug & play power unit for low-grade waste heat recovery applications. The heat to power conversion system is based on the Trilateral Flash Cycle (TFC), a bottoming thermodynamic cycle particularly suitable for waste heat sources at temperatures below 100 °C which, on a European scale, account for 469 TWh in industry and are particularly concentrated in the chemical and petrochemical sectors. The industrial test case refers to a UK tire manufacturing company in which a 2 MW water stream at 85 °C involved in the rubber curing process was chosen as hot source of the TFC system while a pond was considered the heat sink. The design of the industrial scale power unit, which is presented at end of the manuscript, was carried out based on the outcomes of a theoretical modelling platform that allowed to investigate and optimize multiple design parameters using energy and exergy analyses. In particular, the model exploitation identified R1233zd(E) and R245fa as the most suitable pure working fluids for the current application, given the higher net power output and the lower ratio between pumping and expander powers. At nominal operating conditions, the designed TFC system is expected to recover 120 kWe and have an overall efficiency of 6%.
12/01/2017 00:00:00
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1.6.2 1.6 Trilateral flash cycle
Development of the Trilateral Flash Cycle System: Part 1: Fundamental Considerations
The world market for systems for power recovery from low-grade heat sources is of the order of £1 billion per annum. Many of these sources are hot liquids or gases from which conventional power systems convert less than 2.5 per cent of the available heat into useful power when the fluid is initially at a temperature of 100° C rising to 8–9 per cent at an initial temperature of 200°C. Consideration of the maximum work recoverable from such single-phase heat sources leads to the concept of an ideal trilateral cycle as the optimum means of power recovery. The trilateral flash cycle (TFC) system is one means of approaching this ideal which involves liquid heating only and two-phase expansion of vapour. Previous work related to this is reviewed and details of analytical studies are given which compare such a system with various types of simple Rankine cycle. It is shown that provided two-phase expanders can be made to attain adiabatic efficiencies of more than 75 per cent, the TFC system can produce outputs of...
08/01/1993 00:00:00
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1.6.3 1.6 Trilateral flash cycle
Techno-economic survey and design of a pilot test rig for a trilateral flash cycle system in a steel production plant
Abstract In recent years the interest in recovering rejected low-grade heat within industry has intensified. Around 30% of global primary energy consumption is attributed to the industrial sector and a significant portion of this is rejected as heat. The majority of this wasted energy is available at temperatures below 100°C and as such conventional waste heat to power conversion systems cannot economically recover the energy, producing simple pay backs that are unacceptable to industry. The Trilateral Flash Cycle (TFC) is however a promising technology with the ability to harness the rejected heat found in these low grade waste streams. The current research work presents a techno-economic assessment of the installation potential for a low grade heat to power conversion system using a TFC system. In particular, thermodynamic modelling is utilised to estimate the expected energy recovery and, in turn, the potential savings achievable through the TFC solution. The survey investigated three diverse and challenging heat sources at steel production plants. Annual energy recovery from the chosen heat source is expected to be 782 MWh. Prior to the upscaling of the system to the 2MW waste thermal power, a pilot test rig was designed and built. Preliminary tests showed a net electrical power output up to 6.2 kW and an overall efficiency of 4.3%.
09/01/2017 00:00:00
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1.6.4 1.6 Trilateral flash cycle
Waste Heat Recovery in the EU industry and proposed new technologies
Abstract In the European Union (EU), industrial sectors use 26% of the primary energy consumption and are characterized by large amounts of energy losses in the form of waste heat at different temperature levels. Their recovery is a challenge but also an opportunity for science and business. In this study, after a brief description of the conventional Waste Heat Recovery (WHR) approaches, the novel technologies under development within the I-ThERM Horizon 2020 project are presented and assessed from an energy and market perspectives. These technologies are: heat to power conversion systems based on bottoming thermodynamic cycles (Trilateral Flash Cycle for low grade waste heat and Joule-Brayton cycle working with supercritical carbon dioxide for high temperature waste heat sources); heat recovery devices based on heat pipes (flat heat pipe for high grade radiative heat sources and condensing economizer for acidic effluents).
03/01/2019 00:00:00
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2. 2. Solid-state generators for heat conversion

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Solid state thermal to electrical energy converters are heat engines, or small generators, and energy harvesters capable of transforming heat directly into electricity. The governing physical principles with solid state thermal to electrical energy converters work over several orders of magnitude and enable the utilization of previously unexplored low grade thermal energy and waste heat. With solid state heat engines, small quantities of low grade thermal energy and waste heat, at temperatures just above ambient, can be directly converted into electrical power in the microwatt to milliwatt range. The generated electrical power allows to locally power a large number of small scale electronic devices as well as autonomous and self-sustaining applications, without the need for maintenance and additional costs.


2.1 2.1 Thermoelectric generator

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A thermoelectric generator (TEG), also called a Seebeck generator, is a solid state device that converts heat flux (temperature differences) directly into electrical energy through a phenomenon called the Seebeck effect (a form of thermoelectric effect). Thermoelectric generators function like heat engines, but are less bulky and have no moving parts. However, TEGs are typically more expensive and less efficient. Thermoelectric generators could be used in power plants in order to convert waste heat into additional electrical power and in automobiles as automotive thermoelectric generators (ATGs) to increase fuel efficiency. Another application is radioisotope thermoelectric generators which are used in space probes, which has the same mechanism but use radioisotopes to generate the required heat difference. [[Wiki]](https://en.wikipedia.org/wiki/Thermoelectric_generator) Thermoelectric devices, or thermoelectric generators (TEG), are solid state heat engines and convert thermal energy directly into electrical energy. Thermal energy from a hot heat source and a cold heat sink creates a spatial temperature difference which can be utilized in a TEG. When the TEG is place between the hot heat source and a cold heat sink, the temperature difference is converted into an electric current across the generator terminals. This effect is based on the thermoelectric, or Seebeck, effect. The Seebeck effect describes the voltage developed across two dissimilar electrical conductor materials creating a hot thermoelectric junction. The assembly of thermoelectric junctions is known as a TEG module and acts as an electric power generator continuously driving a direct electric current (DC) through an external electrical load. Art. [#ARTNUM](#article-29719-2902616540)

2.1.1 2.1 Thermoelectric generator
A review of thermoelectric power generation systems: Roles of existing test rigs/ prototypes and their associated cooling units on output performance
Abstract Thermoelectric technology is a promising solution to recover waste heat from different resources. There are numerous researches in the literature that measure performance of thermoelectric modules (TEMs). A comprehensive review of research studies that classifies and expounds disparities between various thermoelectric power generation (TEPG) systems is still unavailable and therefore, this paper reviews major concerns on their designs and performances. Firstly, various main elements of TEPG systems, which affect the output power of TEMs such as stabilizer or heat exchanger, interface, contact pressure, insulation, cooling system, and integrity are studied. Secondly, performances of test rigs and various prototypes are reviewed in detail based on their cooling methods since cooling is the most prominent factor among other counterparts. In general, the cooling unit is divided into either passive or active cooling system, which is selected based on its well-defined use. A comprehensive study on various test rigs with active cooling systems is given while a broader range in prototypes is covered and classified under detailed surveys. This review is expected to be of value for researchers in the field of thermoelectric. Overall, in order to have a prospective future towards commercialization of TEPG systems, the existing prototypes in the literature are still subjected to many enhancements in their design aspects, while further improvements are needed to be achieved independently in TEMs’ development.
10/01/2018 00:00:00
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2.1.2 2.1 Thermoelectric generator
A Review on Organic Polymer-Based Thermoelectric Materials
Converting heat energy directly into useable electricity by harvesting low-cost energy resources, such as solar energy and the waste heat, has attracted great interest recent years. Thermoelectricity offers a promising technology to convert heat from solar energy and to recover waste heat from industrial sectors and automobile exhausts. Classically, a number of inorganic compounds have been considered as the best thermoelectric materials. Organic materials in particular intrinsically conducting polymers had been considered as competitors of classical thermoelectric since their figure of merit has been improved several orders of magnitude in last year. In addition, the applications of thermoelectric polymers at low temperatures have shown various advantages such as easy and low cost of fabrication, light weight, and flexibility. Therefore, organic thermoelectric materials will be the best candidates to compete with inorganic materials in the future. In this review, we focused on exploring different types of organic thermoelectric materials and the factors affecting their thermoelectric properties, and discussed various strategies to improve the performance of thermoelectric materials. In addition, a review on theoretical studies of thermoelectric transport in polymers is also given.
12/01/2017 00:00:00
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2.1.3 2.1 Thermoelectric generator
Advancements in thermoelectric generators for enhanced hybrid photovoltaic system performance
Effective thermal management of photovoltaic cells is essential for improving its conversion efficiency and increasing its life span. Solar cell temperature and efficiency have an inverse relationship therefore, cooling of solar cells is a critical research objective which numerous researchers have paid attention to. Among the widely adopted thermal management techniques is the use of thermoelectric generators to enhance the performance of photovoltaics. Photovoltaic cells can convert the ultra-violent and visible regions of the solar spectrum into electrical energy directly while thermoelectric modules utilize the infrared region to generate electrical energy. Consequently, the combination of photovoltaic and thermoelectric generators would enable the utilization of a wider solar spectrum. In addition, the combination of both systems has the potential to provide enhanced performance due to the compensating effects of both systems. The waste heat produced from the photovoltaic can be used by the thermoelectric generator to produce additional energy thereby increasing the overall power output and efficiency of the hybrid system. However, the integration of both systems is complex because of their opposing characteristics thus, effective coupling of both systems is essential. This review presents the concepts of photovoltaics and thermoelectric energy conversion, research focus areas in the hybrid systems, applications of such systems, discussion of the most recent research accomplishments and recommendations for future research. All the essential elements and research areas in hybrid photovoltaic/thermoelectric generator are discussed in detailed therefore, this review would serve as a valuable reference literature.
07/01/2019 00:00:00
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2.1.4 2.1 Thermoelectric generator
Analysis of a Thermoelectric Generator in a Gas Carburizing Furnace
: Thermoelectric generation technology, as one entirely solid-state energy conversion method, can directly transform thermal energy into electricity by using thermoelectric transformation materials. A thermoelectric power converter has no moving parts, and is compact, quiet, highly reliable and environmentally friendly. Therefore, the whole system can be simplified and operated over an extended period of time with minimal maintenance. In addition, it has wider choice of thermal sources. It can utilize both the high- and low-quality heat to generate electricity. The low-quality heat may not be utilized effectively by conventional methods such as ORC technology. In this study, a direct heat to electricity (DHE) technology using the thermoelectric effect, without the need to change through mechanical energy, was applied to harvest low-enthalpy thermal work. Such a power generation system has been designed and built using thermoelectric generator (TEG) modules manufactured using a new technique. The targets of this technique were low cost and high thermal to electricity efficiency. Experiments have been conducted to measure the output power at different conditions: different inlet -temperature and temperature differences between hot and cold sides. TEG modules manufactured with different materials have also been tested. The power generator assembled with TEG modules had an installed power of 30W at a temperature difference of around 140 °C. The power generated by the thermoelectric system is almost directly proportional to the temperature difference between the hot and the cold sides. The cost of the DHE power generator is much lower than that of photo voltaic (PV) in terms of equivalent energy generated. The TEG systems are ready to be applied practically to many gas carburizing furnaces for the efficient usage of thermal power.
03/01/2017 00:00:00
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2.1.5 2.1 Thermoelectric generator
Analysis of the use of thermoelectric generator and heat pipe for waste heat utilization
Waste heat recovery is one way to reduce the use of fossil fuels, one of them is by using thermoelectric generator to convert waste heat into Thermoelectric Generator (TEGs) is a module that can convert heat into electrical power directly, using Seebeck effect and Peltier effect as its working principle, so it can increase efficiency of energy consumption by utilizing waste heat from an instrument that generate waste heat. The focus of this research is to find the output voltage of TEG by utilizing the temperature difference on the cold side and the heat side of the TEGs. The heat side of the module will be given heat from the heater as a simulation of the heat from hot water, and on the cold side heat pipes will be used to remove the heat on the cold side of TEGs. The result, output voltage that generated by using 4 module TEGs that arranged to Thermal Series - Series Circuit and using 2 heat pipes is 2.1-volt, and then it is possible to use for phone charger.
01/01/2018 00:00:00
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2.1.6 2.1 Thermoelectric generator
Development of a System for Thermoelectric Heat Recovery from Stationary Industrial Processes
The hot forming process of steel requires temperatures of up to 1300°C. Usually, the invested energy is lost to the environment by the subsequent cooling of the forged parts to room temperature. Thermoelectric systems are able to recover this wasted heat by converting the heat into electrical energy and feeding it into the power grid. The proposed thermoelectric system covers an absorption surface of half a square meter, and it is equipped with 50 Bismuth-Telluride based thermoelectric generators, five cold plates, and five inverters. Measurements were performed under production conditions of the industrial environment of the forging process. The heat distribution and temperature profiles are measured and modeled based on the prevailing production conditions and geometric boundary conditions. Under quasi-stationary conditions, the thermoelectric system absorbs a heat radiation of 14.8 kW and feeds electrical power of 388 W into the power grid. The discussed model predicts the measured values with slight deviations.
07/01/2016 00:00:00
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2.1.7 2.1 Thermoelectric generator
Exhaust Heat Recovery Using Thermoelectric Generators: A Review
With the major concern to increase the efficiency of internal combustion (IC) engines, various technologies and innovations have been implemented to improvise efficiency and reduction of emissions. Since 60–70% of the energy produced during combustion is rejected as heat through exhaust and coolant channels, it is important to recover that waste heat. Numerous technologies have been invented and applied to the diesel engine unit to harness the waste heat. One such is the use of solid-state device thermoelectric generator (TEG). In the late 1980s, many automobile manufacturers implemented automotive exhaust thermoelectric generators (AETEGs) in their respective vehicles, and since then, the work on AETEGs has picked at gradual pace. Advantages of using TEG are its noise-free operation, low failure rate and lack of moving components. However, it is not a very popular solution due to the low energy conversion efficiency (~6–8%) of thermoelectric modules and the incompetence to produce high power at low-temperature gradient. Engineers and researchers are basically working for improving the conversion efficiency of TEG modules by developing and doping semiconductors and optimization of the AETEG system to utilize and recover maximum heat available from the exhaust line by designing efficient heat exchanger systems, thus trying to improve its feasibility. This chapter covers the wide spectrum of feasibility of application of TEG modules in diesel engines with possible ways to utilize the generated power.
01/01/2018 00:00:00
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2.1.8 2.1 Thermoelectric generator
Power generation by coupling reverse electrodialysis and ammonium bicarbonate: Implication for recovery of waste heat
Abstract Utilization of waste heat has attracted increasing attentions due to energy crisis and environmental problems. Efficiency of traditional thermodynamic cycles for waste heat conversion is limited by the temperature of heat sources. We propose here the concept of a novel waste heat conversion system, namely a thermal-driven electrochemical generator (TDEG), which comprises a reverse electrodialysis (RED) stack and a distillation column. By using thermally instable ammonium bicarbonate solutions as working fluids, waste heat can be converted to electricity. The feasibility of NH 4 HCO 3 to generate electricity for TDEG was validated in a RED stack for the first time. Two important operating conditions influencing power output of RED stack, i.e. concentration of low concentration solution and flow rate of feed solutions were optimized to be 0.02 M and 800 mL/min, respectively. A maximum power density of 0.33 W/m 2 was obtained for the specific RED stack. Ionic flux efficiency and energy efficiency under the optimal condition were 88% and 31%, respectively. The study lays a foundation for the establishment of the promising TDEG.
06/01/2012 00:00:00
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2.1.9 2.1 Thermoelectric generator
Solid state generators and energy harvesters for waste heat recovery and thermal energy harvesting
Abstract This review covers solid state thermal to electrical energy converters capable of transforming low grade heat directly into electricity for waste heat recovery and thermal energy harvesting. Direct solid state heat engines such, as thermoelectric modules and thermionic converters for spatial temperature gradients, are compared with pyroelectric energy harvesters and thermomagnetic generators for transient changes in temperature. Temperature and size limitations along with the maturity of the technologies are discussed based on energy density and temperature range for the different generator technologies. Despite the low energy conversion efficiency with solid state generators, electric power density ranges from 4 nW/mm 2 to 324 mW/mm 2 . The most promising sector to implement changes while reducing the primary energy consumption and saving resources, is the processing industry along with stationary and mobile electronics.
03/01/2019 00:00:00
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2.1.10 2.1 Thermoelectric generator
Thermoelectric materials and heat exchangers for power generation – A review
Abstract Around 60–70% of the fuel energy in an internal combustion engine is lost as waste heat through engine exhaust and coolant. Hence, waste heat recovery techniques can be used to increase the efficiency of the engine. Thermoelectric systems are widely used for converting heat energy to electric energy. A considerable attention of researchers has been drawn by the thermoelectric generator, for the waste heat recovery from engine exhaust. The thermoelectric generator is one of the promising green energy source and the most desirable option to recover useful energy from engine exhaust. A high-efficiency heat exchanger, which is an integral part of the thermoelectric generator, is necessary to increase the amount of heat energy extracted from engine exhaust at the cost of acceptable pressure drop. The present work is a summary of thermoelectric materials, and heat exchanger studies on heat transfer rate, thermal uniformity, and pressure drop. The heat exchangers with different internal structures enhance heat transfer rate and thermal uniformity, which increase the power output and the conversion efficiency of the thermoelectric generator. The presence of flow-impeding inserts/internal structures results in an adverse increase in pressure drop and has a negative effect on the performance of waste heat source.
11/01/2018 00:00:00
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2.2 2.2 Thermionic energy converter (TEC)

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A thermionic converter consists of a hot electrode which thermionically emits electrons over a potential energy barrier to a cooler electrode, producing a useful electric power output. Caesium vapor is used to optimize the electrode work functions and provide an ion supply (by surface ionization or electron impact ionization in a plasma) to neutralize the electron space charge. [[Wiki]](https://en.wikipedia.org/wiki/Thermionic_converter) When a TIC is placed between a hot heat source and a cold heat sink, the hot electrode surface emits charge carriers (electrons). This charge emission process is based on the effect of thermionic emission, or the space charge effect, and enables a continuous surplus of electrons at the cold electrode which act as an electric power supply, continuously driving a direct electric current (DC) across an external load. Usually a high temperature is used. **Research findings:** - At high temperatures, over 15% conversion efficiency is possible with respective hot and cold electrode temperatures between 570 °C and 1300 °C, revealing that this technology is remarkably suitable for industrial and nuclear heat recovery applications. Experimental devices show a high power density of 320 000 μW/mm2 at temperatures in excess of 1000 °C. However, with thermionic device the power density rapidly decreases at temperatures below 1000 °C, only generating 0.04 μW/mm2 (9 nW/0.25 mm2) at low temperatures. When pure metal and semi-conductor electrodes are used in TICs, decreasing heat source temperatures lead to a diminishing electrode emission. As shown in Fig. 6, the maximum conversion efficiency of a TIC with an electrode WF of 0.75 eV, at 127 °C hot electrode temperature and 27 °C cold electrode temperature, is close to 20%. In order to maintain the electron emission process at low temperatures, the corresponding electrode WF also needs to be low. Alkali metals and their oxides such as e.g. Lithium (Li), Potassium (K), and Cesium (Cs) have WFs lower than most metals and semiconductors, with typical values in the range between 2.1 eV and 2.49 eV and their respective oxides between 0.4 eV and 1.8 eV. Art. [#ARTNUM](#article-33270-2902616540)

2.2.1 2.2 Thermionic energy converter (TEC)
Solid state generators and energy harvesters for waste heat recovery and thermal energy harvesting
Abstract This review covers solid state thermal to electrical energy converters capable of transforming low grade heat directly into electricity for waste heat recovery and thermal energy harvesting. Direct solid state heat engines such, as thermoelectric modules and thermionic converters for spatial temperature gradients, are compared with pyroelectric energy harvesters and thermomagnetic generators for transient changes in temperature. Temperature and size limitations along with the maturity of the technologies are discussed based on energy density and temperature range for the different generator technologies. Despite the low energy conversion efficiency with solid state generators, electric power density ranges from 4 nW/mm 2 to 324 mW/mm 2 . The most promising sector to implement changes while reducing the primary energy consumption and saving resources, is the processing industry along with stationary and mobile electronics.
03/01/2019 00:00:00
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2.2.2 2.2 Thermionic energy converter (TEC)
TEC as electric generator in an automobile catalytic converter
Modern cars use more and more electric power due to more on-board electric systems. A modern car may be equipped with an electric generator (generally an alternator) with an output current of maximum 60-90 A at 12 V. A belt driven generator has a rather low total efficiency and so it is interesting to find alternative solutions for this electricity generation problem. One possible energy source for electricity generation is to use the waste heat from the car's engine, which generally is as much as much as 80% of the total energy from the combustion of the gasoline. Maybe the best location to tap the excess heat is the catalytic converter (Cat) in the exhaust system or perhaps at the exhaust pipes close to the engine. The Cat must be kept within a certain temperature interval. Large amounts of heat are dissipated through the walls of the Cat. A thermionic energy converter (TEC) in a coaxial form could conveniently be located around the ceramic cartridge of the Cat. Since the TEC is a rather good heat insulator before it reaches its working temperature, the Cat will reach working temperature faster and its final temperature can be controlled better when encapsulated in a concentric TEC arrangement. It is also possible to regulate the temperature of the Cat and the TEC by controlling the electrical load of the TEC. The possible working temperatures of present and future Cats appear very suitable for the authors' new low work function collector TEC, which has been demonstrated to work down to 470 K.
01/01/1996 00:00:00
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2.3 2.3 Thermomagnetic generators

