Abstract:
A modular based heat sink which can be easily optimized for a given heat source relies upon both phase change based heat transfer and condenser modules that combine the efficiency of folded fin cooling and the efficiency of the two phase heat transfer.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to heat sinks for use in electronics, and more particularly to phase change based heat sinks. 
     BACKGROUND OF THE INVENTION 
     Single phase heat exchangers, such as “parallel flow” heat exchangers having multiple fluid conduits are described in U.S. Pat. No. 5,771,964. In such parallel flow heat exchangers, each tube is divided into a plurality of parallel flow paths of relatively small hydraulic diameter (e.g., 0.070 inch or less), which are often referred to as “microchannels”, to accommodate the flow of heat transfer fluid. Parallel flow heat exchangers may be of the “tube and fin” type in which flat tubes are laced through a plurality of heat transfer enhancing fins or of the “folded fin” type in which folded fins are coupled between the flat tubes. These types of heat exchangers have been used as cooling condensers in applications where space is at a premium. U.S. Pat. Nos. 6,347,662; 6,325,141; 5,865,243; and 5,689,881 further describe such heat exchangers having multiple conduits that serve as condensers. 
     The prior art associated with the cooling of computer chips and electronic components has utilized heat sinks of several basic types. Metal extrusions such as aluminum heat sinks have been used since the early days of computers when power densities were relatively low. These well known heat sinks have the disadvantage of low thermal performance (slow heat transfer), particularly when applied to systems operating at the high power density conditions of today&#39;s electronic devices and systems. 
     A second type of thermal management structure includes metal extrusions in combination with bases made formed from high thermal conductivity materials, such as copper or engineered materials or, even flat heat pipes. While addressing the heat spreading problem of metal extrusions, this type of heat sink still relies, in part, upon heat conduction through extended fins to external surfaces. Current extrusion techniques do not easily produce fins at the pitch and height required for high performance applications. 
     A third type of thermal management structure is a tower heat sink. Tower heat sinks often have a high conductivity core that is made of solid metal or heat pipes. Plate fins or machined structures surround the core to provide extended heat transfer surfaces. Heat is transferred upward through the core, then across the extended surfaces to be dissipated to the ambient environment. Assembly of plate fins to the core often requires manual labor which is expensive and sometimes yields inconsistent quality. 
     As a consequence, there continues to be a need for an improved heat sink for cooling electronic devices that satisfactorily meet today&#39;s high power density requirements while providing manufacturing flexibility. 
     SUMMARY OF THE INVENTION 
     The present invention provides a modular heat sink that has a modular construction comprising a heat sink module and one or more condenser modules. In one preferred embodiment, a modular heat sink is provided including an evaporator chamber defined between a base and a first plate. The base has a wick disposed on an interior facing surface so as to be located within the evaporator chamber. The wick is spaced away from an interior facing surface of the first plate, and is at times saturated with a two-phase vaporizable fluid. The first plate defines a pair of spaced apart openings that communicate with the evaporator chamber. A pair of conduits, one positioned within each of the first plate openings, each have a passageway arranged in fluid flow communication with the evaporator chamber. A condenser chamber is defined between a second plate and a third plate. The second plate defines a pair of spaced apart second openings that communicate with a respective one of the conduits so as to allow for cyclic fluid flow communication between the evaporator chamber and the condenser chamber. The third plate is disposed in spaced apart confronting relation to the second plate. Advantageously, the first plate and the second plate are spaced apart from one another so as to form a void between them and between the pair of conduits so that a folded fin may be positioned within the void to improve heat transfer. A plurality of modules may be stacked together, as needed, to provide improved heat transfer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will be more fully disclosed in, or rendered obvious by, the following detailed description of the preferred embodiments of the invention, which are to be considered together with the accompanying drawings wherein like numbers refer to like parts and further wherein: 
         FIG. 1  is a perspective view of a modular heat sink formed in accordance with one embodiment of the invention; 
         FIG. 2  is an exploded perspective view of the modular heat sink shown in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of a modular heat sink, as taken along lines  3 - 3  in  FIG. 1 ; 
         FIG. 4  is a perspective view of an eight module stacked heat sink formed according to one embodiment of the present invention; 
         FIG. 5  is an exploded perspective view of a first module of the stacked modular heat sink shown in  FIG. 4 ; 
         FIG. 6  is a cross-sectional view, similar to that of  FIG. 3 , of a first module in the stacked modular heat sink shown in  FIG. 4 ; 
         FIG. 7  is a cross-sectional view of a portion of three stack modular heat sink arranged in accordance with an embodiment of the invention; and 
         FIG. 8  is a cross-sectional view of another embodiment of a module having a center separator plate. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     This description of preferred embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. The drawing figures are not necessarily to scale and certain features of the invention may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness. In the description, relative terms such as “horizontal,” “vertical,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms including “inwardly” versus “outwardly,” “longitudinal” versus “lateral” and the like are to be interpreted relative to one another or relative to an axis of elongation, or an axis or center of rotation, as appropriate. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. The term “operatively connected” is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship. In the claims, means-plus-function clauses are intended to cover the structures described, suggested, or rendered obvious by the written description or drawings for performing the recited function, including not only structural equivalents but also equivalent structures. 
