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. Further, four to six apertures are placed in the corners/edges of these plates. Alternate plates are arranged at 180° to each other resulting in formation of the inlet and outlet port manifolds for the various process fluid circuits. [#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. Plate heat exchangers are widely used for phase-change heat transfer in refrigeration, residential heating and air-conditioning applications. [#ARTNUM](#article-26232-1752739663). They are also employed in natural gas liquefaction (LNG) plants. [#ARTNUM](#article-26232-2792430176) They are used especially when corrosion can be an issue. In Brazed Plate Heat Exchangers, the brazing process eliminates gasketed joints which allows for higher design pressure and temperatures. [Source](http://www.graham-mfg.com/gasketed-and-brazed-plate-heat-exchanger-advantages)

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/) GPHE are employed in direct heating and HVAC applications.

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/) Typical applications of module welded plate heat exchangers in the chemical industry are acid coolers, thermal oil coolers, or condensers for hydrocarbon mixtures.[#ARTNUM](#article-26241-2062888851)

The main advantage of the SHE 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.) A compact SHE may be used to have a smaller footprint and thus lower all-around capital costs, or an oversized SHE may be used to have less pressure drop, less pumping energy, higher thermal efficiency, and lower energy costs. The Spiral heat exchanger is good for applications such as pasteurization, digester heating, heat recovery, pre-heating (see: recuperator), and effluent cooling. For sludge treatment, SHEs are generally smaller than other types of heat exchangers. [Wiki](https://en.wikipedia.org/wiki/Heat_exchanger#Helical-coil_heat_exchangers) 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. [#ARTNUM](#article-26228-2342724403) **Research findings:** - Spiral heat exchanger is a self cleaning equipment with low fouling tendencies, easily accessible for inspection or mechanical cleaning and with minimum space requirements. [#ARTNUM](#article-26228-2065526122)

PCHE is a plate-type compact heat exchanger and its core is composed of thin plates (of thickness1.5–3 mm) made of alloys like stainless steel or inconel alloys [3], 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.[#ARTNUM](#article-26243-2767695692) The complete microchannel heat exchangers are highly compact, typically comprising about onefifth 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. [#ARTNUM](#article-26243-1980144440) The field of applications is 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.[#ARTNUM](#article-26243-1980144440)

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. 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. 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) Pillowplate 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 pillowplates alternate with outer channels between the adjacent plates, and thus, a structure with alternating inner and outer channels is 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 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. [#ARTNUM](#article-26310-2779667980)

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 platepack (the 'Plate side' flowpath). The fully welded platepack is assembled into an outer shell that creates a second flowpath ( the 'Shell side'). Plate and shell technology offers high heat transfer, high pressure, high operating temperature, uling and close approach temperature. 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) 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. The round plates ensure an even distribution of mechanical loads, without the stress concentrations that occur in the corners of rectangular plates.

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. Scraped-surface heat exchangers (SSHEs) are extensively used in a wide variety of industrial settings where the continuous processing of fluids and fluid-like materials is involved. They are often used in the pharmaceutical and chemical industries (for example, in dewaxing oils and producing paints); however, they are most commonly found within the food-manufacturing sector, where they are used for mixing and heating or cooling foodstuffs during processes such as sterilisation, crystallisation and gelatinisation. Unlike the simpler plate heat exchangers which are commonly used for low-viscosity process fluids, SSHEs are designed to deal with the problems that arise when processing very viscous products.[#ARTNUM](#article-26537-2014080855)

The wide gap heat exchanger is similar to a gasketed heat exchangers, accept 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.[#ARTNUM](#article-26309-2377641195).

The capsule-type plate heat exchanger is proposed to address high viscosity fluid which has concave and convex ellipsoidal embossing similar to half capsules[#ARTNUM](#article-26138-2503965242) and has the advantages of low pressure drop and less deposition due to the straight passages in the channels. [#ARTNUM](#article-26138-2914453957)

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. [Source](https://www.engineeringpage.com/heat_exchangers/tema.html)

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. **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.

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) **Research findings:** The analyzing result shows that the twisted oval tube heat exchangers is preferred to work at low tube side flow rate and high shell side flow rate.

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 flowpaths for a given exchanger length. In addition, the high velocities achieved for the tube fluid help increase heat transfer coefficients and reduce surface fouling. [#ARTNUM](#article-26148-1985475579) Using multipass systems, gives more flexibilty in optimising fluid velocity, pressure drop and heat transfer. Industries: - Industrial waste heat recovery solutions - Energy - Oil and gas industry - Chemical industry

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. It is often used as an evaporator in industry, to concentrate solutions. [Wiki](https://en.wikipedia.org/wiki/Falling_film_evaporator)

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.[#ARTNUM](#article-26213-1536994987)

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 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. [#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.

