A brazed plate heat exchanger (BPHE) is built up from a package of (corrugated) stainless steel plates which are brazed together using materials such as copper and nickel. The plate package is generally sealed by front and rear plate packages to form a self-contained unit. Each plate has a characteristic corrugation pattern that governs the degree of thermal efficiency and hydraulic behavior of the BPHE unit. Four to six apertures are placed in the corners/edges of these plates. Alternate plates are arranged at 180° to each other resulting in the formation of the inlet and outlet port manifolds for the various process fluid circuits. Art. [#ARTNUM](#article-26232-1752739663). Compactness, low volume, scalability, possibility to achieve close temperature approaches, relatively high values of the heat transfer coefficients make brazed plate heat exchangers suitable for a very wide range of applications. They are used especially when corrosion can be an issue since the plates are available in a wide range of materials (copper, copper+, SS brazing materials). In Brazed Plate Heat Exchangers, the brazing process eliminates gasketed joints which allow for higher design pressure and temperatures. [\[Source\]](http://www.graham-mfg.com/gasketed-and-brazed-plate-heat-exchanger-advantages) They can be used with multiple phases. High turbulent flows at low flow rates can be reached due to the patterns on the plates. This also reduces the fouling within the plates. However, fouling can still occur. The brazed plate heat exchanger is permanently sealed. Due to this backflushing is required for cleaning purposes. Soft debris will be removed, weak acids can be used to enhance the cleaning. **Applications:** Art. [#ARTNUM](#article-26232-1752739663); [#ARTNUM](#article-26232-2792430176) * Refridgeration * Residential heating * HVAC * LNG plants * Dairy/food/beverage industry

In Gasketed Plate Heat Exchangers, each heat transfer plate is fitted with an elastomeric gasket, which seals and distributes the process fluids. The heads, normally referred to as channel covers, include connections to permit the entry of the process fluid into the plate pack. [\[Source\]](http://www.graham-mfg.com/gasketed-and-brazed-plate-heat-exchanger-advantages) The plates can easily be removed for cleaning, expansion, or replacing purposes, drastically reducing maintenance costs. Gasketed Plate Heat Exchangers are limited in high fluid temperatures, by the temperature limitations of the gasket. [\[Source\]](https://www.thermaxxjackets.com/plate-and-frame-heat-exchangers-explained/) [\[Hestia GPHE\]](https://www.neimagazine.com/features/featurepossibilities-for-gasketed-plate-heat-exchangers-4633881/) The GPHE can handle flows rates up to 2000 m³/hr with a duty up to 30000 kW. Suspensions with a concentration of less than 10 mg/L can be handled. Particles size smaller than 0.6 mm however, cause a rapid increase in pressure drop. Often the system is unsuitable for gas two-phase flow. The main benefit of using GPHE is the ability to easily dismantle the system. This allows for easy cleaning of the system and the flexibility to increase the heater duty of the heat exchanger during usage. Furthermore, the system is normally the most economical if applicable. **Applications:** * District heating * HVAC * Nuclear power plants

Welded plate heat exchangers are similar to Gasketed plate heat exchangers, but instead, the plates are welded together. They are extremely durable and are ideal for transferring fluids with high temperatures or corrosive materials. The plates are all welded together in one block, they, therefore, can’t be fully dismantled and the heating/cooling capacity is fixed. However, they do allow higher pressure and temperature fluids to be used so you’ll find these mostly in heavy industrial, power plants and oil refinery applications. [\[Source\]](https://theengineeringmindset.com/plate-heat-exchanger-applications/) Can be used for liquid-liquid and biphasic applications. Also for condensation, evaporation, heating, cooling, heat exchange and vacuum conditions. With a condensation output up to 200 MW. Media which contain fibres and solids can also be used in the tube-side, due to the large open flow area. The strong construction of the WPHE makes it able to have pressure differentials of up to 60 bar. **Applications:** Art. [#ARTNUM](#article-26241-2062888851) * Chemical industry: coolers/condensers * Heavy industrial * Power plants * Petrochemical * Oil and gas * Pharma/food

