GB2636881A

GB2636881A - A heat transfer layer for a heat exchanger

Info

Publication number: GB2636881A
Application number: GB2400550.6A
Authority: GB
Inventors: Di Caterino Antonio; Mitzalis Faidon; Pietropaoli Marco; Raske Nicholas; Tomlin Ruben; Furino Stefano; Rees Thomas
Original assignee: Toffeex Ltd
Current assignee: Toffeex Ltd
Priority date: 2023-12-19
Filing date: 2024-01-15
Publication date: 2025-07-02
Also published as: GB202400550D0

Abstract

A heat transfer layer 300 for a two-fluid heat exchanger and comprising a planar plate 301 comprising at least a first fluid contacting surface; and a plurality of discrete heat conducting structures 304 positioned on the first fluid contacting surface of the plate. Each of the heat conducting structures having a base on the first fluid contacting surface of the plate and protruding away from the first fluid contacting surface to an elevated portion, the heat conducting structures defining a plurality of channels separating the plurality of heat conducting structures through which fluid may flow from a fluid inlet to a fluid outlet. The heat conducting structures are tapered such that a cross-sectional area of each heat conducting structure in a plane parallel to the planar plate decreases from its base to its elevated portion. A heat transfer layer where the heat conducting sections comprise a plurality of discrete microstructures that define a plurality of microchannels is also claimed. A heat exchanger comprising a plurality of heat transfer layers and a method of filling said heat exchanger is also claimed.

Description

A HEAT TRANSFER LAYER FOR A HEAT EXCHANGER

Field of Invention

The present disclosure relates to heat transfer layers for heat exchangers, and more specifically, to heat transfer layers for two-fluid heat exchangers.

Background

Heat exchangers are devices that are used to transfer thermal energy between a source and a working fluid. More specifically, two-fluid heat exchangers are devices that are used to transfer thermal energy from one fluid to another without mixing the two fluids. The purpose of this may be to remove heat from one of the fluids, or to heat up the other fluid, or both.

Existing two-fluid heat exchangers may include printed circuit heat exchangers (PCHX), in which the two fluids are separated by thin sheets of metal and stacked on top of one another in a sandwich-like structure. In addition to being separated by sheets of metal, the flow path for each fluid is populated with repeating structures, which often take the form of regular geometric shapes. The presence of the structures in the fluid paths increases the surface area of the heat transfer surface, increasing the overall heat duty of the heat exchanger. However, they also increase the pressure drop across the heat exchanger by adding additional friction and pressure blockage effects. Conventional designs often include repeating, uniform structures, which may be prone to larger pressures losses and less efficient heat transfer.

Other existing heat exchangers may include plate and fin heat exchangers. Traditional designs are made from layers of corrugated metal sheets separated by metal plates, which separate the two fluids. The principles of operation are similar to printed circuit heat exchangers, although the relative sizes of the parts used are quite different. The corrugated metal sheets are generally very thin (compared to the machined structures present in PCHX) and are manufactured separately from the plates. The different layers are generally brazed together (rather than diffusion bonded). To tune the performance of the heat exchanger (generally measured as a ratio of heat transfer to pressure drop), the layout of the corrugated sheets can be changed and adapted to give the performance required. Again, such heat exchangers often comprise repeating, uniform layouts and as such are also prone to increased pressure drops between the fluid inlet and the fluid outlet, as well as reduced efficiency.

The present invention aims to solve these problems, among others.

Summary

Aspects of the invention are as set out in the independent claims and optional features are set out in the dependent claims. Aspects of the invention may be provided in conjunction with each other and features of one aspect may be applied to other aspects.

An aspect of the disclosure provides a heat transfer layer for use in a two-fluid heat exchanger, the heat transfer layer comprising: a planar plate comprising at least a first fluid contacting surface; and a plurality of discrete heat conducting structures positioned on the first fluid contacting surface of the plate, each of the heat conducting structures having a base on the first fluid contacting surface of the plate and protruding away from the first fluid contacting surface to an elevated portion, the heat conducting structures defining a plurality of channels separating the plurality of heat conducting structures, and through which fluid may flow from a fluid inlet to a fluid outlet; wherein the heat conducting structures are tapered such that a cross-sectional area of each heat conducting structure in a plane parallel to the planar plate decreases from its base to its elevated portion.

Additionally, the heat conducting structures may be arranged such that: an average cross-sectional area of the base of each respective heat conducting structure proximate to the fluid inlet is greater than an average cross-sectional area of the base of each respective heat conducting structure proximate to the fluid outlet; and a number of channels proximate to the fluid inlet is smaller than a number of channels proximate to the fluid outlet. Because larger structures generally have lower heat transfer coefficients and lower pressure loss, while smaller structures have higher heat transfer coefficients and pressure losses, this helps to provide a reduction in pressure loss near the fluid inlet while still maintaining a large (in absolute terms) heat transfer due to the large temperature difference. Having smaller structures nearer the fluid outlet may help to compromise for the lower temperature difference by accepting a larger pressure loss.

Additionally, the channels proximate to the fluid inlet may have greater dimensions than the channels proximate to the fluid outlet. These dimensions may be the widths and lengths of the channels in the plane of the plate. This arrangement may help to transport larger amounts of fluid from regions of the heat transfer layer near the inlet to regions near the outlet more quickly, thus helping to ensure that heat transfer is conducted more efficiently across the entirety of the layer.

Additionally, the channels may comprise primary channels, secondary channels and tertiary channels, wherein: the primary channels extend from regions of the heat transfer layer proximate to the fluid inlet to regions of the heat transfer layer proximate to the fluid outlet; the secondary channels extend from the primary channels to the regions of the heat transfer layer proximate to the fluid outlet; the tertiary channels extend between any of: primary channels and other primary channels; secondary channels and other secondary channels; and primary channels and secondary channels; and wherein the primary channels have greater dimensions than the secondary channels and the secondary channels have greater dimensions than the tertiary channels. This may help to optimise heat transfer efficiency across the heat transfer layer.

Additionally, each heat conducting structure may have a taper angle of no more than 45 degrees from the plate. This may help to increase the heat transfer surface area of the heat transfer layer and may also ensure that it can be manufactured efficiently through side-up additive manufacturing.

Additionally, each heat conducting structure may protrude substantially the same distance from the first fluid contacting surface, such that the elevated portions of each heat conducting structure are substantially level. This enables another heat transfer layer to be placed on top of the heat transfer layer and remain stable, for example when manufacturing a heat exchanger comprising multiple heat transfer layers. Alternatively, a subset of the heat conducting structures may protrude a first distance from the first fluid contacting surface, and the remaining heat conducting structures may protrude distances smaller than the first distance.

Additionally, the elevated portion of each heat conducting structure may comprise a substantially flat surface. This enables another heat transfer layer to be placed on top of the heat transfer layer and remain stable, for example when manufacturing a heat exchanger comprising multiple heat transfer layers.

Another aspect of the disclosure provides a heat transfer layer for use in a two-fluid heat exchanger, the heat transfer layer comprising: a planar plate comprising at least a first fluid contacting surface; and a plurality of heat conducting structures positioned on the first fluid contacting surface of the plate, each of the heat conducting structures protruding away from the first fluid contacting surface of the plate, the heat conducting structures defining a plurality of channels separating the plurality of heat conducting structures, and through which fluid may flow from a fluid inlet to a fluid outlet; wherein each of the heat conducting structures comprises a plurality of discrete microstructures grouped together, the microstructures of each heat conducting structure each having a base on the first fluid contacting surface and protruding away from the first fluid contacting surface of the plate to an elevated portion, the microstructures defining a plurality of microchannels separating the plurality microstructures, and through which fluid may flow from the fluid inlet to the fluid outlet; wherein the microchannels have smaller dimensions than the channels.

Additionally, the microstructures may comprise pins of a uniform cross-section, each pin having a height that is proportionally much larger than its width. This may help to increase the heat transfer surface area of the heat transfer layer.

Additionally, each microstructure may have a circular cross-section.

Additionally, for each heat conducting structure, each microstructure may protrude substantially the same distance from the first fluid contacting surface, such that the elevated portions of each microstructure within a heat conducting structure are substantially level. This may help to provide a level surface for stacking another heat transfer layer on top of the heat transfer layer, for example when producing a heat exchanger.

Additionally, the elevated portion of each microstructure may comprise a substantially flat surface. This may help to provide a level surface for stacking another heat transfer layer on top of the heat transfer layer, for example when producing a heat exchanger.

Additionally, the heat conducting structures may be arranged such that: an average cross-sectional area of the heat conducting structures proximate to the fluid inlet is greater than an average cross-sectional area of the heat conducting structures proximate to the fluid outlet; and a number of channels proximate to the fluid inlet is smaller than a number of channels proximate to the fluid outlet. Because larger structures generally have lower heat transfer coefficients and lower pressure loss, while smaller structures have higher heat transfer coefficients and pressure losses, this helps to provide a reduction in pressure loss near the fluid inlet while still maintaining a large (in absolute terms) heat transfer due to the large temperature difference. Having smaller structures nearer the fluid outlet may help to compromise for the lower temperature difference by accepting a larger pressure loss.