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 researches have also hold 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. [#ARTNUM](#article-26215-2519485646) - The performance of the heat exchanger and the pressure drop are in a close interaction with the geometry. [#ARTNUM](#article-26215-2771080156)

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 annularspace and a thermal fluid is passed through an inner annular space. The triple tube heat exchanger contributes higher heat exchanger effectiveness and more energy saving compared with double tube heat exchanger per unit length.[#ARTNUM](#article-26134-2245358019)

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 pushing 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 helical coil are higher as compared to a straight tube heat exchanger. Compact structure. - It requires small amount of floor area compared to other heat exchangers. - Larger heat transfer surface area. **Applications:** - Heat exchangers with helical coils are widely used in industries. The most common industries where heat exchangers are used a lot are power generation plants, nuclear plants, process plants, refrigeration, heat recovery systems, food processing industries, etc. - Helical coil heat exchanger is used for residual heat removal system in islanded or barge mounted nuclear reactor system, where nuclear energy is used for desalination of sea water. - In cryogenic applications including LNG plant. [#ARTNUM](#article-26208-2593188271)

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. **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 scaleunit, good thermal compensation performance and multi-stream heat transfer capability. [#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. [#ARTNUM](#article-26124-2774313722)

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, louvered 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. [#ARTNUM](#article-26207-2013946548)

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 [#ARTNUM](#article-26132-2470079271) Several designs exist for the fins. 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. [#ARTNUM](#article-26132-2900762659)

The plate fin-and-tube heat exchangers are widely used in 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 perpedicular, 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. [#ARTNUM](#article-26206-840680848)

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. [#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. [#ARTNUM](#article-26751-2519485646)

A twisted tape insert is one of the most efficient heat transfer enhancement methods which has a wide range ofusages due to simplicity, low cost, easy installment and routinemaintenance[79]. Generally, twisted tape performs as a continuous swirl generator which causes turbulence on flow. This leads to a better mixing of the fluid which eventually results in a higher heat transfer rate. [#ARTNUM](#article-26311-2519485646)

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.[#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.[#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. [#ARTNUM](#article-27304-2196335867)

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.

Rotary heat exchangers or heat wheels are popularly used for heat recovery in many industrial and domestic applications.[#ARTNUM](#article-26250-2790684841). They employ rotary 'heat storing elements' that rotate between cold and hot streams to exchange heat. The rotor consists of large scale of heat transfer plates known as matrix. The matrix can be made of steel, ceramic, 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 vapor is condensed on the wall of the matrix as the decrease in temperature of flue gas. [#ARTNUM](#article-26250-2902036760)

In a rotating hood regenerating, the heat storage elements are stationary, while the elements trhough which the fluids flow rotate. In principle it is the opposite from a rotary heat exchanger. **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. 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.[#ARTNUM](#article-26253-2875827312)

When a hot fluid flows through the cell, heat from the fluid is transferred to the cell wells, 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. [#ARTNUM](#article-26764-1997390424)

Gas-solid heat exchange is facilitated by bed-type heat exchangers, most commonly by solid granules forming a bed.

A spray tower (or spray column or spray chamber) is 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) Cooling towers also use a spray-type system

A plate column (or tray column) is a 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 exists, such as disk and donut, sieve trays etc.

This paper describes the development of heat exchanger with microjet technology, proposed for a waste heat recovery from a range of processes. The article presents a comprehensive study on the heat transfer enhancement in prototype heat exchanger. The heat exchanger is based on multiple jet impingement on the cylindrical heat transfer surface. It comprises four coaxial pipes (a supply channel and a return channel for two fluids). The design of the heat is based on available on the market standardized materials. [#ARTNUM](#article-26216-2571195246) Its essential core is a series of plates. Impinging jets are created by introducing plates with four nozzles of 400 and 600 µm in diameter. The nozzles were created by drilling 1 mm thick plate. These plates are separated by spacers/gaskets made of PTFE. Microjet geometry can be varied by exchanging the nozzle plates and spacers of heat exchanger. [#ARTNUM](#article-26216-2278329116)

The Marbond heat exchanger/reactor family of products is the latest truly innovative design to enter the CHE marketplace. Produced by Chart Marston at their UK factory, an ‘opened up' version of the Marbond unit is shown in Fig. 3 (scale — the unit shown is about the size of a lap-top computer with channels about 1 mm hydraulic diameter). It extends the choice of users who are looking for high integrity, highly compact units able to operate over a range of pressures and temperatures not met with more conventional gasketed or welded CHEs. The manufacturing procedures are similar to those of the PCHE (chemical etching and diffusion bonding), but the construction allows the use of small passageways, which significantly increases the porosity of the heat exchanger core. This can result, in appropriate applications, in a substantially higher area density than the PCHE. For example, a doubling of porosity, other factors being equal, results in a halving of the volume for a given surface area. The design is particularly versatile in terms of the number of passes and number of streams, and the type can be used for a wide variety of duties involving single phase liquids and gases or two phase streams, as well as for reactions. [#ARTNUM](#article-26535-1989674565)

By 3D printing complex structures can be made, usually of the shell and tube type heat exchangers. Common shapes that are employed are Y-type and H-type tubes, as well as spirals, but the possibilities of 3D-printed heat exchangers are almost limitless. Especially for compact heat exchangers they are interesting. **Research findings:** - In the present study, threedimensional (3D) fractaltreelike heat exchangers were designed and manufactured using 3D printing technology.[#ARTNUM](#article-26220-2884496616)