A SPHE consists of two sheets that are rolled around a central rod and therefore two separated concentric channels are made. The ends of the channels are sealed through welding. There are two possibilities to seal the sides of the heat exchanger: using bolts and gaskets to fasten the covering sheets to the heat exchanger or welding the covering sheets to the heat exchanger. Art. [#ARTNUM](#article-26228-2342724403) The main advantage of the SPHE is its highly efficient use of space. This attribute is often leveraged and partially reallocated to gain other improvements in performance, according to well-known tradeoffs in heat exchanger design. (A notable tradeoff is capital cost vs operating cost.) The structure of the SPHE also results in no dead spots and a close temperature approach. A compact SPHE may be used to have a smaller footprint and thus lower all-around capital costs, or an oversized SPHE may be used to have less pressure drop, less pumping energy, higher thermal efficiency, and lower energy costs. Thermal efficiencies up to 2-3 times higher than a conventional shell and tube heat exchanger can be reached. The SPHE is great against fouling and high viscous or particulate media. This makes the SPHE good for applications such as pasteurization, digester heating, heat recovery, pre-heating, and effluent cooling. For sludge treatment, SPHEs are generally smaller than other types of heat exchangers. [\[Wiki\]](https://en.wikipedia.org/wiki/Heat_exchanger#Helical-coil_heat_exchangers) The system is great for liquid-liquid and two-phase duties and ideal for vacuum condensation and can be used for steam heater duties. Differential pressures of up to 50 bar are possible. The easy to open design of the SPHE allows for quick and simple cleaning. **Research findings:** * The spiral heat exchanger is self-cleaning equipment with low fouling tendencies, easily accessible for inspection or mechanical cleaning and with minimum space requirements. Art. [#ARTNUM](#article-26228-2065526122) Two-phase application is possible, as well as liquid-liquid. Especially good for fouling liquids. **Applications:** * Dairy/food/beverage industry * Biogas industry * Wastewater industry * Pulp and paper industry * Heavy industry * Petrochemical industry * Chemical industry

The PCHE is a plate-type compact heat exchanger and its core is composed of thin plates (of thickness 1.5–3 mm) made of alloys like stainless steel or inconel alloys, with flow channels etched on them by chemical etching process. The etched plates are stacked one over the other and are bonded together using diffusion bonding. These blocks are welded together to construct the core of the PCHE and the headers are connected to the core for external connections. Printed Circuit Heat Exchanger (PCHE) is a widely chosen plate type compact heat exchanger for high-pressure applications. Art. [#ARTNUM](#article-26243-2767695692) The complete microchannel heat exchangers are highly compact, typically comprising about one-fifth the size and weight of conventional heat exchangers for the same thermal duty and pressure drops. PCHEs can be constructed out of a range of materials, including austenitic stainless steels suitable for design temperatures up to 800°C, and nickel alloys such as Incoloy 800HT suitable for design temperatures more than 900°C. Single units ranging from a few grams up to 100 tonnes have been manufactured. Art. [#ARTNUM](#article-26243-1980144440) High heat fluxes of 13 kW/cm2 are possible, because of the high surface to volume ratios. The system is immune to the effect of fluid pressure pulsation and fluid low vibration, has an extremely low fluid inventory, the ability to introduce multiple streams in a cross, counter and or co-flow. The system is also capable of handling gases, liquid, and two-phase applications. With a wide range of possible materials to use. Thus, the field of applications is also very varied, including specialised chemicals processing, and PCHEs are even to be found orbiting the Earth in the International Space Station! Due to the inherent flexibility of the etching process, the basic construction may readily be applied to both a wider range and more complex integration of process unit operations. Chemical reaction, rectification, stripping, mixing, and absorption, as well as boiling and condensation, can be incorporated into compact integrated process modules. Art. [#ARTNUM](#article-26243-1980144440) **Applications:** * Marine * Energy * Oil and gas * Petrochemical * Refridgeration * Air separation * Nuclear

The pillow plate is constructed using a thin sheet of metal spot-welded to the surface of another thicker sheet of metal. The thin plate is welded in a regular pattern of dots or with a serpentine pattern of weld lines. The welding can be done relative cost-effective and the plates used can be made thinner. After welding the enclosed space is pressurised with sufficient force to cause the thin metal to bulge out around the welds, providing a space for heat exchanger liquids to flow, and creating a characteristic appearance of a swelled pillow formed out of metal. There are various types of design possibilities possible. A pillow plate exchanger is commonly used in the dairy industry for cooling milk in large direct-expansion stainless steel bulk tanks. The pillow plate allows for cooling across nearly the entire surface area of the tank, without gaps that would occur between pipes welded to the exterior of the tank. [\[Wiki\]](https://en.wikipedia.org/wiki/Heat_exchanger#Helical-coil_heat_exchangers) PPHE are a novel heat exchanger type based on wavy pillowlike plate geometry. Typically, they are composed of parallel plates arranged as a stack. In this way, inner channels within the pillow-plates alternate with outer channels between the adjacent plates, and thus, a structure with alternating inner and outer channels are arranged for the heat transfer media. In heat exchanger applications, several pillow-plates are arranged vertically as a stack, parallel to each other, with alternating channels within and between the pillow-plates. The medium inside the pillow-plates is being continuously redirected by the welding point pattern. This leads to thin boundary layers and good heat transfer performance, and hence, to lower the required heat transfer area and lower investment. On the other hand, internal pressure loss also increases, leading to high operating costs for pumps and compressors. Art. [#ARTNUM](#article-26310-2779667980) Phase-change applications possible, mainly used for its low fouling capabilities. The system has great cleaning possibilities even sometimes possible while running. Making the PPHE ideal for high hygiene applications (food) and heavy fouling processes. **Applications:** * Dairy/food/beverage * Process industry * Heat storage * Automotive * Pharmaceutical