     Referring to  FIGS. 1-3 , a modular heat sink  1  formed according to one embodiment of the invention provides a single module  5  that includes a base plate  10 , a first spacer  20 , a first separator plate  25 , two conduits  30 , a folded fin core  33 , a second separator plate  35 , a second spacer  40 , and a top plate  45 . Base plate  10  includes an inner surface  47 , and is often formed as a rectangular sheet of thermally conductive material, such as copper, molybdenum, aluminum, or the like metal alloys, or thermally conductive composite structures. Inner surface  47  is often coated with a wick  55 , such as a sintered or brazed porous metal, screen, or felt layer of the type known in the art. When a module  5  is fully assembled, a working fluid saturates wick  55 . The working fluid may be selected from any of the well know two phase vaporizable liquids, e.g., water, alcohol, freon, methanol, acetone, fluorocarbons or other hydrocarbons, etc. 
     First spacer  20  comprises a thermally conductive frame formed from a pair of spaced-apart lateral rails  60  and a pair of spaced-apart longitudinal rails  65  that together define a central opening  67 . First spacer  20  often has a rectangular shape that complements base  10 . Lateral rails  60  and longitudinal rails  65  have a similar width and thickness. First separator plate  25  comprises a sheet of thermally conductive material having a central surface  69  located between spaced-apart lateral openings  70  that are defined adjacent to the lateral side edges of the sheet. Each opening  70  is defined by a lateral rail  75  and spaced-apart longitudinal rails  80  that together define an elongate opening. The size and shape of first separator plate  25  is substantially the same as the size and shape of first spacer  20 . 
     Conduits  30  each comprise an open ended tube, often having an ellipsoidal or rectangular cross-sectional shape, with an outer surface  35 . Each conduit  30  is formed from a thermally conductive material, such as copper, molybdenum, aluminum, or the like metal alloys, or thermally conductive composite structures, and has a shape and size that is substantially the same as the shape and size of lateral openings  70  of first separator plate  25 . 
     Folded fin core  33  may be formed from a continuous sheet of thermally conductive material, that has been folded into alternating flat ridges  100  and troughs  105 . In aggregate, flat ridges  100  combine to define two substantially planar outwardly directed faces  108  at the top and bottom of folded fin core  33 . Flat ridges  100  and troughs  105  define spaced fin walls  110 , with the end most walls comprising two external side walls  115 . Folded fin core  33  also defines two end edges  120  that follow the contour defined by flat ridges  100  and troughs  105 . 
     Second separator plate  35  has a structure similar to that of first separator plate  25 . In particular, second separator plate  35  comprises a sheet of thermally conductive material having a central surface  125  located between spaced apart lateral openings  140  defined adjacent to the lateral side edges of the sheet. Each opening  140  is defined by a lateral rail  145  and spaced-apart longitudinal rails  148 . The size and shape of second separator plate  35  is substantially the same as the size and shape of first separator plate  25 . Second spacer  40  has a structure similar to that of first spacer plate  20 . Second spacer  40  comprises a thermally conductive frame formed from a pair of spaced-apart lateral rails  160  and a pair of spaced-apart longitudinal rails  165  that together define a central opening  167 . Second spacer  20  often has a rectangular shape that is substantially similar to base  10 . Lateral rails  160  and longitudinal rails  165  have a similar width and thickness to one another. When only a single module is to be formed, a top plate  45  is provided that is similar to base  10  in that it is often formed as a rectangular sheet of thermally conductive material, such as copper, molybdenum, aluminum, or like metal alloys or thermally conductive composite structures. 
     A single module  5  that may form a portion of a modular heat sink  1  is assembled in the following manner. Base  10  is first positioned on a flat surface such that wick  55  is exposed on upwardly facing inner surface  47 . Spacer  20  is then circumferentially positioned on a peripheral edge surface of base  10  so as to encircle a preponderance of wick  55 . First separator plate  25  is then positioned atop first spacer  20  such that lateral rails  75  and longitudinal rails  80  lie atop corresponding portions of first spacer  20  with central surface  69  facing upwardly. Conduits  30  are positioned within openings  70  of first separator plate  25  so as to project upwardly. Conduits  30 , first separator plate  25  and first spacer  20  together define a void space  180  ( FIG. 3 ) separating the lower edge of conduit  30  from the top surface of wick  55  on base  10 . With conduits  30  positioned within first separator  25 , folded fin core  33  is positioned between conduits  30  so that a bottom face  108  of folded fin core  33  is arranged with the outer surfaces of flat ridges  100  in engaged thermal communication with central surface  69  of first separator  25 . In this arrangement, external side walls  115  thermally engage the interior portion of outer surface  35  of each conduit  30 . Thus, folded fin core  33  is arranged within module  5  so as to be in thermal conduction communication with first separator plate  25  and conduits  30 . 