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Thermomagnetic generators, or thermo-magneto-electric generators, are solid state heat engines and convert thermal energy directly into electrical energy. In a thermomagnetic generator every change in temperature (ΔT) translates into an electric current across the generator terminals. When heated, the ferromagnetic material in the thermomagnetic generator experiences a crystallographic phase transition followed by a rapid change in the magnetic moment. This change in magnetic moment induces an electromagnetic induction force (EMF), or electromotive force, and drives an electric current across an external electric load. For cyclic, or time variant (Δt), heating and cooling (ΔT/Δt) the thermomagnetic generator drives an alternating current (AC) across the generator terminals proportional to the experienced change in temperature. Art. [#ARTNUM](#article-33241-2902616540)

2.3.1 2.3 Thermomagnetic generators
High-Performance Thermomagnetic Generators Based on Heusler Alloy Films
Recent developments on Heusler alloys including Ni–Mn–X and Ni–Co–Mn–X (X = Ga, In, Sn,…) demonstrate multiferroic phase transformations with large abrupt changes in lattice parameters of several percent and corresponding abrupt changes in ferromagnetic ordering near the transition temperatures. These materials enable a new generation of thermomagnetic generators that convert heat to electricity within a small temperature difference below 5 K. While thermodynamic calculations on this energy conversion method predict a power density normalized to material volume of up to 300 mW cm−3, experimental results have been in the range of µW cm−3. Challenges are related to the development of materials with bulk-like single-crystal properties as well as geometries with large surface-to-volume ratio for rapid heat exchange. This study demonstrates efficient thermomagnetic generation via resonant actuation of freely movable thin-film devices of the Heusler alloy Ni–Mn–Ga with unprecedented power density of 118 mW cm−3 that compares favorably with the best thermoelectric generators. Due to the large temperature-dependent change of magnetization of the films, a periodic temperature change of only 3 K is required for operation. The duration of thermomagnetic duty cycle is only about 12 ms, which matches with the period of oscillatory motion.
03/01/2017 00:00:00
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2.3.2 2.3 Thermomagnetic generators
Performance analysis of energy conversion via caloric effects in first-order ferroic phase transformations
A finite-time thermodynamic model of ferroic refrigerators and generators, based on first order phase transformation, is given. We use this model to evaluate a novel method of converting heat directly into electricity based on the martensitic phase transformation accompanied by an abrupt change in magnetic ordering recently discovered [Srivastava et al., Adv. Energy Mater., 2011, 1, 97]. In this paper, we study the efficiency and power output of this method. The formulas of efficiency and power output in terms of material constants, design parameters, and working conditions are derived. The Clausius–Clapeyron coefficient is shown to be important to the efficiency. The figure of merit, as a dimensionless parameter, of energy conversion using the new method is introduced. It is shown that, as the figure of merit goes to infinity, the efficiency approaches the Carnot efficiency. Thermodynamic cycles of the new energy conversion method are optimized for a maximum power output. The matching criteria between materials and working temperatures of such optimized cycles are derived. Using these criteria, one can choose the most suitable materials under given working conditions, or decide the best working conditions for available materials.
01/01/2014 00:00:00
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2.3.3 2.3 Thermomagnetic generators
Solid state generators and energy harvesters for waste heat recovery and thermal energy harvesting
Abstract This review covers solid state thermal to electrical energy converters capable of transforming low grade heat directly into electricity for waste heat recovery and thermal energy harvesting. Direct solid state heat engines such, as thermoelectric modules and thermionic converters for spatial temperature gradients, are compared with pyroelectric energy harvesters and thermomagnetic generators for transient changes in temperature. Temperature and size limitations along with the maturity of the technologies are discussed based on energy density and temperature range for the different generator technologies. Despite the low energy conversion efficiency with solid state generators, electric power density ranges from 4 nW/mm 2 to 324 mW/mm 2 . The most promising sector to implement changes while reducing the primary energy consumption and saving resources, is the processing industry along with stationary and mobile electronics.
03/01/2019 00:00:00
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2.4 2.4 Pyroelectric generator

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Pyroelectricity (from the two Greek words pyr meaning fire, and electricity) is a property of certain crystals which are naturally electrically polarized and as a result contain large electric fields. Pyroelectricity can be described as the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change gives rise to a voltage across the crystal. If the temperature stays constant at its new value, the pyroelectric voltage gradually disappears due to leakage current. [Wiki](https://en.wikipedia.org/wiki/Pyroelectricity) Pyroelectric generators, or pyroelectric energy harvesters, are solid state heat engines and convert thermal energy directly into electrical energy. In a pyroelectric harvester every change in temperature translates into an electric potential difference across the generator terminals. This potential difference is based on the pyroelectric effect, which describes the change in the crystallographic polarization moment of a pyroelectric material, in response to the change in temperature ΔT. For cyclic, or time variant (Δt), heating and cooling (ΔT/Δt) the pyroelectric energy harvester generates an alternating current (AC) across the generator terminals proportional to experienced change in temperature. In this way, pyroelectric energy harvesters are different from the previously discussed thermoelectric generators and thermionic converters where the current is proportional to the spatial temperature gradient. Art. [#ARTNUM](#article-33256-2902616540) **Research findings:** - In 2014, almost 60% of thermal energy produced in the United States was lost to the environment as waste heat. Ferroelectric based pyroelectric devices can be used to convert some of this waste heat into usable electrical energy using the Olsen cycle, an ideal thermodynamic cycle, but there are a number of barriers to its realization in a practical device. This study uses the Olsen cycle to benchmark a less efficient thermodynamic cycle that is more easily implemented in devices. The ferroelectric pyroelectric material used was (Pb0.97La0.02)(Zr0.55Sn0.32Ti0.13)O3 ceramic, a ferroelectric material that undergoes a temperature driven phase transformation. A net energy density of 0.27 J cm−3 per cycle was obtained from the ferroelectric material using the modified cycle with a temperature change between 25°C and 180°C. This is 15.5% of the Olsen cycle result with the same temperature range and 1–8 MV m−1 applied electric field range. The power density was estimated to 13.5 mW cm−3 with given experimental conditions. A model is presented that quantitatively describes the effect of several parameters on output energy density and can be used to design ferroelectric based pyroelectric energy converters. The model indicates that optimization of material geometry and heating conditions can increase the output power by an order or magnitude. Art. [#ARTNUM](#article-33256-2271477211)

2.4.1 2.4 Pyroelectric generator
Phase transformation based pyroelectric waste heat energy harvesting with improved practicality
In 2014, almost 60% of thermal energy produced in the United States was lost to the environment as waste heat. Ferroelectric based pyroelectric devices can be used to convert some of this waste heat into usable electrical energy using the Olsen cycle, an ideal thermodynamic cycle, but there are a number of barriers to its realization in a practical device. This study uses the Olsen cycle to benchmark a less efficient thermodynamic cycle that is more easily implemented in devices. The ferroelectric pyroelectric material used was (Pb0.97La0.02)(Zr0.55Sn0.32Ti0.13)O3 ceramic, a ferroelectric material that undergoes a temperature driven phase transformation. A net energy density of 0.27 J cm−3 per cycle was obtained from the ferroelectric material using the modified cycle with a temperature change between 25°C and 180°C. This is 15.5% of the Olsen cycle result with the same temperature range and 1–8 MV m−1 applied electric field range. The power density was estimated to 13.5 mW cm−3 with given experimental conditions. A model is presented that quantitatively describes the effect of several parameters on output energy density and can be used to design ferroelectric based pyroelectric energy converters. The model indicates that optimization of material geometry and heating conditions can increase the output power by an order or magnitude.
03/01/2016 00:00:00
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2.4.2 2.4 Pyroelectric generator
Pyroelectric Energy Harvesting
Energy harvesting (or energy scavenging) technology captures unused ambient energy, such as vibration, strain, light, temperature gradients, temperature variations, gas flow energy, and liquid flow energy, and converts it into usable electrical energy. Even though advances have been made, the batteries that power portable microelectronics and wireless devices provide only a finite amount of power. Energy harvesting is a perfect solution for the problem of finite battery power for various low-power applications, providing sustained, cost-effective, and environmentally friendlier sources of power. Unconventional methods for waste-energy harvesting and scavenging are being explored to provide sustained power to these micro- and nanodevices. Efforts are being made to garner electric power from mechanical vibrations, light, spatial variations, and temporal temperature variations. Another potential source for low-power electronics is the thermal- and mechanical-waste energy of asphalt pavement, especially via pyroelectricity. However, this potential has not yet been extensively explored. An exception is Israel's current large-scale effort to pave kilometers of roads with a specially designed series of piezoelectric modules in the pavement. Pyroelectric materials are able to convert most of the electromagnetic radiation's spectrum (ultraviolet, IR, microwave, x rays, and terahertz) energy into electrical energy; that is, they transform photons to phonons and then to electrons.5 Since it follows that these materials can be exploited for conversion of thermal energy to electricity, they have been investigated recently for energy harvesting via pyroelectric linear and nonlinear properties. One key advantage of pyroelectrics over thermoelectrics is the stability of many pyroelectric materials at up to 1200 °C or more, which enables energy harvesting from high-temperature sources, thereby increasing thermodynamic efficiency. It is noteworthy that annually more than 100 TJ of low-grade waste heat (10 °C to 250 °C) is discharged by industries worldwide, such as electric power stations, glass manufacturers, petrochemical plants, pulp and paper mills, steel and other foundries, and the automobile industry. In the United States in 2009, around 55% of the energy generated from all of the sources was lost as waste heat.6 Technology to recover this low-grade waste heat or convert into usable electricity could save industrial sectors billions of dollars annually and reduce greenhouse gases. Pyroelectric electric generators (PEGs) can play a significant role in such technology. This chapter presents a review of PEGs with discussions on linear and nonlinear energy harvesting processes, thermodynamics of pyroelectrics, and an investigation of important pyroelectric materials with modeling of numerically simulated results for energy conversion.
09/24/2013 00:00:00
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2.4.3 2.4 Pyroelectric generator
Pyroelectric Harvesters for Generating Cyclic Energy
Pyroelectric energy conversion is a novel energy process which directly transforms waste heat energy from cyclic heating into electricity via the pyroelectric effect. Application of a periodic temperature profile to pyroelectric cells is necessary to achieve temperature variation rates for generating an electrical output. The critical consideration in the periodic temperature profile is the frequency or work cycle which is related to the properties and dimensions of the air layer; radiation power and material properties, as well as the dimensions and structure of the pyroelectric cells. This article aims to optimize pyroelectric harvesters by matching all these requirements. The optimal induced charge per period increases about 157% and the efficient period band decreases about 77%, when the thickness of the PZT cell decreases from 200 μm to 50 μm, about a 75% reduction. Moreover, when using the thinner PZT cell for harvesting the pyroelectric energy it is not easy to focus on a narrow band with the efficient period. However, the optimal output voltage and stored energy per period decrease about 50% and 74%, respectively, because the electrical capacitance of the 50 μm thick pyroelectric cell is about four times greater than that of the 200 μm thick pyroelectric cell. In addition, an experiment is used to verify that the work cycle to be able to critically affect the efficiency of PZT pyroelectric harvesters. Periods in the range between 3.6 s and 12.2 s are useful for harvesting thermal cyclic energy by pyroelectricity. The optimal frequency or work cycle can be applied in the design of a rotating shutter in order to control the heated and unheated periods of the pyroelectric cells to further enhance the amount of stored energy.
04/27/2015 00:00:00
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2.4.4 2.4 Pyroelectric generator
Solid state generators and energy harvesters for waste heat recovery and thermal energy harvesting
Abstract This review covers solid state thermal to electrical energy converters capable of transforming low grade heat directly into electricity for waste heat recovery and thermal energy harvesting. Direct solid state heat engines such, as thermoelectric modules and thermionic converters for spatial temperature gradients, are compared with pyroelectric energy harvesters and thermomagnetic generators for transient changes in temperature. Temperature and size limitations along with the maturity of the technologies are discussed based on energy density and temperature range for the different generator technologies. Despite the low energy conversion efficiency with solid state generators, electric power density ranges from 4 nW/mm 2 to 324 mW/mm 2 . The most promising sector to implement changes while reducing the primary energy consumption and saving resources, is the processing industry along with stationary and mobile electronics.
03/01/2019 00:00:00
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2.5 2.5 Thermally regenerative battery

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In thermal regenerative batteries, conversion to electricity is realized by charging–discharging an electrochemical cell at different temperatures. **Research findings:** - In a thermal regenerative ammonia battery, electrical power is obtained from the formation of metal ammine complexes, which are produced by adding ammonia to the anolyte, but not to the catholyte, of a battery consisting of two copper electrodes in a copper-nitrate electrolyte. The added ammonia generates a potential difference between the electrodes according to the reactions: (1)Cu2+(aq) + 2e− → Cu (s)  E0 = +0.34 V (2)Cu (s) + 4 NH3(aq) → Cu(NH3)42+ (aq) + 2e−   E0 = –0.04 V where E0 is the standard reduction potential in V vs. the standard hydrogen electrode (SHE). After discharging the cell and generating electrical power, ammonia is separated from the anolyte using conventional distillation with low-grade waste heat. The distilled ammonia is then added to the other electrolyte chamber for the next discharge cycle. While discharging the battery results in copper loss from the anode, the electrode can be regenerated when the ammonia is added to the other chamber, where copper will be re-deposited back onto the electrode. Art. [#ARTNUM](#article-33265-2530731371) - The use of ethylenediamine as an alternative ligand to ammonia was explored here as a method to increase the power production as well as improve ACE. In theory, the anode open circuit potential of a TRB can be improved by using a ligand in which the complexation reaction (Cu + n L → [Cu(L)n]2+ + 2e−; L: ligand) has a higher standard reduction potential than the copper ammonia complex (Eq. (2); −0.04 V). Art. [#ARTNUM](#article-33265-2598227859)

2.5.1 2.5 Thermally regenerative battery
Electrical power production from low-grade waste heat using a thermally regenerative ethylenediamine battery
Abstract Thermally regenerative ammonia-based batteries (TRABs) have been developed to harvest low-grade waste heat as electricity. To improve the power production and anodic coulombic efficiency, the use of ethylenediamine as an alternative ligand to ammonia was explored here. The power density of the ethylenediamine-based battery (TRENB) was 85 ± 3 W m −2 -electrode area with 2 M ethylenediamine, and 119 ± 4 W m −2 with 3 M ethylenediamine. This power density was 68% higher than that of TRAB. The energy density was 478 Wh m −3 -anolyte, which was ∼50% higher than that produced by TRAB. The anodic coulombic efficiency of the TRENB was 77 ± 2%, which was more than twice that obtained using ammonia in a TRAB (35%). The higher anodic efficiency reduced the difference between the anode dissolution and cathode deposition rates, resulting in a process more suitable for closed loop operation. The thermal-electric efficiency based on ethylenediamine separation using waste heat was estimated to be 0.52%, which was lower than that of TRAB (0.86%), mainly due to the more complex separation process. However, this energy recovery could likely be improved through optimization of the ethylenediamine separation process.
05/01/2017 00:00:00
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2.5.2 2.5 Thermally regenerative battery
Removal of copper from water using a thermally regenerative electrodeposition battery
Abstract A thermally regenerative ammonia battery (TRAB) recently developed for electricity generation using waste heat was adapted and used here as a treatment process for solutions containing high concentrations of copper ions. Copper removal reached a maximum of 77% at an initial copper concentration ( C i ) of 0.05 M, with a maximum power density ( P ) of 31 W m −2 -electrode area. Lowering the initial copper concentration decreased the percentage of copper removal from 51% ( C i  = 0.01 M, P  = 13 W m −2 ) to 2% ( C i  = 0.002 M, P  = 2 W m −2 ). Although the final solution may require additional treatment, the adapted TRAB process removed much of the copper while producing electrical power that could be used in later treatment stages. These results show that the adapted TRAB can be a promising technology for removing copper ions and producing electricity by using waste heat as a highly available and free source of energy at many industrial sites.
01/01/2017 00:00:00
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2.6 2.6 Piezoelectric heat conversion

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Piezoelectricity is the electric charge that accumulates in certain solid materials (such as crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure and latent heat. [[Wiki]](https://en.wikipedia.org/wiki/Piezoelectricity) Piezoelectricity can be used to convert waste heat into power, usually in very small scale applications. **Research findings:** - In this paper, we present the working principle and first experimental demonstration of an innovative approach to harvest lowquality heat sources, the SelfOscillating Fluidic Heat Engine (SOFHE). Thermal energy is first converted into pressure pulsations by a selfexcited thermofluidic oscillator driven by periodic phase change of a fluid in an enclosed channel. A piezoelectric membrane then converts this mechanical energy into an electrical power. After describing the working principle, an experimental demonstration is presented. The PV diagram of this new thermodynamic cycle is measured, showing a mechanical power of 3.3mW. Combined with a piezoelectric spiral membrane, the converted electrical power generation achieved is close to 1μ W in a 1MΩ load. This work sets the basis for future development of this new type of heat engine for waste heat recovery and to power wireless sensors. Art. [#ARTNUM](#article-33435-2561074235)

2.6.1 2.6 Piezoelectric heat conversion
First experimental demonstration of a Self-Oscillating Fluidic Heat Engine (SOFHE) with piezoelectric power generation
In this paper, we present the working principle and first experimental demonstration of an innovative approach to harvest low-quality heat sources, the Self-Oscillating Fluidic Heat Engine (SOFHE). Thermal energy is first converted into pressure pulsations by a selfexcited thermo-fluidic oscillator driven by periodic phase change of a fluid in an enclosed channel. A piezoelectric membrane then converts this mechanical energy into an electrical power. After describing the working principle, an experimental demonstration is presented. The P-V diagram of this new thermodynamic cycle is measured, showing a mechanical power of 3.3mW. Combined with a piezoelectric spiral membrane, the converted electrical power generation achieved is close to 1μ W in a 1MΩ load. This work sets the basis for future development of this new type of heat engine for waste heat recovery and to power wireless sensors.
11/01/2016 00:00:00
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2.6.2 2.6 Piezoelectric heat conversion
Piezoelectric Vibration Harvesters Based on Vibrations of Cantilevered Bimorphs: A Review
With the advancement in the technologies around the world over the past few years, the micro- electromechanical systems (MEMS) have gained much attention in harvesting the energy for wire- less, self-powered and MEMS devices. In the present era, many devices are available for energy harnessing such as electromagnetic, electrostatic and piezoelectric generator and these devices are designed based on its ability to capture the different form of environment energy such as solar energy, wind energy, thermal energy and convert it into the useful energy form. Out of these de- vices, the use of a piezoelectric generator for energy harvesting is very attractive for MEMS appli- cations. There are various sources of harvestable energy including waste heat, solar energy, wind energy, energy in floating water and mechanical vibrations which are used by the researchers for energy harvesting purposes. This paper reviews the state-of-the-art in harvesting mechanical vi- brations as an energy source by various generators (such as electromagnetic, electrostatic and piezoelectric generators). Also, the design and characteristics of piezoelectric generators, using vibrations of cantilevered bimorphs, for MEMS have also been reviewed here. Electromagnetic, electrostatic and piezoelectric generators presented in the literature are reviewed by taking into an account the power output, frequency, acceleration, dimension and application of each genera- tor and the coupling factor of each transduction mechanism has also been discussed for all the de- vices.
01/01/2015 00:00:00
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3. 3. Oher heat conversion technologies

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3.1 3.1 Thermoacoustic heat engine (TAHE)

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Thermoacoustic engines (sometimes called "TA engines") are thermoacoustic devices which use high-amplitude sound waves to pump heat from one place to another (this require work, which is provided by the loudspeaker). Or use a heat difference to produce work in the form of sound waves; these waves can then be converted into electrical current the same way as a microphone does. These device can be designed to use either standing wave or travelling wave. [[Wiki]](https://en.wikipedia.org/wiki/Thermoacoustic_heat_engine) The thermoacoustic heat engine in the figure consists of two heat exchangers. Those are the engine's heat source and heat sink, a stack where input thermal power is converted to acoustic power (a form of mechanical power), and a resonator which is a cylindrical tube encompassing all components and is the solid container for the acoustic wave generated. The key mechanism for energy conversion from thermal to acoustic is the thermoacoustic effect, occurring in the TAHE when certain conditions are satisfied. A compressible fluid is used as the working fluid within the engine, which in most cases is an inert gas such as helium. Acoustic waves occur naturally as a result of a temperature gradient across the stack as heat transfer occurs between the compressible fluid and a solid boundary (stack). The transfer of thermal energy to and from the compressible fluid and the stack creates local changes of pressure and velocity in the working fluid. When there is the correct pressure–velocity phasing, acoustic oscillations appear spontaneously creating an acoustic wave. Depending on the pressure–velocity phasing either a standing-wave or a travelling-wave is created. A standing-wave pressure–velocity phasing is shown in the Figure. The pressure the acoustic wave generates creates mechanical work, which can then be easily recovered to generate for example electric power. In this work a standing-wave thermoacoustic heat engine is evaluated due to its simple design, as can be seen in the figure. Art. [#ARTNUM](#article-29718-2146632007) **Research findings:** - In this present work the application of a standingwave TAHE to utilise waste heat from baking ovens in biscuit manufacturing is investigated. An iterative design methodology is employed to determine the design parameter values of the device that not only maximise acoustic power output and ultimately overall efficiency, but also utilise as much of the high volume waste heat as possible. At the core of the methodology employed is DeltaEC, a simulation software which calculates performance of thermoacoustic equipment. Our investigation has shown that even at such a comparatively low temperature of 150 °C it is possible to recover waste heat to deliver an output of 1029.10 W of acoustic power with a thermal engine efficiency of 5.42%. Art. [#ARTNUM](#article-29718-2146632007)