Additionally, the microstructures may be positioned such that fluid flows through the channels more quickly and in greater quantities than through the microchannels.

Another aspect of the disclosure provides a two-fluid heat exchanger configured to exchange heat between two fluids, the heat exchanger comprising a first set of heat transfer layers as set out above, each of the first set of heat transfer layers arranged to channel a first of the two fluids from its respective fluid inlet to its respective fluid outlet; and a second set of heat transfer layers as set out above, each of the second heat transfer layers arranged to channel a second of the two fluids from its respective fluid inlet to its respective fluid outlet; wherein the first set of heat transfer layers and the second set of heat transfer layers are stacked so as to alternate between members of the first set and members of the second set, such that each of the first set of heat transfer layers is closer to a member of the second set of heat transfer layers than a member of the first set of heat transfer layers, and each of the second set of heat transfer layers is closer to a 113 member of the first set of heat transfer layers than a member of the second set of heat transfer layers; wherein the first set of heat transfer layers comprises at least one heat transfer layer and the second set of heat transfer layers comprises at least one heat transfer layer; and wherein the heat conducting structures of each of the first set of heat transfer layers are arranged in a first arrangement and the heat conducting structures of the second set of heat transfer layers are arranged in a second arrangement.

Additionally, the second arrangement may be non-identical to the first arrangement.

Additionally, the respective fluid inlets of each of the first set of heat transfer layers may be located at a first end of the heat exchanger.

Additionally, the respective fluid outlets of each of the first set of heat transfer layers may be located at a second end of the heat exchanger opposite the first end.

Additionally, the respective fluid inlets of each of the second set of heat transfer layers may be located at the second end of the heat exchanger opposite the respective fluid inlets of each of the first set of heat transfer layers, and the respective fluid outlets of each of the second set of heat transfer layers may be located at the first end of the heat exchanger, such that a direction of flow of the second fluid is substantially opposite to a direction of flow of the first fluid. This may enable the heat exchanger to operate in a counterflow configuration.

Alternatively, the respective fluid inlets of each of the second set of heat transfer layers may be located along a first side of the heat exchanger and the respective fluid outlets of each of the second set of heat transfer layers may be located along a second side of the heat exchanger opposite the first side. This may enable the heat exchanger to operate in a crossflow configuration.

Additionally, the respective fluid inlets of each of the second set of heat transfer layers may be located closer to the first end of the heat exchanger than the second end, and the respective fluid outlets of each of the second set of heat transfer layers may be located closer to the second end of the heat exchanger than the first end, such that a direction of flow of the second fluid crosses a direction of flow of the first fluid.

113 Alternatively, the respective fluid outlets of each of the second set of heat transfer layers may be located opposite the respective fluid inlets of each of the second set of heat transfer layers, such that a direction of flow of the second fluid crosses a direction of flow of the first fluid and is substantially perpendicular to the direction of flow of the first fluid.

Additionally, each of the first set of heat transfer layers and each of the second set of heat transfer layers may comprise at least one baffle that effects a change in fluid direction. This may help to increase the thermodynamic efficiency of the heat exchanger by ensuring that the coldest parts of the hot fluid are cooled by the coldest parts of the cold fluid and vice versa.

Additionally, the at least one baffle of each of the heat transfer layers may protrude away from the first fluid contacting surface, the at least one baffle defining at least a first region of heat conducting structures and a second region of heat conducting structures.

Additionally, the second region may be on an opposite side of the baffle to the first region, such that the fluid is channelled through the first region in a first direction and then through the second region in a second direction, the second direction being substantially opposite to the first direction, the first region and the second region defining a pass.

Additionally, the at least one baffle may comprise an odd number of baffles defining an odd number of passes, such that the respective fluid outlet is at a same end of the heat exchanger as the respective fluid inlet.

Additionally, the at least one baffle may comprise an even number of baffles defining an even number of passes, such that the respective fluid outlet is at an opposite end of the heat exchanger to the respective fluid inlet.

Additionally, the first set of heat transfer layers and the second set of heat transfer layers may be configured to receive fluids of different temperatures.

Additionally, the stacked heat transfer layers may be joined by diffusion bonding. This allows for much higher pressure flows.

Additionally, the heat exchanger may further comprise: a top plate positioned on top of the top heat transfer layer in the stack; and side walls configured to enclose the heat transfer layers and ensure that fluid does not pass from one heat transfer layer to another. This helps to seal the heat exchanger and keep the fluids separate from each other.

Another aspect of the disclosure provides a method of producing a heat exchanger as defined above, the method comprising: executing a fluid topology optimization program to determine the first arrangement of heat conducting structures and the second arrangement of heat conducting structures; providing the first set of heat transfer layers based on the first arrangement determined by the fluid topology optimization program; providing the second set of heat transfer layers based on the second arrangement determined by the fluid topology optimization program; and diffusion bonding the heat transfer layers.

Additionally, the determination of the first arrangement may be based on properties of the first fluid and the determination of the second arrangement may be based on properties of the second fluid. This may enable a greater range of fluids to be used.

Additionally, providing the first set of heat transfer layers may comprise producing the first set of heat transfer layers through an additive manufacturing process, and providing the second set of heat transfer layers may comprise producing the second set of heat transfer layers through an additive manufacturing process. This may result in a quicker and more efficient manufacturing process.

Another aspect of the disclosure provides a method of heat exchange using a heat exchanger as defined above, the method comprising: feeding each of the first set of heat transfer layers with the first fluid; and feeding each of the second set of heat transfer layers with the second fluid.

Additionally, the feeding of each of the first set of heat transfer layers with the first fluid may be performed in parallel, such that each of the first set of heat transfer layers is fed with the first fluid at the same time; and the feeding of each of the second set of layers with the second fluid may be performed in parallel, such that each of the second set of heat transfer layers is fed with the second fluid at the same time.

Additionally, the feeding of each of the first set of heat transfer layers with the first fluid may be staggered, such that each of the first set of heat transfer layers is fed with the first fluid at a different time; and the feeding of each of the second set of heat transfer layers with the second fluid may be staggered, such that each of the second set of heat transfer layers is fed with the second fluid at a different time.

Additionally, the heat transfer layers may be fed in an alternating manner such that the feeding of one of the first set of heat transfer layers is preceded and/or followed by the feeding of a neighbouring one of the second set of heat transfer layers, and the feeding of one of the second set of heat transfer layers is preceded and/or followed by the feeding of a neighbouring one of the first set of heat transfer layers.

Another aspect of the disclosure provides a small modular reactor comprising at least one heat exchanger as defined above.

Figures Embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings.

Figure 1 shows an example of a conventional two-fluid heat exchanger.

Figure 2A shows a perspective view of a heat transfer layer of a conventional heat exchanger.

Figure 2B shows a top view of the heat transfer of Figure 2A.

Figure 3 shows a perspective view of a heat transfer layer of a heat exchanger in accordance with the present invention.

Figure 4A shows a perspective view of heat conducting structures from a heat transfer layer in which the heat conducting structures are tapered, in accordance with the present invention.

Figure 4B shows a top view of the heat conducting structures of Figure 4A.

Figure 4C shows a side view of the heat conducting structures of Figures 4A-B.

Figure 5A shows a perspective view of a heat transfer layer of a heat exchanger in accordance with the present invention.

Figure 5B shows a perspective view of a heat transfer layer in which each heat conducting structure comprises a plurality of discrete microstructures grouped together, in accordance with the present invention.

Figure 6A shows a perspective view of four heat transfer layers of a heat exchanger in a crossflow configuration in accordance with the present invention.

Figure 6B shows a perspective view of two heat transfer layers of a heat exchanger in a counterflow configuration in accordance with the present invention.

Figure 7A shows temperature and velocity streamlines for the conventional heat exchanger of Figures 2A-B.

Figure 7B shows temperature and velocity streamlines for a counterflow heat exchanger layer of a heat exchanger in accordance with the present invention.

Figure 8 shows a perspective view of a heat transfer layer of a heat exchanger comprising a plurality of passes in accordance with the present invention.

Detailed Description

Figure 1 shows an example of a conventional prior art two-fluid heat exchanger 100. The heat exchanger 100 comprises a set of first heat transfer layers 101 and a set of second heat transfer layers 102. The heat transfer layers are arranged in a planar stack and alternate between members of the set of first heat transfer layers 101 and members of the set of second heat transfer layers 102. Working down the stack, a first heat transfer layer 101 is followed by a second heat transfer layer 102, which is then followed by another first heat transfer layer 101, and so forth. In this manner, each first heat transfer layer 101 is closer to a second heat transfer layer 102 than to another first heat transfer layer 101, and each second heat transfer layer 102 is closer to a first heat transfer layer 101 than to another second heat transfer layer 102.

