Abstract:
A fluid heat exchanger unit cools an electronic device with a cooling fluid supplied to an upper portion of a cooling housing. A refrigerant is disposed in a lower portion of the cooling housing for liquid-to-vapor transformation. A partition divides the upper portion of the cooling housing from the lower portion. A heat rejecter is disposed on and above the upper wall of the cooling housing with a first header extending from and in fluid communication with the liquid coolant outlet. A second header extends upwardly from a rejecter outlet. A plurality of first tubes extend between and in fluid communication with the first header and the second header with a plurality of first air fins disposed between the upper wall and the first tubes. A single unit defines both the cooling housing and the air cooled heat rejecter to thereby allow the manufacture of the unit in a single process with the attendant reduction in shipping, handling and installation.

Description:
RELATED APPLICATIONS  
       [0001]     The subject invention has widespread utility as illustrated in the co-pending application Ser. No. 11/040,989 (DP-312789); Ser. No. 11/040,321 (DP-311408) and Ser. No. 11/040,988 (DP-311409), all filed on Jan. 21, 2005.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     A fluid heat exchanger unit for cooling an electronic device.  
         [0004]     2. Description of the Prior Art  
         [0005]     Research activities have focused on developing assemblies to efficiently dissipate heat from electronic devices that are highly concentrated heat sources, such as microprocessors and computer chips. These electronic devices typically have power densities in the range of about 5 to 35 W/cm 2  and relatively small available space for placement of fans, heat exchangers, heat sink assemblies and the like. However, these electronic devices are increasingly being miniaturized and designed to achieve increased computing speeds that generate heat up to 200 W/cm 2 .  
         [0006]     Heat exchangers and heat sink assemblies have been used that apply natural or forced convection cooling methods to cool the electronic devices. These heat exchangers typically use air to directly remove heat from the electronic devices. However, air has a relatively low heat capacity. Such heat sink assemblies are suitable for removing heat from relatively low power heat sources with power density in the range of 5 to 15 W/cm 2 . The increased computing speeds result in corresponding increases in the power density of the electronic devices in the order of 20 to 35 W/cm 2  thus requiring more effective heat sink assemblies.  
         [0007]     In response to the increased heat to be dissipated, liquid-cooled units called LCUs employing a cold plate in conjunction with high heat capacity fluids, like water and water-glycol solutions, have been used to remove heat from these types of high power density heat sources. One type of LCU circulates the cooling liquid so that the liquid removes heat from the heat source, like a computer chip, affixed to the cold plate, and is then transferred to a remote location where the heat is easily dissipated into a flowing air stream with the use of a liquid-to-air heat exchanger and an air moving device such as a fan or a blower. These types of LCUs are characterized as indirect cooling units since they remove heat from the heat source indirectly by a secondary working fluid, generally a single-phase liquid, which first removes heat from the heat source and then dissipates it into the air stream flowing through the remotely located liquid-to-air heat exchanger. Such LCUs are satisfactory for moderate heat flux less than 35 to 45 W/cm 2  at the cold plate.  
         [0008]     In the prior art heat sinks, such as those disclosed in U.S. Pat. Nos. 6,422,307 and 5,304,846, the single-phase working fluid of the liquid cooled unit (LCU) flows directly over the cold plate causing cold plate corrosion and leakage problems.  
         [0009]     As computing speeds continue to increase even more dramatically, the corresponding power densities of the devices rise up to 200 W/cm 2 . The constraints of the miniaturization coupled with high heat flux generated by such devices call for extremely efficient, compact, and reliable thermosiphon cooling units called TCUs. Such TCUs perform better than LCUs above 45 W/cm 2  heat flux at the cold plate. A typical TCU absorbs heat generated by the electronic device by vaporizing the captive working fluid on a boiler plate of the unit. The boiling of the working fluid constitutes a phase change from liquid-to-vapor state and as such the working fluid of the TCU is considered to be a two-phase fluid. The vapor generated during boiling of the working fluid is then transferred to an air-cooled condenser, in close proximity to the boiler plate, where it is liquefied by the process of film condensation over the condensing surface of the TCU. The heat is rejected into an air stream flowing over a finned external surface of the condenser. The condensed liquid is returned back to the boiler plate by gravity to continue the boiling-condensing cycle.  
