Abstract:
The subject invention provides a heat sink for cooling electronic devices. The heat sink includes an upper chamber and a lower chamber separated by a baffle therebetween. The lower chamber includes a base having a central axis and a plurality of curvilinear fins disposed radially about the central axis of the base. The upper chamber includes a lid defining an inlet and an inlet tube interconnecting the upper chamber and the lower chamber for directing a fluid through the upper chamber and impinging the fluid on the base in the lower chamber. A sidewall extends between the base and the lid and is disposed about the fins. The sidewall includes a peripheral inlet for directing the fluid perpendicular to the central axis and at the fins.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The subject invention provides a heat sink assembly for removing heat from an electronic device such as a microprocessor or a computer chip 
   2. Description of the Prior Art 
   These electronic devices generate a high concentration of heat, typically a power density in the range of 5 to 35 W/cm 2 . Accordingly, research activities have focused on developing more efficient cooling assemblies capable of efficiently dissipating the heat generated from such electronic devices, while occupying a minimum of space. 
   A forced air cooling assembly typically includes a heat exchanger and a heat sink, and cools the electronic device by natural or forced convection cooling methods. The electronic device is attached to the heat sink and transfers heat thereto. The heat exchanger typically uses air to directly remove the heat from the heat sink. However, air has a relatively low heat capacity. Such forced air cooling assemblies are suitable for removing heat from relatively low power heat sources with a power density in the range of 5 to 15 W/cm 2 . However, the increased computing speeds have resulted in a corresponding increase in the power density of the electronic devices in the order of 20 to 35 W/cm 2 , thus requiring more effective cooling assemblies. 
   In response to the increased heat produced by the electronic devices, liquid-cooled cooling assemblies, commonly referred to as liquid cooled units (“LCUs”) were developed. The LCUs employ a heat sink in conjunction with a high heat capacity cooling fluid, like water or water-glycol solutions, to remove heat from these types of higher power density heat sources. One type of LCU circulates the cooling fluid through the heat sink to remove the heat absorbed from the heat source affixed thereto. The cooling fluid 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 first removes heat from the heat sink and then dissipates it into the air stream flowing through the remotely located liquid-to-air heat exchanger. Such LCUs are satisfactory for a moderate heat flux less than 35 to 45 W/cm 2 . 
   The amount of heat transferred between the heat sink and the cooling fluid is dependent upon a heat transfer coefficient therebetween. The heat transfer coefficient is dependent upon a temperature gradient between the heat sink and the cooing fluid, with the higher heat transfer coefficient corresponding to higher temperature gradients, i.e., the higher the temperature gradient between the heat sink and the cooling fluid, the more heat the cooling fluid will remove. The amount of heat stored in the heat sink varies according to the distance from the heat source, with the highest concentration of heat occurring directly above the heat source in the base plate. 
   SUMMARY OF THE INVENTION AND ADVANTAGES 
   The subject invention provides a heat sink assembly for removing heat from an electronic device. The assembly includes a base having a top surface and a central axis perpendicular thereto. A plurality of fins extend upwardly from the top surface of the base a distance to a top edge and are disposed radially about the central axis. A lid having a bottom surface is in spaced relationship with the top edge of the plurality of fins and is parallel to the top surface of the base. A sidewall extends between the top surface of the base and the bottom surface of the lid and is disposed about the plurality of fins. An axial inlet is disposed in the lid for directing a fluid parallel to the central axis and onto the top surface of the base. An outlet is disposed in the sidewall between the top edge of the plurality of fins and the bottom surface of the lid for discharging the fluid. A peripheral inlet is disposed in the sidewall between the top edge of the plurality of fins and the top surface of the base for directing the fluid perpendicular to the central axis and at the plurality of fins. 
   Accordingly, the peripheral inlet directs the fluid at the plurality of fins, thus creating a circular flow circulating between the plurality of fins and the sidewall of the heat sink. This circular flow of fluid from the peripheral inlet mixes with the fluid directed at the base from the axial inlet, which is directed radially outward by the plurality of fins, thereby minimizing the temperature increase in the fluid and maximizing the heat transfer capacity of the heat sink assembly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       FIG. 1  is a schematic view of a liquid cooling system; 
       FIG. 2  is a perspective view of a heat sink assembly; and 
       FIG. 3  is an exploded perspective view of the heat sink assembly. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, a heat sink assembly is shown generally at  20  in the Figures. 
   Referring to  FIG. 1 , the operation of the heat sink  20  is incorporated into a liquid cooling system, generally shown at  22 , and is for cooling an electronic device  24 . A working fluid mover, such as a pump  26 , moves a flow of cooling fluid, usually a liquid, through a fluid storage tank  28 , which stores excess fluid. The pump  26  moves the fluid through a heat exchanger, generally shown at  30 , to dissipate heat from the fluid. The heat exchanger  30  includes a fan  32  and a radiator  34 . The radiator  34  can be of the well known type including tubes with cooling fins between the tubes to exchange heat between the fluid passing through the tubes and air forced through the radiator  34  by the fan  32 . 
   Referring to  FIGS. 2 and 3 , the heat sink  20  includes a base  38  having a top surface  40  and a central axis C perpendicular thereto. The base  38  is circular in shape with the central axis C disposed at the center of the base  38 . The base  38  includes a contact surface, which is for contacting the electronic device  24  and absorbing heat produced thereby. 
   A plurality of fins  36  extend upwardly from the top surface  40  of the base  38  a distance to a top edge  42  and are disposed radially about the central axis C. The plurality of fins  36  include a curvilinear shape, and are spaced from the center of the base  38  and the central axis C a distance. The plurality of fins  36  are identical in configuration and extend radially outward along a curved path to an outer periphery  44  of the plurality of fins  36 . The outer periphery  44  of the plurality of fins  36  includes a circular shape, concentric with base  38 . 