3.1.1 3.1 Thermoacoustic heat engine (TAHE)
A thermoacoustic Stirling heat engine
Electrical and mechanical power, together with other forms of useful work, are generated worldwide at a rate of about 10 12 watts, mostly using heat engines. The efficiency of such engines is limited by the laws of thermodynamics and by practical considerations such as the cost of building and operating them. Engines with high efficiency help to conserve fossil fuels and other natural resources reducing global-warming emissions and pollutants. In practice, the highest efficiencies are obtained only in the most expensive, sophisticated engines, such as the turbines in central utility electrical plants. Here we demonstrate an inexpensive thermoacoustic engine that employs the inherently efficient Stirling cycle 1 . The design is based on a simple acoustic apparatus with no moving parts. Our first small laboratory prototype, constructed using inexpensive hardware (steel pipes), achieves an efficiency of 0.30, which exceeds the values of 0.10-0.25 attained in other heat engines with no moving parts. Moreover, the efficiency of our prototype is comparable to that of the common internal combustion engine 2 (0.25-0.40) and piston-driven Stirling engines 3,4 (0.20-0.38).
05/01/1999 00:00:00
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3.1.2 3.1 Thermoacoustic heat engine (TAHE)
Design of a thermoacoustic heat engine for low temperature waste heat recovery in food manufacturing: A thermoacoustic device for heat recovery
Abstract There is currently an urgent demand to reuse waste heat from industrial processes with approaches that require minimal investment and low cost of ownership. Thermoacoustic heat engines (TAHEs) are a kind of prime mover that convert thermal energy to acoustic energy, consisting of two heat exchangers and a stack of parallel plates, all enclosed in a cylindrical casing. This simple design and the absence of any moving mechanical parts make such devices suitable for a variety of heat recovery applications in industry. In this present work the application of a standing-wave TAHE to utilise waste heat from baking ovens in biscuit manufacturing is investigated. An iterative design methodology is employed to determine the design parameter values of the device that not only maximise acoustic power output and ultimately overall efficiency, but also utilise as much of the high volume waste heat as possible. At the core of the methodology employed is DeltaEC, a simulation software which calculates performance of thermoacoustic equipment. Our investigation has shown that even at such a comparatively low temperature of 150 °C it is possible to recover waste heat to deliver an output of 1029.10 W of acoustic power with a thermal engine efficiency of 5.42%.
04/01/2014 00:00:00
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3.1.3 3.1 Thermoacoustic heat engine (TAHE)
Design of two-stage thermoacoustic stirling engine coupled with push-pull linear alternator for waste heat recovery
Thermoacoustics is suitable technology for recovering waste heat and generating electricity. In this paper, a novel thermoacoustic electricity generator using a push-pull linear alternator is proposed. It is aimed to recover part of the internal combustion engine exhaust waste heat and produce useful electricity. It consists of two half wave length identical stages and a linear alternator connected in between them. The physically identical stages produce identical wave halves with acoustic pressure out of phase. The availability of two points having the same pressure amplitude out of phase provides the opportunity to connect the linear alternator to two points in each stage to run the alternator in a "push and pull" mode. The proposed engine is able to produce more than 138.4W of electricity at thermal-to-electrical efficiency of 25.1% equivalent to a fraction of Carnot efficiency of 45.1% while using helium pressurized at 40 bar.
08/21/2015 00:00:00
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3.1.4 3.1 Thermoacoustic heat engine (TAHE)
Development of Thermoacoustic Engine Operating by Waste Heat from Cooking Stove
There are about 1.5 billion people worldwide use biomass as their primary form of energy in household cooking[1]. They do not have access to electricity, and are too remote to benefit from grid electrical supply. In many rural communities, stoves are made without technical advancements, mostly using open fires cooking stoves which have been proven to be extremely low efficiency, and about 93% of the energy generated is lost during cooking. The cooking is done inside a dwelling and creates significant health hazard to the family members and pollution to environment. SCORE (www.score.uk.com) is an international collaboration research project to design and build a low-cost, high efficiency woodstove that uses about half amount of the wood of an open wood fire, and uses the waste heat of the stove to power a thermoacoustic engine (TAE) to produce electricity for applications such as LED lighting, charging mobile phones or charging a 12V battery. This paper reviews on the development of two types of the thermo...
01/01/2012 00:00:00
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3.1.5 3.1 Thermoacoustic heat engine (TAHE)
Energy conversion through thermoacoustics and piezoelectricity
Waste or prime heat can be converted into electricity with thermoacoustic-Stirling engines coupled to piezoelectric alternators. An inline arrangement of engines and alternators allows a vibration balanced, multiphase power generator that is compact, light weight and low cost. The engines convert heat into high amplitude ≈400 Hz oscillations in pressurized helium gas. These pressure oscillations cause a thin steel diaphragm to flex like a drumhead. The diaphragm is supported at its perimeter by a ring of piezoelectric elements. As the diaphragm flexes in either direction, it pulls inward on the piezoelectric elements causing a large amplified ≈800 Hz fluctuating compressive stress in the elements which then convert the stress into electricity with high efficiency. The flexible-diaphragm piezoelectric alternator overcomes the large acoustic impedance mismatch between the helium and piezoelectric elements without exceeding the limited fatigue strength of available materials. So far, a prototype generator ha...
10/01/2011 00:00:00
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3.1.6 3.1 Thermoacoustic heat engine (TAHE)
Low-temperature energy conversion using a phase-change acoustic heat engine
Abstract Low-temperature heat is abundant, accessible through solar collectors or as waste heat from a large variety of sources. Thermoacoustic engines convert heat to acoustic work, and are simple, robust devices, potentially containing no moving parts. Currently, such devices generally require high temperatures to operate efficiently and with high power densities. Here, we present a thermoacoustic engine that converts heat to acoustic work at temperature gradients as low as ∼4–5 K/cm, corresponding with a hot-side temperature of ∼50 °C. The system is based on a typical standing-wave design, but the working cycle is modified to include mass transfer, via evaporation and condensation, from a solid surface to the gas mixture sustaining the acoustic field. This introduces a mode of isothermal heat transfer with the potential of providing increased efficiencies – experiments demonstrate a significant reduction in the operating temperature difference, which may be as low as 30 K, and increased output – this ‘wet’ system produces up to 8 times more power than its dry equivalent. Furthermore, a simplified model is formulated and corresponds quite well with experimental observations and offering insight into the underlying mechanism as well as projections for the potential performance of other mixtures. Our results illustrate the potential of such devices for harvesting energy from low-temperature heat sources. The acoustic power may be converted to electricity or, in a reverse cycle, produce cooling – providing a potential path towards solar heat-driven air conditioners.
12/01/2018 00:00:00
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3.2 3.2 Water desalination

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Waste heat can be used to desalinate water. **Research findings:** - A new desalination method was proposed in this work, utilizing lowgrade waste heat from the power plant, allowing cogeneration of fresh water with electricity. The desalination system analysed in this study makes use of simple concepts, such as Torricelli vacuum, flash evaporation and siphon effect, to reduce the overall operating power consumption of the plant. An experimental plant has been built and tested in an existing thermal power plant at Chennai, India. The plant utilized the warm saline reject water from the power plant condenser to feed the evaporator without using a separate feed water pump. The amount of freshwater produced by this plant is nearly 1/200 times of the sea water supplied for the available temperature gradient of 8.7°C. It is a lowcost system when compared with conventional desalination technologies, with energy consumption per unit volume estimated at 2.62 kWh/m3 of fresh water generated. Art. [#ARTNUM](#article-33254-2177896336)

3.2.1 3.2 Water desalination
A desalination method utilising low-grade waste heat energy
AbstractA new desalination method was proposed in this work, utilizing low-grade waste heat from the power plant, allowing co-generation of fresh water with electricity. The desalination system analysed in this study makes use of simple concepts, such as Torricelli vacuum, flash evaporation and siphon effect, to reduce the overall operating power consumption of the plant. An experimental plant has been built and tested in an existing thermal power plant at Chennai, India. The plant utilized the warm saline reject water from the power plant condenser to feed the evaporator without using a separate feed water pump. The amount of freshwater produced by this plant is nearly 1/200 times of the sea water supplied for the available temperature gradient of 8.7°C. It is a low-cost system when compared with conventional desalination technologies, with energy consumption per unit volume estimated at 2.62 kWh/m3 of fresh water generated. It operates at low temperatures, low pressure conditions and produces fresh wate...
11/20/2015 00:00:00
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3.2.2 3.2 Water desalination
Desalination process system utilizing waste heat
The invention relates to a desalination process system utilizing waste heat. The system comprises a multi-effect evaporator, a heat exchanger, a pipeline, a desalination water pump, a water supply pump, a crystallization tank, a boiler, a desalination water tank and a circulating pump. Boiler flue gas waste heat or low-enthalpy-value steam pumped out from a low-pressure cylinder of a steam turbine is used as an energy source, and through the heat exchanger and the multi-effect evaporator, salt-containing water is changed into distilled water to realize a desalination purpose; the produced distilled water can be directly used as production water for a power plant or domestic water. According to the system, compared with the prior art, the electricity consumption, the occupied land size and the operation cost are greatly reduced, and secondary pollution caused by medicine utilization is avoided; the system is safe, simple, practical and reliable; by recycling flue gas exhaust heat discharged from the boiler or low-enthalpy-value steam pumped out from the steam turbine, the desalination process operation cost is greatly reduced, and a very high economic value is realized.
02/03/2016 00:00:00
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3.2.3 3.2 Water desalination
Development and analysis of a novel biomass-based integrated system for multigeneration with hydrogen production
Abstract Energy and exergy analyses of an integrated system based on anaerobic digestion (AD) of sewage sludge from wastewater treatment plant (WWTP) for multi-generation are investigated in this study. The multigeneration system is operated by the biogas produced from digestion process. The useful outputs of this system are power, freshwater, heat, and hydrogen while there are some heat recoveries within the system for improving efficiency. An open-air Brayton cycle, as well as organic Rankine cycle (ORC) with R-245fa as working fluid, are employed for power generation. Also, desalination is performed using the waste heat of power generation unit through a parallel/cross multi-effect desalination (MED) system for water purification. Moreover, a proton exchange membrane (PEM) electrolyzer is used for electrochemical hydrogen production option in the case of excess electricity generation. The heating process is performed via the rejected heat of the ORC's working fluid. The production rates for products including the power, freshwater, hydrogen, and hot water are obtained as 1102 kW, 0.94 kg/s, 0.347 kg/h, and 1.82 kg/s, respectively, in the base case conditions. Besides, the overall energy and exergy efficiencies of 63.6% and 40% are obtained for the developed system, respectively.
02/01/2019 00:00:00
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3.3 3.3 Shape-memory metals/alloys

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A shape-memory alloy is an alloy that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. It may also be called memory metal, memory alloy, smart metal, smart alloy, or muscle wire. [[Wiki]](https://en.wikipedia.org/wiki/Shape-memory_alloy) By creating movement through heating or cooling, power can be produced by memory alloys. **Research findings:** - Few technologies can produce meaningful power from low temperature waste heat sources below 250°C, particularly on a permass basis. Since the 1970’s energy crisis, NiTi shape memory alloy (SMA) and associated thermal engines have been considered a viable heattopower transducer but were not adopted due to previously poor material quality, low supply, design complexity, and cost. Decades of subsequent material development, research, and commercialization have resulted in the availability of consistently highquality, wellcharacterized, low cost alloys and a renewed interest in SMA as a waste heat energy recovery technology. The Lightweight Thermal Energy Recovery System (LighTERS) is an ongoing ARPAE funded collaboration between General Motors Company, HRL Laboratories, Dynalloy, Inc., and the University of Michigan. In this paper we will present initial results from investigations of a closed loop SMA thermal engine (a refinement of the Dr. Johnson design) using a helical coil element and forcedair heat exchange. This engine generates mechanical power by continuously pulling itself through separate hot and cold air streams using the shape memory phase transformation to alternately expand and contract at frequencies between 0.25 and 2 Hz. This work cycle occurs continuously along the length of the coil loop and produces steady state power against an external moment. We present engine features and the thermal envelope that resulted in devices achieving between 0.1 and 0.5 W/g of shape memory alloy material using only forced air heat exchangers and room temperature cooling. Art. [#ARTNUM](#article-33430-2064257673) - An energy harvesting prototype (EHP) was designed to convert lowtemperature heat loss from fluid into electricity. The method for energy conversion uses two antagonistically connected shape memory alloy (SMA) actuators to rotate a shaft that is connected to a generator. Heat transfer equations for concentric annular flow are modeled. The relationship between SMA temperature and shaft angular rotation is derived from a semiempirical SMA stress–temperature model and Ozdemir's SMA stress–strain equations. The simulated generator shaft rotation and generator voltage are in close agreement with the corresponding experimental results. Additional experiments were conducted to compare the ability of spring and linear SMA wires to convert lowtemperature heat lost from water into electricity. The linear SMA generated a peak 0.3 V, whereas the springshaped SMA generated a peak of nearly 5 V. On average, 7.4 mJ of energy per 2.5 s cycle was stored in a 6F capacitor attached to the generator output. It is concluded that the EHP has a strong potential to recuperate lowtemperature wasted heat. Art. [#ARTNUM](#article-33430-2346496296)

3.3.1 3.3 Shape-memory metals/alloys
Development of a Shape Memory Alloy Heat Engine Through Experiment and Modeling
Few technologies can produce meaningful power from low temperature waste heat sources below 250°C, particularly on a per-mass basis. Since the 1970’s energy crisis, NiTi shape memory alloy (SMA) and associated thermal engines have been considered a viable heat-to-power transducer but were not adopted due to previously poor material quality, low supply, design complexity, and cost. Decades of subsequent material development, research, and commercialization have resulted in the availability of consistently high-quality, well-characterized, low cost alloys and a renewed interest in SMA as a waste heat energy recovery technology. The Lightweight Thermal Energy Recovery System (LighTERS) is an ongoing ARPA-E funded collaboration between General Motors Company, HRL Laboratories, Dynalloy, Inc., and the University of Michigan. In this paper we will present initial results from investigations of a closed loop SMA thermal engine (a refinement of the Dr. Johnson design) using a helical coil element and forced-air heat exchange. This engine generates mechanical power by continuously pulling itself through separate hot and cold air streams using the shape memory phase transformation to alternately expand and contract at frequencies between 0.25 and 2 Hz. This work cycle occurs continuously along the length of the coil loop and produces steady state power against an external moment. We present engine features and the thermal envelope that resulted in devices achieving between 0.1 and 0.5 W/g of shape memory alloy material using only forced air heat exchangers and room temperature cooling.Copyright © 2011 by ASME and General Motors
01/01/2011 00:00:00
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3.3.2 3.3 Shape-memory metals/alloys
Electromechanical Conversion of Low-Temperature Waste Heat Via Helical Shape Memory Alloy Actuators
An energy harvesting prototype (EHP) was designed to convert low-temperature heat loss from fluid into electricity. The method for energy conversion uses two antagonistically connected shape memory alloy (SMA) actuators to rotate a shaft that is connected to a generator. Heat transfer equations for concentric annular flow are modeled. The relationship between SMA temperature and shaft angular rotation is derived from a semiempirical SMA stress–temperature model and Ozdemir's SMA stress–strain equations. The simulated generator shaft rotation and generator voltage are in close agreement with the corresponding experimental results. Additional experiments were conducted to compare the ability of spring and linear SMA wires to convert low-temperature heat lost from water into electricity. The linear SMA generated a peak 0.3 V, whereas the spring-shaped SMA generated a peak of nearly 5 V. On average, 7.4 mJ of energy per 2.5 s cycle was stored in a 6-F capacitor attached to the generator output. It is concluded that the EHP has a strong potential to recuperate low-temperature wasted heat.
06/01/2016 00:00:00
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3.3.3 3.3 Shape-memory metals/alloys
Lightweight thermal energy recovery system based on shape memory alloys: a DOE ARPA-E initiative
Over 60% of energy that is generated is lost as waste heat with close to 90% of this waste heat being classified as low grade being at temperatures less than 200°C. Many technologies such as thermoelectrics have been proposed as means for harvesting this lost thermal energy. Among them, that of SMA (shape memory alloy) heat engines appears to be a strong candidate for converting this low grade thermal output to useful mechanical work. Unfortunately, though proposed initially in the late 60's and the subject of significant development work in the 70's, significant technical roadblocks have existed preventing this technology from moving from a scientific curiosity to a practical reality. This paper/presentation provides an overview of the work performed on SMA heat engines under the US DOE (Department of Energy) ARPA-E (Advanced Research Projects Agency - Energy) initiative. It begins with a review of the previous art, covers the identified technical roadblocks to past advancement, presents the solution path taken to remove these roadblocks, and describes significant breakthroughs during the project. The presentation concludes with details of the functioning prototypes developed, which, being able to operate in air as well as fluids, dramatically expand the operational envelop and make significant strides towards the ultimate goal of commercial viability.
04/26/2012 00:00:00
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Final Results

Published 09/11/2019

After the midway results meeting, 16 heat conversion technologies have been reviewed and deepened. The results are organised based on the concept and presented per heat conversion technologies comprising a description, findings, suppliers (if applicable), images, videos, useful links and a reference list. By using the concept links below, you can quickly navigate to the concepts and their heat conversion technologies descriptions.

Table of concepts:

  1. 1. Cycles used in heat conversion
  2. 2. Solid-state generators for heat conversion
  3. 3. Oher heat conversion technologies


1. Cycles used in heat conversion

Back

Different (thermodynamic) cycles are possible for the conversion of thermal energy into mechnical energy or electricity.


