Abstract:
An integrated cooling unit configured to effect the removal of heat via a circulating liquid coolant includes a reservoir to contain the liquid coolant, a tubing arrangement disposed at an outer surface of the reservoir, a pump disposed within the reservoir, and a fan configured to provide a flow of air across the tubing arrangement to remove the heat. The tubing arrangement is fluidly communicable with a heat exchanging device, and the pump is configured to circulate the liquid coolant through the tubing arrangement to the heat exchanging device.

Description:
BACKGROUND 
     The present invention relates generally to a heat dissipating component and, more particularly, to an evaporator with backup thermal conductance for use with an electronic device. 
     The removal of heat from electronic components is a problem continuously faced by electronic packaging engineers. As electronic components have become smaller and more densely packed on integrated boards and chips, designers and manufacturers now are faced with the challenge of how to dissipate the heat generated by these components. It is well known that many electronic components, especially semiconductor components such as transistors and microprocessors, are more prone to failure or malfunction at high temperatures. Thus, the ability to dissipate heat often is a limiting factor on the performance of the component. 
     Electronic components within integrated circuits have been traditionally cooled via forced or natural convective circulation of air within the housing of the device. In this regard, cooling fins have been provided as an integral part of the component package or as separately attached elements thereto for increasing the surface area of the package exposed to convectively-developed air currents. Electric fans have also been employed to increase the volumetric flow rate of air circulated within the housing. For high power circuits (as well as smaller, more densely packed circuits of presently existing designs), however, simple air circulation often has been found to be insufficient to adequately cool the circuit components. 
     It is also well known that heat dissipation, beyond that which is attainable by simple air circulation, may be effected by the direct mounting of the electronic component to a thermal dissipation member such as a “cold-plate”, evaporator, or other heat sink. 
     Such applications oftentimes incorporate the heat removal capabilities of refrigeration cooling systems at electronic modules of the circuitry by utilizing water-to-air cooling loop configurations, for example. Water-to-air cooling loop configurations generally include discretely positioned units between which fluid communication is maintained via tubing lines or similar conduits. The units of such configurations include pumps to circulate cooling water, heat exchange devices to transfer heat from the circuitry to the water, fans for providing cooling air flow across the heated water, and water storage reservoirs. The aggregated componentry of such configurations may occupy considerable volumes within their respective systems. Because space is at a premium in most electronics applications, particularly as the sizes of the systems are reduced to keep pace with technological trends, cooling systems may be likewise reduced in size. In addition, higher end modules having increased density of electronic circuitry require redundant or backup cooling means in the event that the primary refrigeration cooling unit fails, while limiting the space needed to employ such a redundant or secondary cooling means. 
     SUMMARY 
     This disclosure presents an apparatus for integrating the individual components of a cooling unit for electronics applications. The integrated cooling unit removes heat primarily via a refrigerant system having circulating refrigerant coolant and including a reservoir to contain the coolant, a tubing arrangement disposed at an outer surface of the reservoir, a pump disposed within the reservoir, and a fan to provide a flow of air across the tubing arrangement to remove the heat. The tubing arrangement is fluidly communicable with a heat exchanging device, and the pump circulates the liquid coolant through the tubing arrangement to the heat exchanging device. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The present disclosure will be better understood by those skilled in the pertinent art by referencing the accompanying drawings, where like elements are numbered alike in the several FIGURES, in which: 
     FIG. 1 is an exploded perspective view of an exemplary embodiment of an or unit in thermal communication with a backup air cooling unit. 
     FIG. 2 is a perspective view of the evaporator unit in thermal communication with the backup air cooling unit of FIG. 1 assembled with insulation around inlet and outlet tubing to the evaporator unit and connected to a cooling reservoir. 
     FIG. 3 is a perspective view of the evaporator unit in thermal communication with the backup air cooling unit of FIG. 2 in further thermal communication with a blower unit. 
     FIG. 4 is a cutaway view of the evaporator unit illustrating evaporator channels for flow of cooling liquid therein. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, an exemplary embodiment of an integrated cooling unit is shown generally at  10  and is hereinafter referred to as “cooling unit  10 .” Cooling unit  10  provides for the removal of heat from electronic circuitry via circulation of a liquid coolant and the dissipation of the removed heat via forced convection of air. The circulation of the liquid coolant allows heat to be transferred to the coolant and subsequently removed by a fan, for example, that forces air over the circulating coolant. Although cooling unit  10  is described as being incorporable into computer-based applications in which heat is removed from electronic circuitry and dissipated through a liquid medium, it should be understood by those of skill in the art that cooling unit  10  may be utilized in other applications in which heat is generated and is to be dissipated to the surrounding environment. Furthermore, although cooling unit  10  is referred to as utilizing water as the circulating coolant, it should be understood by those of skill in the art that other liquids such as brine, alcohols, fluorocarbons, and halogenated. hydrocarbons may be used. 