The plate and shell heat exchanger combines the plate heat exchanger with shell and tube heat exchanger technologies. The heart of the heat exchanger contains a fully welded circular plate pack made by pressing and cutting round plates and welding them together. Nozzles carry flow in and out of the plate pack (the 'Plate side' flow path). The fully welded plate pack is assembled into an outer shell that creates a second flow path ( the 'Shell side'). Plate and shell technology offers high heat transfer, high pressure, high operating temperature, and close approach temperature (up to 1 ° C). While also being able to handle large temperature differences between the introduced fluids. In particular, it does completely without gaskets, which provides security against leakage at high pressures and temperatures. [\[Wiki\]](https://en.wikipedia.org/wiki/Heat_exchanger#Plate_and_shell_heat_exchanger) The system is resistant to thermal shocks and thermal and pressure fatigue, making it a good option for temperature fluctuations. Plate-and-shell exchangers combine the pressure and temperature capabilities of a cylindrical shell with the excellent heat transfer performance of a plate heat exchanger. While being 60-70 % smaller than a traditional shell and tube heat exchanger. The round plates ensure an even distribution of mechanical loads, without the stress concentrations that occur in the corners of rectangular plates. The system is available in two types of configurations. The bolted and fully welded system, the bolted systems can be opened for cleaning purposes. And the full welded system is used for higher pressure and temperature applications. Multi-phase applications are possible. **Applications:** * HVAC industry * Marine/offshore industry * Dairy/food/beverage industry * Sugar industry * Biogas industry * Refrigeration industry * Pulp and paper industry * Heavy industry * Mining industry * Petrochemical industry * Chemical industry * Condensation * Steam heating * Oil coolers * Gas heaters/coolers

An SSHE basically consists of a cylindrical rotating shaft (the “rotor”) within a concentric hollow stationary cylinder (the “stator”) so as to form an annular region along which the process fluid is pumped. The stator acts as the heat-transfer surface, and it is normally enclosed within another cylindrical tube which provides a gap through which a heating or cooling service fluid (for example, steam or ammonia) passes. Attached to the rotor are a number of pivoted blades, each of which scrapes the heat-transfer surface, removing processed fluid and hence allowing unprocessed fluid to come closer to the stator. A cut-away schematic of a typical SSHE is shown in the figure. SSHE are effective for heavily fouling fluids due to constant removal of containment by the rotors. Moreover, highly viscous fluids can also be used, because of the mixing of the rotors, resulting in a distributed temperature. The systems can also be used for cooling crystallization processes as the crystal are removed constantly from the surface. The usual size of a SSHE is 4-16 m long, the system is able to handle fluids as high as 65 % wt. of solids. In terms of viscosity, it can handle up to 10000 cP. The near plug-flow behaviour of the systems allows for a transition from a batch to a continuous process. Applications: Art. [#ARTNUM](#article-26537-2014080855) * Viscous fluids * Food * Pharmaceutical * Chemical

The wide gap heat exchanger is similar to a gasketed heat exchangers, except that one or more of the channels are wider. It has excellent heat transfer and a compact structure with deeper corrugation, therefore, it is especially suitable for heat exchanging between fibrous and viscous materials/fluids and solid particle-containing fluids. Art. [#ARTNUM](#article-26309-2377641195). The easy opening of the systems allows for cleaning possibilities. The system can results in a higher pressure drop due to the created high turbulence. **Applications:** * Biotech and Pharmaceutical * Chemicals * Energy and Utilities * Food and Beverages * Mining, Minerals and Pigments * Pulp and Paper * Water and Waste treatment

The capsule-type plate heat exchanger is proposed to address high viscosity fluid which has concave and convex ellipsoidal embossing similar to half capsules. Art. [#ARTNUM](#article-26138-2503965242); and has the advantages of low pressure drop and less deposition due to the straight passages in the channels. Art. [#ARTNUM](#article-26138-2914453957) Phase-change applications possible, low fouling type. It is still under development and is not industrially applied.

A shell and tube heat exchanger is a class of heat exchanger designs. It is the most common type of heat exchanger in oil refineries and other large chemical processes and is suited for higher-pressure applications. [\[Wiki\]](https://en.wikipedia.org/wiki/Shell_and_tube_heat_exchanger) There are different design elements that can be used in a shell and tube, the Tubular Exchanger Manufacturer’s Association (TEMA) has provided standard nomenclature for describing different configurations of common shell & tube heat exchangers, as can be seen in the figure. [\[TEMA source\]](https://www.engineeringpage.com/heat_exchangers/tema.html) **Design considerations:** * The fluids with high velocity, fouling tendency, corrosivity, high temperatures or pressures should go on the tube-side. * The shell side has lower pressure drops and is usually better suited for condensing vapours (except steam) * With temperature changes higher than 150 °C thermal expansion may be an issue: floating heads can help. On tube side: * Cooling water – The more-fouling, erosive or corrosive fluid – The less-viscous fluid – The fluid at a higher pressure – The hotter fluid – The smaller volumetric flowrate **Applications:** * Process liquid or gas cooling * Process or refrigerant vapor or steam condensing * Process liquid, steam or refrigerant evaporation * Process heat removal and preheating of feed water * Thermal energy conservation efforts, heat recovery * Compressor, turbine and engine cooling, oil and jacket water * Hydraulic and lube oil cooling **Application Areas:** * Power Generation * HVAC * Marine Applications * Pulp and Paper * Refrigeration * Pharmaceuticals * Air Processing and Compressor Cooling * Metals and Mining * Transport

