None.
Not Applicable.
Not Applicable.
1. Field of the Invention
This invention pertains to heat exchangers. More particularly, the present invention pertains to heat exchangers that are ideally suited for transferring heat between two gaseous fluids.
2. General Background
Heat exchangers are used in numerous industries and devices for numerous purposes. Many types of heat exchangers rely on the transfer of heat between two fluids. For example, many internal-combustion engines are typically water cooled and typically utilize a heat exchanger (radiator) to transfer heat from the liquid water or coolant to air. Some heat exchangers are gas-to-gas heat exchangers, wherein heat is transferred between two separate streams of gaseous fluid. The steady-state efficiency of a gas-to-gas heat exchanger is typically dependent upon the amount of surface area of the heat exchanger that contacts each of the fluid streams and the thermal conductivity of the material that separates the two fluid streams. Thus, it is advantageous to maximize the surface area of the heat exchanger that separates the fluid streams, while also minimizing the amount of material that separates the fluid streams. However, increasing the surface area to volume ratio of a heat exchanger can greatly complicate the fabrication or the size of heat exchangers, and therefore the cost and/or space required.
Another thing impacting the amount of heat transferred by a heat exchanger is the differences in the temperatures of the fluid streams as they pass through the heat exchanger. It is known that by flowing the streams of fluid in opposite directions through a heat exchanger, the temperature differential of the fluid streams can be kept more uniform throughout the heat exchanger. Such “counter-flow” heat exchangers typically operate with a higher efficiency than heat exchangers wherein the streams flow in the same direction along opposite surfaces of the walls of the heat exchanger and with a higher efficiency than cross-flow heat exchangers.
Unlike liquid fluids, gaseous fluids are easily compressed. As such, the temperature of fluids in a gas state can be altered by expanding or compressing such fluids. Likewise, as heat is removed from a gaseous fluid under constant pressure, the volume occupied by the fluid decreases. Thus, as a gaseous fluid stream of constant cross-sectional area passes through a heat exchanger and loses heat, the flow velocity normally decreases as the gaseous fluid passes through the heat exchanger as a result of the volume decrease.
The present invention provides several advantages over prior art heat exchangers. One such advantage is that the invention allows for a relatively simplistic method of fabricating a highly efficient heat exchanger. The preferred embodiment of the present invention is configured such that the cross-sectional area of the stream of fluid being cooled decreases as said stream passes through the heat exchanger and, conversely, the cross-sectional area of the stream of fluid being heated increases as said stream passes through the heat exchanger. Assuming the fluid stream being cooled is gaseous, the reduction of the cross-sectional area of said fluid stream has the effect of decreasing the volume of said fluid stream which minimizes the reduction of the temperature of said fluid stream as said fluid stream passes through the heat exchanger. Likewise, assuming the fluid stream being heated is gaseous, the increases of the cross-sectional area of said fluid stream has the effect of increasing the volume of said fluid stream which minimizes the increase of the temperature of said fluid stream as said fluid stream passes through the heat exchanger. This is advantageous in that it maximizes the temperature differential between the fluid streams as they pass through the heat exchanger and therefore increases the overall amount of heat exchanged between the fluid streams.
In one aspect of the invention, a method of transferring heat from a warmer stream of gas to a cooler stream of gas comprises flowing the warmer stream of gas through a heat exchanger in a manner such that the warmer stream of gas converges as the warmer stream of gas flows through the heat exchanger and in a manner such that the warmer stream of gas is at least partially bound by a wall of the heat exchanger. The method further comprises flowing the cooler stream of gas through the heat exchanger in a manner such that the cooler stream of gas diverges as the cooler stream of gas flows through the heat exchanger and in a manner such that the cooler stream of gas is at least partially bound by the wall of the heat exchanger. Still further, the method comprises allowing heat to conduct through the wall from the warmer stream of gas to the cooler stream of gas.
In another aspect of the invention, a heat exchanger extends at least partially around and along a central axis (the central axis defining axial and radial directions). The heat exchanger at least partially encircles an interior fluid containing region and is at least partial encircled by an exterior fluid containing region. The heat exchanger comprises a plurality of arcuate fluid passageways alternating in the axial direction with a plurality of arcuate fluid cavities. Each of the arcuate fluid passageways extends radially through the heat exchanger and creates a fluid connection between the interior and exterior fluid containing regions. The heat exchanger also comprises first and second axially extending fluid passageways that traverse each of the arcuate fluid passageways and that are in fluid communication with each of the arcuate fluid cavities in a manner connecting the arcuate fluid cavities in parallel. The first axially extending fluid passageway is a first radial distance from the central axis and the second axially extending fluid passageway is a second radial distance from the central axis. The second radial distance is greater than the first radial distance.
