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:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority under 35 USC § 119(e) to U.S. patent application Ser. No. 60/282,170, filed on Apr. 9, 2001, the entire contents of which are incorporated by reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    This invention relates to a laminated heat transfer device for cooling or thermal energy transport applications.  
         BACKGROUND  
         [0003]    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.  
           [0004]    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&#39;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.  
           [0005]    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.  
           [0006]    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  
         [0007]    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.  
           [0008]    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.  
           [0009]    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.  
           [0010]    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.  
           [0011]    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.  
           [0012]    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.  
           [0013]    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  
       [0014]    Exemplary implementations are depicted in the attached figures, in which:  
         [0015]    [0015]FIG. 1 a  illustrates an implementation of a laminated ducting-type heat sink;  
         [0016]    [0016]FIG. 1 b  is an exploded perspective view of the individual lamina of FIG. 1 a;    
         [0017]    [0017]FIG. 1 c  shows illustrates an implementation of a laminated ducting-type heat sink with cross-linkages;  
         [0018]    [0018]FIG. 2 a  illustrates a laminated porous-type heat sink with an integrated base;  
         [0019]    [0019]FIG. 2 b  is a cross-sectional view of the porous structure of FIG. 2 a;    
         [0020]    [0020]FIG. 2 c  is an exploded perspective view of the individual lamina of FIG. 2 a;    
         [0021]    [0021]FIG. 2 d  is another exploded perspective view of the individual lamina of FIG. 2 a;    
         [0022]    [0022]FIG. 2 e  is another exploded perspective view of the individual lamina of a porous-type heat sink with varying pores;  
         [0023]    [0023]FIG. 3 a  illustrates an implementation of a laminated ducting-type heat sink for natural convection applications;  
         [0024]    [0024]FIG. 3 b  is an exploded perspective view of the individual lamina of FIG. 3 a;    
         [0025]    [0025]FIG. 4 a  illustrates a laminated heat-pipe;  
         [0026]    [0026]FIG. 4 b  is an exploded perspective view of the individual lamina of the laminated heat-pipe with an integrated wicking structure;  
         [0027]    [0027]FIG. 4 c  is another exploded perspective view of the laminated heat-pipe with another integrated wicking structure;  
         [0028]    [0028]FIG. 4 d  is a close-up view of laminae of the heat-pipe with a wicking structure;  
         [0029]    [0029]FIG. 5 a  illustrates a laminated split-body Peltier device;  
         [0030]    [0030]FIG. 5 b  is an exploded perspective view of the individual lamina of the device of FIG. 5 a;    
         [0031]    [0031]FIG. 6 a  illustrates an implementation of a porous heat sink with an integrated heat-pipe; and  
         [0032]    [0032]FIG. 6 b  illustrates an implementation of a split-body Peltier device with an integrated heat-pipe. 
     
    
       [0033]    Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0034]    [0034]FIG. 1 a  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.  
         [0035]    [0035]FIG. 1 b  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.  
         [0036]    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.  
         [0037]    Another implementation of the laminated ducting-type heat sink includes cross-linkages between the guiding vanes. As shown in FIG. 1 c,  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.  
         [0038]    [0038]FIG. 2 a  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. 2 b,  the porous structure allows the working fluid to pass through in three directions. As shown in FIG. 2 c,  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. 2 d ). 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. 2 e ). 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.  
         [0039]    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. 3 b.  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).  
         [0040]    Another implementation is the laminated heat-pipe shown in FIG. 4 a.  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. 4 b ). 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.  
         [0041]    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. 4 c  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. 4 d,  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.  
         [0042]    [0042]FIG. 5 a  shows another implementation called a laminated split-body Peltier device. This device  500  includes laminae  510  containing thermoelectric 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.  
         [0043]    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.  
         [0044]    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. 6 a,  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. 6 b ).  
         [0045]    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.