Flat tube heat exchangers use flat tubes. This can result in better heat transfer, especially when other design elements, like fins or vortex generators, are used. Flat tubes are often used in cooling applications. The system is optimized for poor heat transfer fluids like oils. The flat tube geometry also results in a low-pressure drop. **Research findings:** * The heat exchanger element with flat tubes and vortex generators gives nearly twice as much heat transfer and only half as much pressure loss as the corresponding heat exchanger element with round tubes. Art. [#ARTNUM](#article-26308-1994346551)

A twisted (oval) tube heat exchanger is a type of heat exchanger that aims at improving the heat transfer coefficient of the tube side and also decreasing the pressure drop of the shell side. Tubes that play an important role in this heat transfer enhancement technique are made from normal round tubes. They are formed into an oval section with a superimposed twist by some special techniques. Two ends of the tubes remain round on the consideration of assembling them with the tube sheet. [#ARTNUM](#article-26126-2049240625) The tube geometry is a self-supporting structure which eliminates the requirements of baffles. The lack of baffles provides a longitudinal flow pattern. This flow eliminates damage-inducing vibration in the shell, the creation of dead spots and a lower pressure drop. The twisted tube configuration can have up to 40% more heat transfer area than the traditional shell and tube HEX of the same volume. The twist of the tubes results in a swirl flow around the tube side. This increases the shear velocity and thus decreasing the fluid boundary layer around the tubes, resulting in an enhanced heat transfer. Bundles in the centre of the shell can be cleaned by a triangular pitch which allows the cleaning of multiple lanes. The shell side can be hydro blasted and chemical cleaning can be used effectively due to the uniform flow pattern. **Research findings:** * The analyzing result shows that the twisted oval tube heat exchangers are preferred to work at low tube side flow rate and high shell-side flow rate. Art. [#ARTNUM](#article-26126-2049240625) Fouling is inhibited compared to conventional STHE; heat transfer enhanced. **Applications:** * Petrochemical * Refining * Offshore O&G * Chemical * Pulp/paper * Mining/ Minerals * Crude preheat; Feed/effluent for reformer (CCR and semi-regeneration); Hydrotreater; Hydrocracker; Alkylation; Overhead condensers; Reboilers (kettle and J-Shell); Lean/rich amine; Compressor interstage coolers; Texas Towers; Hydrotreating/Reforming; KBR Rose Exchangers.

In a multipass type heat exchanger, one fluid moves through the shell multiple times, usually through the use of U-tubes. Multiple-pass shell-and-tube heat exchangers allow thermal expansion and easy mechanical cleaning, as well as longer flow paths for a given exchanger length. In addition, the high velocities achieved for the tube fluid help increase heat transfer coefficients and reduce surface fouling. Art. [#ARTNUM](#article-26148-1985475579) Using multipass systems gives more flexibility in optimising fluid velocity, pressure drop and heat transfer. A multipass is required if the outlet temperature of the hot stream is below the outlet temperature of the cold stream (temperature cross). **Applications:** * Industrial waste heat recovery solutions * Energy * Oil and gas industry * Chemical industry * Food * Processes of heating, evaporation, condensation or cooling of products such as oils, effluents, sewage, wastewater, biogas, asphalts, hydrocarbons, exhaust gases, biodiesel, methanol.

A falling-film heat exchanger is characterized by one fluid forming a film on the inside of a tube while being cooled or heated from the shell side. Usually, the film is facilitated by gravity (vertically), although other types do exist. The created film results in a short residence time with a high evaporation rate. It is essential that the whole column stays wetted during operation. It is often used as an evaporator in industry, to concentrate solutions. [\[Wiki\]](https://en.wikipedia.org/wiki/Falling_film_evaporator) The capacity of a falling-film heat exchanger is 150 ton/hr with a possible heat transfer area of 0.3-4800 m². The heat exchanger is suited for temperature-sensitive materials with a low viscosity with small quantities of solids. The system has a low-pressure drop and low susceptibility for fouling. **Applications:** * Chemical * Petrochemical * Polymer

The efforts to improve the shell side flow characteristics are made using the spiral baffle plates instead of vertical baffle plates. In this type of heat exchanger, fluid contacts with tubes flowing rotationally in the shell. It could improve heat exchanger performance considerably because stagnation portions in the shell could be removed. It is proved that the shell-and-tube heat exchanger with spiral baffle plates is superior to the conventional heat exchanger in terms of heat transfer. Art. [#ARTNUM](#article-26213-1536994987) The required heat transfer can be reduced up to 35%. Furthermore, it can be used to reduce the created pressure drop, damaging vibrations and acoustic rumbling. The shell-side fouling is also reduced which allows for extended operating time.