In yet another aspect of the invention, a method of fabricating a heat exchanger comprises solid state welding a plurality of substantially identical first laminate members to a plurality of substantially identical second laminate members in a manner creating a bonded stack of the first and second laminate members comprised of alternating first and second laminate members. Each of the first laminate members comprises a bottom surface, a top surface, at least two pass-through passageways, and at least one recess. The recess of each of the plurality first laminate members extends down into such first laminate member from the top surface and extends from an edge of such first laminate member to an opposite edge of such first laminate member. Each of the pass-through passageways extends through such first laminate member from the top surface to the bottom surface of such first laminate member. Each of the second laminate members comprises a bottom surface, a top surface, at least two openings, and at least one recess. The recess of each of the second laminate members extends down into such second laminate member from the top surface of such second laminate member. Each of the openings of each of the second laminate members extends from the bottom surface and opens into the recess of such second laminate member in a manner such that said recess operatively joins said openings. Each of the pass-through passageways of each of the first laminate members operative connects at least one of the openings of an adjacent one of the second laminate members to the recess of another adjacent one of the second laminate members.
Further features and advantages of the present invention, as well as the operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
Reference numerals in the written specification and in the drawing figures indicate corresponding items.
A heat exchanger in accordance with the present invention is shown in
Each of the sub assemblies 12 preferably comprises an upper 14 end plate, a lower end plate 16, and a stack 18 of alternating first laminate members 20 and second laminate members 22. As discussed in greater detail below, these components are preferably formed of metal and are preferably diffusion bonded to each other (also referred to as diffusion welded).
The upper end plate 14 preferably has a polygonal arcuate outer edge 24 and a smooth arcuate inner edge 26. A plurality of mounting holes 28 are circumferential spaced along the inner edge 26 and the outer edge 24 and extend through the upper end plate 14. A plurality of oval fluid passageway openings 30 also extend through the upper end plate 14 and are circumferentially spaced adjacent the mounting holes 28 nearest the inner edge 26. A gasket groove 32 having a semicircular cross-section extends down into the upper end plate 14 from the top surface 34 of the upper end plate and encircles the fluid passageway openings 30. The bottom surface 36 of the upper end plate 14 is preferably a contiguous planar surface.
The lower end plate 16 is similar to the upper end plate and preferably comprises a polygonal arcuate outer edge 24, a smooth arcuate inner edge 26, a plurality of mounting holes 28 that are identical to those of the upper end plate 14. However, the fluid passageway openings 30 that extend through the lower end plate 16 are circumferentially spaced adjacent the mounting holes 28 nearest the outer edge 26 of the lower end plate and are preferably circular rather than oval. The total cross-sectional area of all the fluid passageway openings 30 of the lower end plate 16 is preferably appreciably greater than the total cross-sectional area of all of the fluid passageway openings of the upper end plate 14. Similar to the upper end plate 14, a gasket groove 32 having a semicircular cross-section extends upward into the lower end plate 16 from the bottom surface 36 of the lower end plate and encircles the fluid passageway openings 30. The top surface 34 of the lower end plate 16 is preferably a contiguous planar surface.
As mentioned above, the stack 18 laminate members comprises alternating first laminate members 20 and second laminate members 22. One of the first laminate members 20 is shown in
One of the second laminate members 22 is shown in
As mentioned above, each of the subassemblies 12 of the heat exchanger 10 is preferably assembled using a diffusion bonding technique. Although diffusion bonding can be a complicated process, the use of diffusion bonding renders the subassemblies 12 suitable for high temperature materials such as Nickel based alloys and titanium alloys and reduces the number of steps required to fabricate the subassemblies. Moreover, the inter-metallic bonds formed by diffusion bonding are superior to conventional brazed or welded bonds, reducing fatigue failure.
During the assembly process, the stack 18 of alternating first laminate members 20 and second laminate members 22 is created using one-hundred and sixty of each of the first laminate members and the second laminate members. To ensure that the laminate members are properly aligned with each other, alignment rods can be inserted through the tooling holes 56, 76 of the laminate members. The stack 18 is then sandwiched between the upper end plate 14 and the lower end plate 16 and the assembly is then diffusion bonded to secure the laminate members to each other and to the end plates. The diffusion bonding step bonds the top surface of each of the laminate members to the bottom surface of the laminate member directly above (except for the upper most laminate, which bonds to the bottom surface of the upper plate. The diamond shaped protrusions transfer the axial compressive load generated during the diffusion bonding process from each laminate member to the next, ensuring that the entire top surface of each laminate becomes bonded.
As assembled, the pass-through passageways 48 of the first laminate members 20 and the openings 68 of the second laminate members 22 form axial fluid passageways that extend from the top of the stack 18 to the bottom of the stack. These axial fluid passageways connect the recesses 60 of the second laminate members 22 in parallel. The fluid passageway openings 30 of the upper end plate 14 are aligned with the axial fluid passageways that are adjacent the inner radial edges 46, 66 of the first and second laminate members 20, 22. Similarly, the fluid passageway openings 30 of the lower end plate 16 are aligned with the axial fluid passageways that are adjacent the outer radial edges 44, 64 of the first and second laminate members 20, 22. The recesses 40 of the first laminate members 20 allow fluid to pass radially through the stack 18 of laminate members, without directly communicating with fluid in the recesses 60 of the second laminate members 22 or the fluid in the pass-through passageways 48 of the first laminate members.