         [0010]     The aforementioned co-pending applications disclose a cooling housing with a partition dividing the cooling housing into a upper portion having an upper wall, with a liquid coolant inlet for receiving liquid coolant from the system and a liquid coolant outlet, and a lower portion. The upper portion defines a coolant passage between the partition and the upper wall for liquid coolant flow from the liquid coolant inlet to the liquid coolant outlet. A refrigerant is disposed in the lower portion of the cooling housing for liquid-to-vapor transformation. An electronic device generates an amount of heat to be dissipated and the heat is transferred from the electronic device to the bottom of the heat exchanger cooling housing. The heat is then conducted from the bottom to the refrigerant in the lower portion. A working fluid mover, such as a pump, moves a coolant liquid through a cooling fluid storage vessel that stores excess coolant. The pump moves the cooling fluid through a heat extractor or radiator to dissipate heat from the coolant. However, in that system the radiator is separate and spaced remotely from the cooling housing, to thereby require separate manufacturing, shipping, handling and installation.  
       SUMMARY OF THE INVENTION AND ADVANTAGES  
       [0011]     In accordance with the subject invention, heat generated by an electronic device is also transferred to the lower portion of such a cooling housing having a refrigerant therein for liquid-to-vapor transformation as liquid coolant flows above a partition defining a coolant passage in the upper portion of the cooling housing. In addition, a heat rejecter is disposed on and above the upper wall of the cooling housing with a rejecter inlet adjacent and in fluid communication with the liquid coolant outlet of the cooling housing and a rejecter outlet adjacent the liquid coolant inlet of the cooling housing for returning liquid coolant to the system.  
         [0012]     The present invention utilizes a single unit to define both the cooling housing and the air cooled heat rejecter to thereby allow the manufacture of the unit in a single process with the attendant reduction in shipping, handling and installation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0014]      FIG. 1  is schematic view of the system with the cooling housing and the air cooled radiator being completely separate;  
         [0015]      FIG. 2  is perspective view of the unit of the subject invention;  
         [0016]      FIG. 3  is an exploded perspective view, partially cut away;  
         [0017]      FIG. 4  is a cross sectional view of the unit shown in  FIG. 2 ;  
         [0018]      FIG. 5  is another embodiment of the unit of the subject invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]     As alluded to above, the fluid heat exchanger unit of the subject invention incorporates a cooling housing  20  of the type disclosed in the aforementioned co-pending patent applications. The cooling housing  20  includes a liquid coolant inlet  22  and a liquid coolant outlet  24  and an upper portion  26  defining a top or upper wall  27  and a lower portion  28  extending between the liquid coolant inlet  22  and the liquid coolant outlet  24  for establishing a direction of flow from the liquid coolant inlet  22  to the liquid coolant outlet  24 . The cooling housing  20  is used to cool an electronic device  30  engaging or secured to the lower portion  28  of the cooling housing  20 . The electronic device  30  or component is preferably adhesively secured in a recess  29  in the bottom  40  of the cooling housing  20 .  
         [0020]     A partition  32  divides the cooling housing  20  into the upper portion  26  and the lower portion  28  for establishing a direction of flow of liquid coolant in a coolant passage  33  defined between the upper wall  27  and the partition  32  from the liquid coolant inlet  22  to the liquid coolant outlet  24  in the upper portion  26 . The cooling housing  20  is hermetically sealed about the partition  32  to contain a refrigerant in the lower portion  28  for liquid-to-vapor transformation. In other words, the partition  32  separates the refrigerant in the lower portion  28  from the liquid coolant in the coolant passage  33  of the upper portion  26 .  
         [0021]     The partition  32  and the upper wall  27  are undulated or corrugated transversely to the direction of flow from the liquid coolant inlet  22  to the liquid coolant outlet  24  to define the flow passage. The partition  32  defines a lower wall of the coolant passage  33  in the upper portion  26  and the upper wall  27  of the upper portion  26  defines a top of the coolant passage  33 , which top or upper wall  27  is also undulated transversely to the direction of flow from the liquid coolant inlet  22  to the liquid coolant outlet  24  to define the coolant passage  33 . Disposed inside the coolant passage  33  are the flow interrupters  34  extending vertically upward into the coolant stream. The purpose of the flow interrupters  34  is to interrupt the thermal boundary layer growing from the upper corrugated wall and the lower corrugated wall of the coolant passage  33 . The interruption of the thermal boundary layer causes the heat transfer coefficient to attain a higher value at the point of interruption.  