The ROD baffle heat exchanger can slightly enhance the shell side heat transfer coefficient with the significant reduction of pressure loss due to the shell side fluid flowing longitudinally through a tube bundle, which leads to the reduction of the manufacture and running cost and in some cases to the dimensions reduction of the heat exchangers. Art. [#ARTNUM](#article-26129-2047878495) The RODbaffle exchanger offers a solution to the vexing problem of tube failures in shell-and-tube exchangers resulting from tube vibration. Thus the RODbaffled heat exchanger is used when the pressure drop or damaging vibration is a crucial constraint.

One of the most simple and applicable heat exchangers is double pipe heat exchanger (DPHE), also called the concentric tube heat exchanger. This kind of heat exchanger is widely used in chemical, food, oil and gas industries. Upon having a relatively small diameter, many precise studies have also held firmly the belief that this type of heat exchanger is used in high-pressure applications. They are also of great importance where a wide range of temperature is needed. Art. [#ARTNUM](#article-26215-2519485646) The system is a simple compact design which is resistant against thermal fatigue. For a single unit capacities of 29 kW with a liquid flow of 2.3 m³/hr are shown. The simple systems allow for easy maintenance. The performance of the heat exchanger and the pressure drop are in close interaction with the geometry. Art. [#ARTNUM](#article-26215-2771080156) **Applications:** * High temperature, high pressure, low flow * Multi-phase fluids & slurries * High thermal stress * Steam condensing * Seal cooling * Liquid/Gas * Sampling * Sewage sludge heating * Effluent water cooling * Food * Detergents and dyes

In the TCTHE, there are three sections: central tube, inner annular space and outer annular space. Heat transfer mediums are passed through the central tube and outer annular space and a thermal fluid is passed through inner annular space. This type of heat exchanger can be used for higher viscosity fluids. The triple tube heat exchanger contributes to higher heat exchanger effectiveness and more energy saving compared with double tube heat exchanger per unit length. Art. [#ARTNUM](#article-26134-2245358019) **Applications:** * Food

Helical coil heat exchangers contain a helical tube. They are a simpler version of a spiral wound heat exchanger. Helical coils are very alluring for various processes such as heat exchangers and reactors because they can accommodate a large heat transfer area in a small space, with high heat transfer coefficients and narrow residence time distributions. The modification of the flow in the helically coiled tubes is due to the centrifugal forces. The curvature of the tube produces a secondary flow field with a circulatory motion, which pushes the fluid particles toward the core region of the tube. Thus the application of curved tubes in heat exchange process can be highly beneficial in comparison with the straight tube. These applications can arise in the food processing industry for heating and cooling of highly viscous liquid food, such as pastes, or for products that are sensitive to high shear stresses. **Advantages:** * Heat transfer rate in the helical coil is higher as compared to a straight tube heat exchanger. Compact structure. * It requires a small amount of floor area compared to other heat exchangers. * Larger heat transfer surface area. **Applications:** Art. [#ARTNUM](#article-26208-2593188271) * Power plants * Nuclear plants * Chemical processing * Refrigeration * Food * LNG plants * Pools/water industry * Electronics

A spiral wound heat exchanger is very compact heat exchanger composed of spiralled coils. It can be used in a shell and tube type of exchanger. They can also be used for multi-phase and multi-stream applications. They are commonly used in large-scale applications: Refinery plants; (petro)chemical plants. **Research findings:** * Spiral wound heat exchanger (SWHE) has been used as the main cryogenic heat exchanger in 90% of land-based liquefied natural gas (LNG) plants, due to the advantages of compact structure, high-pressure resistance, large scale unit, good thermal compensation performance and multi-stream heat transfer capability. Art. [#ARTNUM](#article-26124-2748655173) * A spiral-wound heat exchanger (SWHE) has many significant advantages over other heat exchangers, such as high robustness, high effectiveness and large exchanger area per volume. As such, it has been widely used in liquefied natural gas (LNG) plants, air separation plants, petroleum plants and nuclear reactor plants. Especially in the large-scale land-based LNG plants and offshore floating LNG plants, the SWHE is the preferred choice of the main cryogenic heat exchanger. Art. [#ARTNUM](#article-26124-2774313722) Applications: * Liquid-to-liquid * Cryogenic * High pressure * Natural gas heaters * Vent condensers * Mechanical seal coolers * Compressor inter/aftercoolers * Supercritical fluid * Water heaters * Steam or process fluid vaporizers * Boiler or process sample coolers * LNG plants * Petroleum/ air separation and nuclear reactor plants.