   A lid  46  having a bottom surface  48  is in spaced relationship with the top edge  42  of the plurality of fins  36  and is parallel to the top surface  40  of the base  38 . The lid  46  includes a circular shape and is identical in size and concentric with the base  38 . A sidewall  50  extends between the top surface  40  of the base  38  and the bottom surface  48  of the lid  46  and is disposed about the outer periphery  44  of the plurality of fins  36 . The sidewall  50  is in spaced relationship with the outer periphery  44  of the plurality of fins  36  so that the fluid may circulate between the outer periphery  44  of the fins  36  and the sidewall  50 . 
   A baffle  52  is disposed between the top edge  42  of the plurality of fins  36  and the lid  46 . The baffle  52  defines an upper chamber  54  above the plurality of fins  36  and a lower chamber  56  enclosing the plurality of fins  36 . The baffle  52  includes a plurality of ports  58  interconnecting the upper chamber  54  and the lower chamber  56  for allowing the fluid to pass from the lower chamber  56  to the upper chamber  54 . Preferably, the plurality of ports  58  include a curvilinear shape corresponding to the plurality of fins  36 , and positioned between adjacent fins  36  such that fluid flowing between any two of the plurality of fins  36  may flow directly upward through the curvilinear port  58  and into the upper chamber  54 . 
   A slotted wall  60  is disposed between the sidewall  50  and the outer periphery  44  of the plurality of fins  36  and extends between the base  38  and the baffle  52 . The slotted wall  60  includes a plurality of slots  62  for directing the fluid between adjacent pairs of the plurality of fins  36 . The slotted wall  60  includes a circular shape that is concentric with the outer periphery  44  of the fins  36  and the base  38 . 
   An axial inlet  64  is disposed in the lid  46  for directing the fluid parallel to the central axis C and onto the top surface  40  of the base  38 . The inlet is aligned with the central axis C and concentric with the base  38  and the lid  46 . The baffle  52  includes an inlet tube  66  extending between the baffle  52  and the bottom surface  48  of the lid  46  for interconnecting the inlet and the lower chamber  56  of the heat sink  20 . The inlet tube  66  directs the fluid entering the inlet to the lower chamber  56  and onto the top surface  40  of the base  38 . 
   An outlet  68  is disposed in the sidewall  50  adjacent the upper chamber  54  of the heat sink  20  between the top edge  42  of the plurality of fins  36  and the bottom surface  48  of the lid  46  for discharging the fluid. The fluid flows from the lower chamber  56 , through the ports  58  in the baffle  52  and into the upper chamber  54  where the fluid exits the heat sink  20  through the outlet  68 . The heat exchanger  30  receives the fluid from the outlet  68  and removes heat from the fluid. 
   A peripheral inlet  70  is disposed in the sidewall  50  adjacent the lower chamber  56  of the heat sink  20  between the top edge  42  of the plurality of fins  36  and the top surface  40  of the base  38 . The peripheral inlet  70  directs the fluid perpendicular to the central axis C and at the slotted wall  60  and the plurality of fins  36 . The circular shape of the slotted wall  60  helps direct the fluid around the slotted wall  60  and the outer periphery  44  of the fins  36  between the slotted wall  60  and the sidewall  50 . 
   The base  38 , the plurality of fins  36 , and the slotted wall  60  are constructed of a thermally conductive material, such as aluminum. However, any thermally conductive material suitable for absorbing and transferring heat may be utilized. Accordingly, the scope of the invention should not be limited to the type of material utilized for the base  38 , the plurality of fins  36 , or the slotted wall  60 . 
   During operation, the pump  26  circulates the cooling fluid to the two fluid inlets of the heat sink  20 , the axial inlet  64  and the peripheral inlet  70 . The inlet tube  66  directs the fluid from the axial inlet  64  through the upper chamber  54  and into the lower chamber  56 , where the fluid is impinged upon the top surface  40  of the base  38 . The fluid from the axial inlet  64  flows radially outward between the plurality of fins  36 . The peripheral inlet  70  directs the fluid perpendicular to the slotted wall  60  and the plurality of fins  36 . The slotted wall  60  directs the fluid around the outer periphery  44  of the fins  36 ; through the slots  62  and between adjacent pairs of the fins  36 . The fluid from the axial inlet  64  and the peripheral inlet  70  meet as opposing fluid streams between adjacent pairs of the fins  36 , resulting in an upwelling of the fluid through the ports  58  of the baffle  52  and into the upper chamber  54  of the heat sink  20 . The fluid then exits the heat sink  20  through the outlet  68 . The pump  26  moves the fluid through the heat exchanger  30 , which removes the heat stored within the fluid and then re-circulates the fluid back to the axial inlet  64  and the peripheral inlet  70 . 
   As the fluid from the axial inlet  64  flows radially outward, the fluid absorbs heat from the base  38  and the plurality of fins  36 . Similarly, as the fluid from the peripheral inlet  70  flows around the outer periphery  44  of the fins  36 , through the slotted wall  60  and between adjacent pairs of fins  36 , the fluid absorbs heat from the base  38 , the slotted wall  60 , and the plurality of fins  36 . As the temperature of the fluid increases, the heat transfer capacity of the fluid decreases due to a decrease in the temperature differential between the fluid and the heat sink  20 . However, because the fluid is introduced from both the axial inlet  64  and the peripheral inlet  70 , the decrease in the temperature differential between the fluid and the heat sink  20  is minimized, therefore maximizing the efficiency of the liquid cooling system  22 . 
   The foregoing invention has been described in accordance with the relevant legal standards; thus, the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and do come within the scope of the invention. Accordingly, the scope of legal protection afforded this invention can only be determined by studying the following claims.