WO2002082536A2

WO2002082536A2 - Laminated heat transfer device and method of producing thereof

Info

Publication number: WO2002082536A2
Application number: PCT/GB2002/001657
Authority: WO
Inventors: Chun Hung Samuel IP; Wing Ming Siu
Original assignee: Piesold, Alexander, James
Priority date: 2001-04-09
Filing date: 2002-04-09
Publication date: 2002-10-17
Also published as: US20020144809A1; WO2002082536A3; TW531632B

Abstract

A laminated heat transfer device for cooling or thermal energy transport applications and a method of manufacture thereof. In various implementations, the laminated heat transfer device provides complex duct channels for efficient cooling. The various implementations are compatible and integrateable with each other. The method of producing a laminated heat transfer device includes specifying a three-dimensional structure as a plurality of laminae, producing the laminae from sheets of working material, stacking the laminae according to a predetermined sequence with a guiding structure, and connecting the laminae.

Description

LAMINATED HEAT TRANSFER DEVICE AND METHOD OF PRODUCING THEREOF

TECHNICAL FIELD

This invention relates to a laminated heat transfer device for cooling or thermal energy transport applications.

BACKGROUND

Heat is a by-product of electronic systems and the efficient removal of heat is key to preventing failure of electronics. For electronics, the most common methods of heat removal are of heat sinks, heat-pipes, and Peltier devices. Heat sinks (also known as heat-fins) are conduction-convection devices that remove heat by conducting heat away from a given source and then rejecting the heat into a working fluid through convection. A heat sink balances the conduction and the convection processes so that the conduction resistance is not too large, while the convection resistance is small. In general, the conduction resistance will increase as the fin's design is changed to yield a smaller convection resistance. Heat sinks can be either a ducting type or a porous type. A ducting-type heat sink channels the flow from a source so that the fluid flows over a maximum area of the heat sink. This is particularly important, for example, where the size of the heat sink is larger than the fan, and without the channeling function, less surface undergoes forced-convective cooling. In contrast, a porous-type heat sink does not channel the flow, but instead allows the fluid to flow through from three directions. One example is porous metallic foam, where the fluid flow can come from any of the three orthogonal directions, and as such, these heat sinks are useful in situations where the flow area is larger than the heat sink. A heat-pipe is a heat-transfer device that relies on the evaporation and condensation of a working liquid. Normally, the liquid evaporates from the hot-side (called evaporator side) and travels as a vapor to the cold-side where it condenses back into liquid (called condenser side). The liquid must then be carried back to the evaporator side so that the cycle can start anew, which is typically done by using a porous wick and the capillary action of the liquid. As the heat of vaporization is typically very large, the heat-pipe is generally capable of a relatively large heat transfer rate. Indeed, heat-flux as high as 20 W/sq-cm has been reported for complex wicking structures.

A Peltier device is a thermoelectric device where heat is absorbed and rejected as an electric current flows through dissimilar conductors. Current Peltier devices have thermal back-diffusion.

SUMMARY

A laminated heat transfer device maybe a laminated ducting-type heat sink, a laminated porous-type heat sink with an integrated base, a laminated heat-pipe, a laminated split-body Peltier device, or any combination of these. A laminated ducting-type heat sink includes ducting channels to allow for efficient air-flow. In one implementation, naturally convecting heat sinks include chimneys with varying cross-sectional areas for flow-acceleration to provide fanless solutions. In another implementation, a ducting-type heat sink includes cross-linkages to better utilize the spaces between the guiding vanes. This device is a cost-effective alternative to complex heat sinks, such as the radially ducting type. Additionally, this device is compatible and integrateable with the laminated heat-pipe and/or laminated split-body Peltier devices, described below.

A laminated porous-type heat sink contains an integrated base structure, which minimizes the contact resistance. The depth of the base and its footprint can be changed to suit the specific thermal requirement. This device accommodates a spatially varying porous structure to better balance the convective and conductive thermal resistances. This device is also compatible and integrateable with the laminated heat-pipe and/or laminated split-body Peltier devices, described below.