     Cooling unit  10  comprises an evaporator shown generally at  12 . Evaporator  12  includes a base plate portion  14  configured to receive a flow plate portion  16  of evaporator  12  therein and configured to receive and return liquid coolant via a tubing arrangement  18 . Tubing arrangement  18  at one end  22  is configured to be received by an inlet and outlet manifold  20  configured in base plate portion  14 . Tubing arrangement  18  at another end  24  includes couplings  26  for coupling with a condenser or coolant reservoir (not shown). Coupling caps  28  are removably attached to an open end of each coupling  26  which is attached to each tube of tubing arrangement  18  to prevent debris from entering before installation or during shipment of cooling unit  10 . 
     A portion of insulation material  30  is shown in FIG. 1 used to surround a length of tubing arrangement  18  to insulate liquid coolant in tubing arrangement  18  from ambient air outside tubing arrangement  18 . 
     Flow plate portion  16  is received in a cavity  32  configured in base plate portion  14  to receive a complementary configured edge  34  of flow plate portion  16  defining its periphery. An inner surface  36  defining a bottom of cavity  32  is substantially planar to abut an outer surface  38  defining a bottom surface of flow plate portion  16 . 
     On a top surface  40  opposite bottom surface  38  of flow plate portion  16 , a heat sink assembly  42  is disposed. In an exemplary embodiment, heat sink assembly  42  includes an evaporator lid  44  having a plurality of parallel spaced heat sink fins  46  extending from a top surface  45  of lid  44 . Evaporator lid  44  and plurality of heat sink fins  46  are preferably fabricated of copper, although other suitable thermally conductive materials may be employed. In addition, fins  46  are preferably nickel plated in the event of local condensation occurs over the coldest regions of evaporator  12 . The plurality of heat sink fins  46  are preferably soldered or brazed to evaporator lid  44 . Generally, the fin arrangement is stamped as a continuous piece from sheet metal having a high thermal conductivity value. Other exemplary materials from which fins  46  can be fabricated include, but are not limited to, copper alloys, aluminum, aluminum alloys, and combinations of the foregoing materials. An adhesive, such as a solder or a thermal epoxy compound, is optionally employed to attach the fin arrangement to lid  44 . 
     Lid  44  includes a plurality of apertures  50  configured therethrough and aligned with corresponding apertures  52  configured in evaporator  12  for receiving corresponding fasteners  54  to secure heat sink assy  42  to evaporator  12 . It will be recognized that an area above each aperture  50  of lid  44  is vacated by the plurality of parallel spaced heat sink fins  46  to allow access of a tool (not shown) to the corresponding fastener and to allow air circulation of ambient air to a top surface of lid  44  in thermal contact with a top surface a evaporator  12 . 
     A fin cover or shroud  56  is disposed opposite lid  44  having fin  46  therebetween. Shroud  56  is configured as a three-sided box structure having two sides  58  disposed at opposite ends and substantially perpendicular to a top cover  60 . Shroud  56  is configured to protect fins  46  at an end portion and two sides thereof while allowing air flow to pass through fins  46  without limitation. Shroud  56  is configured with holes  61  in top cover  60  aligned with corresponding apertures  50  in lid  44  to provide access to fasteners  54 , as well as provide additional air flow access through fins  46  substantially perpendicular to air flow through fins  46  between sides  58  of shroud  56 . Each of the two sides  58  is further configured with a mounting means extending therefrom for attachment to base plate portion  14 . In an exemplary embodiment, the mounting means includes a pair of flanges  62  extending from each side  58  and configured to engage a fastener  64  for engagement with a corresponding receiving flange  66  extending from base plate portion  14 . 
     Referring now to FIG. 2, cooling unit  10  of FIG. 1 is shown coupled with a cooling reservoir  70  to provide coolant to evaporator  12  for cooling a processor module or multi-chip module (MCM)  72  interfacing an opposite surface  74  to inner surface  32  of base plate portion  14 . MCM  72  is operably coupled to base plate portion  14  using a coupling means through a corresponding aperture  76  configured in MCM  74  and base plate portion  14  (See FIG.  1 ). The coupling means optionally includes one centrally located of nine fasteners  54  depicted in FIG.  1 . 