Each first heat transfer layer 101 comprises a first plate 103, into which a plurality of first channels 104 have been cut (or milled, etched etc). The first channels 104 extend across a length of the first plate 103 from a first end to a second end.

The first channels 104 are substantially parallel with one another and have substantially identical cross-sections. The first channels 104 may also have a uniform spacing.

Each second heat transfer layer 102 comprises a second plate 105, into which a plurality of second channels 106 have been cut. The second channels 106 start on a first side of the second plate 105 close to a first end of the second plate 105 and extend inwards along a width of the second plate 105. The second channels 106 then turn 90 degrees and continue to extend along a length of the second plate 105 towards the second end. The second channels 106 then turn again and continue to extend to a second side of the second plate 105 close to the second end, where the second channels 106 end.

In use, a first fluid passes through the first channels 104 of the first heat transfer layers 101 and a second fluid passes through the second channels 106 of the second heat transfer layers 102. One of the two fluids has a higher temperature than the other fluid and heat may be transferred from the hotter fluid to the cooler fluid via the heat transfer layers 101 and 102.

Figures 2A-B show views of a heat transfer layer of a conventional heat exchanger, as can be found in the prior art. More specifically, Figure 2A shows a perspective view of a heat transfer layer 200 and Figure 2B shows a top view of the same heat transfer layer 200.

The heat transfer layer 200 comprises a plate 201 having a first end 202 and a second end 203. A fluid inlet (not shown) may be present at the first end 202 and a fluid outlet (not shown) may be present at the second end 203, so that fluid may travel from the first end 202 to the second end 203.

The heat transfer layer 200 also comprises a plurality of heat conducting structures 204 extending upwards from a top surface of the plate 201. Each of the heat conducting structures 204 are identical in shape and size and together they define a number of channels 205 through which the fluid may travel. The structures 204 are arranged in a staggered-aerofoil configuration. The uniformity of the structures 204, as well as their arrangement on the plate 201, results in uniformity of the channels 205. Heat may be transferred between the fluid and the heat conducting structures 204 as the fluid travels through the channels 205.

Figure 3 shows a perspective view of a heat transfer layer for use in a heat exchanger, in accordance with the present invention.

Specifically, Figure 3 shows a heat transfer layer 300 for use in a heat exchanger. The heat transfer layer 300 comprises a planar plate 301 comprising at least a first fluid contacting surface, which may be substantially flat. The planar plate 301 may be substantially rectangular in shape, although it should be appreciated that other shapes are possible. For example, the planar plate may have an irregular shape, as can be seen in Figures 5A-B.

The heat transfer layer 300 may have a first end 302 and a second end 303 opposite the first end 302. The heat transfer layer 300 may also comprise a fluid inlet (not shown) and a fluid outlet (not shown). The fluid inlet may be located at the first end 302 and the fluid outlet may be located at the second end 302. Alternatively, the fluid inlet may be located at the second end 302 and the fluid outlet may be located at the first end 301. Other positions of the fluid inlet and fluid outlet are possible, as will be discussed with reference to Figures 6A-B.

The heat transfer layer 300 also comprises a plurality of heat conducting structures 304.

The heat conducting structures 304 may be positioned on the first fluid contacting surface of the plate 301. Specifically, each heat conducting structure 304 may have a base on the first fluid conducting surface of the plate 301. Each heat conducting structure 304 may be discrete in the sense that each one is separate from the others.

The heat conducting structures 304 may protrude away from the first fluid contacting surface of the plate 301 to an elevated portion. Each of the heat conducting structures 304 therefore extends from its base to its elevated portion, and the height of each heat conducting structure 304 can be calculated as the perpendicular distance (with respect to the planar plate 301) between its base and its elevated portion. The elevated portion may comprise a substantially flat surface, so that another heat transfer layer 300 can be stacked on top if necessary (e.g. to form a heat exchanger).

Each heat conducting structure 304 may protrude substantially the same distance from the first fluid contacting surface (i.e. each heat conducting structure 304 may have substantially the same height), such that the elevated portions of each heat conducting structure 304 are substantially level. Alternatively, a subset of the heat conducting structures 304 may protrude a first distance from the first fluid contacting surface (i.e. a subset of the heat conducting structures 304 may have a first height), while the remaining heat conducting structures 304 may protrude distances smaller than the first distance (i.e. the remaining heat conducting structures 304 may have a smaller height than those in the subset). The subset may comprise any fraction of the heat conducting structures 304, although preferably, a majority (i.e. more than half) of the heat conducting structures 304 are in the subset, as this enables a more stable connection to any other heat transfer layer 300 that may be stacked on top.

The heat conducting structures 304 may comprise a variety of different shapes and sizes. The shapes of the heat conducting structures 304 may be largely irregular, with some of the heat conducting structures 304 having similar lengths and widths, and others having significantly larger lengths than widths (or vice versa).

The heat conducting structures 304 define a plurality of channels 305 separating the plurality of heat conducting structures 304, and through which fluid may flow from the fluid inlet to the fluid outlet. The channels 305 may comprise primary channels 306, secondary channels 307 and tertiary channels 308. The primary channels 306 may extend from regions of the heat transfer layer 300 proximate to the fluid inlet to regions of the heat transfer layer 300 proximate to the fluid outlet. For example, if the fluid inlet is positioned at the first end 301 of the heat transfer layer 300 and the fluid outlet is positioned at the second end 302 of the heat transfer layer 300, the primary channels 306 may extend from regions of the heat transfer layer proximate to the first end 301 to regions of the heat transfer layer proximate to the second end 302.

The secondary channels 307 may extend from the primary channels 306 to the regions of the heat transfer layer 300 proximate to the fluid outlet. For example, if the fluid inlet is positioned at the first end 301 of the heat transfer layer 300 and the fluid outlet is positioned at the second end 302 of the heat transfer layer 300, the secondary channels 307 may extend from the primary channels 306 to the regions of the heat transfer layer 300 proximate to the second end 302.

The tertiary channels 308 may extend from a primary channel 306 to another primary 20 channel 306, from a secondary channel 307 to another secondary channel 307, or from a primary channel 306 to a secondary channel 307.

Of the channels 305, the primary channels 306 have the greatest dimensions (both in terms of length and width) and therefore have greater dimensions than the secondary channels 307 and the tertiary channels 308. The secondary channels 307 have greater dimensions than the tertiary channels 308. The tertiary channels 308 have the smallest dimensions of the channels 305.

The heat conducting structures 304 and channels 305 may be arranged such that an average cross-sectional area of the base of each respective heat conducting structure 304 proximate to the fluid inlet is greater than an average cross-sectional area of base of each respective heat conducting structure 304 proximate to the fluid outlet.

The heat conducting structures 304 and channels 305 may be arranged such that the number of channels 305 proximate to the fluid inlet is smaller than the number of channels 305 proximate to the fluid outlet. This is partly to do with the fact that proximate to the fluid inlet, there is a greater concentration of primary channels 306 than other types of channels 305, and partly to do with the fact that the heat conducting structures 304 are larger near the fluid inlet and therefore take up more room.

The heat conducting structures 304 and channels 305 may also be arranged such that the channels 305 proximate to the fluid inlet have greater dimensions than the channels 305 proximate to the fluid outlet. As discussed above, this may be because the region of the heat transfer layer 300 proximate to the fluid inlet is dominated by primary channels 306, which have greater dimensions than the secondary channels 307 and the tertiary channels 308, which are more concentrated in the regions nearer the fluid outlet.

The function of the heat transfer layer 300 is to enable heat exchange between a fluid flowing through the heat transfer layer 300 and the heat transfer layer 300 itself. For example, heat may be transferred from a hot fluid flowing through the heat transfer layer 300, or may be transferred to a cold fluid flowing through the heat transfer layer 300.

The plate 301 performs the function of keeping the fluid passing through the heat transfer layer 300 separate from any other fluids (e.g. those passing through another heat transfer layer 300 in a heat exchanger, as will be explained later on), so that they do not mix. This helps to ensure that heat exchange is conducted through the physical apparatus, rather than through direct mixing of fluids. The plate 301 also performs the function of supporting the heat conducting structures 304.

The fluid inlet 302 is configured to allow fluid to enter the heat transfer layer 300 and the fluid outlet 303 is configured to allow fluid to exit the heat transfer layer 300 after heat exchange has taken place.

The heat conducting structures 304 are arranged to channel fluid from the fluid inlet to the fluid outlet. Furthermore, the heat conducting structures 304 are configured such that as the fluid passes through the channels 305 and against the sides of the structures 304, heat exchange between the structures 304 and the fluid may be enabled. As described above, if the heat transfer layer 300 is channelling a hot fluid, the heat conducting structures 304 are configured to transfer heat from the fluid, and if the heat transfer layer 300 is channelling a cooler fluid, the heat conducting structures 304 are configured to transfer heat to the fluid.