A plate-fin heat exchanger is a form of compact heat exchanger consisting of a block of alternating layers of corrugated fins and flat separators known as parting sheets. These heat exchangers can be made in a variety of materials such as aluminium, stainless steels, nickel, copper, etc. depending upon the operating temperatures and pressures. They are widely used in aerospace, automobile and cryogenic industries due to its compactness (i.e., high heat transfer surface-area-to-volume ratio) for desired thermal performance, resulting in reduced space, weight, support structure, footprint, energy requirement and cost. Depending on the application, various types of augmented heat transfer surfaces such as plain fins, wavy fins, offset strip fins, louvred fins and perforated fins are used. They have a high degree of surface compactness and substantial heat transfer enhancement obtained as a result of the periodic starting and development of laminar boundary layers over interrupted channels formed by the fins and their dissipation in the fin wakes. Art. [#ARTNUM](#article-26207-2013946548) There are different designs possible, as can be seen in the figure. High thermal efficiencies can be reached up to 90% in heat recovery applications. **Applications:** * Cryogenic * Air separation plants * Natural gas liquefaction plants * Petrochemical plants * Gas treatment plants * Helium liquefaction plants

Finned tube heat exchangers have tubes with extended outer surface area or fins to enhance the heat transfer rate from the additional area of fins. Finned tubes or tubes with extended outer surface area enhance the heat transfer rate by increasing the effective heat transfer area between the tubes and surrounding fluid. There are several types of fins. [\[Source\]](https://www.enggcyclopedia.com/2012/03/finned-tube-heat-exchangers/) Fin and tube heat exchangers are most widely used due to the extended surface for heat transfer in many industrial applications such as waste heat recovery units, heating, ventilation, and air conditioning and refrigeration systems. Art. [#ARTNUM](#article-26132-2470079271) Several designs exist for the fins, as can be seen from the figures. New heat exchange tube types with higher performance have been designed, such as the 3-D finned tube, spiral finned tube, serrated finned tube, H-type finned tube, slotted finned tube and so on. Art. [#ARTNUM](#article-26132-2900762659) Finned tubes are often employed in cooling applications. With the finned tubes, heat recovery up to 90% can be reached. And the maintenance of the finned tube is considered as low. **Applications:** * HVAC * Energy * Oil and gas * Petrochemical * Air cooling * Chemical

The plate fin-and-tube heat exchangers are widely used in a variety of industrial applications, particularly in the heating, airconditioning and refrigeration, HVAC industries. There are many different types of geometry for heat exchangers available. Commonly they are composed of tubes, with plates perpendicular, resulting in a cross-flow profile as seen in the figure. There are different types of plate-fin geometry, the most common being the plain fin, where the fins are parallel plates attached to a hot element in the form of tubes or some other shape. These fins act as a sink, absorbing the heat out of the hot element with the help of conductive heat transfer. And then dissipating this absorbed heat onto the outside environment which is at a lower temperature. Art. [#ARTNUM](#article-26206-840680848) There are numerous design options in this type of heat exchangers, as can be seen in the figure. **Applications:** * HVAC * Refridgeration

The corrugated plate heat exchanger consists of a number of gasketed plates constrained between an upper carrying bar and a lower guide bar. The plates are compressed between the fixed frame and the movable frame by using many tie bolts. In addition to the plate efficiency, corrugation patterns that produce turbulent flows, it is not only cause's unmatched efficiency; it also produces a heat exchanger self-cleaning nature, which in turn reducing the fouling effect. There are several patterns possible on corrugated plates. Art. [#ARTNUM](#article-26205-2561023270)

To enhance the mixing in a tube, and therefore improve heat transfer a wired coil helical structure can be added to the tube. Art. [#ARTNUM](#article-26751-2519485646) The coil can induce an increased pressure drop, but reduce the fouling of the system.

A twisted tape insert is one of the most efficient heat transfer enhancement methods which has a wide range of usages due to simplicity, low cost, easy instalment and routine maintenance. Generally, twisted tape performs as a continuous swirl generator which causes turbulence on flow. The induced swirl on the tube side results in higher near-wall velocities. This leads to better mixing of the fluid which eventually results in a higher heat transfer rate. Art. [#ARTNUM](#article-26311-2519485646) Twisted tape requires a reasonable high flow for the induced effect. This makes twisted tape most effective with turbulent flows with a limited pressure drop, while with laminar flow the improvement are limited. The twisted tape induces a higher pressure drop on the tube side.