1.1 Steam rankine cycle

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A Rankine cycle is a closed-cycle system where a working fluid circulates through a minimum of an evaporator, turbine, condenser and a pump to convert heat into work, see figure. The evaporator can incorporate or be followed by a superheater if the working fluid/heat source temperature allows it. The conventional working fluid for Rankine cycle plants is water. [\[Source\]](https://www.dieselnet.com/tech/engine_whr_rankine.php) The most commonly used system for power generation from waste heat involves using the heat to generate steam in a waste heat boiler, which then drives a steam turbine. Steam Rankine cycles are not very efficient and can only use higher temperature waste streams. Art. [#ARTNUM](#article-33275-2903781546)

1.1.1 Steam rankine cycle
A review of unconventional bottoming cycles for waste heat recovery: Part I – Analysis, design, and optimization
Abstract In this paper, an extensive overview of unconventional waste heat recovery power cycles is presented. The three-unconventional waste heat recovery bottoming cycles discussed in this paper are the air bottoming cycle, carbon dioxide-based power cycles and Kalina bottoming cycle. The review paper is divided into two parts; first part is about a detailed discussion of energy, exergy, economic analysis, as well as reviewing part load analysis, component design, power augmentation and comparative studies. Whereas, the second part of the review paper demonstrate and thoroughly review the applications of the aforementioned unconventional bottoming cycles, including renewable energy sources. According to the literature, it was found that the air bottoming cycle is not as competitive when compared to the conventional bottoming cycle, such as the steam Rankine cycle. Nevertheless, air bottoming cycle can be economically competitive for low system capacities. Furthermore, CO 2 power cycles have shown better performance in terms of energetic and exergetic analyses when compared to the conventional bottoming cycles. The transcritical and supercritical CO 2 power cycles excel to recover low and medium grade waste heat, respectively. Finally, Kalina bottoming cycle was found to be competitive to recover the low-grade waste heat when compared to organic Rankine cycle. In addition, optimizing the ammonia-water concentrations at different stages of the cycle has the most notable effect in improving the cycle’s performance.
12/01/2018 00:00:00
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1.1.2 Steam rankine cycle
Investigation of a cascade waste heat recovery system based on coupling of steam Rankine cycle and NH 3 -H 2 O absorption refrigeration cycle
Abstract Cogeneration system based on cascade utilization of heat has been proved to be a promising technology to enhance energy conversion efficiency. An electricity-cooling cogeneration system (ECCS) based on coupling of a steam Rankine cycle (SRC) and an absorption refrigeration system (ARS) is proposed to recover the waste heat of marine engine to meet the electricity and cooling demand aboard. The SRC absorbed heat from the exhaust gas of engine to generate electricity, and the ARS makes use of the condensation heat of SRC to provide cooling needed on ship. Electricity output, cooling capacity, equivalent electricity output, exergy efficiency, and equivalent thermal efficiency are adopted to evaluate the performance of ECCS. The simulation results indicate that recovering the expansion work in the absorption refrigeration cycle is an effective way to increase electricity output at the cost of decreasing cooling capacity. The equivalent electricity output of the WHR system is 5223 kW, accounting for 7.61% of the rated power output of the marine engine.
06/01/2018 00:00:00
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1.2 Organic Rankine cycle

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The Organic Rankine Cycle (ORC) is named for its use of an organic, high molecular mass fluid with a liquid-vapor phase change, or boiling point, occurring at a lower temperature than the water-steam phase change. The fluid allows Rankine cycle heat recovery from lower temperature sources such as biomass combustion, industrial waste heat, geothermal heat, solar ponds etc. The low-temperature heat is converted into useful work, that can itself be converted into electricity. [\[Wiki\]](https://en.wikipedia.org/wiki/Organic_Rankine_cycle) There are several configurations and several working fluids possible for organic Rankine cycles. **Research findings:** * Organic working fluids because of the lower boiling points compared to water, make it possible to recover energy from low-temperature waste heat sources. The thermal efficiency of an ORC system depends on the thermodynamic properties of the working fluid and operating conditions of heat source, sink and cycle. Generally, the range of average thermal efficiency of an ORC system is from 0.02 to 0.19, and for small systems (lower than 5 kW) has lower thermal efficiency. Waste heat recoveries/efficiencies are between 5 and 40% depending on configuration and working fluids, using waste temperatures between 50 and 280 °C. [#ARTNUM](#article-29721-1966156747)

1.2.1 Organic Rankine cycle
A proposed coal-to-methanol process with CO2 capture combined Organic Rankine Cycle (ORC) for waste heat recovery
Abstract Coal-to-methanol (CTM) is the main methanol production process in China. Application of carbon capture and storage (CCS) technology in CTM is a possible way for CO 2 reduction. However, the increase of energy consumption caused by CCS and related increase of Green House Gas footprint has to be minimised. This paper presents a CTM combined with CO 2 capture and Organic Rankine Cycle (ORC) power generation, which improves energy efficiency simultaneously. The electricity generated from ORC is through the thermodynamic cycle converted the waste heat recovered from the CO 2 compression and water gas shift unit in CTM process. The proposed process is simulated and analysed from energy efficiency and economic viewpoints. The analysis indicates several points: (1) Heat Integration of CO 2 compression and water gas shift unit produce the heated water as the heat source of ORC; (2) With the CO 2 ratio of 60%, the energy efficiency of the proposed CTM combined ORC system is 45.5%; (3) From economic point of view, electricity generated from waste heat conversion is around 4.8 MW, and the payback period of the ORC invested in CTM with CO 2 capture process is 2.7 y.
08/01/2016 00:00:00
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1.2.2 Organic Rankine cycle
A recent review of waste heat recovery by Organic Rankine Cycle
Abstract The increment of using fossil fuels has caused many perilous environmental problems such as acid precipitation, global climate change and air pollution. More than 50% of the energy that is used in the world is wasted as heat. Recovering the wasted heat could increase the system efficiency and lead to lower fuel consumption and CO2 production. Organic Rankine cycle (ORC) which is a reliable technology to efficiently convert low and medium temperature heat sources into electricity, has been known as a promising solution to recover the waste heat. There are numerous studies about ORC technology in a wide range of application and condition. The main objective of this paper is to presents a review of studies both theoretical and experimental on ORC usage for waste heat recovery and investigation on the effect of cycle configuration, working fluid selection and operating condition on the system performance, that have been developed during the last four years. Finally, the related statistics are reported and compared regarding the configuration and the employed working fluid with type of the heat source.
10/01/2018 00:00:00
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1.2.3 Organic Rankine cycle
A review of thermodynamic cycles used in low temperature recovery systems over the last two years
This review explores the potential of low and medium grade heat in different thermodynamic cycles used to transform wasted heat into mechanical work. The aim of this review is to study the state of the art of the thermodynamic cycles used to recover low-grade heat. The relevance of researching low grade heat or waste heat applications is that a vast amount of heat energy is available at negligible cost within the range of medium and low temperatures, with the drawback that existing thermal cycles cannot make efficient use of such available low temperature heat due to their low efficiency. The different types of Organic Rankine Cycles have been reviewed, highlighting their relevant characteristics where Simple Organic Rankine Cycle, Regenerative Organic Rankine Cycle, Cascade Organic Rankine Cycle, Organic Flash Cycles, Other Rankine Configurations and Trilateral Cycles are included. Reviews were conducted of specific applications of the low-grade heat recovery. In contrast, there are no actual publications which summarise the current state of the art of the thermodynamic cycles used to convert wasted heat into mechanical power. This paper offers a different approach and analyses low-grade heat recovery from a thermodynamic point of view and compares their efficiency. The analysis shows that cycles using closed processes are by far the most efficient published thermal cycles for low-grade heat recovery. Rankine cycles reviewed show similar low efficiencies. In contrast, closed process cycles have a configuration, which allows efficient exploitation of low-grade heat.
01/01/2018 00:00:00
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1.2.4 Organic Rankine cycle
Heat Conversion into Power Using Small Scale Organic Rankine Cycles
The world economy heavily relies on fossil fuels. Their use leads to carbon dioxide emissions responsible of global warming and fuels international tensions. Renewable energy sources and energy efficiency are alternatives. An Organic Rankine Cycle is similar to a steam cycle but uses an organic fluid instead of water. It is suitable for conversion of solar radiation, geothermal energy, biomass energy, ocean thermal gradient, and waste heat into power. Although investigated in the 1970s, it was soon abandoned after the oil crisis. With the growing concern on the environment, the interest for this technology for electricity generation was renewed. The technology for medium and large scale systems is already mature but solutions are still sought for small systems. This book presents results of investigation on micro organic Rankine cycles of less than 2 kW power output. Overview of different organic Rankine cycle applications, working fluid selection, cycle performance analysis, and economic evaluation constitute the content of the book and will be useful to energy professionals, researchers working on thermodynamics and those interested in next generation power systems.
10/24/2012 00:00:00
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1.2.5 Organic Rankine cycle
Low-grade heat conversion into power using organic Rankine cycles – A review of various applications
An organic Rankine cycle (ORC) machine is similar to a conventional steam cycle energy conversion system, but uses an organic fluid such as refrigerants and hydrocarbons instead of water. In recent years, research was intensified on this device as it is being progressively adopted as premier technology to convert low-temperature heat resources into power. Available heat resources are: solar energy, geothermal energy, biomass products, surface seawater, and waste heat from various thermal processes. This paper presents existing applications and analyzes their maturity. Binary geothermal and binary biomass CHP are already mature. Provided the interest to recover waste heat rejected by thermal devices and industrial processes continue to grow, and favorable legislative conditions are adopted, waste heat recovery organic Rankine cycle systems in the near future will experience a rapid growth. Solar modular power plants are being intensely investigated at smaller scale for cogeneration applications in buildings but larger plants are also expected in tropical or Sahel regions with constant and low solar radiation intensity. OTEC power plants operating mainly on offshore installations at very low temperature have been advertised as total resource systems and interest on this technology is growing in large isolated islands.
10/01/2011 00:00:00
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1.2.6 Organic Rankine cycle
Organic Rankine Cycle Working Fluid Selection and Performance Analysis for Combined Application With a 2 MW Class Industrial Gas Turbine
The selection of suitable working fluids for use in Organic Rankine Cycles (ORC) is strongly addicted to the intended application of the ORC system. The design of the ORC, the kind of heat source and the ambient condition has an influence on the performance of the Organic Rankine Cycle and on the selection of the working fluid. It can come to a discrepancy between the best candidate from the thermodynamic point of view and the transformation into a real machine design. If an axial turbine design is considered for expansion and energy conversion within the ORC, the vapor volume flow ratios within the expansion path, the pressure ratio and of course the number of stages have to be considered within the fluid selection process and for the design parameters. Furthermore, environmental aspects have to be taken into account, e.g. the global warming potential (GWP) and the flammability of the selected fluid.This paper shows the results of the design and fluid selection process for an Organic Rankine Cycle for application in a combined operation with a 2MW class industrial gas turbine.The gas turbine contains two radial compressor stages with an integrated intercooler. To further increase the thermal cycle efficiency, a recuperator has been implemented to the gas turbine cycle, which uses the exhaust gas waste heat to preheat the compressed air after the second compressor, before it enters the combustion chamber. The shaft power is generated by a three stage axial turbine, whereby the first stage is a convection cooled stage, due to a turbine inlet temperature of 1100°C.To further increase the electrical efficiency and the power output of the energy conversion cycle, a combined operation with an organic Rankine cycle is intended. Therefore the waste heat from the GT compressor intercooler is used as first heat source and the waste heat of the exhaust gas after the recuperator as second heat source for the Organic Rankine Cycle. It is intended that the ORC fluid acts as heat absorption fluid within the compressor intercooler. Due to these specifications for the ORC, a detailed thermodynamic analysis has been performed to determine the optimal design parameter and the best working fluid for the ORC, in order to obtain a maximum power output of the combined cycle.Due to the twice coupling of the ORC to the GT cycle, the heat exchange between the two cycles is bounded by each other and a detailed analysis of the coupled cycles is necessary. E.g. the ambient temperature has an enormous influence on the transferred heat from the intercooler to the ORC cycle, which itself affects the heat transfer and temperatures of the transferable heat from the second heat source. Thus, a detailed analysis by considering the ambient operation conditions has been performed, in order to provide a most efficient energy conversion system over a wide operation range.The performance analysis has shown that by application of an ORC for a combined operation with the intercooled and recuperated gas turbine, the combined cycle efficiency can be increased, for a wide ambient conditions range, by more than 3 %pts. and the electrical power output by more than 10 %, in comparison to the stand alone intercooled and recuperated gas turbine.Copyright © 2014 by ASME
06/16/2014 00:00:00
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1.2.7 Organic Rankine cycle
Vapor Rankine and organic Rankine combined cycle electricity generation device
The utility model relates to a vapor Rankine and organic Rankine combined cycle electricity generation device. Organic working media in an organic Rankine cycle are used for cooling vapor in a vapor Rankine cycle, latent heat of vaporization of the vapor in the vapor Rankine cycle is recovered to be used for electricity generation of the organic Rankine cycle, and accordingly the vapor Rankine cycle and the organic Rankine cycle are compounded together to form the enforceable combined cycle device. Meanwhile, the safety difficult problem that the organic Rankine cycle recovers waste heat of exhaust gas is solved, the exhaust gas temperature is effectively reduced, low-temperature corrosion of the exhaust gas is avoided, and waste gas, waste water and waste heat of waste vapor in a vapor Rankine cycle system can be recycled effectively. The vapor Rankine and organic Rankine combined cycle electricity generation device not only can be used for energy-saving transformation of an existing set, but also can be used for design and construction of a new set, especially is suitable for new construction, extension and rebuilding of an electricity generation set in areas such as severe cold areas, water-deficient areas and electricity-deficient areas, and is significant in economic benefits, social benefits and environment protection benefits.
07/31/2013 00:00:00
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1.3 Supercritical/transcritical CO₂ rankine cycles

0

In supercritical Rankine cycle (Figure), a stream of the working fluid is pumped above its critical pressure (1–2), and then heated isobarically from liquid directly to supercritical vapor (2–3); the supercritical vapor is expanded in the turbine to extract mechanical work (3–4); after expansion, the fluid is condensed in the condenser by dissipating heat to a heat sink (4–1); the condensed liquid is then pumped to the high pressure again, which completes the cycle. A basic supercritical CO2 Rankine cycle consists of gas heater, expansion turbine, condenser and pump. Art. [#ARTNUM](#article-29717-1999416566) Besides CO2 there are other working fluids that could be used for a supercritical Rankine cycle, but they remain largely unexplored. The temperature glide for CO2 above the critical point allows for better matching to the heat source temperature glide than an organic working fluid working below the critical point. Therefore, the so-called pinching problem, which may occur in ORC׳s counter-current heat exchanger, can be avoided by carbon dioxide transcritical power cycle. Compared to organic and steam-based Rankine Cycle systems, supercritical CO2 Rankine cycle can achieve high efficiencies (up to 30% higher) over a wide temperature range of heat sources with compact components resulting in a smaller system footprint, lower capital and operating costs. Art. [#ARTNUM](#article-29717-1999416566)

1.3.1 Supercritical/transcritical CO₂ rankine cycles
A review of unconventional bottoming cycles for waste heat recovery: Part I – Analysis, design, and optimization
Abstract In this paper, an extensive overview of unconventional waste heat recovery power cycles is presented. The three-unconventional waste heat recovery bottoming cycles discussed in this paper are the air bottoming cycle, carbon dioxide-based power cycles and Kalina bottoming cycle. The review paper is divided into two parts; first part is about a detailed discussion of energy, exergy, economic analysis, as well as reviewing part load analysis, component design, power augmentation and comparative studies. Whereas, the second part of the review paper demonstrate and thoroughly review the applications of the aforementioned unconventional bottoming cycles, including renewable energy sources. According to the literature, it was found that the air bottoming cycle is not as competitive when compared to the conventional bottoming cycle, such as the steam Rankine cycle. Nevertheless, air bottoming cycle can be economically competitive for low system capacities. Furthermore, CO 2 power cycles have shown better performance in terms of energetic and exergetic analyses when compared to the conventional bottoming cycles. The transcritical and supercritical CO 2 power cycles excel to recover low and medium grade waste heat, respectively. Finally, Kalina bottoming cycle was found to be competitive to recover the low-grade waste heat when compared to organic Rankine cycle. In addition, optimizing the ammonia-water concentrations at different stages of the cycle has the most notable effect in improving the cycle’s performance.
12/01/2018 00:00:00
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1.3.2 Supercritical/transcritical CO₂ rankine cycles
A thermodynamic analysis and economic assessment of a modified de-carbonization coal-fired power plant incorporating a supercritical CO2 power cycle and an absorption heat transformer
Abstract An improved de-carbonization coal-fired power plant configuration incorporating a supercritical CO 2 (S-CO 2 ) power cycle and an absorption heat transformer (AHT) was proposed. The adopted S-CO 2 power cycle efficiently absorbs the process waste heat within the CO 2 capture process to drive a S-CO 2 turbine to produce work, and the exhaust S-CO 2 is beneficially utilized to preheat the air prior to the air preheater, saving a part of the flue gas energy, which can then be absorbed by the low-temperature economizer (LTE). An AHT is employed here to recover the remaining waste heat within the CO 2 capture unit to vaporize the reboiler condensate for solvent regeneration. The mass and energy balance and the overall performance of the proposed system were determined by the developed models and process simulation. The detailed energy/exergy distributions of the reference and proposed plants were also investigated. Finally, the economics of the proposed system were assessed by the cost of electricity (COE) and the cost of CO 2 avoided (COA). Results showed that the energy/exergy efficiency could reach 34.38% and 33.36%, respectively, better than the reference plant. The COE and COA of the proposed system were $92.21/MWh and $46.27/t CO 2 , also showing an advantage over the reference one.
05/01/2019 00:00:00
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1.3.3 Supercritical/transcritical CO₂ rankine cycles
An improved CO2-based transcritical Rankine cycle (CTRC) used for engine waste heat recovery
CO2-based transcritical Rankine cycle (CTRC) is a promising technology for the waste heat recovery of an engine considering its safety and environment friendly characteristics, which also matchs the high temperature of the exhaust gas and satisfies the miniaturization demand of recovery systems. But the traditional CTRC system with a basic configuration (B-CTRC) has a poor thermodynamic performance. This paper introduces an improved CTRC system containing both a preheater and regenerator (PR-CTRC), for recovering waste heat in exhaust gas and engine coolant of an engine, and compares its performance with that of the B-CTRC system and also with that of the traditional excellent Organic Rankine Cycle (ORC) systems using R123 as a working fluid. The utilization rate of waste heat, total cooling load, net power output, thermal efficiency, exergy loss, exergy efficiency and component size have been investigated. Results show that, the net power output of the PR-CTRC could reach up to 9.0kW for a 43.8kW engine, which increases by 150% compared with that of the B-CTRC (3.6kW). The PR-CTRC also improves the thermal efficiency and exergy efficiency of the B-CTRC, with increases of 184% and 227%, respectively. Compared with the ORC system, the PR-CTRC shows the significant advantage of highly recycling the exhaust gas and engine coolant simultaneously due to the special property of supercritical CO2’s specific heat capacity. The supercritical property of CO2 also generates a better heat transfer and flowing performances. Meanwhile, the PR-CTRC possesses a smaller SP (0.010–0.020m) than that of R123 systems (0.055–0.070m). Therefore, the PR-CTRC system is suitable for the waste heat recovery of an engine, especially for recovering both high-grade and low-grade waste heat.
08/01/2016 00:00:00
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1.3.4 Supercritical/transcritical CO₂ rankine cycles
Configurations selection maps of CO2-based transcritical Rankine cycle (CTRC) for thermal energy management of engine waste heat
CO2-based transcritical Rankine cycle (CTRC) can be used for the waste heat recovery due to its safety and environment-friendly characteristics, and also fits for the high temperature of exhaust gas and satisfy the miniaturization demand of recovery systems. It can provide a reasonable pathway toward thermal energy management of engine. This work proposes novel configurations selection maps of four CTRC configurations for waste heat recovery of engines. Except for considering a regenerator added to traditional CTRC (basic CTRC) recovering exhaust waste heat, a preheater driven by engine coolant will be also taken into account in this paper. Thus, the four configurations include the basic CTRC (B-CTRC), the CTRC with a preheater (P-CTRC), the CTRC with a regenerator (R-CTRC) and the CTRC with both of the preheater and the regenerator (PR-CTRC). As different CTRC configurations have advantage of performance indicators under different conditions, and the focused indicators may also be various with applications, this paper focuses on proposing a kind of selection maps, which is used for the selection of the four CTRC configurations in the field of engine waste heat recovery. Comprehensive performance comparison are researched in this paper from three aspects, net power output based on the first law of thermodynamics, exergy efficiency based on the second law of thermodynamics and electricity production cost (EPC) as an indicator of the economic performance. After the comparative analysis, three selection maps separately based on the three performance indicators are proposed to give the selection reference of the CTRC configurations under different design conditions, which refer to turbine inlet pressure and temperature in this paper. It is meaningful for the design and operating of the CTRC configuration used for waste heat recovery of engines. Besides, it can also be a new method that can be expanded to other recovery system selection (e.g. ORCs) in engine field or other fields (e.g. solar, geothermal).
01/01/2017 00:00:00
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1.3.5 Supercritical/transcritical CO₂ rankine cycles
Exergoeconomic analysis of utilizing the transcritical CO2 cycle and the ORC for a recompression supercritical CO2 cycle waste heat recovery: A comparative study
Two combined cogeneration cycles are examined in which the waste heat from a recompression supercritical CO2 Brayton cycle (sCO2) is recovered by either a transcritical CO2 cycle (tCO2) or an Organic Rankine Cycle (ORC) for generating electricity. An exergoeconomic analysis is performed for sCO2/tCO2 cycle performance and its comparison to the sCO2/ORC cycle. The following organic fluids are considered as the working fluids in the ORC: R123, R245fa, toluene, isobutane, isopentane and cyclohexane. Thermodynamic and exergoeconomic models are developed for the cycles on the basis of mass and energy conservations, exergy balance and exergy cost equations. Parametric investigations are conducted to evaluate the influence of decision variables on the performance of sCO2/tCO2 and sCO2/ORC cycles. The performance of these cycles is optimized and then compared. The results show that the sCO2/tCO2 cycle is preferable and performs better than the sCO2/ORC cycle at lower PRc. When the sCO2 cycle operates at a cycle maximum pressure of around 20MPa (∼2.8 of PRc), the tCO2 cycle is preferable to be integrated with the recompression sCO2 cycle considering the off-design conditions. Moreover, contrary to the sCO2/ORC system, a higher tCO2 turbine inlet temperature improves exergoeconomic performance of the sCO2/tCO2 cycle. The thermodynamic optimization study reveals that the sCO2/tCO2 cycle has comparable second law efficiency with the sCO2/ORC cycle. When the optimization is conducted based on the exergoeconomics, the total product unit cost of the sCO2/ORC is slightly lower than that of the sCO2/tCO2 cycle.
05/01/2016 00:00:00
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1.3.6 Supercritical/transcritical CO₂ rankine cycles
High-Temperature Receiver Designs for Supercritical CO2 Closed-Loop Brayton Cycles
High-temperature receiver designs for solar powered supercritical CO2 Brayton cycles that can produce ∼1 MW of electricity are being investigated. Advantages of a supercritical CO2 closed-loop Brayton cycle with recuperation include high efficiency (∼50%) and a small footprint relative to equivalent systems employing steam Rankine power cycles. Heating for the supercritical CO2 system occurs in a high-temperature solar receiver that can produce temperatures of at least 700 °C. Depending on whether the CO2 is heated directly or indirectly, the receiver may need to withstand pressures up to 20 MPa (200 bar). This paper reviews several high-temperature receiver designs that have been investigated as part of the SERIIUS program. Designs for direct heating of CO2 include volumetric receivers and tubular receivers, while designs for indirect heating include volumetric air receivers, molten-salt and liquid-metal tubular receivers, and falling particle receivers. Indirect receiver designs also allow storage of thermal energy for dispatchable electricity generation. Advantages and disadvantages of alternative designs are presented. Current results show that the most viable options include tubular receiver designs for direct and indirect heating of CO2 and falling particle receiver designs for indirect heating and storage.Copyright © 2014 by ASME
06/30/2014 00:00:00
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1.3.7 Supercritical/transcritical CO₂ rankine cycles
Hybrid type supercritical CO2 power generation system
The present invention relates to a hybrid power generation system, in which a supercritical carbon dioxide power generation system generating electric energy by using supercritical carbon dioxide as operation fluid and a cogeneration system generating thermal energy and electric energy by burning fuel are mixed, comprises at least one pump which circulates the operation fluid; at least one recuperator which primarily heats the operation fluid passing through the pump; at least one heat exchanger which reheats the operation fluid heated by the recuperator by using waste heat as a heat source; a plurality of turbines which are driven by the operation fluid reheated by the heat exchanger; and a complex heat exchanger which exchanges between heating water of the cogeneration system and the operation fluid to heat the heating water and to cool the operation fluid. The operation fluid passing through the turbine exchanges heat with the operation fluid passing through the pump to be cooled, and is supplied to the complex heat exchanger. The supercritical carbon dioxide power generation system and the cogeneration system share the complex heat exchanger. According to the present invention, there is an advantage of improving efficiency of electricity generation and heating heat generation by integrally operating the supercritical carbon dioxide power generation and cogeneration. In addition, heat efficiency of a power generation cycle is improved, and it is possible to actively cope with power demand since it varies seasonally.
04/12/2018 00:00:00
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1.3.8 Supercritical/transcritical CO₂ rankine cycles
Performance improvement of a preheating supercritical CO2 (S-CO2) cycle based system for engine waste heat recovery
Abstract Due to the compact structure in addition to the system safety level and environmental friendly characteristics, supercritical CO 2 (S-CO 2 ) cycle has emerged as a promising method to be used in engine waste heat recovery. This paper explores the potential of using a preheating S-CO 2 cycle based system to recover the waste heat of a diesel engine. An original preheating system is presented, in which the high temperature engine exhaust gas is firstly utilized in the evaporator and then it is further cooled through preheating process together with the low temperature jacket cooling water. Though the entire heat load from these two heat sources could be entirely recovered, the high preheating temperature suppresses the heat transfer in the regenerator. An improved preheating S-CO 2 cycle based system with a regeneration branch is then presented. S-CO 2 flow from the compressor is divided into two parts, one of which is still preheated by the jacket cooling water and the cooled engine exhaust gas in series while the other is heated in a low temperature regenerator. The two flows converge and then continues to be heated in the high temperature regenerator and in the evaporator. The simulation results reveal that the improved system could achieve a deeper utilization of the regeneration heat load hence improve the system performance. The maximum net power output of the improved system reaches 68.4 kW, which is 7.4% higher than that of the original system, 63.7 kW. Adopting the improved preheating S-CO 2 cycle based system for waste heat recovery, the engine power output (996 kW) can be increased by 6.9%.
04/01/2018 00:00:00
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1.3.9 Supercritical/transcritical CO₂ rankine cycles
Review and future trends of supercritical CO2 Rankine cycle for low-grade heat conversion
Due to personal and environmental safeties along with various advantages, CO2 became a potential choice as working fluid for both heat engine and heat pump cycles. Because of better temperature glide matching between heat source and working fluid during heat addition leading to no pinch limitation, CO2 has been proposed recently as working fluid for supercritical Rankine cycle with low grade heat sources. Supercritical Rankine cycle and its various working fluids, heat sources, heat sinks and analysis approaches, and performance analyses and optimization of various supercritical CO2 Rankine cycle configurations along with comparison with other working fluids, prototype development, component design and challenges are well-grouped and discussed. Supercritical CO2 Rankine cycle is superior to both steam and organic Rankine cycles, whereas yields mix results compared to other fluids in supercritical Rankine cycle with system compactness and environmental benefit as unique advantages. Future research pathways regarding to system components, experimentation, operating parameter optimizations, control strategies, etc. are discussed as well. Although, there is no supercritical CO2 Rankine cycle in operation up to now, it is becoming a future pathway due to its promising research outcomes and this review will be useful for further progress.
08/01/2015 00:00:00
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1.3.10 Supercritical/transcritical CO₂ rankine cycles
Review of supercritical CO2 power cycle technology and current status of research and development
The supercritical CO2 (S-CO2) Brayton cycle has recently been gaining a lot of attention for application to next generation nuclear reactors. The advantages of the S-CO2 cycle are high efficiency in the mild turbine inlet temperature region and a small physical footprint with a simple layout, compact turbomachinery, and heat exchangers. Several heat sources including nuclear, fossil fuel, waste heat, and renewable heat sources such as solar thermal or fuel cells are potential application areas of the S-CO2 cycle. In this paper, the current development progress of the S-CO2 cycle is introduced. Moreover, a quick comparison of various S-CO2 layouts is presented in terms of cycle performance.
10/01/2015 00:00:00
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1.3.11 Supercritical/transcritical CO₂ rankine cycles
Supercritical CO2 Power Cycle Developments and Commercialization: Why sCO2
The U.S. DOE estimates that 280,000 MW discharged annually in the U.S. as waste heat could be recycled as usable energy to provide 20 percent of U.S. electricity needs while slashing GHG by 20 percent and saving USD $70-150B per year on energy costs. Waste heat can be considered as the other green energy because it is a renewable energy equivalent resource that improves energy efficiency from existing fossil fuel usage, while reducing grid demand by converting the recovered heat into usable electricity, heating and/or cooling. While various sources of independent data suggest that this waste heat recovery opportunity is valued at over USD $600B for the U.S. market, similar large opportunities exist worldwide. Echogen Power Systems LLC (Akron, OH U.S.A.) is developing power generation technologies that transform heat from waste and renewable energy sources into electricity and process heat. The thermal engine technology; the Thermafficient ® Heat Engine converts waste heat to power using a breakthrough supercritical CO2-based power cycle. Compared to organic and steam-based Rankine Cycle systems, supercritical CO2 can achieve high efficiencies over a wide temperature range of heat sources with compact components resulting in a smaller system footprint, lower capital and operating costs. The Levelized Cost of Electricity (LCOE) is calculated at an average USD $0.025 per kWh for the CO2-based heat engine and averages at USD $0.065 per kWh for a complete combined cycle gas turbine system utilizing the supercritical CO2 heat engine for bottom cycling. This paper presents an exemplary trade study comparison between the CO2 and steam-based heat recovery systems. An update is also provided for the Echogen 250 kW demonstration thermal engine which completed initial testing at the American Electric Power’s research center during 2011. Also presented is current status of long term testing with this system at a commercial district heating organization, and a multi-megawatt heat engine that will be installed at a U.S. customer host site during 2013.
01/01/2012 00:00:00
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1.4 Supercritical CO₂ brayton cycle