The sizes and shapes of the heat conducting structures 304 increases the surface area of the heat transfer surface, increasing the overall heat duty of the heat transfer layer 300.

However, they also increase the pressure drop across the heat transfer layer 300 by adding additional friction and pressure blockage effects.

The heat conducting structures 304 may be larger proximate to the fluid inlet than proximate to the fluid outlet because larger structures generally have lower heat transfer coefficients and lower pressure loss, while smaller structures have higher heat transfer coefficients and pressure losses.

The example shown in Figure 3 uses a small number of relatively large channels 305 (i.e. the primary channels 306) which transport larger amounts of fluid from the regions of the heat transfer layer proximate to the fluid inlet to regions of the heat transfer layer proximate to the fluid outlet, where the fluid may be split into much smaller channels (i.e. secondary channels 307 and tertiary channels 308) to ensure a larger temperature difference near the outlet. This may improve the overall performance of the heat transfer layer 300. By using the primary channels 306 to deliver fluid to different parts of the heat transfer layer, heat exchange may take place across the heat transfer layer 300, rather than just in regions proximate to the fluid inlet. Once the fluid reaches regions where the heat must be exchanged (i.e. with smaller channels 305 and smaller heat conducting structures 304), the tertiary channels 308 may have a substantially uniform cross section around the structures 304 to ensure a uniform heat exchange.

Figures 4A-C show different views of the heat conducting structures 304 of another example of a heat transfer layer 300. Specifically, Figure 4A shows a perspective view of some of the heat conducting structures 304 from Figure 3, but in which the heat conducting structures 304 are tapered. Figure 4B shows a top view of the same heat conducting structures 304 from Figure 4A, and Figure 4C shows a side view of same heat conducting structures 304 from Figures 4A-B.

As has been descried, the heat conducting structures 304 have a variety of different shapes and sizes. In the embodiment of Figures 4A-C, the heat conducting structures 304 are tapered such that a cross-sectional area of each heat conducting structure 304 in a plane parallel to the planar plate 301 decreases from its base to its elevated portion. In other words, the cross-sectional area of each heat conducting structure 304 decreases with distance from the plate 301.

Each heat conducting structure 304 may have a taper angle a, which represents the slope of the side of the heat conducting structure 304. As can be seen in Figure 4C, this angle a is the internal angle between the side of the heat conducting structure 304 and the plate 301. Each heat conducting structure 304 has a taper angle of no more than 45 degrees from the plate 301. Each heat conducting structure 304 may have the same taper angle a, or alternatively different heat conducting structures 304 within the heat transfer layer 300 may have different taper angles a.

By incorporating a taper into the heat conducting structures 304, the surface area of each heat conducting structure 304 is increased, thus increasing the heat transfer surface area.

The presence of the taper also reduces the potential blockage of any fluid following through the channels 305, therefore decreasing pressure losses across a heat transfer system incorporating such a heat transfer layer 300.

Furthermore, incorporating a taper into the heat conducting structures also provides benefits with regard to manufacturing the heat transfer layer. As mentioned, the heat transfer 300 layer can be produced through additive manufacturing (e.g. 3D printing).

A key issue that affects additive manufacturing is the so-called overhang angle constraint.

This constraint describes the maximum angle at which the additive process can build new features. If a feature in an object overhangs the "layer" beneath it by more than 45 degrees, it cannot be printed since there will not be enough material beneath it to support it during the manufacturing process.

In a conventional heat transfer layer, the heat conducting structures extend upwards perpendicularly to the plate, with sides that are also perpendicular to the plate (e.g. Figures 2A-B). In the plane of the plate itself, this results in an overhang angle of 0 degrees (so additive manufacturing is possible), but in a plane perpendicular to the plate, this results in an overhang angle of 90 degrees (meaning additive manufacturing is not possible). This means that if such layers are to be produced through additive manufacturing, it is necessary to build the layer upwards (i.e. in a direction perpendicular to the plate). Firstly, the plate must be printed as a horizontal slab, and then the heat conducting structures may be printed on top of this. Printing in this manner is time consuming and inefficient, resulting in greater costs.

By incorporating a taper angle a of no more than 45 degrees into the heat conducting structures 304 in the present heat transfer layer 300, the heat transfer layer 300 can be built side-up (i.e. in a direction parallel to the plate), since the overhang angle is no more than 45 degrees. This results in a quicker and more efficient print, reducing costs. Such an effect is not possible with conventional heat exchangers incorporating non-tapered heat conducting structures.

Figures 5A-B show different views of heat conducting structures 304 of a heat transfer layer 300 according to another embodiment of the invention. Specifically, Figure 5A shows a perspective view of a heat transfer layer 300 from Figure 3, but in which each heat conducting structure 304 comprises a plurality of discrete microstructures 501 grouped together. Figure 5B shows a perspective view of the same heat transfer layer 300 from Figure 5A.

The microstructures 501 of each heat conducting structure 304 each have a base on the first fluid contacting surface of the plate 301 and each protrude away from the first fluid contacting surface of the plate 301 to an elevated portion. The elevated portion of each microstructure may comprise a substantially flat surface.

For each heat conducting structure 304, its respective microstructures 501 define a plurality of microchannels 502 separating the plurality of microstructures 501 and through which fluid may flow from the fluid inlet to the fluid outlet. The microchannels 502 have smaller dimensions than the channels 305, both in terms of length and width in the plane of the plate 301. The microstructures 501 may be positioned such that fluid flows through the channels 305 more quickly and in greater quantities than through the microchannels 501, due to their respective sizes.

It is to be noted that, due to their small size, there are no arrows pointing to any of the individual microchannels 502 in Figure 5B, but the skilled person will understand that they separate the microstructures 501 within each heat conducting structure 304. In Figure 5B, some of the heat conducting structures 304 have been circled to show how the microstructures 501 are grouped together to provide discrete heat conducting structures 304. Specifically, the microstructures 501 may have a bulk outline corresponding to that of the heat conducting structures 304. In this way, when viewed on a macro scale, the collective outline of each group of microstructures 501 is the same as the outline of their respective heat conducting structure 304.

For each individual heat conducting structure 304, the microstructures 501 of that particular heat conducting structure 304 may protrude substantially the same distance from the first fluid contacting surface (i.e. each microstructure 501 within a heat conducting structure 304 may have substantially the same height), such that the elevated portions of each microstructure 501 within a given heat conducting structure 304 are substantially level.

The microstructures 501 of a given heat conducting structure 304 may protrude substantially the same distance from the first fluid contacting surface as the microstructures 501 of the other heat conducting structures 304 in the heat transfer layer 300. In this way, the height of each heat conducting structure 304 may be substantially equal.

The microstructures 501 may each have an identical cross-sectional profile, and may each have a uniform cross-section. The shapes of the cross-sections of the microstructures 501 may be any suitable shape. For example, each microstructure 501 may have a circular cross-section. It should be appreciated that many other shapes are possible, such as square.

As shown in Fig. 5B, the microstructures 501 may comprise pins protruding away from the first fluid contacting surface. Each pin may have a height (i.e. distance from base to elevated portion) that is proportionally much larger than its width (i.e. distance across the pin in the plane of the plate 301).

The use of microstructures 501 effectively builds a smaller scale structure within the heat conducting structures 304. This increases the heat transfer surface area of the heat conducting structures 304 significantly. Any increased pressure losses due to the microstructures 501 is offset by the fact that the presence of larger scale heat conducting structures 304 (e.g. those found nearer the fluid inlet) mitigates any pressure losses.

The heat transfer layer 300 as described in any of the embodiments of Figures 3, 4A-C and 5A-B may be one of a plurality of heat transfer layers 300 that together make up a heat exchanger. For example, the heat transfer layers 300 may be stacked such that each layer of heat conducting structures 304 is in contact with two plates 301 (one being its own associated plate 301). The heat transfer layers 300 may be joined by diffusion bonding, which allows for much higher pressure flows compared to conventional heat exchangers.

Some of the heat transfer layers 300 may be configured to receive a hot fluid, whereas some of the heat transfer layers 300 may be configured to receive a cooler fluid. This will be described in greater detail later on, in particular with respect to Figures 6A-B.

A heat exchanger comprising the heat transfer layers 300 may be a printed circuit heat exchanger. This enables each heat transfer layer 300 to be manufactured in one piece, rather than separately manufacturing the plate 301 and heat conducting structures 304 separately.

More specifically, a two-fluid heat exchanger may comprise a first set of heat transfer layers 300 and a second set of heat transfer layers. The first set may comprise at least one heat transfer layer 300 and the second set may comprise at least one heat transfer layer 300. Preferably, the if the number of heat transfer layers 300 in the first set is M, and the number of heat transfer layers 300 in the second set is N, then the heat exchanger satisfies either M=N, M=N+1, or M=N-1.