         [0022]     A plurality of fins  36  extend from the bottom  40  of the cooling housing  20  for increasing heat transfer from the electronic device  30  to the interior of the lower portion  28  of the cooling housing  20 . The fins  36  extend linearly across the direction of flow under the partition  32  and between the liquid coolant inlet  22  and the liquid coolant outlet  24  in the upper portion  26 . The heat transfer fins  36  are disposed in the lower portion  28  of the cooling housing  20  for transferring heat from the electronic device  30  disposed on the exterior of the lower portion  28  of the cooling housing  20 . The fins  36  vary in height and, more specifically, the fins  36  are of the greatest height midway between the liquid coolant inlet  22  and the liquid coolant outlet  24  and are of progressively lesser height from the midpoint toward the liquid coolant inlet  22  and the liquid coolant outlet  24  respectively. The middle fin  36  may extend all the way to the lower corrugated wall and be brazed to it to provide reinforcement to the vapor chamber below the lower corrugated wall.  
         [0023]     The upper portion  26  of the cooling housing  20  presents a generally rectangular footprint and the lower portion  28  of the cooling housing  20  is coextensive with the upper portion  26 . The entire cooling housing  20 , including the flow passage with upper corrugated wall and lower corrugated wall along with end sections, and the pan-shaped lower portion  28  having integrally formed therewith the fins  36  and the recess  29  for the electronic device  30 , may be extruded as a single or integral piece thereby obviating the need for various brazing operations. Sections of the extrusion are cut and end sheets with braze coating are stamped out of sheet stock and bonded to the edges of the extruded sections, thereby hermetically sealing the upper portion  26  and lower portions  28  of the cooling housing  20 .  
         [0024]     In addition, the spaces between the undulations of the upper wall  27  may be filled in with the metal material of the upper wall  27  or filler material  38  for providing a flat surface for banding to the first fins  54 .  
         [0025]     The upper portion  26  of the housing  20  is generally rectangular and the lower portion  28  of the housing  20  is generally rectangular and generally coextensive with the upper portion  26 . A recess  29  extends into the lower portion  28  of the housing  20  for receiving the electronic device  30 . The entire housing  20 , including the flow passage with upper corrugated wall and lower corrugated wall along with end sections defining a gallery  42  or tank  42 , and the pan-shaped lower portion  28  having integrally formed therewith the fins  36  and the recess  29  for the electronic device  30 , may be extruded as a single or integral piece thereby obviating the need for various brazing operations. Sections of the extrusion are cut and end plates  44  with braze coating are stamped out of sheet stock. During the stamping of the end plates  44 , various grooves are formed in the end plates  44  to receive and facilitate bonding to the edges of the extruded sections, thereby hermetically sealing the upper portion  26  and lower portions  28  of the housing  20 . A simple machining operation is used to drill holes in one end plate  44  and in the gallery  42  or tank  42  that feeds the coolant passage  33 . A refrigerant charge tube  46  is welded to the hole drilled in the end plate  44 , and the tubular coolant is welded to the gallery  42  or tank  42 .  
         [0026]     The liquid cooling system illustrated in  FIG. 1  incorporates the heat exchanger cooling housing  20  for cooling an electronic device  30 . As alluded to above, a working fluid mover, such as a pump P, moves a cooling fluid, usually a liquid, through a cooling fluid storage vessel T, that stores excess cooling fluid. The pump P moves the cooling fluid through a heat extractor or radiator unit to dissipate heat from the cooling fluid, the heat extractor or radiator unit including a fan F and radiator R. The radiator R is separate and spaced from the cooling housing  20 .  
         [0027]     In accordance with the subject invention, a heat rejecter  48  is integrally fabricated with the cooling housing  20  whereby liquid coolant flows directly out of the coolant outlet  24  of the cooling housing  20  and into an air cooled heat rejecter  48 . The heat rejecter  48  is disposed on and above the upper wall  27  of the cooling housing  20  with a rejecter inlet  50  adjacent and in fluid communication with the liquid coolant outlet  24  and a gallery  42  or a rejecter outlet  52  adjacent the liquid coolant inlet  22  for returning liquid coolant to the system.  