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To successfully utilize the high reactor outlet temperature, interest in alternative power conversion systems is also increasing. The steam Rankine cycle and gas turbine systems have been utilized by large size power plants for several decades. When the turbine inlet temperature is > 550 °C, the ultra-supercritical (USC) steam cycle is required to further improve the efficiency of a steam Rankine cycle. However, the USC steam cycle inevitably suffers from material degradation due to high temperature and pressure operating conditions. Therefore, when the USC steam Rankine cycle is coupled to a nuclear power plant, the plant reliability can be a significant issue if the system is composed only of existing materials. As a result, an alternative power conversion system which can operate in the mild turbine inlet temperature region (500–900°C) is essential to improve the next generation nuclear power plant performance and safety at the same time. Among various candidates, the S-CO₂ power cycle is considered as one of the promising alternatives to potentially provide high efficiency in the Gen IV reactor operating temperature region, better stability with conventional structure materials, and eventually improved safety and reliability of the power conversion system. Art. [#ARTNUM](#article-36507-1163097982) Applications in nuclear, coal, renewables

1.4.1 Supercritical CO₂ brayton cycle
A Supercritical CO2 Brayton Cycle Power Converter for a Sodium-Cooled Fast Reactor Small Modular Reactor
Although a number of power conversion applications have been identified or have even been developed (e.g., waste heat recovery) for supercritical carbon dioxide (S-CO2) cycles including fossil fuel combustors, concentrated solar power (i.e., solar power towers), and marine propulsion, the benefits of S-CO2 Brayton cycle power conversion are especially prominent for applications to nuclear power reactors. In particular, the S-CO2 Brayton cycle is well matched to the Sodium-Cooled Fast Reactor (SFR) nuclear power reactor system and offers significant benefits for SFRs. The recompression closed Brayton cycle is highly recuperated and wants to operate with an approximate optimal S-CO2 temperature rise in the sodium-to-CO2 heat exchangers of about 150 °C which is well matched to the sodium temperature rise through the core that is also about 150 °C. Use of the S-CO2 Brayton cycle eliminates sodium-water reactions and can reduce the nuclear power plant cost per unit electrical power. A conceptual design of an optimized S-CO2 Brayton cycle power converter and supporting systems has been developed for the Advanced Fast Reactor – 100 (AFR-100) 100 MWe-class (250 MWt) SFR Small Modular Reactor (SMR). The AFR-100 is under ongoing development at Argonne National Laboratory (ANL) to target emerging markets where a clean, secure, and stable source of electricity is required but a large-scale power plant cannot be accommodated. The S-CO2 Brayton cycle components and cycle conditions were optimized to minimize the power plant cost per unit electrical power (i.e., $/kWe). For a core outlet temperature of 550 °C and turbine inlet temperature of 517 °C, a cycle efficiency of 42.3 % is calculated that exceeds that obtained with a traditional superheated steam cycle by one percentage point or more. A normal shutdown heat removal system incorporating a pressurized pumped S-CO2 loop slightly above the critical pressure on each of the two intermediate sodium loops has been developed to remove heat from the reactor when the power converter is shut down. Three-dimensional layouts of S-CO2 Brayton cycle power converter and shutdown heat removal components and piping have been determined and three-dimensional CAD drawings prepared. The S-CO2 Brayton cycle power converter is found to have a small footprint reducing the space requirements for components and systems inside of both the turbine generator building and reactor building. The results continue to validate earlier notions about the benefits of S-CO2 Brayton cycle power conversion for SFRs including higher efficiency, improved economics, elimination of sodium-water reactions, load following, and smaller footprint.Copyright © 2015 by ASME
06/28/2015 00:00:00
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1.4.2 Supercritical CO₂ brayton cycle
Integration between supercritical CO2 Brayton cycles and molten salt solar power towers: A review and a comprehensive comparison of different cycle layouts
In the present study, several current S-CO2 Brayton cycle layouts are reviewed, and considered to be integrated into the existing mature molten salt solar power tower (SPT) systems. The SPT systems integrated with S-CO2 Brayton cycles are completely modeled by an integrative approach. The performances of these different cycles are compared comprehensively for applications in molten salt SPT systems from the aspects of the efficiency, the specific work, and the incorporation ability with the thermal energy storage indicated by the molten salt temperature difference across the solar receiver. The results indicate: (1) The intercooling cycle can generally offer the highest efficiency, followed by the partial-cooling cycle, and the recompression cycle; The precompression cycle can yield higher efficiency than the recompression cycle when the compressor inlet temperature is high; The increase in the hot salt temperature cannot always result in the efficiency improvement of the SPT systems. (2) The partial-cooling cycle can offer the largest specific work, while the recompression cycle and the split expansion cycle yield the lowest specific work. (3) The molten salt temperature differences of SPT systems with the simple recuperation cycle, the partial-cooling cycle, and the precompression cycle are slightly larger than those of SPT systems with the recompression cycle, the split expansion cycle, and the intercooling cycle. (4) As a classical approach to improve efficiency, reheating can decrease the system efficiency in the cases with high hot molten salt temperature; SPT systems without reheating can yield larger molten salt temperature difference than those with reheating. (5) Although the current S-CO2 Brayton cycle layouts can offer high efficiency, there are still several challenges for integrating them into the SPT systems: the specific work is relatively small, and the temperature difference across the solar receiver is narrow. Further work remains to build novel S-CO2 cycle layouts with high efficiency, large specific work, and wide temperature difference.
06/01/2017 00:00:00
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1.4.3 Supercritical CO₂ brayton cycle
Review of supercritical CO2 power cycle technology and current status of research and development
The supercritical CO2 (S-CO2) Brayton cycle has recently been gaining a lot of attention for application to next generation nuclear reactors. The advantages of the S-CO2 cycle are high efficiency in the mild turbine inlet temperature region and a small physical footprint with a simple layout, compact turbomachinery, and heat exchangers. Several heat sources including nuclear, fossil fuel, waste heat, and renewable heat sources such as solar thermal or fuel cells are potential application areas of the S-CO2 cycle. In this paper, the current development progress of the S-CO2 cycle is introduced. Moreover, a quick comparison of various S-CO2 layouts is presented in terms of cycle performance.
10/01/2015 00:00:00
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1.5 Kalina cycle

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It uses a solution of 2 fluids with different boiling points for its working fluid. Since the solution boils over a range of temperatures as in distillation, more of the heat can be extracted from the source than with a pure working fluid. The same applies to the exhaust (condensing) end. This provides efficiency comparable to a Combined cycle, with less complexity. [\[Wiki\]](https://en.wikipedia.org/wiki/Kalina_cycle) By appropriate choice of the ratio between the components of the solution, the boiling point of the working solution can be adjusted to suit the heat input temperature. Water and ammonia is the most widely used combination, but other combinations are feasible. In the 1980s, Kalina proposed a thermodynamic power cycle with high thermoelectric efficiency using ammonia-water as the working medium. It is suitable for use in low and medium-temperature heat sources and small-power demand. The ammonia gas is volatilized of the mixed working fluid during the heating. The reduction of residual liquid concentration increases the saturated vapor pressure, and the system is more flexible than zeotropic evaporation. The schematic diagram is shown in the figure. Art. [#ARTNUM](#article-33257-2902891177). In the second figure: The super-heated ammonia-water solution at state 1, which gains its heat from a boiler, heat recovery exchanger, or a renewable energy source, expands in a turbine for power generation. The expanded working solution then recovers some of its heat to other streams via two recuperators. At state 4, the working solution is mixed with a lean liquid (low ammonia concentration) to dilute the mixture before entering the first stage condenser at state 5. The basic solution exiting the mixer enters the condenser to cool down and then pumped by a low-pressure pump to a splitter at state 7. The splitter splits a part of the basic solution to get preheated in a heat exchanger before entering the separator at state 10. The separator separates the solution into lean liquid (low ammonia concentration) at state 12 and rich vapor (high ammonia concentration) at state 11. The lean liquid goes to the first mixer mentioned earlier to dilute the working mixture at stage 5 before it enters the first stage condenser. Whereas the rich vapor goes to the second mixer to recover back the ammonia concentration at stage 14 before entering the second stage condenser. At stage 15, the working solution gets pumped in a high-pressure pump at stage 16, which then recovers some of the heat rejected from the steam turbine at stage 17 before it gets superheated from the heat source to repeat the process again. Art. [#ARTNUM](#article-33257-2903781546)

1.5.1 Kalina cycle
A review of low-temperature heat recovery technologies for industry processes
Abstract The amount of low-temperature heat generated in industrial processes is high, but recycling is limited due to low grade and low recycling efficiency, which is one of the reasons for low energy efficiency. It implies that there is a great potential for low-temperature heat recovery and utilization. This article provided a detailed review of recent advances in the development of low-temperature thermal upgrades, power generation, refrigeration, and thermal energy storage. The detailed description will be given from the aspects of system structure improvement, work medium improvement, and thermodynamic and economic performance evaluation. It also pointed out the development bottlenecks and future development trends of various technologies. The low-temperature heat combined utilization technology can recover waste heat in an all-round and effective manner, and has great development prospects.
11/01/2018 00:00:00
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1.5.2 Kalina cycle
A review of unconventional bottoming cycles for waste heat recovery: Part I – Analysis, design, and optimization
Abstract In this paper, an extensive overview of unconventional waste heat recovery power cycles is presented. The three-unconventional waste heat recovery bottoming cycles discussed in this paper are the air bottoming cycle, carbon dioxide-based power cycles and Kalina bottoming cycle. The review paper is divided into two parts; first part is about a detailed discussion of energy, exergy, economic analysis, as well as reviewing part load analysis, component design, power augmentation and comparative studies. Whereas, the second part of the review paper demonstrate and thoroughly review the applications of the aforementioned unconventional bottoming cycles, including renewable energy sources. According to the literature, it was found that the air bottoming cycle is not as competitive when compared to the conventional bottoming cycle, such as the steam Rankine cycle. Nevertheless, air bottoming cycle can be economically competitive for low system capacities. Furthermore, CO 2 power cycles have shown better performance in terms of energetic and exergetic analyses when compared to the conventional bottoming cycles. The transcritical and supercritical CO 2 power cycles excel to recover low and medium grade waste heat, respectively. Finally, Kalina bottoming cycle was found to be competitive to recover the low-grade waste heat when compared to organic Rankine cycle. In addition, optimizing the ammonia-water concentrations at different stages of the cycle has the most notable effect in improving the cycle’s performance.
12/01/2018 00:00:00
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1.5.3 Kalina cycle
The Kalina cycle for cement kiln waste heat recovery power plants
Cement production is one of the most energy intensive industrial processes in the world. In many world regions, energy cost is 50% to 60% of the direct production cost of cement. Energy cost is incurred due to the need for large quantities of thermal heat for the kiln, calcination and drying processes and electrical energy for operation of motors for grinding mills, fans, conveyers and other motor driven process equipment. The Kalina Cycle/spl reg/ utilizes the waste heat from the cement production process to generate electrical energy with no additional fuel consumption, and reduces the cost of electric energy for cement production. The thermal efficiency improvement of the Kalina Cycle is 20% to 40% in comparison with conventional waste heat power plants that utilize the hot gases available in a cement plant. A Kalina Cycle power plant offers the best environmentally friendly alternative for power generation from low-grade waste heat. It maximizes kW-hrs generated using a closed loop system to recover heat for electricity production without hazard to the environment. The Kalina Cycle uses a mixture of ammonia and water as its working fluid; a common solution used extensively world wide for refrigeration plants. In the event of an accidental release, ammonia is considered a biodegradable fluid. It does not contribute to photochemical smog, global pollution or global warming; and will not deplete the ozone layer. Its use as an industrial fluid is well documented with a proven track record for safety in industrial plants. This paper is a summary of Kalina Cycle Technology for cement plant waste heat applications. Specific plant designs are referenced to present a summary of the power plant systems and to describe the financial advantages of the Kalina Cycle waste heat power plant to the cement plant owner.
01/01/2005 00:00:00
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1.6 Stirling cycle

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Due to the great capability of recovering low-grade heat with potentially high efficiencies, Stirling cycle engines have attracted increasing attention in recent decades. They operate with a closed regenerative thermodynamic cycle that has the same theoretical thermal efficiency of the Carnot cycle. The compressible working fluid in a Stirling cycle engine, such as air, helium, hydrogen, nitrogen, etc., experiences periodical compression and expansion at different temperature levels to convert thermal energy into mechanical work. The lack of valves and absence of periodic explosions in Stirling cycle engines enable them to be operated more quietly than other piston engines. In Stirling cycle engines, the thermal energy is externally supplied through recuperative heat exchangers. Therefore, they have great flexibility to be powered by any kind of heat sources at any temperature levels. The Stirling cycle engines working at low and moderate temperatures with simple constructions and low costs have a wide application prospect for recovering small-scale distributed low-grade thermal energy. Art. [#ARTNUM](#article-33278-2346231020)