Each of the first set of heat transfer layers 300 may be arranged to channel a first of the two fluids from its respective fluid inlet to its respective fluid outlet, and each of the second set of heat transfer layers 300 may be arranged to channel a second of the two fluids from its respective fluid inlet to its respective fluid outlet.

Each of the first set of heat transfer layers may have a first arrangement of heat conducting structures 304 and each of the second set of heat transfer layers may have a second arrangement of heat conducting structures 304. Preferably, the second arrangement is non-identical to the first arrangement.

The heat transfer layers 300 of the heat exchanger may be stacked so as to alternate between members of the first set and members of the second set. In this way, each of the first set of heat transfer layers 300 is closer to a member of the second set of heat transfer layers 300 than a member of the first set of heat transfer layers 300, and each of the second set of heat transfer layers 300 is closer to a member of the first set of heat transfer layers 300 than a member of the second set of heat transfer layers 300.

The heat exchanger may further comprise a top plate positioned on top of the top heat transfer layer 300 in the stack and side walls configured to enclose the heat transfer layers 300. These features help to seal the heat exchanger by enclosing the heat transfer layers 300, and also ensure that fluid does not pass from one heat transfer layer 300 to another.

The first set of heat transfer layers 300 and the second set of heat transfer layers 300 may be configured to receive fluids of different temperatures. As mentioned, the first set of heat transfer layers 300 may be configured to receive a first fluid and the second set of heat transfer layers 300 may be configured to receive a second fluid. The first fluid may be hotter than the second fluid, or the second fluid may be hotter than the first fluid.

At the fluid inlet, where the temperature difference between the fluids is relatively high, larger structures 304 allow a reduction in pressure loss while still maintaining a large (in absolute terms) heat transfer due to the large temperature difference. Near the fluid outlet, the heat exchanger compromises for the lower temperature difference by using smaller structures 304 and accepting a larger pressure loss.

The dimensions of the channels 305 between the heat conducting structures 304 are chosen to increase the performance of the heat exchanger. In a conventional heat exchanger, the arrangement of structures and channels is generally uniform, which means that a cold fluid passing through the layer warms up uniformly (or a hot fluid passing through the layer cools down uniformly). This means that at the exit of the fluid path, the temperature differences between the two fluids are relatively small, reducing heat transfer.

As mentioned above, a heat exchanger as described may comprise heat transfer layers 300 in accordance with the embodiments of Figures 3, 4A-C or 5A-B. Although this lends itself to the possibility of incorporating different embodiments into the same heat exchanger, preferably the heat exchanger comprises: (a) only heat transfer layers 300 according to Figure 3, (b) only heat transfer layers 300 according to Figures 4A-C, or (c) only heat transfer layers 300 according to Figures 5A-B. However, it should be understood that combinations of different embodiments in one heat exchanger may be possible.

Figures 6A-B show perspective views of a heat exchanger as described above, but with particular flow configurations. Specifically, Figure 6A shows a perspective view 600 of several layers of a heat exchanger in a crossflow configuration, whereas Figure 6B shows a perspective view 650 of two layers of a heat exchanger in a counterflow configuration.

Referring to both Figures 6A and 6B, the heat exchanger may comprise a first set 601 of heat transfer layers 300 and a second set 602 of heat transfer layers 300. Although Figure 6A shows each set as having two heat transfer layers 300, and Figure 6B shows each set as having only one heat transfer layer 300, it is to be understood that different numbers of heat transfer layers 300 are possible, provided that each set has at least one heat transfer layer 300 and provided that the requirement of alternating the sets of layers is adhered to, as described earlier. Each heat transfer layer 300 comprises a plate 301 and heat conducting structures 304. In this way, each of the heat transfer layers 300 in the first set 601 and the second set 602 may correspond to the heat transfer layer 300 from any of Figures 3, 4A-C or 5A-B.

Referring still to both Figures 6A and 6B, the heat transfer layers 300 belonging to the first set 601 may be configured to receive a first fluid of the two fluids and the heat transfer layers 300 belonging to the second set 602 may be configured to receive a second fluid of the two fluids. Prior to being fed into the heat exchanger, the first fluid may have a higher temperature than the second fluid. In other words, a temperature of the second fluid at the respective fluid inlets of the second set 601 of heat transfer layers 300 may be lower than a temperature of the first fluid at the respective fluid inlets of the first set 601 of heat transfer layers 300. Alternatively, prior to being fed into the heat exchanger, the second fluid may have a higher temperature than the first fluid. In other words, a temperature of the first fluid at the respective fluid inlets of the first set 601 of heat transfer layers 300 may be lower than a temperature of the second fluid at the respective fluid inlets of the second set 602 of heat transfer layers 300. In this way, the first set 601 of heat transfer layers 300 and the second set 602 of heat transfer layers 300 may be configured to receive fluids of different temperatures.

As mentioned, each of the heat transfer layers 300 belonging to the first set 601 may have the same first arrangement of heat conducting structures 304 and each of the heat transfer layers 300 belonging to the second set 602 may have the same second arrangement of heat conducting structures 304. The first arrangement may be non-identical to the second arrangement. The respective arrangements of the heat transfer layers 300 may be determined based on the properties of the particular fluid that will pass through the heat transfer layers 300.

Referring still to Figures 6A and 6B, the heat exchanger may comprise a first end 302 and a second end 303. The heat exchanger may also comprise a first side and a second side opposite the first side. As has been described, each layer may be substantially rectangular, with two ends and two sides, although other shapes are possible. As described with reference to Figure 3, each heat transfer layer 300 comprises a fluid inlet and a fluid outlet.

Referring now to Figure 6A only, each of the heat transfer layers 300 belonging to the first set 601 may comprise a fluid inlet located at the first end 302 and a fluid outlet located at the second end 303.

Each of the heat transfer layers 300 belonging to the second set 602 may comprise a fluid inlet located along the first side and a fluid outlet located along the second side. For each of the heat transfer layers 300 belonging to the second set 602, the fluid inlet may be located closer to the first end 302 than the second end 303 and the fluid outlet may be located closer to the second end 303 than the first end 302, such that a direction of flow of the second fluid crosses a direction of flow of the first fluid. Alternatively, for each of the heat transfer layers 300 belonging to the second set 602, the fluid outlet may be located opposite the fluid inlet, such that the direction of flow of the second fluid crosses the direction of flow of the first fluid and is substantially perpendicular to the direction of flow of the first fluid.

In an alternative embodiment, the arrangements of the fluid inlets and outlets for the first and second sets may be switched. Each of the heat transfer layers 300 belonging to the second set 602 may comprise a fluid inlet located at the first end 302 and a fluid outlet located at the second end 303. Each of the heat transfer layers 300 belonging to the first set 601 may comprise a fluid inlet located along the first side and a fluid outlet located along the second side. For each of the heat transfer layers 300 belonging to the first set 601, the fluid inlet may be located closer to the first end 302 than the second end 303 and the fluid outlet may be located closer to the second end 303 than the first end 302, such that a direction of flow of the first fluid crosses a direction of flow of the second fluid.

Alternatively, for each of the heat transfer layers 300 belonging to the first set 601, the fluid outlet may be located opposite the fluid inlet, such that the direction of flow of the first fluid crosses the direction of flow of the second fluid and is substantially perpendicular to the direction of flow of the second fluid.

In this way, the heat transfer layers 300 belonging to the first set 601 and the heat transfer layers 300 belonging to the second set 602 are arranged so that they enable the heat exchanger to operate in a crossflow configuration.

Referring now to Figure 6B only, each of the heat transfer layers 300 belonging to the first set 601 may comprise a fluid inlet located at the first end 302 and a fluid outlet located at the second end 303. Each of the heat transfer layers 300 belonging to the second set 602 may comprise a fluid inlet located at the second end 303 and a fluid inlet located at the first end 302, such that a direction of flow of the second fluid is substantially opposite to a direction of flow of the first fluid.

In an alternative embodiment, the arrangements of the fluid inlets and outlets for the first set 601 of heat transfer layers 300 and the second set 602 of heat transfer layers 300 may be switched. Each of the heat transfer layers 300 belonging to the second set 602 may comprise a fluid inlet located at the first end 302 and a fluid outlet located at the second end 303. Each of the heat transfer layers 300 belonging to the first set 601 may comprise a fluid inlet located at the second end 303 and a fluid inlet located at the first end 302, such that a direction of flow of the first fluid is substantially opposite to a direction of flow of the second fluid.

In this way, the heat transfers layers 300 of the first set 601 and the second set 602 are arranged so that they enable the heat exchanger to operate in a counterflow configuration.

A method of using a heat exchanger as described with reference to Figures 6A-B may comprise the steps of feeding each of the first set 601 of heat transfer layers 300 with the first fluid and feeding each of the second set 602 of heat transfer layers 300 with the second fluid. Such a method can be employed on a heat exchanger with a crossflow configuration or a counterflow configuration, as described above.