         [0028]     The heat rejecter  48  includes at least one layer of first air fins  54  and at least one layer of first tubes  56  for conducting liquid coolant from the rejecter inlet  50  to the rejecter outlet  52  for transferring heat from the first tubes  56  to the first air fins  54 . The plurality of first air fins  54  are disposed along the filler material  38  and upper wall  27  to extend between the rejecter inlet  50  and the rejecter outlet  52 . To facilitate the first tubes  56 , the heat rejecter  48  includes a first header  58  extending from the rejecter inlet  50  in a direction transverse to the upper wall  27  and a second header  60  extending from the rejecter outlet  52  in a direction transverse to the upper wall  27 . The first header  58  is defined by a pair of parallel and spaced walls formed integrally with the upper wall  27  of the cooling housing  20  and the bottom  40  wall of the lower portion  26 ,  28  and/or the partition  32 . Likewise, the second header  60  is defined by a pair of parallel and spaced walls extending upwardly from the rejecter outlet  52  or gallery  42 . Although there are normally a plurality of laterally spaced first tubes  56 , at least one first tube  56  extends between and in fluid communication with the first header  58  and the second header  60  with the first air fins  54  disposed between the upper wall  27  and the first tube  56  or first tubes  56 . As illustrated in  FIGS. 4 and 5 , the rejecter would frequently include a plurality of second air fins  62  disposed above the first tube  56  and at least one second tube  64  is disposed above the second air fins  62  and extends between and in fluid communication with the first header  58  and the second header  60 .  
         [0029]     The heat rejecter  48  includes a tunnel-shaped casing  66  extending from the liquid coolant inlet  22  upwardly with the second header  60  and across the unit and downwardly with the first header  58  to the liquid coolant outlet  24 . The casing  66  and the first air fins  54  and the second air fins  62  extend parallel to one another for air to pass through the casing  66  and the first air fins  54  and the second air fins  62  in a direction transverse to the first tubes  56  and the second tubes  64 . The casing  66  is an inverted U-shape with the legs secured to the cooling housing  20 . A plurality of third air fins  68  are disposed between and parallel to the casing  66  and the first header  58  and are disposed between and parallel to the casing  66  and the second header  60  and extend across the unit between the first header  58  and the second header  60 . In other words, the third air fins  68  extend through the same U-shaped path of the casing  66 .  
         [0030]     Although as shown, the second header  60  includes a separate passage for each of the first tube  56  and the second tube  64 , either one of the first header  58  and the second header  60  may include a separate passage for each of the first tube  56  and the second tube  64 , as illustrated in  FIG. 4 .  
         [0031]     The end plates  44  include header plates  70  integral with the end plates  44  and extending upwardly to close and seal the open sides of the first header  58  and the second header  60 . All of the components may be made of metal and wired together and placed in a brazing furnace.  
         [0032]     The liquid coolant inlet  22  to the cooling housing  20  is disposed above the rejecter outlet  52 . The liquid coolant inlet  22  to the cooling housing  20  feeds an inlet gallery  42  and is defined by a tubular liquid coolant inlet  22 . A tubular outlet  72  empties the rejecter outlet  52 . Both tubular members are also brazed into position in spaced and parallel relationship to one another. The rejecter outlet  52  defines an outlet gallery  42  joined to the inlet gallery  42 , as by sharing a common wall.  
         [0033]     The electronic device  30  generates heat that is transferred through the fins  36  to the captive refrigerant sealed in the lower portion  28  of the cooling housing  20  to boil and vaporize the refrigerant. The vaporized refrigerant rises in the lower portion  28  of the cooling housing  20  and into the V-shaped cavities between the crests of the coolant flow passage. The liquid coolant flowing through the undulating coolant passage  33  absorbs heat from the refrigerant vapor thereby condensing the vapor back into liquid refrigerant pooled in the lower portion  28  where it again absorbs heat from the electronic device  30  to repeat the cycle. At the same time, liquid coolant exits the cooling housing  20  and immediately into the first header  58  for distribution to the first tubes  56 , and likely second tubes  64 , whereby the liquid coolant is further cooled by heat transfer with the fist fins  36 , and likely the second fins  36 . The liquid coolant then flows into the rejecter outlet  52  gallery  42  for return to the system. The third fins  36  further enhance the heat transfer, particulary with the first header  58  and the second header  60 .  
         [0034]     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims, wherein recitations should be interpreted to cover any combination in which the incentive novelty exercises its utility.