It should be appreciated that the heat exchanger 10 is well suited for exchanging heat between two gaseous fluid streams. More particularly, the heat exchanger 10 is configured and adapted to serve as a recuperator for recovering heat energy from a stream of combustion exhaust gas and transferring such energy to a stream of combustion intake gas. In use, exhaust gas travels radially inward through the heat exchanger 10 from the region of space around the heat exchanger via the recesses 40 of the first laminate members 20 and is expelled into the region of space encircled by the heat exchanger. Simultaneously, intake gas is preferably drawn into the fluid passageway openings 30 of the upper end plate 14 and out the fluid passageway openings 30 of the lower end plate 16. As it does this, the intake gas is channeled radially outward through the recesses 60 of the second laminate members 22 from the axial fluid passageways adjacent the inner radial edges 46, 66 of the first and second laminate members 20, 22 and to the axial fluid passageways that are adjacent the outer radial edges 44, 64 of the first and second laminate members.
Due to the arcuate shape of the fluid passageways created by the recesses 40, 60 of the first and second laminate members 20, 22, the fluid passageways through which the exhaust gas travels narrow in cross-sectional area and the fluid passageways through which the intake gas travels expand in cross-sectional area. The narrowing of the fluid passageways through which the exhaust gas passes prevents the temperature of the exhaust gas from dropping as much as it would if the passageways maintained a constant cross-sectional area. Similarly, the expansion of the fluid passageways through which the intake gas passes prevents the temperature of the intake gas from increasing as much as it would if the passageways maintained a constant cross-sectional area. This increases the temperature differential between the exhaust gas and the intake gas throughout the heat exchanger and therefore increases the heat conducted through the laminate members from the exhaust gas to the intake gas. As a result, the stagnation temperature of the exhaust gas is actually reduced more than it otherwise would have reduced and the stagnation temperature of intake gas is increased beyond what it otherwise would have increased.
As the fluids pass through the heat exchanger, the diamond shaped protrusions provide tie the laminations to each other in a manner preventing appreciable material deformation that could otherwise result from pressure differences between the two fluids. The diamond shaped protrusions also improve the flow direction and mixing of each of fluid stream. Still further, the diamond shaped protrusions increase heat transfer coefficient by disrupting the laminar flow, which creates regions having undeveloped velocity profiles.
In view of the forgoing, it should be appreciated that the heat exchanger of the present invention provides a large amount of surface area for heat conduction per unit volume of the heat exchanger. Moreover, it should be appreciated that the heat exchanger of the present invention is highly efficient at transferring heat between two gaseous (i.e., compressible) fluid streams. Still further is should be appreciated that the method of manufacturing the heat exchanger is relatively simplistic and strait forward.
The assembly 80 just described is particularly well suited for use in connection with fuel cells and more particularly for separating steam for hydrogen as a mix of the same is cooled via the heat exchanger 10. This is done by passing vaporized steam and hydrogen mixture into the assembly 80 via the hot fluid inlet 90, while simultaneously passing cooler air or another cooler fluid into the assembly via the cooling fluid inlet 86 and out of the cooling fluid outlet 88. The vaporized steam and hydrogen mixture is thereby cooled as it passes through the heat exchanger 10 and into the region of space encircled by the heat exchanger. The cooling of the vaporized steam and hydrogen mixture causes the steam to condense and thereafter gravity causes the lighter hydrogen to move upward and out of the assembly via the hot fluid outlet 92, and causes the heavier liquid water to travel downward and out of the assembly via the condensed fluid outlet 94.
Another embodiment of the invention is shown in
During the assembly of the heatsink 100, a plurality of identical heatsinks are preferably from together. As shown in
In use, cooling fluid is passed into the fluid inlet 102. The cooling fluid then travels through the etched regions 116 of the laminates 108 and subsequently out of the fluid outlet 104. As such, heat conducted into the main body 106 of the heat sink 100 from an object being cooled is conducted and/or radiated into the cooling fluid and out of the heat sink.
As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.
It should also be understood that when introducing elements of the present invention in the claims or in the above description of the preferred embodiment of the invention, the terms “comprising,” “including,” and “having” are intended to be open-ended and mean that there may be additional elements other than the listed elements. Additionally, the term “portion” should be construed as meaning some or all of the item or element that it qualifies. Moreover, use of identifiers such as first, second, and third should not be construed in a manner imposing any relative position or time sequence between limitations. Still further, the order in which the steps of any method claim that follows are presented should not be construed in a manner limiting the order in which such steps must be performed.