The feeding of each of the first set 601 of heat transfer layers 300 may be performed in parallel, such that each of the first set 601 of heat transfer layers 300 is fed with the first fluid at the same time. The feeding of each of the second set 602 of heat transfer layers 300 may also be performed in parallel, such that each of the second set 602 of heat transfer layers 300 is fed with the second fluid at the same time. The heat transfer layers 300 belonging to the first set 601 may be fed with the first fluid at the same time as the heat transfer layers 300 belonging to the second set 602 are fed with the second fluid. Alternatively, the heat transfer layers 300 belonging to the first set 601 may be fed with the first fluid before or after the heat transfer layers 300 belonging to the second set 602 are fed with the second fluid.

The feeding of each of the first set 601 of heat transfer layers 300 may be staggered (i.e. performed in series), such that each of the first set 601 of heat transfer layers 300 is fed with the first fluid at a different time. The feeding of each of the second set 602 of heat transfer layers 300 may also be staggered (i.e. performed in series), such that each of the second set 602 of heat transfer layers 300 is fed with the second fluid at a different time.

The heat transfer layers 300 may be fed in an alternating manner, such that the feeding of one of the first set 601 of heat transfer layers 300 is preceded and/or followed by the feeding of a neighbouring one of the second set 602 of heat transfer layers 300, and the feeding of one of the second set 602 of heat transfer layers 300 is preceded and/or followed by the feeding of a neighbouring one of the first set 601 of heat transfer layers 300. For example, assuming that the top heat transfer layer 300 of the heat exchanger belongs to the first set 601, the top layer may be fed with the first fluid, followed by the next layer down (which is a heat transfer layer 300 belonging to the second set 602) being fed with the second fluid. The next layer down after this may be a heat transfer layer 300 belonging to the first set 601 and may then be fed with the first fluid, followed by the next layer down after this (which may be a heat transfer layer 300 belonging to the second set 602) being fed with the second fluid, and so forth. Each layer of the stack is therefore fed with its respective fluid in turn.

Figure 7A shows an illustration 700 of temperature and velocity streamlines for a layer 701 of a conventional heat exchanger, such as the heat exchanger described with reference to Figures 2A-B. The layer 701 may directly correspond to the heat transfer layer 200 from Figures 2A-B.

As a fluid moves through the channels of the layer 701, the temperature gradually decreases or increases as it interacts with the heat conducting structures of the layer 701, depending on whether the fluid is hot or cool at the inlet. Since the channels and the structures are substantially uniform, the velocity streamlines are also substantially uniform. The fluid progresses at a reasonably constant speed through the layer 701 and thus produces substantially uniform velocity streamlines.

Figure 7B shows an illustration 750 of temperature and velocity streamlines for a counterflow heat exchanger layer 702 of a heat exchanger in accordance with the present invention. The layer 702 may directly correspond to heat transfer layer 300, in particular with regard to Figures 3, 4A-C, 5A-B and 6A-B.

Due to the non-uniform nature of the heat conducting structures and the channels in the layer 702, the velocity streamlines are less regular. The fluid moves more quickly through the primary channels, but is slowed when it reaches secondary or tertiary channels. The more rapid movement through the primary channels also means that the temperature streamlines are less regular.

The performances of both a conventional heat exchanger comprising layers 701 from Figure 7A and a heat exchanger comprising layers 702 from Figure 7B have been analysed under two different flow conditions. The first of these conditions was a laminar flow with a Reynolds number of approximately 239 and the second of these conditions was a laminar flow with a larger Reynolds number of approximately 4788. For each flow condition, the same channel dimensions, temperatures and reference pressures were used, as can be seen in Table 1 below, which shows the parameters used for each flow condition.

LAMINAR FLOW TURBULENT FLOW

Reynolds Number 239 4788 Channel Height (mm) 1.15 Plate Thickness (mm) 1 Channel Length (mm) 200 Hot inlet temperature (°C) 850 Cold inlet temperature (°C) 625 Reference Pressure (MPa) 6.8 Hot channel flow rate (kg/s) 2.56e-4 5.12e-3 Cold channel flow rate (kg/s) 2.06e 4 4.12e-3 Table 1: Parameters used for each flow condition The fluid media were helium/helium while the solid medium was an Inconel alloy. Turbulence was modelled using a k-epsilon RANS model. As has been described, illustrative diagrams of the temperature and velocity streamlines are shown in Figures 7A-B. For each heat exchanger, the heat transfer performance was quantified using the non-dimensional Nusselt number, which is defined by Equation 1 below.

EQUATION 1: hDh Nu = In Equation 1, h is the heat transfer coefficient, Dh is the hydraulic diameter of the heat exchanger and k is the thermal conductivity of the fluid. The Nusselt number represents the ratio of heat transfer by convection to heat transfer by conduction across the heat exchanger. Higher Nusselt numbers indicate more efficient heat exchangers.

The losses across the heat exchangers were quantified using the non-dimensional Fanning friction factor, which is defined by Equation 2 below.

EQUATION 2: f = 2L pu2 Ail Dh In Equation 2, Ap is the static pressure drop across the heat exchanger, L is the length of the heat exchanger, p is the fluid density and u is the fluid velocity. The Fanning friction factor represents a normalised pressure drop across the heat exchanger. Lower values indicate higher efficiencies.

The Nusselt and Fanning numbers of the conventional heat exchanger are shown below

in Table 2.

FLOW PERFORMANCE PARAMETER SIMULATION OF DESIGN

CONDITION

Cold Side Hot Side Laminar Nu 8.41 9.99 f 0.6 0.51 Turbulent Nu 19.5 20.6 f 0.072 0.065 Table 2. Performance of conventional counterflow heat exchanger The Nusselt and Fanning numbers of the heat exchanger of the present disclosure are shown below in Table 3.

FLOW PERFORMANCE PARAMETER SIMULATION OF DESIGN

CONDITION

Cold Side Hot Side Laminar Nu 9.36 9.6 f 0.59 0.52 Turbulent Nu 21.1 22.5 f 0.094 0.040 Table 3: Performance of counterflow heat exchanger according to present disclosure The results show that at lower Reynolds numbers (i.e. laminar flow), a heat exchanger according to the present disclosure has a 3% higher Nusselt number for an equivalent Fanning friction factor.

At higher Reynolds numbers (i.e. turbulent flow), a heat exchanger according to the present disclosure has an 8.5% higher Nusselt number for an only 4% higher Fanning zo friction factor.

There are therefore significant gains in heat exchanger performance when the layers comprise arrangements as shown in Figures 3, 4A-C, 5A-B and 6A-B, compared to conventional heat exchangers comprising layers as shown in Figures 2A-B.

Referring now to Figure 8, a perspective view of a layer 800 of a heat exchanger comprising a plurality of passes in accordance with the present invention can be seen. The layer 800 may correspond to the heat transfer layer 300 from Figures 3, 4A-C, 5A-B or 6A-B.

As with layer 300, layer 800 comprises a plate 301 and a plurality of heat conducting structures 304, the heat conducting structures 304 protruding away from a first fluid contacting surface of the plate 301. The heat conducting structures 304 define a plurality of channels 305 through which fluid may pass. The channels 305 may be a mixture of primary channels, secondary channels and tertiary channels, as has been described with reference to Figure 3.

The layer 800 may comprise a fluid inlet 801 located at a first end 302 of the heat exchanger and a fluid outlet 802 located at the first end 302 of the heat exchanger. As will be discussed, it should be understood that the fluid inlet 801 and fluid outlet 802 may be located at the second end 302. Alternatively, the fluid inlet 801 may be located at the first end 302 and the fluid outlet 802 may be located at the second end 303. Alternatively, the fluid inlet 801 may be located at the second end 303 and the fluid outlet 802 may be located at the first end 302.

The layer may comprise at least one baffle 803. Figure 8 shows a layer 800 comprising three baffles 803, but the disclosure below will initially describe a layer 800 comprising just one baffle 803. The possibility of multiple baffle 803 will then be discussed afterwards. The purpose of the baffle 803 is to effect a change in fluid direction, as will be discussed below.

The baffle 803 may protrude away from the first fluid contacting surface of the plate 301 to the same height as the plurality of heat conducting structures 304. If the heat conducting structures 304 are of different heights, then the baffle 803 may protrude to the same height as the tallest heat conducting structures 304 in the heat transfer layer 800. It should be noted that Figure 8 shows only a boxed area where the baffle 803 is located, but it should be understood that this is simply to help the skilled person understand the path that the fluid will take through the layer. The baffle 803 may function as a dividing wall to channel the fluid from one part of the heat transfer layer 800 to another. The baffle 803 may start at the first end 302 and may have a length that extends substantially across the layer 800 towards the second end 303, but not the whole way across. In this way, the baffle 803 may define a first region of heat conducting structures 304 of the layer 800 and a second region of heat conducting structures 304 of the layer 800. The first region may be located proximate to the fluid inlet 801 on a first side of the baffle 803 and the second region may be located on an opposite side of the baffle 803 to the first region. The fluid may travel in a different direction in the second region compared to the first region, and in this sense, the baffle 803 effects a change in fluid flow direction.