A laminated heat-pipe provides a low-cost heat-pipe solution. This laminated heat-pipe can be made in different sizes and can have different wicking structures without using a sintering process. The wicking structure is an integral part of the overall heat-pipe to minimize thermal resistances, by stacking multiple laminae such that the final product is a hollow enclosure with the wicking structure coming from either the stacking arrangement of the laminae and/or by using perforated laminae. This device is compatible and integrateable with the laminated heat sinks and/or the laminated split-body Peltier devices. A laminated split-body Peltier device is a low-cost vehicle to implement a split-body Peltier device. This implementation stacks multiple laminae such that each layer is an electrically conducting element consisting of P-type and N-type materials. This device is also compatible and integrateable with the laminated heat sinks and/or the laminated heat-pipe.

A method to produce the different implementations of a laminated heat transfer device is also provided. The method includes: designing a three-dimensional structure into series of planar elements (laminae), which may or may not be self- repeating depending on the three-dimensional requirements; producing the laminae from sheets of working material by stamping, punching, etching, cutting, plating or other material forming process that are known in the art; stacking the laminae together according to a predetermined sequence; and functionally connecting the parts of each lamina by diffusive bonding, welding, weaving, plating, bonding with inter- connective material, or any inter-connective method, or combination of inter- connective method and material forming process, or any combination thereof.

Alternatively, the laminae can be formed from laminated working materials. The stacking process is accomplished with the usage of a guiding structure, which may or may not be integrated with the final product. The attachment process is accomplished through thermal, pressure, sonic, chemical driven process, or any combination thereof. The attachment process may also involve additional interfacial material, and may occur at the same time or after the stacking of some or all laminae.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

Exemplary implementations are depicted in the attached figures, in which:

Fig. la illustrates an implementation of a laminated ducting-type heat sink;

Fig. lb is an exploded perspective view of the individual lamina of Fig. la;

Fig. lc shows illustrates an implementation of a laminated ducting-type heat sink with cross-linkages;

Fig. 2a illustrates a laminated porous-type heat sink with an integrated base; Fig. 2b is a cross-sectional view of the porous structure of Fig. 2a;

Fig. 2c is an exploded perspective view of the individual lamina of Fig. 2a;

Fig. 2d is another exploded perspective view of the individual lamina of Fig. 2a; Fig. 2e is another exploded perspective view of the individual lamina of a porous-type heat sink with varying pores;

Fig. 3a illustrates an implementation of a laminated ducting-type heat sink for natural convection applications;

Fig. 3b is an exploded perspective view of the individual lamina of Fig. 3 a; Fig. 4a illustrates a laminated heat-pipe;

Fig. 4b is an exploded perspective view of the individual lamina of the laminated heat-pipe with an integrated wicking structure;

Fig. 4c is another exploded perspective view of the laminated heat-pipe with another integrated wicking structure; Fig. 4d is a close-up view of laminae of the heat-pipe with a wicking structure;

Fig. 5a illustrates a laminated split-body Peltier device;

Fig. 5b is an exploded perspective view of the individual lamina of the device of Fig. 5 a;

Fig. 6a illustrates an implementation of a porous heat sink with an integrated heat-pipe; and

Fig. 6b illustrates an implementation of a split-body Peltier device with an integrated heat-pipe.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION Fig. la illustrates an implementation of a laminated ducting-type heat sink

100. Alternatively, the heat sink could have a spiral- vane configuration. The heat sink 100 includes a base 110 and the vanes 130. The base 110 conducts heat from the source (not shown), such as an electronic device, to the vanes 130. The base 110 is made out of thermally-conductive materials, such as copper, and its thickness is a function of the applied heat-flux and the airflow over the vanes. In general, the larger the applied heat-flux, the thicker the base needs to be in order to assure that the heat spreads over most of the base. Typically, the base 110 is approximately 5 mm.