     Still referring to FIG. 2, tubing arrangement  18  is encased with insulation  30  to insulate coolant from reservoir  70  to evaporator  12 . In an exemplary embodiment, insulation  30  is fabricated of a polyurethane structural foam, however other suitable insulation materials are contemplated to aid in insulating coolant in tubing arrangement  18 . In an exemplary embodiment, tubing arrangement  18  is fabricated with two {fraction (5/16)} inch nitrogenized copper refrigeration tubing. Again, other suitable refrigeration tubing is contemplated suitable to withstand the pressures generated during operation of cooling unit  10  and the temperatures associated with the electronic circuitry. The tubing arrangement is optionally arranged as a coil to effectively optimize available space between reservoir  70  and cooling unit  10 . 
     As will be recognized by one skilled in the pertinent art, in one embodiment, reservoir  70  is in operable communication with a motor (not shown) that is operable communication with a pump (not shown) to provide coolant flow through tubing arrangement  18  and manifold  20  to evaporator  12  to effect heat removal from MCM  72 . 
     In order to facilitate the cooling when refrigeration as a primary cooling means is not operational, a secondary cooling means includes a flow of air from lid  44  to effect the removal of sensible heat from MCM  72  in thermal contact with lid  44 . The arrangement of fins  46  is disposed over lid  44  facilitates air flow cooling of MCM  72 . Each fin of the plurality of fins  46  extends a length defining a length of lid  44 . Shroud  60  is disposed over fins  46  and extends over the height of cooling unit  10  and around outboard fins  46  disposed on opposite sides of lid  44 . A pair of openings  78  defined by shroud  60  at opposite ends serves as a primary air inlet (shown with arrows  80 ). The primary air inlet allows air to be inducted within shroud  60  and fins  46 . As discussed above, shroud  60  also includes a plurality of secondary air inlets through holes  61  (discussed as apertures with reference to FIG. 1) through which air is drawn in the directions of arrows  84 , between adjacently positioned fins  46 , and over lid  44 . 
     Referring now to FIG. 3, a primary air flow pattern is defined by air inducted through inlets  82  defined by the space between parallel spaced fins  46  and openings  78  defined by open sides of shroud  56 . The air inducted through openings  78  and inlets  82  is preferably and ultimately exhausted through a fan  86  in the direction indicated by arrows  88 . Fan  86  is preferably turned off when the refrigeration system is working properly and turned on when it is not. Shroud  60  further provides some degree of protection to fins  46  from being bent, crushed, or otherwise damaged. 
     Referring now to FIG. 4, a sectional view of evaporator  12  of cooling unit  10  is shown. In an exemplary embodiment, manifold  20  includes an inlet port  90  and an outlet port  92  in fluid communication with each other via a plurality of evaporator channels  94 . Evaporator channels  94  are preferably configured having low aspect ratios to reduce the thermal resistance path through evaporator  12  to heat sink assembly  42 . Evaporator channels  94  are preferably configured to bring the coldest refrigerant from inlet port  90  to a center portion generally shown at  96  of evaporator  12  first. As the refrigerant continues to flow through evaporator channels  94 , the refrigerant becomes superheated by the heat load of MCM  72  in thermal contact with an outside surface  74  of evaporator  12 . As the superheated refrigerant approaches outlet port  92 , evaporator channels  94  reside proximate a perimeter portion  98  defining evaporator  12 . In this manner, when MCM  72  and evaporator  12  have centers substantially coaxially aligned, whereby the coldest refrigerant entering evaporator  12  through inlet port  90  traverse to center portion  96  coinciding with a center portion of MCM  72  and then exiting from evaporator  12  at a warmer temperature as refrigerant approaches outlet port  92  at perimeter portion  98  of evaporator  72  where condensation may form and provide little impact on MCM  72  temperature. 
     The above discussed configuration for evaporator channels  94  used in conjunction with a superheat control code of a selected refrigerant lowers the achievable junction temperature of a non-sealed evaporator. In an exemplary embodiment illustrated in FIG. 4, inlet port  90  is further defined to lower the achievable junction temperature of evaporator  12  to mitigate condensation when the coldest incoming refrigerant enters evaporator  12  via inlet port  90 . More specifically, inlet port  90  is further configured with a first narrowing orifice or aperture  100  for increasing the pressure of incoming refrigerant to increase a temperature of the refrigerant and tubing entering evaporator  12  proximate perimeter portion  98  of evaporator  12 . The temperature increase is about 30° C. or more. In this manner, condensation is mitigated proximate perimeter portion  98  without use of large cumbersome insulation that is impractical with an industry direction to increase processor density. Furthermore, as the pressurized refrigerant traverses to center portion  96 , inlet port  90  is further configured having a second expansion orifice or aperture  102  showing the warmed refrigerant a decreased pressure and corresponding decrease in temperature, thereby providing cold refrigerant (e.g., about −20° C.) near the evaporator center without external condensation on either the incoming tubing arrangement  18  or evaporator  12  perimeter. In the event of a failure of the refrigeration system, fins  46  provide suitable backup cooling, although at higher temperatures compared to the primary cooling method by refrigeration, until the refrigerant system is repaired. In addition, a filter (not shown) is optionally disposed at aperture  100  to prevent plugging therethrough by contaminates within the refrigerant. 