As can be seen in Figure 8, the baffle 800 may have a substantially rectangular cross-section, which results in the fluid changing direction by approximately 180 degrees.

Alternatively, the baffle 803 may have a substantially square cross-section, which may result in a more gradual change in fluid direction. In such a case, the baffle 803 functions as a dividing block, rather than wall. The fluid may firstly change direction by approximately 90 degrees as it turns around a first corner of the block, and may then change direction by another 90 degrees as it turns around a second corner of the block. The end result is a change in fluid direction by approximately 180 degrees.

It should also be appreciated that turns of less than 180 degrees are possible. For example, if the baffle 803 is positioned to be at an angle to the first direction of the fluid (i.e. the direction at the inlet), this may result in turns of different angles.

A turn of the fluid around a baffle 803 may be referred to as a pass. Specifically, a baffle 803 that effects a change in fluid flow direction such that the fluid is travelling in the opposite direction to its previous direction may result in such a pass. The first and second regions may define this pass.

The layer 800 may further comprise a second baffle 803 starting at the second end 303 and having a length that extends substantially across the layer 800 towards the first end 302, but not the whole way across. In this way, the second baffle 803 may define the second region of the layer 800 and a third region of the layer 800. The second region may be located on a first side of the second baffle 803 and the third region may be located on an opposite side of the second baffle 803 to the second region.

The layer 800 may comprise any number of baffles 803. Preferably, each subsequent baffle 803 originates from the opposite end of the layer to the previous baffle 803, such that the heat transfer layer 800 comprises a number of turns or passes through which the fluid may travel. The presence of a single baffle 803 results in the fluid being channelled through the first section in a first direction, turning, and then passing through the second section in a second direction. Preferably, the second direction is substantially opposite to the first direction. In this way, the first region and the second region (and indeed the first baffle 803 separating them) define a pass.

The layer 800 may comprise an odd number of baffles 803 (such as one baffle 803, or three baffles 803, as shown in Figure 8). An odd number of baffles 803 results in an odd number of passes, meaning that in the final section of the layer 800, the fluid is travelling in the opposite direction to the direction it started in. As such, the fluid outlet will be located at the same end of the heat exchanger as the fluid inlet.

Alternatively, the layer 800 may comprise an even number of baffles 803 (such as four baffles 803). An even number of baffles 803 results in an even number of passes, meaning that in the final section of the layer 800, the fluid is travelling in the same direction as the direction it started in. As such, the fluid outlet will be located at the opposite end of the heat exchanger to the fluid inlet.

As described, the function of the baffles 803 is to define a path through which the fluid may travel and to define a number of passes of the layer 800. Incorporating a number of passes into the layers 800 of a heat exchanger by way of at least one baffle 803 on each layer 800 means that the thermodynamic efficiency of the heat exchanger can be increased further, since it helps to ensure that the coldest parts of the hot fluid are cooled by the coldest parts of the cold fluid and vice versa.

In operation, the heat transfer layers 800 of the heat exchanger function in the same way as the heat transfer layers 300. The only difference is the fact that the fluid completes a number of passes on its way to the fluid outlet 802. The principles of heat exchange as the fluid interacts with the heat conducting structures 304 is the same as in Figures 3, 4A-C, 5A-B and 6A-B.

The heat transfer layer 800, and indeed the heat transfer layers 300, may be designed by a fluid topology optimization program. Such a program may take into account properties of the two fluids that will be fed into a heat exchanger and, based on these properties, an arrangement of the heat transfer layer of each layer can be determined by executing a fluid topology optimization program. A plurality of heat transfer layers based on the determined arrangement can then be provided and diffusion bonded together in order to produce a heat exchanger.

With this in mind, a method of producing a heat exchanger may comprise a first step of executing a fluid topology optimization program to determine a first arrangement of heat conducting structures and a second arrangement of heat conducting structures. The method may then comprise providing a first set of heat transfer layers based on the first arrangement determined by the fluid topology optimization program and then providing a second set of heat transfer layers based on the second arrangement determined by the fluid topology optimization program. The method may then comprise diffusion bonding these heat transfer layers, thus producing a heat exchanger.

As mentioned above, the determination of the two arrangements may be based on the properties of the fluids to be used in the heat exchanger. Specifically, the determination of the first arrangement may be based on the properties of the first fluid and the determination of the second arrangement may be based on the properties of the second fluid.

Providing the first set of heat transfer layers may comprise producing the first set of heat transfer layers through an additive manufacturing process, and providing the second set of heat transfer layers may comprise producing the second set of heat transfer layers through an additive manufacturing process. It should be understood that other ways of producing the sets of heat transfer layers are possible (e.g. subtractive manufacturing processes such as milling, etching etc.).

Heat exchangers comprising layers as described with reference to Figures 3, 4A-C, 5A-B, 6A-B, 7B and 8 may be used in small modular reactors. Such reactors have the potential to support decarbonisation beyond simply supplying low-carbon electricity, but due to their higher operating temperatures, are incompatible with many conventional heat exchangers. Heat exchangers as described with reference to the present disclosure may be used in small modular reactors due to their improved performance with respect to conventional heat exchangers. The present disclosure therefore includes a small modular reactor comprising at least one heat exchanger as described above.

It will be appreciated from the discussion above that the embodiments shown in the Figures are merely exemplary, and include features which may be generalised, removed or replaced as described herein and as set out in the claims.

Further embodiments are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Where ranges are recited herein these are to be understood as disclosures of the limits of said range and any intermediate values between the two limits.

With reference to the drawings in general, it will be appreciated that schematic functional block diagrams are used to indicate functionality of systems and apparatus described herein. It will be appreciated however that the functionality need not be divided in this way and should not be taken to imply any particular structure of hardware other than that described and claimed below. The function of one or more of the elements shown in the drawings may be further subdivided, and/or distributed throughout apparatus of the disclosure. In some embodiments the function of one or more elements shown in the drawings may be integrated into a single functional unit.

Method embodiments may be implemented using the apparatus described herein.

The above embodiments are to be understood as illustrative examples. Further embodiments are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

These claims are to be interpreted with due regard for equivalents.

