Abstract:
A method for cooling a computer uses thermal coupling for conveying heat from powered components of an electronic system. A fluid heat-exchanger is attached to the surface of the electronic system and filled with fluid coolant. A vacuum is applied between the heat-exchanger and the surface to seal the heat-exchanger to the electronic system. The fluid coolant is circulated through the heat-exchanger to convey heat from the fluid to an external cooling apparatus.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of, and claims priority to, U.S. patent application Ser. No. 12/550,090, filed on Aug. 28, 2009, which is incorporated in its entirety as if fully set forth herein. 
    
    
     FIELD OF THE INVENTION 
     The invention disclosed broadly relates to the field of microprocessor chip cooling and more particularly relates to the field of water cooling. 
     BACKGROUND OF THE INVENTION 
     The evolution towards high power microprocessor chips has driven an increased interest in water cooling. Water cooling allows both high performance and energy-efficient computing. However, bringing water inside a computer has many drawbacks, including: 1) a risk of leaks, and therefore of computer down-time or failure. The risk increases when the number of water connections and couplings is large, which is the case in a multi-processor server; 2) difficult rework, servicing and upgrade of the server, due to the added complexity of the water connections; and 3) high cost. Some of the high cost is due to the larger number of costly no-drip water connectors. 
     There is a need for a cooling method that affords the advantages of water cooling without the above-stated drawbacks. 
     SUMMARY OF THE INVENTION 
     Briefly, according to an embodiment of the present disclosure, we disclose a method for cooling a computer by using thermal coupling for conveying heat from powered components of an electronic system to a surface of the electronic system. The method includes steps or acts of: removably attaching a fluid heat-exchanger to the surface of the electronic system, thus generating an enclosure bounded by the fluid heat-exchanger and the surface; filling the fluid heat-exchanger with a liquid coolant; applying a vacuum to the enclosure, removably sealing the fluid heat-exchanger to the surface; and circulating the fluid coolant through the fluid heat-exchanger to convey heat from the fluid away from the electronic system to an external cooling apparatus. The method also includes affixing a gasket to the enclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To describe the foregoing and other exemplary purposes, aspects, and advantages, we use the following detailed description of an exemplary embodiment of the disclosure with reference to the drawings, in which: 
         FIG. 1 a    shows a side view of the water sleeve, according to an embodiment of the present disclosure; 
         FIG. 1 b    shows a cross-sectional view of a computer, according to an embodiment of the present disclosure; 
         FIG. 1 c    shows a cross-sectional view of the computer of  FIG. 1 b    coupled with the water sleeve of  FIG. 1 a   , according to an embodiment of the present disclosure; 
         FIG. 2  is an exemplary illustration of a blade server computer, connected to a water sleeve, inside a blade center, according to an embodiment of the present disclosure; 
         FIG. 3  shows an exemplary heat-transfer plane for a blade server, according to an embodiment of the present disclosure; 
         FIG. 4 a    shows the front perspective view of the water sleeve of  FIG. 1 a   , according to an embodiment of the present disclosure; and 
         FIG. 4 b    shows a side view of the water sleeve of  FIG. 1 a   , indicating the inlet and outlet ports, according to an embodiment of the present disclosure. 
     
    
    