     Once folded fin core  33  is secured between conduits  30  and first separator plate  25 , second separator plate  35  is positioned on the top face  108  of folded fin core  33 . In this position, the top edges of each conduit  30  are positioned within lateral openings  140  of second separator plate  35  and secured in position. Second spacer  40  is then positioned atop second separator plate  35  so that lateral rails  160  and longitudinal rails  165  rest atop lateral rails  145  and longitudinal rails  148  of second separator plate  35 , respectively, and with central surface  125  facing upwardly. Top plate  45  is then positioned over second spacer  40  and fastened along a circumferential peripheral edge surface to rails  160 ,  165  of spacer  40 . During the foregoing assembly, each of the individual parts may be fastened to one another by any one of a number of known fixation methods, including welding, brazing, soldering, or through the use of thermal epoxies. 
     Referring to  FIG. 3 , upon full assembly of module  5  a closed loop fluid flow path  182  is formed in which an evaporation chamber  183  is defined between base  10  and first separator plate  25  and a condensation chamber  185  is formed between top plate  45  and second separator  35 . Evaporation chamber  183  and condensation chamber  185  are arranged in fluid communication with one another via conduits  30 . Wick  55  is disposed within evaporation chamber  183 , and is saturated with a two-phase working fluid. 
     In operation, a heat source (not shown) thermally engages an external surface of base  10 . The heat generated by the heat source is transferred through base  10  by conduction and thereby vaporizes the working fluid saturating wick  55  within evaporation chamber  183 . The working fluid vapor flows through conduits  30  and into condensation chamber  185 . At the same time, air flows through folded fin core  33  provides convective heat transfer through spaced fin walls  110 , which in-turn cools the corresponding separator plates  25 ,  35  and conduits  30 . The working fluid condenses substantially within condensation chamber  185  and flows back to evaporation chamber  183  so as to resaturate wick  55  on base  10 , thus completing a two-phase heat transfer cycle. 
     Depending upon the power requirements of the heat source, multiple cooling modules  5   a - h  may be stacked for optimum efficiency of modular heat sink  1  ( FIG. 4 ). In a multiple module embodiment of the present invention, a third separator plate  190  is positioned atop second spacer  40  ( FIG. 5 ). Third separator plate  190  has a structure similar to that of first and second separator plates  25 ,  35 . In particular, third separator plate  190  comprises a sheet of thermally conductive material having a central surface  191  located between spaced apart lateral openings  192  defined adjacent to the lateral side edges of the sheet. Each opening  192  is defined by a lateral rail  195  and spaced-apart longitudinal rails  198 . The size and shape of third separator plate  190  is substantially the same as the size and shape of first and second separator plates  25 ,  35  ( FIG. 5 ). A third spacer has a structure similar to that of first and second spacers  20 ,  40 . 
     A second pair of conduits  30  are positioned within openings  192  of third separator plate  190  so as to project upwardly. Second separator plate  35  and third separator plate  190  together define a void condenser space separating lower module  5   a  from upper module  5   b . With the second pair of conduits  30  positioned within third separator plate  190 , a second folded fin core  213  is positioned between second pair of conduits  30  so that its bottom face  108  is arranged with the outer surfaces of flat ridges  100  in thermal communication with central surface  191  of third separator  190 . Once again, external side walls  115  thermally engage the interior portion of outer surface  35  of each conduit  30 . Thus, the second folded fin core  213  is arranged within second module  5   b  so as to be in thermal conduction communication with third separator plate  190  and second pair of conduits  30 . The foregoing assembly may be repeated by adding additional separator plates, conduits, and folded fin cores until a complete stack is formed ( FIGS. 4 ,  5 , and  7 ). 
     Referring to  FIGS. 4 and 7 , upon full assembly of a stacked module closed loop fluid flow path  182  opens through one or more intermediate flow chambers  220  with evaporation chamber  183  being arranged in fluid communication with a plurality of flow chambers  220 , via pairs of conduits  30 . If additional vapor flow is required, a through opening  225  may be formed in an intermediate separator plate  227  ( FIG. 8 ). 
     It is to be understood that the present invention is by no means limited only to the particular constructions herein disclosed and shown in the drawings, but also comprises any modifications or equivalents within the scope of the claims.