Opencell porous metal foams have received attention for use in compact heat exchangers due to their increasing availability and improved thermal performance. In recent years, considerable research has been conducted on use of metallic and nonmetallic foams to further improve performance of stateoftheart heat exchangers. Art. [#ARTNUM](#article-27304-2070465275). They can be used as an enhancement in plate or tube heat exchangers, as shell-filling material or plate material (see pictures). **Research findings:** * In this paper, open-cell aluminum foam is considered as a highly compact replacement for conventional louver fins in brazed aluminum heat exchangers. Art. [#ARTNUM](#article-27304-1996174950) * The heat exchanger performance is one of the main contributors to the thermodynamic and cost effectiveness of the entire LNG regasification system. Within the paper, the authors discuss a new concept for a compact heat exchanger with a micro-cellular structure medium to minimize volume and mass and to increase thermal efficiency. Numerical calculations have been conducted to design a metal-foam filled plate heat exchanger and a shell-and-tube heat exchanger using published experimental correlations. The results show that the metal-foam plate heat exchanger has the best performance at different channel heights and mass flow rates of fluid. In the optimized configurations, the metal-foam plate heat exchanger has a higher heat transfer rate and lower pressure drop than the shell-and-tube heat exchanger as the mass flow rate of natural gas is increased. Art. [#ARTNUM](#article-27304-2196335867) **Applications:** Enhanced heat exchangers in: * LNG plants * aerospace * electronics * automotive

In a fixed matrix regenerator, a fluid moves through a fixed bed, storing its heat in one direction. When the flow is reversed, another (or the same) fluid can take up this heat again. Phase transitions can also be used, but gas-gas heat exchange is more common. **Applications:** * HVAC * Steel industry * Glass industry * Waste heat recovery * Power plants

Rotary heat exchangers or heat wheels are popularly used for heat recovery in many industrial and domestic applications. Art. [#ARTNUM](#article-26250-2790684841). They employ rotary 'heat-storing elements' that rotate between cold and hot streams to exchange heat. The rotor consists of a large scale of heat transfer plates known as the matrix. The matrix can be made of steel, ceramics, glass and plastic. The rotor rotates continuously with a constant fraction of the core in the flue gas stream and the remaining fraction in the cooling air stream. The saturated wet flue gas is cooled by the matrix, and the water vapour is condensed on the wall of the matrix as the decrease in temperature of flue gas. Art. [#ARTNUM](#article-26250-2902036760) Different type of rotors is available for different purposes. The condensation film which has an aluminium film. This rotor is used for recovering heat or cold from the ambient air. The enthalpy rotors have a hygroscopic surface which supports the heat transfer of moisture. The sorption rotors consisting of a zeolite coating, maximizing heat transfer and moisture all year long especially in warm and humid climates. The epoxy rotor is an epoxy-coated aluminium which offers high corrosion protection. Optimal for envierments where the air can be corrosive used for the heat transfer. The rotors are able to handle airflow from 1000 m³/hr to 150000 m³/hr. The heat transfer efficiency goes up to 85% and the system is frost resistant up to -15 °C. **Applications:** * HVAC (very common) * Waste heat recovery (common) * Shipping * Chemical plants * Power plants * Air/gas handling

In a rotating hood regenerating, the heat storage elements are stationary, while the elements through which the fluids flow rotate. In principle, it is the opposite of a rotary heat exchanger. It is also called a Rothemühle. **Patent findings:** Regenerative heat exchanger for heating > =2 parallel air or gas streams consists of a rotating hood over a fixed chamber of solid material for heat retention. The hood is one of a pair above and below the chamber and is divided into >=2 sections either side of a central axis. The flow area of each pair of sections is the same. These radiate from the centre where there are several concentric ducts for the various parallel gas or air streams. The hood and the central ducts are sealed from the hot exhaust gas flowing outside the hood by flexible seals. These are held in position by springs the tension of which can be adjusted. The device is of use in recovering heat from an exhaust gas stream where two or more temp. controlled air streams are required e.g. for preheating prim. and sec. air. Pat. [#ARTNUM](#article-26253-2875827312) **Applications:** * HVAC * Exhaust gas heat recovery * Air preheater

When a hot fluid flows through the cell, heat from the fluid is transferred to the cell walls and stored there. When the fluid flow reverses direction, heat is transferred from the cell walls back to the fluid. It has a multilayer grating structure in which each layer is offset from the adjacent layer by half a cell which has an opening along both axes perpendicular to the flow axis. Each layer is a composite structure of two sublayers, one of a high thermal conductivity material and another of a low thermal conductivity material. [\[Wiki\]](https://en.wikipedia.org/wiki/Regenerative_heat_exchanger) A micro-scale regenerator has been designed, analytically optimized, and fabricated. The regenerator composed of multiple layers of photoresist-nickel structure in an offset grating pattern. The offset pattern and composite structure minimizes axial conduction losses and disrupts boundary layer formation for improved heat transfer. Art. [#ARTNUM](#article-26764-1997390424) The microscale regenerative heat exchanger is being developed for application in a micro-Stirling engine.

Gas-solid heat exchange is facilitated by bed-type heat exchangers, most commonly by solid granules forming a bed. Moving beds, fluidized beds and conveyor belts are examples.