     While the disclosure as claimed can be modified into alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the present disclosure. 
     DETAILED DESCRIPTION 
     We describe a method for cooling a computer by connecting a heat-transfer plane of a computer to a thermal ground plane, where the thermal ground plane is cooled by a liquid coolant. The thermal ground plane as described herein provides the advantages of water cooling while maintaining most of the water circuitry and complexity outside of the computer enclosure; thereby reducing or eliminating the drawbacks of water cooling, as previously discussed. 
     Water cooling is efficient and the heat generated in the computer can be primarily evacuated through the water. Because of the high efficiency of heat-spreading of vapor chambers or of heat-pipes, the concentrated heat of processors is spread over a large area (the heat-transfer plane). This way, only a small temperature drop occurs (1° to 10° C.) between the computer heat-transfer plane and the water sleeve. Compared to air cooled operation, the processor temperature is lowered more with water cooling. 
     By providing water cooling in a removable sleeve outside of the computer, we reduce the risk of computer down time or failure. The water circuit is primarily kept outside of the computer enclosure. Furthermore, the complexity of the water path is reduced, with few or no water connectors. The water sleeve as described provides for easy maintenance and upgrade, especially for blade servers. Because the water-cooling sleeve is so easily disengaged from the blade server, a blade can be plugged in and out without having to break any water connection. The removable sleeve is easily attached and removed from the computer by applying and removing a vacuum. 
     According to an embodiment of the present invention, a connecting side of the thermal ground plane is a thin, flexible, non-permeable membrane for holding and circulating a liquid coolant such as water or a refrigerant. A partial vacuum is applied between the thermal ground plane and the computer to secure the thermal ground plane to the heat transfer plane. Surface treatments can be applied to the connecting sides to enhance thermal conductivity. 
     Referring now to the drawings and to  FIG. 1 a    in particular, we show one embodiment of the present invention wherein one or more thin sleeves  110  (shown in a side view) are filled with a liquid coolant such as running water  190  and act as a thermal ground plane. Note that other liquid coolants can also be advantageously used within the spirit and scope of the invention, such as water with antifreeze additives like glycol. The liquid coolant is inserted into the sleeve  110  through an inlet connection (a port or pipe connection) and runs continuously through the sleeve  110  and out through an outlet. Further, when filling the sleeve  110  it is preferable not to overfill, but rather to provide enough coolant  190  for cooling purposes, but not so much that the sleeve  110  is stretched taut to the point where it is unable to deform when filled. 
     The surface of the sleeve  110  that comes into contact with the computer is made out of a thin and flexible (preferentially) metallic sheet or membrane  130  (0.1 to 0.5 mm thick). The membrane  130  can be made from thin copper, nickel, aluminum or stainless sheets, as well as polymer sheet (PVC, polyimide . . . ). A gasket  120  (possibly made out of silicone rubber), shown in cross-section here, is provided along a perimeter of the sleeve  110 . 
       FIG. 1 a    shows the water sleeve  110  and  FIG. 1 b    shows the computer  125 .  FIG. 1 c    shows the two assembled together, with a partial vacuum applied between the two. Referring now to  FIG. 1 b   , in order to be applicable to computer cooling, one side of a computer enclosure  125  is made relatively flat, and is designated as a heat-transfer plane  150 . The heat-generating elements within the computer enclosure  125  are thermally connected to the heat-transfer plane  150 . When the sleeve  110  is placed on the heat-transfer plane  150 , with the liquid-filled side  130  in contact with the relatively flat surface of the heat-transfer plane  150 , the membrane  130  of the liquid-filled sleeve  130  is able to conform to the contours of the heat-transfer plane  150 . When contact is made, the gasket  120  is able to removably seal an enclosure defined by the flat surface  150  of the computer  125 , the sleeve  110 , and the gasket  120 . 
     When a vacuum is applied to this enclosure, the fluid-filled sleeve  130  inside of the enclosure is sealed to the flat surface  150  by action of the atmospheric pressure. The sleeve  130  is free to deform in order to match the non-ideal flatness of the surface  150 . A low thermal resistance is realized between the deformed thin sleeve  130  and the flat surface  150 . Thus, a good thermal conduction path is realized between the flat surface  150  of the computer  125  and the thin sleeve  130 . 
       FIG. 1 b    shows a side view of a computer  125 , viewed in cross-section, and where only a few components are displayed: a processor module  128 , a few memory chips  127 , and a plurality of heat-conducting structures  126  and  175 . The heat-conducting structures are lined up close to the flat surface  150  of the computer case  125  or are part of the computer case  125 . They carry the heat from the heat-generating devices, including the processor module  128  and the memory chips  127 , to the heat-transfer plane  150 . 
     For a high power element such as a processor module  128 , the heat conducting structure can be a vapor chamber  175  which provides efficient transfer and spread of heat from the relatively small processor  128  to the relatively wide heat-transfer plane  150 . Alternately, heat-pipes (now commonly used in efficient heat-sinks) can be used to couple the processor to the heat-transfer plane  150 . For the memory chips  127 , heat-pipes or more simple heat conductive structures made out of a good conductive material such as copper or aluminum also provide good thermal conduction between the memory chips  127  and the heat-transfer plane  150 . 
     Referring to  FIG. 1 c   , the computer  125  is shown with the water sleeve  110  attached and filled with water  190  or another suitable liquid coolant. A vacuum is applied between the fluid-filled sleeve  110  and the computer  125 , and therefore a good thermal conduction path is realized between the computer components and the liquid coolant  190 . 
     Referring to  FIG. 2 , we show an exemplary embodiment wherein the computer  125  is a blade (also called a blade server), which is inserted in a blade center  210  (rack with slots). After the blade server  125  is inserted into the blade center  210 , a vacuum is applied between the sleeve  110  and the blade  125 . The vacuum serves to establish a good thermal connection between the sleeve  110  and the blade  125 . Before removal of the blade  125 , the vacuum is first turned off. 
       FIG. 3  shows a blade server  125  with a heat-transfer plane  150  having several discrete sections that are connected to two processor vapor chambers, and two heat-conducting structures attached to memory and to other low power chips. Despite having several discrete sections, the heat-transfer plane  150  is made relatively flat and air tight for vacuum connection to a water sleeve  110 . 
     To enhance the thermal conduction between the sleeve  110  and the computer  125 , one or both surfaces can be coated with a very thin layer (1 to 10 microns) of a soft conductive material, such as silicone, gel, oil, latex, grease, and other like thermal interface materials that are used in the computer industry. It is preferable to coat the surface of the membrane  130  that will come into contact with the heat transfer plane  150 . 
       FIG. 4 a    shows a front view of the water sleeve  110  according to an embodiment of the present invention. The water inlet/outlet ports  410  run perpendicular to the sleeve  110 ; therefore they are shown in cross-section. The gasket seal  120  is also shown surrounding the sleeve  110 .  FIG. 4 b    shows a side view of the sleeve  110 , indicating the circulation of the liquid  190  in and through the membrane  130 , then out through the water port  410 . Circulating the liquid  190  serves to enhance the cooling effect provided by the thermal transfer plane. The liquid  190  is circulated by an external water cooling circuit  450  coupled with the sleeve  110  through the ports  410 . The circulating liquid  190  carries away the heat generated by the computer  125 . The water cooling circuit  450  can include a pump that maintains the fluid in circulation and a cooling device such as a finned radiator with a fan. 
     Therefore, while there has been described what is presently considered to be the preferred embodiment, it will understood by those skilled in the art that other modifications can be made within the spirit of the invention. The above description of an embodiment is not intended to be exhaustive or limiting in scope. The embodiment, as described, was chosen in order to explain the principles of the invention, show its practical application, and enable those with ordinary skill in the art to understand how to make and use the invention. It should be understood that the invention is not limited to the embodiment described above, but rather should be interpreted within the full meaning and scope of the appended claims.