Fig. lb shows two guiding rods 111, which are functionally attached to the base 110 through interference fitting, chemical bonding, soldering, brazing, or any other similar techniques known in the art. The guiding rods 111 are made of metals or polymers, and guide the stacking of the laminae 120 through the guiding holes 121. Each lamina has fins 122 and a conduction core 123, so that the heat conducts from the base 110 through the conduction core 123 toward the fins 122. As the conduction core 123 reduces the overall thermal resistance, its diameter needs to be sufficiently large to enable the heat to effectively from the base 110 to the top-most lamina with minimal resistance. While the exact diameter will depend on the flow rate impinging on the structure, the diameter of the conduction core 123 is generally between 5 and 20 mm. The fins 122 eject heat into the working fluid. The width of the fins is in the range of 0.5 to 2 mm. The base of the fins 122 may touch at the conduction core 123 or may be spaced apart. In addition to ejecting heat, the fins 122 of the laminae 120 form the vanes 130 of the final product 100 to provide radial ducting of the working fluid. The laminae 120 may be identical in shape or different depending on the requirement of the final product 100. Each lamina 120 is a thermal conductor and should preferably be made out of metal. The laminae 120 can be obtained by stamping, punching, etching, and/or plating processes from sheets of working materials. The thickness of each lamina is determined by the lamina production process. For example, a stamping process is applied for copper material with a thickness of approximately 1 mm or less. However, the thinner the working material is, the larger the number of laminae to complete one product. The balance between tool-life, production rate, and product quality is an operational issue determined on the production floor. The laminae 120 are stacked and functionally joined together to yield the final product 100. The joining between the laminae 120 and with the base 110 can be accomplished with soldering, brazing, welding, plating, chemical bonding, diffusion bonding, or any similar process known in the art. The stacking process can be performed through the aforementioned guiding rods 111 or through an appropriate alignment fixture (not shown). Furthermore, the stacking and joining can be accomplished in one or multiple processes.

Another implementation of the laminated ducting-type heat sink includes cross-linkages between the guiding vanes. As shown in Fig. lc, laminae 140 with cross-linkages 141 are introduced periodically to render a structure that effectively utilizes the space between the guiding vanes. These cross-linkages 141 increase the number of heat conduction paths and the amount of convective surface area.

Fig. 2a illustrates a laminated porous-type heat sink with an integrated base. This heat sink 200 includes a base 210 and a porous structure 220. As shown in Fig. 2b, the porous structure allows the working fluid to pass through in three directions. As shown in Fig. 2c, this is obtained by stacking together primary laminae 221 and secondary laminae 222 having different opening designs, so that the base 210 is formed as an integral part of the assembly 200. Alternatively, the primary and secondary laminae 221, 222 can be stacked perpendicular to the base (Fig. 2d). The openings in the laminae are rectangular, but can be oval, circular, or any other convenient shape. In addition, the openings on the individual laminae can be non- uniform in space in order to render a final heat sink with spatially varying porosity (Fig. 2e). This configuration allows optimization of the heat-conduction path relative to the fluid flow. In general, the thickness, materials and process of stacking and joining the laminae are similar to those described above.

One alternative, shown in Fig. 3 a, is a laminated ducting-type heat sink 300 for natural convection applications. This heat sink 300 includes a base 310, an air intake 320, a converging duct 330, guiding vanes 340 and a conduction rod 350. In operation, a heat source (not shown) is applied to the bottom of the base 310, which conducts the heat to the guiding vanes 340 and the conduction rod 350. This conduction rod 350 should be sufficiently large in diameter to allow heat to conduct upwards, but sufficiently small to yield a large surface area to volume ratio. In general, the conduction rod 350 is approximately 3 to 5 mm in diameter, and this rod may be straight or ribbed (not shown) in order to maximize the heat transfer efficiency to the surrounding air. The conduction rod 350 is situated directly above the heat-source so most of the heat will travel up this conduction rod 350 and to the adjacent air, which then rises due to the buoyancy force. As the air rises, it is accelerated by the converging duct 330, which then entrains air at the intake 320 by creating a low-pressure condition. The guiding vanes 340 serve the dual purpose of radially directing air inward, while conducting heat from the base 310 to the converging duct 330, which further heats the air and increases the flow-rate within. The converging duct 330 should be a thermally conducting material, preferably a metal, such as copper or aluminum. In addition, a fan (not shown) can be placed on top of the heat sink to provide forced convective cooling, in which case, the guiding vanes 340 also serve the function of heat fins. As described above, the heat sink 300 is obtained by stacking and joining together the inlet laminae 321 and the duct laminae 331 shown in Fig. 3b. By stacking together the inlet laminae 321, the air intake 320 and the guiding vanes 340 are created, and above these inlet laminae 321, the duct laminae 331 are stacked and functionally joined to render the converging duct structure 330. In general, the thickness, materials and process of stacking and joining the laminae are similar to those described above, with the exception that the duct laminae 331 need to be sufficiently thin to render a smooth curvature. In general, these laminae are approximately 0.5 mm in thickness, although thicker laminae can be accommodated by the appropriate use of chamfers. As before, the stacking process can be performed through guiding rods 311 or through an appropriate alignment fixture (not shown).