1.6.1 Stirling cycle
Review of low-temperature vapour power cycle engines with quasi-isothermal expansion
External combustion heat cycle engines convert thermal energy into useful work. Thermal energy resources include solar, geothermal, bioenergy, and waste heat. To harness these and maximize work output, there has been a renaissance of interest in the investigation of vapour power cycles for quasi-isothermal (near constant temperature) instead of adiabatic expansion. Quasi-isothermal expansion has the advantage of bringing the cycle efficiency closer to the ideal Carnot efficiency, but it requires heat to be transferred to the working fluid as it expands. This paper reviews various low-temperature vapour power cycle heat engines with quasi-isothermal expansion, including the methods employed to realize the heat transfer. The heat engines take the form of the Rankine cycle with continuous heat addition during the expansion process, or the Stirling cycle with a condensable vapour as working fluid. Compared to more standard Stirling engines using gas, the specific work output is higher. Cryogenic heat engines based on the Rankine cycle have also been enhanced with quasi-isothermal expansion. Liquid flooded expansion and expander surface heating are the two main heat transfer methods employed. Liquid flooded expansion has been applied mainly in rotary expanders, including scroll turbines; whereas surface heating has been applied mainly in reciprocating expanders.
06/01/2014 00:00:00
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1.6.2 Stirling cycle
Stirling cycle engines for recovering low and moderate temperature heat: A review
A review is presented for the research development of Stirling cycle engines for recovering low and moderate temperature heat. The Stirling cycle engines are categorized into four types, including kinetic, thermoacoustic, free-piston, and liquid piston types. The working characteristics, features, technological details, and performances of the related Stirling cycle engines are summarized. Upon comparing the available experimental results and the technology potentials, the research directions and the possible applications of different Stirling cycle engines are further discussed and identified. It is concluded that kinetic Stirling engines and thermoacoustic engines have the greatest application prospect in low and moderate temperature heat recoveries in terms of output power scale, conversion efficiency, and costs. In particular, kinetic Stirling engines should be oriented toward two directions for practical applications, including providing low-cost solutions for low temperatures, and moderate efficient solutions with moderate costs for medium temperatures. Thermoacoustic engines for low temperature applications are especially attractive due to their low costs, high efficiencies, superior reliabilities, and simplicities over the other mechanical Stirling engines. This work indicates that a cost effective Stirling cycle engine is practical for recovering small-scale distributed low-grade thermal energy from various sources.
09/01/2016 00:00:00
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1.7 Trilateral flash cycle

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In a TFC system, heat gain is achieved without phase change of the organic working fluid, and the expansion process, therefore, starts from the saturated liquid state rather than a vapor phase. With reference to the plant layout displayed and T-s diagram presented in the figure, the working fluid is pressurized, heated at constant pressure to its saturation point, expanded as a two-phase mixture and eventually condensed at constant pressure. Art. [#ARTNUM](#article-33276-2758081676) **Research findings:** * The current research tackles the energy trilemma of emissions reduction, the security of supply and cost savings in industrial environments by presenting the development of a packaged, plug & play power unit for lowgrade waste heat recovery applications. The heat to power conversion system is based on the Trilateral Flash Cycle (TFC), a bottoming thermodynamic cycle particularly suitable for waste heat sources at temperatures below 100 °C which, on a European scale, account for 469 TWh in industry and are particularly concentrated in the chemical and petrochemical sectors. The industrial test case refers to a UK tire manufacturing company in which a 2 MW water stream at 85 °C involved in the rubber curing process was chosen as a hot source of the TFC system while a pond was considered the heat sink. The design of the industrial scale power unit, which is presented at end of the manuscript, was carried out based on the outcomes of a theoretical modelling platform that allowed to investigate and optimize multiple design parameters using energy and exergy analyses. In particular, the model exploitation identified R1233zd(E) and R245fa as the most suitable pure working fluids for the current application, given the higher net power output and the lower ratio between pumping and expander powers. At nominal operating conditions, the designed TFC system is expected to recover 120 kWe and have an overall efficiency of 6%. Art. [#ARTNUM](#article-33276-2758081676) * The advantage of TFC over an equivalent steam ORC system is that its power recovery potential is high, twice that of ORC. It can also eliminate the requirement for an extra cooling tower/heat rejection system, where the heat in the waste stream will be rejected. Art. [#ARTNUM](#article-33276-2920834504)

1.7.1 Trilateral flash cycle
Development and analysis of a packaged Trilateral Flash Cycle system for low grade heat to power conversion applications
Abstract The current research tackles the energy trilemma of emissions reduction, security of supply and cost savings in industrial environments by presenting the development of a packaged, plug & play power unit for low-grade waste heat recovery applications. The heat to power conversion system is based on the Trilateral Flash Cycle (TFC), a bottoming thermodynamic cycle particularly suitable for waste heat sources at temperatures below 100 °C which, on a European scale, account for 469 TWh in industry and are particularly concentrated in the chemical and petrochemical sectors. The industrial test case refers to a UK tire manufacturing company in which a 2 MW water stream at 85 °C involved in the rubber curing process was chosen as hot source of the TFC system while a pond was considered the heat sink. The design of the industrial scale power unit, which is presented at end of the manuscript, was carried out based on the outcomes of a theoretical modelling platform that allowed to investigate and optimize multiple design parameters using energy and exergy analyses. In particular, the model exploitation identified R1233zd(E) and R245fa as the most suitable pure working fluids for the current application, given the higher net power output and the lower ratio between pumping and expander powers. At nominal operating conditions, the designed TFC system is expected to recover 120 kWe and have an overall efficiency of 6%.
12/01/2017 00:00:00
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1.7.2 Trilateral flash cycle
Development of the Trilateral Flash Cycle System: Part 1: Fundamental Considerations
The world market for systems for power recovery from low-grade heat sources is of the order of £1 billion per annum. Many of these sources are hot liquids or gases from which conventional power systems convert less than 2.5 per cent of the available heat into useful power when the fluid is initially at a temperature of 100° C rising to 8–9 per cent at an initial temperature of 200°C. Consideration of the maximum work recoverable from such single-phase heat sources leads to the concept of an ideal trilateral cycle as the optimum means of power recovery. The trilateral flash cycle (TFC) system is one means of approaching this ideal which involves liquid heating only and two-phase expansion of vapour. Previous work related to this is reviewed and details of analytical studies are given which compare such a system with various types of simple Rankine cycle. It is shown that provided two-phase expanders can be made to attain adiabatic efficiencies of more than 75 per cent, the TFC system can produce outputs of...
08/01/1993 00:00:00
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1.7.3 Trilateral flash cycle
Techno-economic survey and design of a pilot test rig for a trilateral flash cycle system in a steel production plant
Abstract In recent years the interest in recovering rejected low-grade heat within industry has intensified. Around 30% of global primary energy consumption is attributed to the industrial sector and a significant portion of this is rejected as heat. The majority of this wasted energy is available at temperatures below 100°C and as such conventional waste heat to power conversion systems cannot economically recover the energy, producing simple pay backs that are unacceptable to industry. The Trilateral Flash Cycle (TFC) is however a promising technology with the ability to harness the rejected heat found in these low grade waste streams. The current research work presents a techno-economic assessment of the installation potential for a low grade heat to power conversion system using a TFC system. In particular, thermodynamic modelling is utilised to estimate the expected energy recovery and, in turn, the potential savings achievable through the TFC solution. The survey investigated three diverse and challenging heat sources at steel production plants. Annual energy recovery from the chosen heat source is expected to be 782 MWh. Prior to the upscaling of the system to the 2MW waste thermal power, a pilot test rig was designed and built. Preliminary tests showed a net electrical power output up to 6.2 kW and an overall efficiency of 4.3%.
09/01/2017 00:00:00
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1.7.4 Trilateral flash cycle
Waste Heat Recovery in the EU industry and proposed new technologies
Abstract In the European Union (EU), industrial sectors use 26% of the primary energy consumption and are characterized by large amounts of energy losses in the form of waste heat at different temperature levels. Their recovery is a challenge but also an opportunity for science and business. In this study, after a brief description of the conventional Waste Heat Recovery (WHR) approaches, the novel technologies under development within the I-ThERM Horizon 2020 project are presented and assessed from an energy and market perspectives. These technologies are: heat to power conversion systems based on bottoming thermodynamic cycles (Trilateral Flash Cycle for low grade waste heat and Joule-Brayton cycle working with supercritical carbon dioxide for high temperature waste heat sources); heat recovery devices based on heat pipes (flat heat pipe for high grade radiative heat sources and condensing economizer for acidic effluents).
03/01/2019 00:00:00
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2. Solid-state generators for heat conversion

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Solid state thermal to electrical energy converters are heat engines, or small generators, and energy harvesters capable of transforming heat directly into electricity. The governing physical principles with solid state thermal to electrical energy converters work over several orders of magnitude and enable the utilization of previously unexplored low grade thermal energy and waste heat. With solid state heat engines, small quantities of low grade thermal energy and waste heat, at temperatures just above ambient, can be directly converted into electrical power in the microwatt to milliwatt range. The generated electrical power allows to locally power a large number of small scale electronic devices as well as autonomous and self-sustaining applications, without the need for maintenance and additional costs.


2.1 Thermoelectric generator

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A thermoelectric generator (TEG), also called a Seebeck generator, is a solid-state device that converts heat flux (temperature differences) directly into electrical energy through a phenomenon called the Seebeck effect (a form of thermoelectric effect). Thermoelectric generators function like heat engines, but are less bulky and have no moving parts. However, TEGs are typically more expensive and less efficient. Thermoelectric generators could be used in power plants in order to convert waste heat into additional electrical power and in automobiles as automotive thermoelectric generators (ATGs) to increase fuel efficiency. Another application is radioisotope thermoelectric generators which are used in space probes, which has the same mechanism but use radioisotopes to generate the required heat difference. [\[Wiki\]](https://en.wikipedia.org/wiki/Thermoelectric_generator) Thermoelectric devices, or thermoelectric generators (TEG), are solid-state heat engines and convert thermal energy directly into electrical energy. Thermal energy from a hot heat source and a cold heat sink create a spatial temperature difference which can be utilized in a TEG. When the TEG is placed between the hot heat source and a cold heat sink, the temperature difference is converted into an electric current across the generator terminals. This effect is based on the thermoelectric, or Seebeck, effect. The Seebeck effect describes the voltage developed across two dissimilar electrical conductor materials creating a hot thermoelectric junction. The assembly of thermoelectric junctions is known as a TEG module and acts as an electric power generator continuously driving a direct electric current (DC) through an external electrical load. Art. [#ARTNUM](#article-29719-2902616540) In general, they use small temperature differences to generate electricity. Usually in smaller systems.

2.1.1 Thermoelectric generator
A review of thermoelectric power generation systems: Roles of existing test rigs/ prototypes and their associated cooling units on output performance
Abstract Thermoelectric technology is a promising solution to recover waste heat from different resources. There are numerous researches in the literature that measure performance of thermoelectric modules (TEMs). A comprehensive review of research studies that classifies and expounds disparities between various thermoelectric power generation (TEPG) systems is still unavailable and therefore, this paper reviews major concerns on their designs and performances. Firstly, various main elements of TEPG systems, which affect the output power of TEMs such as stabilizer or heat exchanger, interface, contact pressure, insulation, cooling system, and integrity are studied. Secondly, performances of test rigs and various prototypes are reviewed in detail based on their cooling methods since cooling is the most prominent factor among other counterparts. In general, the cooling unit is divided into either passive or active cooling system, which is selected based on its well-defined use. A comprehensive study on various test rigs with active cooling systems is given while a broader range in prototypes is covered and classified under detailed surveys. This review is expected to be of value for researchers in the field of thermoelectric. Overall, in order to have a prospective future towards commercialization of TEPG systems, the existing prototypes in the literature are still subjected to many enhancements in their design aspects, while further improvements are needed to be achieved independently in TEMs’ development.
10/01/2018 00:00:00
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2.1.2 Thermoelectric generator
A Review on Organic Polymer-Based Thermoelectric Materials
Converting heat energy directly into useable electricity by harvesting low-cost energy resources, such as solar energy and the waste heat, has attracted great interest recent years. Thermoelectricity offers a promising technology to convert heat from solar energy and to recover waste heat from industrial sectors and automobile exhausts. Classically, a number of inorganic compounds have been considered as the best thermoelectric materials. Organic materials in particular intrinsically conducting polymers had been considered as competitors of classical thermoelectric since their figure of merit has been improved several orders of magnitude in last year. In addition, the applications of thermoelectric polymers at low temperatures have shown various advantages such as easy and low cost of fabrication, light weight, and flexibility. Therefore, organic thermoelectric materials will be the best candidates to compete with inorganic materials in the future. In this review, we focused on exploring different types of organic thermoelectric materials and the factors affecting their thermoelectric properties, and discussed various strategies to improve the performance of thermoelectric materials. In addition, a review on theoretical studies of thermoelectric transport in polymers is also given.
12/01/2017 00:00:00
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2.1.3 Thermoelectric generator
Advancements in thermoelectric generators for enhanced hybrid photovoltaic system performance
Effective thermal management of photovoltaic cells is essential for improving its conversion efficiency and increasing its life span. Solar cell temperature and efficiency have an inverse relationship therefore, cooling of solar cells is a critical research objective which numerous researchers have paid attention to. Among the widely adopted thermal management techniques is the use of thermoelectric generators to enhance the performance of photovoltaics. Photovoltaic cells can convert the ultra-violent and visible regions of the solar spectrum into electrical energy directly while thermoelectric modules utilize the infrared region to generate electrical energy. Consequently, the combination of photovoltaic and thermoelectric generators would enable the utilization of a wider solar spectrum. In addition, the combination of both systems has the potential to provide enhanced performance due to the compensating effects of both systems. The waste heat produced from the photovoltaic can be used by the thermoelectric generator to produce additional energy thereby increasing the overall power output and efficiency of the hybrid system. However, the integration of both systems is complex because of their opposing characteristics thus, effective coupling of both systems is essential. This review presents the concepts of photovoltaics and thermoelectric energy conversion, research focus areas in the hybrid systems, applications of such systems, discussion of the most recent research accomplishments and recommendations for future research. All the essential elements and research areas in hybrid photovoltaic/thermoelectric generator are discussed in detailed therefore, this review would serve as a valuable reference literature.
07/01/2019 00:00:00
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2.1.4 Thermoelectric generator
Analysis of a Thermoelectric Generator in a Gas Carburizing Furnace
: Thermoelectric generation technology, as one entirely solid-state energy conversion method, can directly transform thermal energy into electricity by using thermoelectric transformation materials. A thermoelectric power converter has no moving parts, and is compact, quiet, highly reliable and environmentally friendly. Therefore, the whole system can be simplified and operated over an extended period of time with minimal maintenance. In addition, it has wider choice of thermal sources. It can utilize both the high- and low-quality heat to generate electricity. The low-quality heat may not be utilized effectively by conventional methods such as ORC technology. In this study, a direct heat to electricity (DHE) technology using the thermoelectric effect, without the need to change through mechanical energy, was applied to harvest low-enthalpy thermal work. Such a power generation system has been designed and built using thermoelectric generator (TEG) modules manufactured using a new technique. The targets of this technique were low cost and high thermal to electricity efficiency. Experiments have been conducted to measure the output power at different conditions: different inlet -temperature and temperature differences between hot and cold sides. TEG modules manufactured with different materials have also been tested. The power generator assembled with TEG modules had an installed power of 30W at a temperature difference of around 140 °C. The power generated by the thermoelectric system is almost directly proportional to the temperature difference between the hot and the cold sides. The cost of the DHE power generator is much lower than that of photo voltaic (PV) in terms of equivalent energy generated. The TEG systems are ready to be applied practically to many gas carburizing furnaces for the efficient usage of thermal power.
03/01/2017 00:00:00
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2.1.5 Thermoelectric generator
Analysis of the use of thermoelectric generator and heat pipe for waste heat utilization
Waste heat recovery is one way to reduce the use of fossil fuels, one of them is by using thermoelectric generator to convert waste heat into Thermoelectric Generator (TEGs) is a module that can convert heat into electrical power directly, using Seebeck effect and Peltier effect as its working principle, so it can increase efficiency of energy consumption by utilizing waste heat from an instrument that generate waste heat. The focus of this research is to find the output voltage of TEG by utilizing the temperature difference on the cold side and the heat side of the TEGs. The heat side of the module will be given heat from the heater as a simulation of the heat from hot water, and on the cold side heat pipes will be used to remove the heat on the cold side of TEGs. The result, output voltage that generated by using 4 module TEGs that arranged to Thermal Series - Series Circuit and using 2 heat pipes is 2.1-volt, and then it is possible to use for phone charger.
01/01/2018 00:00:00
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2.1.6 Thermoelectric generator
Development of a System for Thermoelectric Heat Recovery from Stationary Industrial Processes
The hot forming process of steel requires temperatures of up to 1300°C. Usually, the invested energy is lost to the environment by the subsequent cooling of the forged parts to room temperature. Thermoelectric systems are able to recover this wasted heat by converting the heat into electrical energy and feeding it into the power grid. The proposed thermoelectric system covers an absorption surface of half a square meter, and it is equipped with 50 Bismuth-Telluride based thermoelectric generators, five cold plates, and five inverters. Measurements were performed under production conditions of the industrial environment of the forging process. The heat distribution and temperature profiles are measured and modeled based on the prevailing production conditions and geometric boundary conditions. Under quasi-stationary conditions, the thermoelectric system absorbs a heat radiation of 14.8 kW and feeds electrical power of 388 W into the power grid. The discussed model predicts the measured values with slight deviations.
07/01/2016 00:00:00
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2.1.7 Thermoelectric generator
Exhaust Heat Recovery Using Thermoelectric Generators: A Review
With the major concern to increase the efficiency of internal combustion (IC) engines, various technologies and innovations have been implemented to improvise efficiency and reduction of emissions. Since 60–70% of the energy produced during combustion is rejected as heat through exhaust and coolant channels, it is important to recover that waste heat. Numerous technologies have been invented and applied to the diesel engine unit to harness the waste heat. One such is the use of solid-state device thermoelectric generator (TEG). In the late 1980s, many automobile manufacturers implemented automotive exhaust thermoelectric generators (AETEGs) in their respective vehicles, and since then, the work on AETEGs has picked at gradual pace. Advantages of using TEG are its noise-free operation, low failure rate and lack of moving components. However, it is not a very popular solution due to the low energy conversion efficiency (~6–8%) of thermoelectric modules and the incompetence to produce high power at low-temperature gradient. Engineers and researchers are basically working for improving the conversion efficiency of TEG modules by developing and doping semiconductors and optimization of the AETEG system to utilize and recover maximum heat available from the exhaust line by designing efficient heat exchanger systems, thus trying to improve its feasibility. This chapter covers the wide spectrum of feasibility of application of TEG modules in diesel engines with possible ways to utilize the generated power.
01/01/2018 00:00:00
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2.1.8 Thermoelectric generator
Power generation by coupling reverse electrodialysis and ammonium bicarbonate: Implication for recovery of waste heat
Abstract Utilization of waste heat has attracted increasing attentions due to energy crisis and environmental problems. Efficiency of traditional thermodynamic cycles for waste heat conversion is limited by the temperature of heat sources. We propose here the concept of a novel waste heat conversion system, namely a thermal-driven electrochemical generator (TDEG), which comprises a reverse electrodialysis (RED) stack and a distillation column. By using thermally instable ammonium bicarbonate solutions as working fluids, waste heat can be converted to electricity. The feasibility of NH 4 HCO 3 to generate electricity for TDEG was validated in a RED stack for the first time. Two important operating conditions influencing power output of RED stack, i.e. concentration of low concentration solution and flow rate of feed solutions were optimized to be 0.02 M and 800 mL/min, respectively. A maximum power density of 0.33 W/m 2 was obtained for the specific RED stack. Ionic flux efficiency and energy efficiency under the optimal condition were 88% and 31%, respectively. The study lays a foundation for the establishment of the promising TDEG.
06/01/2012 00:00:00
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2.1.9 Thermoelectric generator
Solid state generators and energy harvesters for waste heat recovery and thermal energy harvesting
Abstract This review covers solid state thermal to electrical energy converters capable of transforming low grade heat directly into electricity for waste heat recovery and thermal energy harvesting. Direct solid state heat engines such, as thermoelectric modules and thermionic converters for spatial temperature gradients, are compared with pyroelectric energy harvesters and thermomagnetic generators for transient changes in temperature. Temperature and size limitations along with the maturity of the technologies are discussed based on energy density and temperature range for the different generator technologies. Despite the low energy conversion efficiency with solid state generators, electric power density ranges from 4 nW/mm 2 to 324 mW/mm 2 . The most promising sector to implement changes while reducing the primary energy consumption and saving resources, is the processing industry along with stationary and mobile electronics.
03/01/2019 00:00:00
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2.1.10 Thermoelectric generator
Thermoelectric materials and heat exchangers for power generation – A review
Abstract Around 60–70% of the fuel energy in an internal combustion engine is lost as waste heat through engine exhaust and coolant. Hence, waste heat recovery techniques can be used to increase the efficiency of the engine. Thermoelectric systems are widely used for converting heat energy to electric energy. A considerable attention of researchers has been drawn by the thermoelectric generator, for the waste heat recovery from engine exhaust. The thermoelectric generator is one of the promising green energy source and the most desirable option to recover useful energy from engine exhaust. A high-efficiency heat exchanger, which is an integral part of the thermoelectric generator, is necessary to increase the amount of heat energy extracted from engine exhaust at the cost of acceptable pressure drop. The present work is a summary of thermoelectric materials, and heat exchanger studies on heat transfer rate, thermal uniformity, and pressure drop. The heat exchangers with different internal structures enhance heat transfer rate and thermal uniformity, which increase the power output and the conversion efficiency of the thermoelectric generator. The presence of flow-impeding inserts/internal structures results in an adverse increase in pressure drop and has a negative effect on the performance of waste heat source.
11/01/2018 00:00:00
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2.2 Thermionic energy converter (TEC)

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A thermionic converter consists of a hot electrode which thermionically emits electrons over a potential energy barrier to a cooler electrode, producing a useful electric power output. Caesium vapor is used to optimize the electrode work functions and provide an ion supply (by surface ionization or electron impact ionization in plasma) to neutralize the electron space charge. [\[Wiki\]](https://en.wikipedia.org/wiki/Thermionic_converter) When a TIC is placed between a hot heat source and a cold heat sink, the hot electrode surface emits charge carriers (electrons). This charge emission process is based on the effect of thermionic emission, or the space charge effect, and enables a continuous surplus of electrons at the cold electrode which acts as an electric power supply, continuously driving a direct electric current (DC) across an external load. Usually, a high temperature is used. **Research findings:** * At high temperatures, over 15% conversion efficiency is possible with respective hot and cold electrode temperatures between 570 °C and 1300 °C, revealing that this technology is remarkably suitable for industrial and nuclear heat recovery applications. Experimental devices show a high power density of 320 000 μW/mm2 at temperatures in excess of 1000 °C. However, with a thermionic device, the power density rapidly decreases at temperatures below 1000 °C, only generating 0.04 μW/mm2 (9 nW/0.25 mm2) at low temperatures. When pure metal and semi-conductor electrodes are used in TICs, decreasing heat source temperatures lead to a diminishing electrode emission. As shown in Fig. 6, the maximum conversion efficiency of a TIC with an electrode WF of 0.75 eV, at 127 °C hot electrode temperature and 27 °C cold electrode temperature, is close to 20%. In order to maintain the electron emission process at low temperatures, the corresponding electrode WF also needs to be low. Alkali metals and their oxides such as e.g. Lithium (Li), Potassium (K), and Cesium (Cs) have WFs lower than most metals and semiconductors, with typical values in the range between 2.1 eV and 2.49 eV and their respective oxides between 0.4 eV and 1.8 eV. Art. [#ARTNUM](#article-33270-2902616540) Particularly suited for high-temperature applications (>1000 °C).