A spray tower (or spray column or spray chamber) is a gas-liquid contactor used to achieve mass and heat transfer between a continuous gas phase (that can contain dispersed solid particles) and a dispersed liquid phase. It consists of an empty cylindrical vessel made of steel or plastic, and nozzles that spray liquid into the vessel. The inlet gas stream usually enters at the bottom of the tower and moves upward, while the liquid is sprayed downward from one or more levels. This flow of inlet gas and liquid in opposite directions is called countercurrent flow. [\[Wiki\]](https://en.wikipedia.org/wiki/Spray_tower) Spray towers can handle flue gas streams up to 200000 m³/hr. The spray tower can be used as scrubber, particle separation and the chemical absorption of harmful substances. Cooling towers also use a spray-type system. The system is highly resistant to fouling, with having little maintenance. Vapours up to 1300 °C can be cooled and scrubbed in one process. Separation degrees up to 98% per scrubber stage are possible with particles as small as 5 µm. The gas and liquid requires to be separted afterwards, this is mostly done with a centrifugal separator. **Applications:** * Oil and gas * Petrochemical & chemical * Metallurgy * Power plant * Spray towers are usually applied for separation and scrubbing.

A plate column (or tray column) is a piece of chemical equipment used to carry out unit operations where it is necessary to transfer mass between a liquid phase and a gas phase. In other words, it is a particular gas-liquid contactor. The peculiarity of this gas-liquid contactor is that the gas comes in contact with liquid through different stages; each stage is delimited by two plates (except the stage at the top of the column and the stage at the bottom of the column). [\[Wiki\]](https://en.wikipedia.org/wiki/Plate_column) Different types of tray columns exist, such as disk and donut, sieve trays etc. Specific tray packings are chosen to enhance mass and heat transfer. Tray column can be as large as 4 m in diameter. Usually used for liquid-liquid or gas-liquid contacting, or distillation. **Applications:** * Distillation * Extraction * Food and beverage * Oil and gas * (Petro)chemical

A bubble column reactor is an apparatus used to generate and control gas-liquid chemical reactions. It consists of a vertically-arranged cylindrical column filled with liquid, at the bottom of which gas is inserted. [\[Wiki\]](https://en.wikipedia.org/wiki/Bubble_column_reactor) A bubble column used in: * Petrochemical industries * Biochemical industries * Chemical industries * Metallurgy * Reactor, stripper, absorber

Microchannels (broadly ⩽1  mm) represent the next step in heat exchanger development. They are a particular target of research due to their higher heat transfer and reduced weight as well as their space, energy, and materials savings potential over regular tube counterparts. Art. [#ARTNUM](#article-26150-2083412469). Microchannel heat exchangers can be used for many applications including high-performance aircraft gas turbine engines, heat pumps and air conditioning. Multiple materials are possible, resulting in high corrosion resistance when needed. Microchannel heat exchangers can be produced in the same way as printed circuits, through etching and diffusion bonding. Art. [#ARTNUM](#article-26150-2475723589) Machining of thin metal foils with specially contoured diamond cutting tools allows the production of small and very smooth fluid microflow channels for micro heat exchanger applications. Heat exchanger plate wall thickness, as well as fin dimensions, can be carefully controlled and machined to dimensions on the order of tens of micrometres. The plates are stacked and bonded with the vacuum diffusion process to form a crossflow, plate-type heat exchanger. Art. [#ARTNUM](#article-26150-2077945856) The compactness of a microchannels heat exchanger can reduce the refrigerant charge by 30-60% under the same conditions as a fin and tube heat exchanger. While achieving an efficiency increase of 10-40%. The small size makes it easy to clean an dthe air side pressure drop is low. Two-phase systems are possible. **Applications:** * Automotive * Residential * Electronics * Power plants * Process industry * HVAC

Hollow fiber heat exchangers are similar to shell and tube heat exchangers, however, they are much more compact and have large surface areas. Usually, they are formed using polymers. They can reduce the weight up to 50% compared to a traditional heat exchanger made out of metal. Hollow fibers have an outer diameter 0.4-1.5 mm and can be produced by the extrusion process from a wide range of polymers such as PP (polypropylene), PC (polycarbonate), PA (polyamide), PEEK (poly-ether ether ketone), etc. The wide range of materials results in an excellent chemical and corrosion-resistant heat exchanger. The heat exchanger is in some cases also environmental friendly as the fibers can be recycled. **Research findings:** \-Despite polymer materials’ low thermal conductivities (0.1–0.4 W/m K, which is 100–300 times lower than metals), by using hollow polymer fibers with the diameters less than 100 μm, the surface area/volume ratio of polymer hollow fiber heat exchangers can be very high. This makes them extremely efficient with superior thermal performance. Art. [#ARTNUM](#article-26752-2303822880) 3000 PP fibers weight 488 g and resulted in a 7.2 m² area of heat transfer. The highest heat transfers shown for liquid-gas are 450 W/m² K and 2100 W/m² K for liquid-liquid. Prototypes were able to handle a flow rate up to 700 L/hr with a heating duty of 6-13 kW. Liquid-liquid, liquid-gas applications possible and liquid-steam. Most suitable for low-temperature temperature applications since the polymers are not resistant against high temperatures. **Applications:** * HVAC * Food * Chemical * Biotech * Building * Automotive * Electronics * Energy storage