Another implementation is the laminated heat-pipe shown in Fig. 4a. This heat-pipe 400 includes alternately stacked primary 410 and secondary 420 laminae, and is terminated at the two ends by the end plates 430. Both the primary and secondary laminae 410, 420 have central openings, and thus rendering these laminae, rings. The openings may be rectangular, circular, oval, or any other convenient shape, and the amount of material remaining in the laminae 411, 421 should be sufficient to enable sealing between the laminae. In addition, the openings on the primary and secondary laminae 410, 420 are slightly different in size (approximately 0.2 to 1 mm) so that capillary grooves 440 are formed when the laminae are stacked together (Fig. 4b). These capillary grooves 440 function as the wick and circulate condensed liquid in the in-plane direction. The whole unit is sealed by functionally joining the two laminae 410, 420 along with the end plates 430. The sealing can be done after, during or before the heat-pipe is charged with liquid, and in the case of the latter, a valve (not shown) would be needed on the end plate. The sealing process can be a pressure and/or temperature activated process involving brazing, soldering, welding, chemical bonding, diffusion bonding or any other similar methods known in the art.

To further improve on the circulation process, the primary and secondary laminae 410, 420 are perforated 412, 422 so that when the laminae are stacked together, these perforations 412, 422 form capillary channels 450 across the laminae and toward the two end plates 430. This is shown in Fig. 4c where the two additional plates 460 with slits are added before the end plates 430 to complete the capillary circuits. The capillary channels 450 should be sufficiently small to enable flow, but not too small to prevent the accurate alignment between the laminae. In general, these channels are approximately 0.1 to 0.5 mm in diameter. In addition, the perforations, as shown in Fig. 4d, can be increased to further increase the capillary action. Finally, the thickness, materials and process of stacking and joining the laminae are similar to those described in the above implementation.

Fig. 5 a shows another implementation called a laminated split-body Peltier device. This device 500 includes laminae 510 containing thermo-electric junctions, such that one group of junctions 511 is functionally attached to the base 520, while the second group of junctions 512 is thermally isolated by distance to render a split- body configuration. In operation, the group 512 at the top is the hot junction, while the group 511 at the base is the cold junction. Attachment to the base can be accomplished by a chemical agent (curable adhesive), diffusive bonding, welding, soldering or any similar methods known in the art. The base 515 should be a thermal conductor and electrically insulated from the laminae 510 through oxides or polymers (not shown). Each lamina is approximately 0.2 to 2 mm thick and is formed from a N-type and a P-type of materials in a "Z" shape, obtained from sheets of dissimilar electrical conductors (metallic or polymeric) through stamping, etching, plating, and/or punching. The junctions 511, 512 are formed by functionally joining together the P-type 513 and N-type 514 materials through welding, plating, soldering, diffusive bonding, and/or any other similar methods that are known in the art.

With the exception of the two ends 516, each individual lamina is electrically insulated by using an oxide or a polymer coating (not shown) and are stacked/joined together similar to the methods discussed for the first embodiment. The two ends 516 of each lamina are not insulated to enable electric current to pass through after the laminae are joined together. Two basic stacking arrangements are possible depending on whether the individual lamina is electrically connected in series or parallel. Electrical wires 517 are then functionally attached to the two ends 516 for connection with an external power source.

The devices shown in Figs. 1-5 can be combined together in different ways to suit the final performance target. For example, as shown in Figs. 6a, the laminated heat sink and the laminated heat-pipe can be produced together as one integral unit. Alternatively, the laminated heat-pipe and the laminated split-body Peltier device can be produced together using the same process (Fig. 6b).

A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other implementations are within the scope of the following claims.