2.2.1 Thermionic energy converter (TEC)
Solid state generators and energy harvesters for waste heat recovery and thermal energy harvesting
Abstract This review covers solid state thermal to electrical energy converters capable of transforming low grade heat directly into electricity for waste heat recovery and thermal energy harvesting. Direct solid state heat engines such, as thermoelectric modules and thermionic converters for spatial temperature gradients, are compared with pyroelectric energy harvesters and thermomagnetic generators for transient changes in temperature. Temperature and size limitations along with the maturity of the technologies are discussed based on energy density and temperature range for the different generator technologies. Despite the low energy conversion efficiency with solid state generators, electric power density ranges from 4 nW/mm 2 to 324 mW/mm 2 . The most promising sector to implement changes while reducing the primary energy consumption and saving resources, is the processing industry along with stationary and mobile electronics.
03/01/2019 00:00:00
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2.2.2 Thermionic energy converter (TEC)
TEC as electric generator in an automobile catalytic converter
Modern cars use more and more electric power due to more on-board electric systems. A modern car may be equipped with an electric generator (generally an alternator) with an output current of maximum 60-90 A at 12 V. A belt driven generator has a rather low total efficiency and so it is interesting to find alternative solutions for this electricity generation problem. One possible energy source for electricity generation is to use the waste heat from the car's engine, which generally is as much as much as 80% of the total energy from the combustion of the gasoline. Maybe the best location to tap the excess heat is the catalytic converter (Cat) in the exhaust system or perhaps at the exhaust pipes close to the engine. The Cat must be kept within a certain temperature interval. Large amounts of heat are dissipated through the walls of the Cat. A thermionic energy converter (TEC) in a coaxial form could conveniently be located around the ceramic cartridge of the Cat. Since the TEC is a rather good heat insulator before it reaches its working temperature, the Cat will reach working temperature faster and its final temperature can be controlled better when encapsulated in a concentric TEC arrangement. It is also possible to regulate the temperature of the Cat and the TEC by controlling the electrical load of the TEC. The possible working temperatures of present and future Cats appear very suitable for the authors' new low work function collector TEC, which has been demonstrated to work down to 470 K.
01/01/1996 00:00:00
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2.3 Thermomagnetic generators

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Thermomagnetic generators, or thermo-magneto-electric generators, are solid-state heat engines and convert thermal energy directly into electrical energy. In a thermomagnetic generator, every change in temperature (ΔT) translates into an electric current across the generator terminals. When heated, the ferromagnetic material in the thermomagnetic generator experiences a crystallographic phase transition followed by a rapid change in the magnetic moment. This change in magnetic moment induces an electromagnetic induction force (EMF), or electromotive force, and drives an electric current across an external electric load. For cyclic, or time-variant (Δt), heating and cooling (ΔT/Δt) the thermomagnetic generator drives an alternating current (AC) across the generator terminals proportional to the experienced change in temperature. Art. [#ARTNUM](#article-33241-2902616540)

2.3.1 Thermomagnetic generators
High-Performance Thermomagnetic Generators Based on Heusler Alloy Films
Recent developments on Heusler alloys including Ni–Mn–X and Ni–Co–Mn–X (X = Ga, In, Sn,…) demonstrate multiferroic phase transformations with large abrupt changes in lattice parameters of several percent and corresponding abrupt changes in ferromagnetic ordering near the transition temperatures. These materials enable a new generation of thermomagnetic generators that convert heat to electricity within a small temperature difference below 5 K. While thermodynamic calculations on this energy conversion method predict a power density normalized to material volume of up to 300 mW cm−3, experimental results have been in the range of µW cm−3. Challenges are related to the development of materials with bulk-like single-crystal properties as well as geometries with large surface-to-volume ratio for rapid heat exchange. This study demonstrates efficient thermomagnetic generation via resonant actuation of freely movable thin-film devices of the Heusler alloy Ni–Mn–Ga with unprecedented power density of 118 mW cm−3 that compares favorably with the best thermoelectric generators. Due to the large temperature-dependent change of magnetization of the films, a periodic temperature change of only 3 K is required for operation. The duration of thermomagnetic duty cycle is only about 12 ms, which matches with the period of oscillatory motion.
03/01/2017 00:00:00
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2.3.2 Thermomagnetic generators
Performance analysis of energy conversion via caloric effects in first-order ferroic phase transformations
A finite-time thermodynamic model of ferroic refrigerators and generators, based on first order phase transformation, is given. We use this model to evaluate a novel method of converting heat directly into electricity based on the martensitic phase transformation accompanied by an abrupt change in magnetic ordering recently discovered [Srivastava et al., Adv. Energy Mater., 2011, 1, 97]. In this paper, we study the efficiency and power output of this method. The formulas of efficiency and power output in terms of material constants, design parameters, and working conditions are derived. The Clausius–Clapeyron coefficient is shown to be important to the efficiency. The figure of merit, as a dimensionless parameter, of energy conversion using the new method is introduced. It is shown that, as the figure of merit goes to infinity, the efficiency approaches the Carnot efficiency. Thermodynamic cycles of the new energy conversion method are optimized for a maximum power output. The matching criteria between materials and working temperatures of such optimized cycles are derived. Using these criteria, one can choose the most suitable materials under given working conditions, or decide the best working conditions for available materials.
01/01/2014 00:00:00
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2.3.3 Thermomagnetic generators
Solid state generators and energy harvesters for waste heat recovery and thermal energy harvesting
Abstract This review covers solid state thermal to electrical energy converters capable of transforming low grade heat directly into electricity for waste heat recovery and thermal energy harvesting. Direct solid state heat engines such, as thermoelectric modules and thermionic converters for spatial temperature gradients, are compared with pyroelectric energy harvesters and thermomagnetic generators for transient changes in temperature. Temperature and size limitations along with the maturity of the technologies are discussed based on energy density and temperature range for the different generator technologies. Despite the low energy conversion efficiency with solid state generators, electric power density ranges from 4 nW/mm 2 to 324 mW/mm 2 . The most promising sector to implement changes while reducing the primary energy consumption and saving resources, is the processing industry along with stationary and mobile electronics.
03/01/2019 00:00:00
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2.4 Pyroelectric generator

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Pyroelectricity (from the two Greek words pyr meaning fire, and electricity) is a property of certain crystals which are naturally electrically polarized and as a result contain large electric fields. Pyroelectricity can be described as the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change gives rise to a voltage across the crystal. If the temperature stays constant at its new value, the pyroelectric voltage gradually disappears due to leakage current. [Wiki](https://en.wikipedia.org/wiki/Pyroelectricity) Pyroelectric generators, or pyroelectric energy harvesters, are solid-state heat engines and convert thermal energy directly into electrical energy. In a pyroelectric harvester, every change in temperature translates into an electric potential difference across the generator terminals. This potential difference is based on the pyroelectric effect, which describes the change in the crystallographic polarization moment of a pyroelectric material, in response to the change in temperature ΔT. For cyclic, or time-variant (Δt), heating and cooling (ΔT/Δt) the pyroelectric energy harvester generates an alternating current (AC) across the generator terminals proportional to the experienced change in temperature. In this way, pyroelectric energy harvesters are different from the previously discussed thermoelectric generators and thermionic converters where the current is proportional to the spatial temperature gradient. Art. [#ARTNUM](#article-33256-2902616540) **Research findings:** * In 2014, almost 60% of thermal energy produced in the United States was lost to the environment as waste heat. Ferroelectric based pyroelectric devices can be used to convert some of this waste heat into usable electrical energy using the Olsen cycle, an ideal thermodynamic cycle, but there are a number of barriers to its realization in a practical device. This study uses the Olsen cycle to benchmark a less efficient thermodynamic cycle that is more easily implemented in devices. The ferroelectric pyroelectric material used was (Pb₀.₉₇La₀.₀₂)(Zr₀.₅₅Sn₀.₃₂Ti₀.₁₃)O₃ ceramic, a ferroelectric material that undergoes a temperature-driven phase transformation. A net energy density of 0.27 J cm⁻³ per cycle was obtained from the ferroelectric material using the modified cycle with a temperature change between 25 °C and 180 °C. This is 15.5% of the Olsen cycle result with the same temperature range and 1–8 MV m⁻¹ applied electric field range. The power density was estimated to 13.5 mW cm⁻³ with given experimental conditions. A model is presented that quantitatively describes the effect of several parameters on output energy density and can be used to design ferroelectric based pyroelectric energy converters. The model indicates that optimization of material geometry and heating conditions can increase the output power by an order of magnitude. Art. [#ARTNUM](#article-33256-2271477211)

2.4.1 Pyroelectric generator
Phase transformation based pyroelectric waste heat energy harvesting with improved practicality
In 2014, almost 60% of thermal energy produced in the United States was lost to the environment as waste heat. Ferroelectric based pyroelectric devices can be used to convert some of this waste heat into usable electrical energy using the Olsen cycle, an ideal thermodynamic cycle, but there are a number of barriers to its realization in a practical device. This study uses the Olsen cycle to benchmark a less efficient thermodynamic cycle that is more easily implemented in devices. The ferroelectric pyroelectric material used was (Pb0.97La0.02)(Zr0.55Sn0.32Ti0.13)O3 ceramic, a ferroelectric material that undergoes a temperature driven phase transformation. A net energy density of 0.27 J cm−3 per cycle was obtained from the ferroelectric material using the modified cycle with a temperature change between 25°C and 180°C. This is 15.5% of the Olsen cycle result with the same temperature range and 1–8 MV m−1 applied electric field range. The power density was estimated to 13.5 mW cm−3 with given experimental conditions. A model is presented that quantitatively describes the effect of several parameters on output energy density and can be used to design ferroelectric based pyroelectric energy converters. The model indicates that optimization of material geometry and heating conditions can increase the output power by an order or magnitude.
03/01/2016 00:00:00
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2.4.2 Pyroelectric generator
Pyroelectric Energy Harvesting
Energy harvesting (or energy scavenging) technology captures unused ambient energy, such as vibration, strain, light, temperature gradients, temperature variations, gas flow energy, and liquid flow energy, and converts it into usable electrical energy. Even though advances have been made, the batteries that power portable microelectronics and wireless devices provide only a finite amount of power. Energy harvesting is a perfect solution for the problem of finite battery power for various low-power applications, providing sustained, cost-effective, and environmentally friendlier sources of power. Unconventional methods for waste-energy harvesting and scavenging are being explored to provide sustained power to these micro- and nanodevices. Efforts are being made to garner electric power from mechanical vibrations, light, spatial variations, and temporal temperature variations. Another potential source for low-power electronics is the thermal- and mechanical-waste energy of asphalt pavement, especially via pyroelectricity. However, this potential has not yet been extensively explored. An exception is Israel's current large-scale effort to pave kilometers of roads with a specially designed series of piezoelectric modules in the pavement. Pyroelectric materials are able to convert most of the electromagnetic radiation's spectrum (ultraviolet, IR, microwave, x rays, and terahertz) energy into electrical energy; that is, they transform photons to phonons and then to electrons.5 Since it follows that these materials can be exploited for conversion of thermal energy to electricity, they have been investigated recently for energy harvesting via pyroelectric linear and nonlinear properties. One key advantage of pyroelectrics over thermoelectrics is the stability of many pyroelectric materials at up to 1200 °C or more, which enables energy harvesting from high-temperature sources, thereby increasing thermodynamic efficiency. It is noteworthy that annually more than 100 TJ of low-grade waste heat (10 °C to 250 °C) is discharged by industries worldwide, such as electric power stations, glass manufacturers, petrochemical plants, pulp and paper mills, steel and other foundries, and the automobile industry. In the United States in 2009, around 55% of the energy generated from all of the sources was lost as waste heat.6 Technology to recover this low-grade waste heat or convert into usable electricity could save industrial sectors billions of dollars annually and reduce greenhouse gases. Pyroelectric electric generators (PEGs) can play a significant role in such technology. This chapter presents a review of PEGs with discussions on linear and nonlinear energy harvesting processes, thermodynamics of pyroelectrics, and an investigation of important pyroelectric materials with modeling of numerically simulated results for energy conversion.
09/24/2013 00:00:00
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2.4.3 Pyroelectric generator
Pyroelectric Harvesters for Generating Cyclic Energy
Pyroelectric energy conversion is a novel energy process which directly transforms waste heat energy from cyclic heating into electricity via the pyroelectric effect. Application of a periodic temperature profile to pyroelectric cells is necessary to achieve temperature variation rates for generating an electrical output. The critical consideration in the periodic temperature profile is the frequency or work cycle which is related to the properties and dimensions of the air layer; radiation power and material properties, as well as the dimensions and structure of the pyroelectric cells. This article aims to optimize pyroelectric harvesters by matching all these requirements. The optimal induced charge per period increases about 157% and the efficient period band decreases about 77%, when the thickness of the PZT cell decreases from 200 μm to 50 μm, about a 75% reduction. Moreover, when using the thinner PZT cell for harvesting the pyroelectric energy it is not easy to focus on a narrow band with the efficient period. However, the optimal output voltage and stored energy per period decrease about 50% and 74%, respectively, because the electrical capacitance of the 50 μm thick pyroelectric cell is about four times greater than that of the 200 μm thick pyroelectric cell. In addition, an experiment is used to verify that the work cycle to be able to critically affect the efficiency of PZT pyroelectric harvesters. Periods in the range between 3.6 s and 12.2 s are useful for harvesting thermal cyclic energy by pyroelectricity. The optimal frequency or work cycle can be applied in the design of a rotating shutter in order to control the heated and unheated periods of the pyroelectric cells to further enhance the amount of stored energy.
04/27/2015 00:00:00
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2.4.4 Pyroelectric generator
Solid state generators and energy harvesters for waste heat recovery and thermal energy harvesting
Abstract This review covers solid state thermal to electrical energy converters capable of transforming low grade heat directly into electricity for waste heat recovery and thermal energy harvesting. Direct solid state heat engines such, as thermoelectric modules and thermionic converters for spatial temperature gradients, are compared with pyroelectric energy harvesters and thermomagnetic generators for transient changes in temperature. Temperature and size limitations along with the maturity of the technologies are discussed based on energy density and temperature range for the different generator technologies. Despite the low energy conversion efficiency with solid state generators, electric power density ranges from 4 nW/mm 2 to 324 mW/mm 2 . The most promising sector to implement changes while reducing the primary energy consumption and saving resources, is the processing industry along with stationary and mobile electronics.
03/01/2019 00:00:00
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2.5 Thermally regenerative battery

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In thermal regenerative batteries, conversion to electricity is realized by charging-discharging an electrochemical cell at different temperatures. **Research findings:** * In a thermal regenerative ammonia battery, electrical power is obtained from the formation of metal ammine complexes, which are produced by adding ammonia to the anolyte, but not to the catholyte, of a battery consisting of two copper electrodes in a copper-nitrate electrolyte. The added ammonia generates a potential difference between the electrodes according to the reactions: (1) Cu²⁺ (aq) + 2e− → Cu (s)  E0 = +0.34 V (2) Cu (s) + 4 NH₃ (aq) → Cu(NH₃)₄²⁺ (aq) + 2e−   E0 = –0.04 V where E0 is the standard reduction potential in V vs. the standard hydrogen electrode (SHE). After discharging the cell and generating electrical power, ammonia is separated from the anolyte using conventional distillation with low-grade waste heat. The distilled ammonia is then added to the other electrolyte chamber for the next discharge cycle. While discharging the battery results in copper loss from the anode, the electrode can be regenerated when the ammonia is added to the other chamber, where the copper will be re-deposited back onto the electrode. Art. [#ARTNUM](#article-33265-2530731371) * The use of ethylenediamine as an alternative ligand to ammonia was explored here as a method to increase power production as well as improve ACE. In theory, the anode open circuit potential of a TRB can be improved by using a ligand in which the complexation reaction (Cu + n L → \[Cu(L)n\]²⁺ + 2e−; L: ligand) has a higher standard reduction potential than the copper ammonia complex (Eq. (2); −0.04 V). Art. [#ARTNUM](#article-33265-2598227859)

2.5.1 Thermally regenerative battery
Electrical power production from low-grade waste heat using a thermally regenerative ethylenediamine battery
Abstract Thermally regenerative ammonia-based batteries (TRABs) have been developed to harvest low-grade waste heat as electricity. To improve the power production and anodic coulombic efficiency, the use of ethylenediamine as an alternative ligand to ammonia was explored here. The power density of the ethylenediamine-based battery (TRENB) was 85 ± 3 W m −2 -electrode area with 2 M ethylenediamine, and 119 ± 4 W m −2 with 3 M ethylenediamine. This power density was 68% higher than that of TRAB. The energy density was 478 Wh m −3 -anolyte, which was ∼50% higher than that produced by TRAB. The anodic coulombic efficiency of the TRENB was 77 ± 2%, which was more than twice that obtained using ammonia in a TRAB (35%). The higher anodic efficiency reduced the difference between the anode dissolution and cathode deposition rates, resulting in a process more suitable for closed loop operation. The thermal-electric efficiency based on ethylenediamine separation using waste heat was estimated to be 0.52%, which was lower than that of TRAB (0.86%), mainly due to the more complex separation process. However, this energy recovery could likely be improved through optimization of the ethylenediamine separation process.
05/01/2017 00:00:00
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2.5.2 Thermally regenerative battery
Removal of copper from water using a thermally regenerative electrodeposition battery
Abstract A thermally regenerative ammonia battery (TRAB) recently developed for electricity generation using waste heat was adapted and used here as a treatment process for solutions containing high concentrations of copper ions. Copper removal reached a maximum of 77% at an initial copper concentration ( C i ) of 0.05 M, with a maximum power density ( P ) of 31 W m −2 -electrode area. Lowering the initial copper concentration decreased the percentage of copper removal from 51% ( C i  = 0.01 M, P  = 13 W m −2 ) to 2% ( C i  = 0.002 M, P  = 2 W m −2 ). Although the final solution may require additional treatment, the adapted TRAB process removed much of the copper while producing electrical power that could be used in later treatment stages. These results show that the adapted TRAB can be a promising technology for removing copper ions and producing electricity by using waste heat as a highly available and free source of energy at many industrial sites.
01/01/2017 00:00:00
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2.6 Piezoelectric heat conversion

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Piezoelectricity is the electric charge that accumulates in certain solid materials (such as crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure and latent heat. [\[Wiki\]](https://en.wikipedia.org/wiki/Piezoelectricity) Piezoelectricity can be used to convert waste heat into power, usually in very small scale applications. **Research findings:** * In this paper, we present the working principle and first experimental demonstration of an innovative approach to harvest low-quality heat sources, the Self Oscillating Fluidic Heat Engine (SOFHE). Thermal energy is first converted into pressure pulsations by a self-excited thermofluidic oscillator driven by the periodic phase change of a fluid in an enclosed channel. A piezoelectric membrane then converts this mechanical energy into electrical power. After describing the working principle, an experimental demonstration is presented. The PV diagram of this new thermodynamic cycle is measured, showing a mechanical power of 3.3mW. Combined with a piezoelectric spiral membrane, the converted electrical power generation achieved is close to 1 μW in a 1 MΩ load. This work sets the basis for the future development of this new type of heat engine for waste heat recovery and to power wireless sensors. Art. [#ARTNUM](#article-33435-2561074235)