Claims

Claims 1. A heat transfer layer for use in a two-fluid heat exchanger, the heat transfer layer comprising: a planar plate comprising at least a first fluid contacting surface; and a plurality of discrete heat conducting structures positioned on the first fluid contacting surface of the plate, each of the heat conducting structures having a base on the first fluid contacting surface of the plate and protruding away from the first fluid contacting surface to an elevated portion, the heat conducting structures defining a plurality of channels separating the plurality of heat conducting structures, and through which fluid may flow from a fluid inlet to a fluid outlet; wherein the heat conducting structures are tapered such that a cross-sectional area of each heat conducting structure in a plane parallel to the planar plate decreases from its base to its elevated portion.
2. The heat transfer layer of claim 1, wherein the heat conducting structures are arranged such that: an average cross-sectional area of the base of each respective heat conducting structure proximate to the fluid inlet is greater than an average cross-sectional area of the base of each respective heat conducting structure proximate to the fluid outlet; and a number of channels proximate to the fluid inlet is smaller than a number of channels proximate to the fluid outlet.
3. The heat transfer layer of claims 1 or 2, wherein the channels proximate to the fluid inlet have greater dimensions than the channels proximate to the fluid outlet.
4. The heat exchanger of any preceding claim, wherein the channels comprise primary channels, secondary channels and tertiary channels, wherein: the primary channels extend from regions of the heat transfer layer proximate to the fluid inlet to regions of the heat transfer layer proximate to the fluid outlet; the secondary channels extend from the primary channels to the regions of the heat transfer layer proximate to the fluid outlet; the tertiary channels extend between any of: primary channels and other primary channels; secondary channels and other secondary channels; and primary channels and secondary channels; and wherein the primary channels have greater dimensions than the secondary channels and the secondary channels have greater dimensions than the tertiary channels.
5. The heat transfer layer of any preceding claim, wherein each heat conducting structure has a taper angle of no more than 45 degrees from the plate.
6. The heat transfer layer of any preceding claim, wherein each heat conducting structure protrudes substantially the same distance from the first fluid contacting surface, such that the elevated portions of each heat conducting structure are substantially level.
7. The heat transfer layer of any of claims 1 to 5, wherein a subset of the heat conducting structures protrude a first distance from the first fluid contacting surface, and the remaining heat conducting structures protrude distances smaller than the first 15 distance.
8. The heat transfer layer of any preceding claim, wherein the elevated portion of each heat conducting structure comprises a substantially flat surface.
9. A heat transfer layer for use in a two-fluid heat exchanger, the heat transfer layer comprising: a planar plate comprising at least a first fluid contacting surface; and a plurality of heat conducting structures positioned on the first fluid contacting surface of the plate, each of the heat conducting structures protruding away from the first fluid contacting surface of the plate, the heat conducting structures defining a plurality of channels separating the plurality of heat conducting structures, and through which fluid may flow from a fluid inlet to a fluid outlet; wherein each of the heat conducting structures comprises a plurality of discrete microstructures grouped together, the microstructures of each heat conducting structure each having a base on the first fluid contacting surface and protruding away from the first fluid contacting surface of the plate to an elevated portion, the microstructures defining a plurality of microchannels separating the plurality of microstructures, and through which fluid may flow from the fluid inlet to the fluid outlet; wherein the microchannels have smaller dimensions than the channels.
10. The heat transfer layer of claim 9, wherein the microstructures comprise pins of a uniform cross-section, each pin having a height that is proportionally much larger than its width.
11. The heat transfer layer of claims 9 or 10, wherein each microstructure has a circular cross-section.
12. The heat transfer layer of any of claims 9 to 11, wherein for each heat conducting structure, each microstructure protrudes substantially the same distance from the first fluid contacting surface, such that the elevated portions of each microstructure within a heat conducting structure are substantially level.
13. The heat transfer layer of any of claims 9 to 12, wherein the elevated portion of each microstructure comprises a substantially flat surface.
14. The heat transfer layer of any of claims 9 to 13, wherein the heat conducting structures are arranged such that: an average cross-sectional area of the heat conducting structures proximate to the fluid inlet is greater than an average cross-sectional area of the heat conducting structures proximate to the fluid outlet; and a number of channels proximate to the fluid inlet is smaller than a number of channels proximate to the fluid outlet.
15. The heat transfer layer of any of claims 9 to 14, wherein the channels proximate to the fluid inlet have greater dimensions than the channels proximate to the fluid outlet.
16. The heat transfer layer of any of claims 9 to 15, wherein the channels comprise primary channels, secondary channels and tertiary channels, wherein: the primary channels extend from regions of the heat transfer layer proximate to the fluid inlet to regions of the heat transfer layer proximate to the fluid outlet; the secondary channels extend from the primary channels to the regions of the heat transfer layer proximate to the fluid outlet; the tertiary channels extend between any of: primary channels and other primary channels; secondary channels and other secondary channels; and primary channels and secondary channels; and wherein the primary channels have greater dimensions than the secondary channels and the secondary channels have greater dimensions than the tertiary channels.
17. The heat transfer layer of any of claims 9 to 16, wherein the microstructures are positioned such that fluid flows through the channels more quickly and in greater quantities than through the microchannels.
18. A two-fluid heat exchanger configured to exchange heat between two fluids, the heat exchanger comprising: a first set of heat transfer layers according to any preceding claim, each of the first set of heat transfer layers arranged to channel a first of the two fluids from its respective fluid inlet to its respective fluid outlet; and a second set of heat transfer layers according to any preceding claim, each of the second heat transfer layers arranged to channel a second of the two fluids from its respective fluid inlet to its respective fluid outlet; wherein the first set of heat transfer layers and the second set of heat transfer layers are stacked so as to alternate between members of the first set and members of the second set, such that each of the first set of heat transfer layers is closer to a member of the second set of heat transfer layers than a member of the first set of heat transfer layers, and each of the second set of heat transfer layers is closer to a member of the first set of heat transfer layers than a member of the second set of heat transfer layers; wherein the first set of heat transfer layers comprises at least one heat transfer layer and the second set of heat transfer layers comprises at least one heat transfer layer; and wherein the heat conducting structures of each of the first set of heat transfer layers are arranged in a first arrangement and the heat conducting structures of the second set of heat transfer layers are arranged in a second arrangement.
19. The heat exchanger of claim 18, wherein the second arrangement is non-identical to the first arrangement.
20. The heat exchanger of claims 18 or 19, wherein the respective fluid inlets of each of the first set of heat transfer layers are located at a first end of the heat exchanger.
21. The heat exchanger of claim 20, wherein the respective fluid outlets of each of the first set of heat transfer layers are located at a second end of the heat exchanger opposite the first end.
22. The heat exchanger of claim 21, wherein the respective fluid inlets of each of the second set of heat transfer layers are located at the second end of the heat exchanger opposite the respective fluid inlets of each of the first set of heat transfer layers, and the respective fluid outlets of each of the second set of heat transfer layers are located at the first end of the heat exchanger, such that a direction of flow of the second fluid is 113 substantially opposite to a direction of flow of the first fluid.
23. The heat exchanger of claim 21, wherein the respective fluid inlets of each of the second set of heat transfer layers are located along a first side of the heat exchanger and the respective fluid outlets of each of the second set of heat transfer layers are located along a second side of the heat exchanger opposite the first side.
24. The heat exchanger of claim 23, wherein the respective fluid inlets of each of the second set of heat transfer layers are located closer to the first end of the heat exchanger than the second end, and the respective fluid outlets of each of the second set of heat transfer layers are located closer to the second end of the heat exchanger than the first end, such that a direction of flow of the second fluid crosses a direction of flow of the first fluid.
25. The heat exchanger of claim 23, wherein the respective fluid outlets of each of the second set of heat transfer layers are located opposite the respective fluid inlets of each of the second set of heat transfer layers, such that a direction of flow of the second fluid crosses a direction of flow of the first fluid and is substantially perpendicular to the direction of flow of the first fluid.
26. The heat exchanger of any of claims 18 to 25, wherein each of the first set of heat transfer layers and each of the second set of heat transfer layers comprises at least one baffle that effects a change in fluid direction.
27. The heat exchanger of claim 26, wherein the at least one baffle of each of the heat transfer layers protrudes away from the first fluid contacting surface, the at least one baffle defining at least a first region of heat conducting structures and a second region of heat conducting structures.
28. The heat exchanger of claim 27, wherein the second region is on an opposite side of the baffle to the first region, such that the fluid is channelled through the first region in a first direction and then through the second region in a second direction, the second direction being substantially opposite to the first direction, the first region and the second region defining a pass.
29. The heat exchanger of claim 28, wherein the at least one baffle comprises an odd number of baffles defining an odd number of passes, such that the respective fluid outlet is at a same end of the heat exchanger as the respective fluid inlet.
30. The heat exchanger of claim 28, wherein the at least one baffle comprises an even number of baffles defining an even number of passes, such that the respective fluid outlet is at an opposite end of the heat exchanger to the respective fluid inlet.
31. The heat exchanger of any of claims 18 to 30, wherein the first set of heat transfer layers and the second set of heat transfer layers are configured to receive fluids of different 20 temperatures.
32. The heat exchanger of any of claims 18 to 31, wherein the stacked heat transfer layers are joined by diffusion bonding.
33. The heat exchanger of any of claims 18 to 32, further comprising: a top plate positioned on top of the top heat transfer layer in the stack; and side walls configured to enclose the heat transfer layers and ensure that fluid does not pass from one heat transfer layer to another.
34. A method of producing the heat exchanger of any of claims 18 to 33, the method comprising: executing a fluid topology optimization program to determine the first arrangement of heat conducting structures and the second arrangement of heat conducting structures; providing the first set of heat transfer layers based on the first arrangement determined by the fluid topology optimization program; providing the second set of heat transfer layers based on the second arrangement determined by the fluid topology optimization program; and diffusion bonding the heat transfer layers.
35. The method of claim 34, wherein the determination of the first arrangement is based on properties of the first fluid and the determination of the second arrangement is based on properties of the second fluid.
36. The method of claims 34 or 35, wherein providing the first set of heat transfer layers comprises producing the first set of heat transfer layers through an additive manufacturing process, and providing the second set of heat transfer layers comprises producing the second set of heat transfer layers through an additive manufacturing process.
37. A method of heat exchange using the heat exchanger of any of claims 18 to 33, the method comprising: feeding each of the first set of heat transfer layers with the first fluid; and feeding each of the second set of heat transfer layers with the second fluid.
38. The method of claim 37, wherein: the feeding of each of the first set of heat transfer layers with the first fluid is performed in parallel, such that each of the first set of heat transfer layers is fed with the first fluid at the same time; and the feeding of each of the second set of layers with the second fluid is performed in parallel, such that each of the second set of heat transfer layers is fed with the second fluid at the same time.
39. The method of claim 37, wherein: the feeding of each of the first set of heat transfer layers with the first fluid is staggered, such that each of the first set of heat transfer layers is fed with the first fluid at a different time; and the feeding of each of the second set of heat transfer layers with the second fluid is staggered, such that each of the second set of heat transfer layers is fed with the second fluid at a different time.
40. The method of claim 39, wherein the heat transfer layers are fed in an alternating manner such that the feeding of one of the first set of heat transfer layers is preceded and/or followed by the feeding of a neighbouring one of the second set of heat transfer layers, and the feeding of one of the second set of heat transfer layers is preceded and/or followed by the feeding of a neighbouring one of the first set of heat transfer layers.
41. A small modular reactor comprising at least one heat exchanger as defined in any of claims 18 to 33.