Claims

CLAIMS:

1. A laminated heat transfer device, comprising a base; and a vane formed from a plurality of laminae, each lamina having a plurality of fins and a conduction core, wherein the laminae are stacked together according to a predetermined sequence.

2. A laminated heat transfer device as claimed in claim 1, further comprising: at least one guide rod to guide the stacking of laminae.

3. A laminated heat transfer device as claimed in claim 1, further comprising: an alignment fixture to guide the stacking of laminae.

4. A laminated heat transfer device as claimed in claim 1, 2 or 3, wherein the laminae are of equal size or varying size.

5. A laminated heat transfer device as claimed in any of claims 1 to 4, wherein the laminae are shaped like spokes of a wheel.

6. A laminated heat transfer device as claimed in any of claims 1 to 4, wherein at least one of the laminae is shaped like a web.

7. A laminated heat transfer device as claimed in any preceding claim, wherein the fins of the heat sink form a spiral.

8. A laminated heat transfer device as claimed in any preceding claim, wherein the heat sink is a ducting-type heat sink.

9. A laminated heat transfer device, comprising a base; and a porous structure formed from a plurality of first and second laminae, each lamina having a plurality of shaped openings, wherein the laminae are stacked together according to a predetermined sequence.

10. A laminated heat transfer device as claimed in claim 9, wherein the first and second lammae are alternately stacked and wherein the laminae are stacked horizontally or vertically.

11. A laminated heat transfer device as claimed in claim 9 or 10, wherein the shaped openings of each laminae are uniformly spaced or non-uniformly spaced.

12. A laminated heat transfer device as claimed in claim 9, 10 or 11 , wherein the shaped openings of each laminae are uniformly sized or non-uniformly sized.

13. A laminated heat transfer device as claimed in any of claims 9 to 12, wherein the shaped openings of each laminae comprise the shapes of a rectangle, an oval, or a circle.

14. A laminated heat transfer device as claimed in any of claims 9 to 13, wherein the laminae are of equal size or varying size.

15. A laminated heat transfer device as claimed in any of claims 9 to 14, wherein the laminated heat transfer device is a heat sink.

16. A laminated heat transfer device as claimed in claim 15, wherein the heat sink is a porous-type heat sink.

17. A laminated heat transfer device as claimed in claim 9, further comprising: two end plates, and wherein the openings of the primary and secondary laminae are different sizes in order to form capillary grooves when the laminae are stacked together.

18. A laminated heat transfer device as claimed in claim 17, wherein the primary and secondary laminae are perforated so that the perforations form capillary channels across the laminae toward the end plates when the laminae are stacked together.

19. A laminated heat transfer device as claimed in claim 17 or 18, further comprising: two plates, each plate being formed with a plurality of slits and positioned before the respective end plate.

20. A laminated heat transfer device as claimed in claim 17, 18 or 19, wherein the laminated heat transfer device is a heat pipe.

21. A laminated heat transfer device, comprising a base; and a plurality of laminae formed with thermo-electric junctions, wherein a first group of laminae are attached to the base and a second group of laminae are thermally isolated, and the laminae are stacked together according to a predetermined sequence.

22. A laminated heat transfer device as claimed in claim 21 , wherein the laminated heat transfer device is a split-body Peltier device.

23. A laminated heat transfer device, comprising the laminated heat transfer device as claimed in claim 1 formed integrally with the laminated heat transfer device as claimed in claim 17.

24. A laminated heat transfer device, comprising the laminated heat transfer device as claimed in claim 9 formed integrally with the laminated heat transfer device as claimed in claim 17.

25. A laminated heat transfer device, comprising the laminated heat transfer device as claimed in claim 17 formed integrally with the laminated heat transfer device as claimed in claim 21.

26. A method of producing a laminated heat device, comprising specifying a three-dimensional structure as a plurality of laminae; producing the laminae from sheets of working material; stacking the laminae according to a predetermined sequence with a guiding structure; and connecting the laminae.

27. A method of producing a laminated heat transfer device of claim 26, wherein the laminated heat transfer device is a heat sink.

28. A method of producing a laminated heat transfer device of claim 26, wherein the laminated heat transfer device is a heat pipe.

29. A method of producing a laminated heat transfer device of claim 26, wherein the laminated heat.