2.6.1 Piezoelectric heat conversion
First experimental demonstration of a Self-Oscillating Fluidic Heat Engine (SOFHE) with piezoelectric power generation
In this paper, we present the working principle and first experimental demonstration of an innovative approach to harvest low-quality heat sources, the Self-Oscillating Fluidic Heat Engine (SOFHE). Thermal energy is first converted into pressure pulsations by a selfexcited thermo-fluidic oscillator driven by periodic phase change of a fluid in an enclosed channel. A piezoelectric membrane then converts this mechanical energy into an electrical power. After describing the working principle, an experimental demonstration is presented. The P-V diagram of this new thermodynamic cycle is measured, showing a mechanical power of 3.3mW. Combined with a piezoelectric spiral membrane, the converted electrical power generation achieved is close to 1μ W in a 1MΩ load. This work sets the basis for future development of this new type of heat engine for waste heat recovery and to power wireless sensors.
11/01/2016 00:00:00
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2.6.2 Piezoelectric heat conversion
Piezoelectric Vibration Harvesters Based on Vibrations of Cantilevered Bimorphs: A Review
With the advancement in the technologies around the world over the past few years, the micro- electromechanical systems (MEMS) have gained much attention in harvesting the energy for wire- less, self-powered and MEMS devices. In the present era, many devices are available for energy harnessing such as electromagnetic, electrostatic and piezoelectric generator and these devices are designed based on its ability to capture the different form of environment energy such as solar energy, wind energy, thermal energy and convert it into the useful energy form. Out of these de- vices, the use of a piezoelectric generator for energy harvesting is very attractive for MEMS appli- cations. There are various sources of harvestable energy including waste heat, solar energy, wind energy, energy in floating water and mechanical vibrations which are used by the researchers for energy harvesting purposes. This paper reviews the state-of-the-art in harvesting mechanical vi- brations as an energy source by various generators (such as electromagnetic, electrostatic and piezoelectric generators). Also, the design and characteristics of piezoelectric generators, using vibrations of cantilevered bimorphs, for MEMS have also been reviewed here. Electromagnetic, electrostatic and piezoelectric generators presented in the literature are reviewed by taking into an account the power output, frequency, acceleration, dimension and application of each genera- tor and the coupling factor of each transduction mechanism has also been discussed for all the de- vices.
01/01/2015 00:00:00
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3. Oher heat conversion technologies

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3.1 Thermoacoustic heat engine (TAHE)

0

Thermoacoustic engines (sometimes called "TA engines") are thermoacoustic devices which use high-amplitude sound waves to pump heat from one place to another (this require work, which is provided by the loudspeaker). Or use a heat difference to produce work in the form of sound waves; these waves can then be converted into electrical current the same way as a microphone does. These devices can be designed to use either a standing wave or travelling wave. [\[Wiki\]](https://en.wikipedia.org/wiki/Thermoacoustic_heat_engine) The thermoacoustic heat engine in the figure consists of two heat exchangers. Those are the engine's heat source and heat sink, a stack where input thermal power is converted to acoustic power (a form of mechanical power), and a resonator which is a cylindrical tube encompassing all components and is the solid container for the acoustic wave generated. The key mechanism for energy conversion from thermal to acoustic is the thermoacoustic effect, occurring in the TAHE when certain conditions are satisfied. A compressible fluid is used as the working fluid within the engine, which in most cases is an inert gas such as helium. Acoustic waves occur naturally as a result of a temperature gradient across the stack as heat transfer occurs between the compressible fluid and a solid boundary (stack). The transfer of thermal energy to and from the compressible fluid and the stack creates local changes of pressure and velocity in the working fluid. When there is the correct pressure–velocity phasing, acoustic oscillations appear spontaneously creating an acoustic wave. Depending on the pressure–velocity phasing either a standing-wave or a travelling-wave is created. A standing-wave pressure–velocity phasing is shown in the Figure. The pressure the acoustic wave generates creates mechanical work, which can then be easily recovered to generate for example electric power. In this work, a standing-wave thermoacoustic heat engine is evaluated due to its simple design, as can be seen in the figure. Art. [#ARTNUM](#article-29718-2146632007) **Research findings:** * In this present work, the application of a standing wave TAHE to utilise waste heat from baking ovens in biscuit manufacturing is investigated. An iterative design methodology is employed to determine the design parameter values of the device that not only maximise acoustic power output and ultimately overall efficiency but also utilise as much of the high volume waste heat as possible. At the core of the methodology employed is DeltaEC, a simulation software which calculates the performance of thermoacoustic equipment. Our investigation has shown that even at such a comparatively low temperature of 150 °C it is possible to recover waste heat to deliver an output of 1029.10 W of acoustic power with a thermal engine efficiency of 5.42%. Art. [#ARTNUM](#article-29718-2146632007)

3.1.1 Thermoacoustic heat engine (TAHE)
A thermoacoustic Stirling heat engine
Electrical and mechanical power, together with other forms of useful work, are generated worldwide at a rate of about 10 12 watts, mostly using heat engines. The efficiency of such engines is limited by the laws of thermodynamics and by practical considerations such as the cost of building and operating them. Engines with high efficiency help to conserve fossil fuels and other natural resources reducing global-warming emissions and pollutants. In practice, the highest efficiencies are obtained only in the most expensive, sophisticated engines, such as the turbines in central utility electrical plants. Here we demonstrate an inexpensive thermoacoustic engine that employs the inherently efficient Stirling cycle 1 . The design is based on a simple acoustic apparatus with no moving parts. Our first small laboratory prototype, constructed using inexpensive hardware (steel pipes), achieves an efficiency of 0.30, which exceeds the values of 0.10-0.25 attained in other heat engines with no moving parts. Moreover, the efficiency of our prototype is comparable to that of the common internal combustion engine 2 (0.25-0.40) and piston-driven Stirling engines 3,4 (0.20-0.38).
05/01/1999 00:00:00
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3.1.2 Thermoacoustic heat engine (TAHE)
Design of a thermoacoustic heat engine for low temperature waste heat recovery in food manufacturing: A thermoacoustic device for heat recovery
Abstract There is currently an urgent demand to reuse waste heat from industrial processes with approaches that require minimal investment and low cost of ownership. Thermoacoustic heat engines (TAHEs) are a kind of prime mover that convert thermal energy to acoustic energy, consisting of two heat exchangers and a stack of parallel plates, all enclosed in a cylindrical casing. This simple design and the absence of any moving mechanical parts make such devices suitable for a variety of heat recovery applications in industry. In this present work the application of a standing-wave TAHE to utilise waste heat from baking ovens in biscuit manufacturing is investigated. An iterative design methodology is employed to determine the design parameter values of the device that not only maximise acoustic power output and ultimately overall efficiency, but also utilise as much of the high volume waste heat as possible. At the core of the methodology employed is DeltaEC, a simulation software which calculates performance of thermoacoustic equipment. Our investigation has shown that even at such a comparatively low temperature of 150 °C it is possible to recover waste heat to deliver an output of 1029.10 W of acoustic power with a thermal engine efficiency of 5.42%.
04/01/2014 00:00:00
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3.1.3 Thermoacoustic heat engine (TAHE)
Design of two-stage thermoacoustic stirling engine coupled with push-pull linear alternator for waste heat recovery
Thermoacoustics is suitable technology for recovering waste heat and generating electricity. In this paper, a novel thermoacoustic electricity generator using a push-pull linear alternator is proposed. It is aimed to recover part of the internal combustion engine exhaust waste heat and produce useful electricity. It consists of two half wave length identical stages and a linear alternator connected in between them. The physically identical stages produce identical wave halves with acoustic pressure out of phase. The availability of two points having the same pressure amplitude out of phase provides the opportunity to connect the linear alternator to two points in each stage to run the alternator in a "push and pull" mode. The proposed engine is able to produce more than 138.4W of electricity at thermal-to-electrical efficiency of 25.1% equivalent to a fraction of Carnot efficiency of 45.1% while using helium pressurized at 40 bar.
08/21/2015 00:00:00
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3.1.4 Thermoacoustic heat engine (TAHE)
Development of Thermoacoustic Engine Operating by Waste Heat from Cooking Stove
There are about 1.5 billion people worldwide use biomass as their primary form of energy in household cooking[1]. They do not have access to electricity, and are too remote to benefit from grid electrical supply. In many rural communities, stoves are made without technical advancements, mostly using open fires cooking stoves which have been proven to be extremely low efficiency, and about 93% of the energy generated is lost during cooking. The cooking is done inside a dwelling and creates significant health hazard to the family members and pollution to environment. SCORE (www.score.uk.com) is an international collaboration research project to design and build a low-cost, high efficiency woodstove that uses about half amount of the wood of an open wood fire, and uses the waste heat of the stove to power a thermoacoustic engine (TAE) to produce electricity for applications such as LED lighting, charging mobile phones or charging a 12V battery. This paper reviews on the development of two types of the thermo...
01/01/2012 00:00:00
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3.1.5 Thermoacoustic heat engine (TAHE)
Energy conversion through thermoacoustics and piezoelectricity
Waste or prime heat can be converted into electricity with thermoacoustic-Stirling engines coupled to piezoelectric alternators. An inline arrangement of engines and alternators allows a vibration balanced, multiphase power generator that is compact, light weight and low cost. The engines convert heat into high amplitude ≈400 Hz oscillations in pressurized helium gas. These pressure oscillations cause a thin steel diaphragm to flex like a drumhead. The diaphragm is supported at its perimeter by a ring of piezoelectric elements. As the diaphragm flexes in either direction, it pulls inward on the piezoelectric elements causing a large amplified ≈800 Hz fluctuating compressive stress in the elements which then convert the stress into electricity with high efficiency. The flexible-diaphragm piezoelectric alternator overcomes the large acoustic impedance mismatch between the helium and piezoelectric elements without exceeding the limited fatigue strength of available materials. So far, a prototype generator ha...
10/01/2011 00:00:00
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3.1.6 Thermoacoustic heat engine (TAHE)
Low-temperature energy conversion using a phase-change acoustic heat engine
Abstract Low-temperature heat is abundant, accessible through solar collectors or as waste heat from a large variety of sources. Thermoacoustic engines convert heat to acoustic work, and are simple, robust devices, potentially containing no moving parts. Currently, such devices generally require high temperatures to operate efficiently and with high power densities. Here, we present a thermoacoustic engine that converts heat to acoustic work at temperature gradients as low as ∼4–5 K/cm, corresponding with a hot-side temperature of ∼50 °C. The system is based on a typical standing-wave design, but the working cycle is modified to include mass transfer, via evaporation and condensation, from a solid surface to the gas mixture sustaining the acoustic field. This introduces a mode of isothermal heat transfer with the potential of providing increased efficiencies – experiments demonstrate a significant reduction in the operating temperature difference, which may be as low as 30 K, and increased output – this ‘wet’ system produces up to 8 times more power than its dry equivalent. Furthermore, a simplified model is formulated and corresponds quite well with experimental observations and offering insight into the underlying mechanism as well as projections for the potential performance of other mixtures. Our results illustrate the potential of such devices for harvesting energy from low-temperature heat sources. The acoustic power may be converted to electricity or, in a reverse cycle, produce cooling – providing a potential path towards solar heat-driven air conditioners.
12/01/2018 00:00:00
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3.2 Water desalination

0

Waste heat can be used to desalinate water. **Research findings:** * A new desalination method was proposed in this work, utilizing lowgrade waste heat from the power plant, allowing cogeneration of freshwater with electricity. The desalination system analysed in this study makes use of simple concepts, such as Torricelli vacuum, flash evaporation and siphon effect, to reduce the overall operating power consumption of the plant. An experimental plant has been built and tested in an existing thermal power plant at Chennai, India. The plant utilized the warm saline reject water from the power plant condenser to feed the evaporator without using a separate feed water pump. The amount of freshwater produced by this plant is nearly 1/200 times of the seawater supplied for the available temperature gradient of 8.7°C. It is a lowcost system when compared with conventional desalination technologies, with energy consumption per unit volume estimated at 2.62 kWh/m3 of freshwater generated. Art. [#ARTNUM](#article-33254-2177896336)

3.2.1 Water desalination
A desalination method utilising low-grade waste heat energy
AbstractA new desalination method was proposed in this work, utilizing low-grade waste heat from the power plant, allowing co-generation of fresh water with electricity. The desalination system analysed in this study makes use of simple concepts, such as Torricelli vacuum, flash evaporation and siphon effect, to reduce the overall operating power consumption of the plant. An experimental plant has been built and tested in an existing thermal power plant at Chennai, India. The plant utilized the warm saline reject water from the power plant condenser to feed the evaporator without using a separate feed water pump. The amount of freshwater produced by this plant is nearly 1/200 times of the sea water supplied for the available temperature gradient of 8.7°C. It is a low-cost system when compared with conventional desalination technologies, with energy consumption per unit volume estimated at 2.62 kWh/m3 of fresh water generated. It operates at low temperatures, low pressure conditions and produces fresh wate...
11/20/2015 00:00:00
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3.2.2 Water desalination
Desalination process system utilizing waste heat
The invention relates to a desalination process system utilizing waste heat. The system comprises a multi-effect evaporator, a heat exchanger, a pipeline, a desalination water pump, a water supply pump, a crystallization tank, a boiler, a desalination water tank and a circulating pump. Boiler flue gas waste heat or low-enthalpy-value steam pumped out from a low-pressure cylinder of a steam turbine is used as an energy source, and through the heat exchanger and the multi-effect evaporator, salt-containing water is changed into distilled water to realize a desalination purpose; the produced distilled water can be directly used as production water for a power plant or domestic water. According to the system, compared with the prior art, the electricity consumption, the occupied land size and the operation cost are greatly reduced, and secondary pollution caused by medicine utilization is avoided; the system is safe, simple, practical and reliable; by recycling flue gas exhaust heat discharged from the boiler or low-enthalpy-value steam pumped out from the steam turbine, the desalination process operation cost is greatly reduced, and a very high economic value is realized.
02/03/2016 00:00:00
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3.2.3 Water desalination
Development and analysis of a novel biomass-based integrated system for multigeneration with hydrogen production
Abstract Energy and exergy analyses of an integrated system based on anaerobic digestion (AD) of sewage sludge from wastewater treatment plant (WWTP) for multi-generation are investigated in this study. The multigeneration system is operated by the biogas produced from digestion process. The useful outputs of this system are power, freshwater, heat, and hydrogen while there are some heat recoveries within the system for improving efficiency. An open-air Brayton cycle, as well as organic Rankine cycle (ORC) with R-245fa as working fluid, are employed for power generation. Also, desalination is performed using the waste heat of power generation unit through a parallel/cross multi-effect desalination (MED) system for water purification. Moreover, a proton exchange membrane (PEM) electrolyzer is used for electrochemical hydrogen production option in the case of excess electricity generation. The heating process is performed via the rejected heat of the ORC's working fluid. The production rates for products including the power, freshwater, hydrogen, and hot water are obtained as 1102 kW, 0.94 kg/s, 0.347 kg/h, and 1.82 kg/s, respectively, in the base case conditions. Besides, the overall energy and exergy efficiencies of 63.6% and 40% are obtained for the developed system, respectively.
02/01/2019 00:00:00
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3.3 Shape-memory metals/alloys

0

A shape-memory alloy is an alloy that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. It may also be called memory metal, memory alloy, smart metal, smart alloy, or muscle wire. [\[Wiki\]](https://en.wikipedia.org/wiki/Shape-memory_alloy) By creating movement through heating or cooling, power can be produced by memory alloys. **Research findings:** * Few technologies can produce meaningful power from low-temperature waste heat sources below 250 °C, particularly on a permass basis. Since the 1970’s energy crisis, NiTi shape memory alloy (SMA) and associated thermal engines have been considered a viable heattopower transducer but were not adopted due to previously poor material quality, low supply, design complexity, and cost. Decades of subsequent material development, research, and commercialization have resulted in the availability of consistently highquality, wellcharacterized, low cost alloys and a renewed interest in SMA as a waste heat energy recovery technology. The Lightweight Thermal Energy Recovery System (LighTERS) is an ongoing ARPAE funded collaboration between General Motors Company, HRL Laboratories, Dynalloy, Inc., and the University of Michigan. In this paper we will present initial results from investigations of a closed loop SMA thermal engine (a refinement of the Dr. Johnson design) using a helical coil element and forcedair heat exchange. This engine generates mechanical power by continuously pulling itself through separate hot and cold air streams using the shape memory phase transformation to alternately expand and contract at frequencies between 0.25 and 2 Hz. This work cycle occurs continuously along the length of the coil loop and produces steady state power against an external moment. We present engine features and the thermal envelope that resulted in devices achieving between 0.1 and 0.5 W/g of shape memory alloy material using only forced air heat exchangers and room temperature cooling. Art. [#ARTNUM](#article-33430-2064257673) * An energy harvesting prototype (EHP) was designed to convert lowtemperature heat loss from fluid into electricity. The method for energy conversion uses two antagonistically connected shape memory alloy (SMA) actuators to rotate a shaft that is connected to a generator. Heat transfer equations for concentric annular flow are modeled. The relationship between SMA temperature and shaft angular rotation is derived from a semiempirical SMA stress–temperature model and Ozdemir's SMA stress–strain equations. The simulated generator shaft rotation and generator voltage are in close agreement with the corresponding experimental results. Additional experiments were conducted to compare the ability of spring and linear SMA wires to convert lowtemperature heat lost from water into electricity. The linear SMA generated a peak 0.3 V, whereas the springshaped SMA generated a peak of nearly 5 V. On average, 7.4 mJ of energy per 2.5 s cycle was stored in a 6F capacitor attached to the generator output. It is concluded that the EHP has a strong potential to recuperate lowtemperature wasted heat. Art. [#ARTNUM](#article-33430-2346496296)

3.3.1 Shape-memory metals/alloys
Development of a Shape Memory Alloy Heat Engine Through Experiment and Modeling
Few technologies can produce meaningful power from low temperature waste heat sources below 250°C, particularly on a per-mass basis. Since the 1970’s energy crisis, NiTi shape memory alloy (SMA) and associated thermal engines have been considered a viable heat-to-power transducer but were not adopted due to previously poor material quality, low supply, design complexity, and cost. Decades of subsequent material development, research, and commercialization have resulted in the availability of consistently high-quality, well-characterized, low cost alloys and a renewed interest in SMA as a waste heat energy recovery technology. The Lightweight Thermal Energy Recovery System (LighTERS) is an ongoing ARPA-E funded collaboration between General Motors Company, HRL Laboratories, Dynalloy, Inc., and the University of Michigan. In this paper we will present initial results from investigations of a closed loop SMA thermal engine (a refinement of the Dr. Johnson design) using a helical coil element and forced-air heat exchange. This engine generates mechanical power by continuously pulling itself through separate hot and cold air streams using the shape memory phase transformation to alternately expand and contract at frequencies between 0.25 and 2 Hz. This work cycle occurs continuously along the length of the coil loop and produces steady state power against an external moment. We present engine features and the thermal envelope that resulted in devices achieving between 0.1 and 0.5 W/g of shape memory alloy material using only forced air heat exchangers and room temperature cooling.Copyright © 2011 by ASME and General Motors
01/01/2011 00:00:00
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3.3.2 Shape-memory metals/alloys
Electromechanical Conversion of Low-Temperature Waste Heat Via Helical Shape Memory Alloy Actuators
An energy harvesting prototype (EHP) was designed to convert low-temperature heat loss from fluid into electricity. The method for energy conversion uses two antagonistically connected shape memory alloy (SMA) actuators to rotate a shaft that is connected to a generator. Heat transfer equations for concentric annular flow are modeled. The relationship between SMA temperature and shaft angular rotation is derived from a semiempirical SMA stress–temperature model and Ozdemir's SMA stress–strain equations. The simulated generator shaft rotation and generator voltage are in close agreement with the corresponding experimental results. Additional experiments were conducted to compare the ability of spring and linear SMA wires to convert low-temperature heat lost from water into electricity. The linear SMA generated a peak 0.3 V, whereas the spring-shaped SMA generated a peak of nearly 5 V. On average, 7.4 mJ of energy per 2.5 s cycle was stored in a 6-F capacitor attached to the generator output. It is concluded that the EHP has a strong potential to recuperate low-temperature wasted heat.
06/01/2016 00:00:00
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3.3.3 Shape-memory metals/alloys
Lightweight thermal energy recovery system based on shape memory alloys: a DOE ARPA-E initiative
Over 60% of energy that is generated is lost as waste heat with close to 90% of this waste heat being classified as low grade being at temperatures less than 200°C. Many technologies such as thermoelectrics have been proposed as means for harvesting this lost thermal energy. Among them, that of SMA (shape memory alloy) heat engines appears to be a strong candidate for converting this low grade thermal output to useful mechanical work. Unfortunately, though proposed initially in the late 60's and the subject of significant development work in the 70's, significant technical roadblocks have existed preventing this technology from moving from a scientific curiosity to a practical reality. This paper/presentation provides an overview of the work performed on SMA heat engines under the US DOE (Department of Energy) ARPA-E (Advanced Research Projects Agency - Energy) initiative. It begins with a review of the previous art, covers the identified technical roadblocks to past advancement, presents the solution path taken to remove these roadblocks, and describes significant breakthroughs during the project. The presentation concludes with details of the functioning prototypes developed, which, being able to operate in air as well as fluids, dramatically expand the operational envelop and make significant strides towards the ultimate goal of commercial viability.
04/26/2012 00:00:00
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