     Still referring to FIG. 4 exemplifying an exemplary embodiment, the plurality of evaporator channels  94  is further defined by three distinct paths numbered  1 - 3  beginning at second expansion orifice  102  and terminating at outlet port  92 . Paths  1 - 3  are configured as serpentine pathways beginning at center portion  96  and traversing toward perimeter portion  98 . It will be recognized that the configuration of paths  1 - 3  illustrated in FIG. 4 is just one embodiment and not to be limited to the configuration as illustrated. FIG. 4 shows path  1  as the shortest path while path  3  is the longest. Path  1  serpentines towards outlet port  92  traversing substantially in an upper portion of evaporator  12  above aperture  76 . Path  2  serpentines towards outlet port  92  traversing substantially in a lower portion of evaporator  12  below aperture  76 . Path  3  serpentines away from outlet port  92  traversing substantially the upper and lower portions of evaporator  12  to the right of aperture  76 , as illustrated, and then traverses the lower portion of evaporator  12  along perimeter portion  98  and then upwards toward outlet port  92  to the left of aperture  76 . 
     Fins  46  thereby define a primary airflow pattern indicated as a first airflow passage indicated by arrows  80  in FIG. 2 and a second air flow passage indicated by arrows  84  wherein first air flow passage is defined by the parallel spaced fins  46  and the second air flow passage is defined by the absence of any fin between holes  61  of shroud  56  and apertures  52  of evaporator  12 . Such a structure allows for the drawing of air over the maximum surface area of the fin arrangement, thereby allowing an optimum transfer of heat from lid  44  to be realized. 
     As stated above, the arrangement of fins  46  facilitates the convective flow of air in directions indicated by arrows  80  and  84 . Fins  46  are generally planar structures that extend longitudinally over the height of cooling unit  10 . The attachment of the fin arrangement to lid  44  is such that major opposing planar surfaces of fins  46  extend substantially normally from lid  44  and longitudinally along the height of cooling unit  10 . 
     Shroud  56 , as stated above, is disposed over fins  46  to provide a protective covering over Fins  46  and to define second airflow passages through holes  61 . Shroud  56  may be fabricated from any material that can be formed or molded into the appropriate shape, such as metal, plastic, or fiberglass. In an exemplary embodiment, shroud  32  is fabricated from metal, preferably aluminum, wherein holes  61  defining secondary air inlet ports can be formed by stamping and bending the material of shroud  56 . Holes  61  are aligned with corresponding apertures  50  and  52  located at various positions along top cover  60  of shroud  56 . Such openings extend through shroud  56  to allow for airflow-communication between lid  44  and the environment immediately adjacent to shroud  56 . Positioning of secondary air inlet port holes  61  to register with the second air flow passages facilitates the drawing of air into the fin arrangement (as is illustrated by arrows  84 ) to mitigate the temperature rise of air flowing in the second air flow passages, thereby improving the overall heat transfer performance of cooling unit  10 . Additionally, the use of secondary air inlet port holes  61  reduces the overall air flow pressure drop over the length of each air flow passage though inlets  82  to result in an increased air flow rate longitudinally along cooling unit  10 . 
     The above described apparatus discloses an evaporator that uses refrigeration as a primary cooling means and uses air cooling as a secondary cooling means for a backup mode of operation for cooling an electronic device. In this manner, the above disclosed evaporator enables the benefits of refrigeration with cost and space savings of air cooling. The above described evaporator also allows lower chip temperatures without use of insulation that would inhibit the effectiveness of the air cooled backup mode. Thus, the primary and secondary cooling means disclosed allows an MCM to operate at faster cycle times with greater reliability when refrigerated and yet be satisfactorily cooled for short term usage with backup air cooling when the refrigerant system becomes inoperable. The redundant cooling provided by the air cooling means allows uninterrupted service in high end servers and avoids system shutdowns while the refrigerant system is repaired. 
     While the disclosure has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.