Patent Publication Number: US-2007109746-A1

Title: Liquid cooling of electronic system and method

Description:
BACKGROUND  
      In many electronic systems, the heat-generating components that process information remain cooled by air cooling systems. The heat that a heat-generating component such as a central processing unit (CPU), for example, generates increases as its data-processing speed rises and also as it performs more and more functions. For example, in order to generate new speeds, CPUs have more transistors and are drawing more power and have higher clock rates. Therefore, the trend in power requirements suggests that processor and memory power may require more cooling capacity than what can be provided by air cooling. Heat sinks, such as radiators, have been added to electronic systems to help alleviate some of the heat produced by the heat-generating components into the surrounding environment. A problem is that the size of radiators heat sinks and fans necessary to dissipate the heat within the housings of electronic systems present unworkable solutions.  
      Liquid cooling systems are known to provide an alternative to air cooling. In a liquid cooling system, a liquid cooling fluid which has a far higher specific heat than air is circulated inside the electronic system to dissipate heat. For example, the liquid cooling fluid can contact a portion of a heat-generating component or a heat sink to transfer heat from the higher temperature heat-generating component to the lower temperature liquid. The temperature of the liquid cooling fluid is elevated and transfers the heat to the ambient air and the temperature of the liquid cooling fluid is lowered again. The liquid cooling fluid then travels back through the system to the heat-generating component to continue the process. A problem, however, is that in many applications the risks involved in liquid cooling can be greater due to down-time in maintenance and repair and the possible damage caused by leaking liquid cooling fluid.  
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
      The example embodiments of the present invention can be understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Also, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
       FIG. 1  is a perspective view of an electronic system having a liquid cooling system, according to an embodiment of the present invention;  
       FIG. 2  is a cross-sectional view of the electronic system of  FIG. 1  along lines  2 - 2  showing a heat-generating component mounted to a printed circuit board and cooled by the liquid cooling system, according to an embodiment of the present invention;  
       FIG. 3  is a perspective view of the electronic system of  FIG. 1  showing a liquid cooling system having a magnetically-driven impeller attachable to a circuit board, according to an embodiment of the present invention; and  
       FIG. 4  is a cut-away perspective view of a portion of an electronic system showing a liquid cooling system having a mechanically-driven impeller attachable to a circuit board, according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
      For convenience, an electronic system in accordance with example embodiments of the present invention is described within the environment of a computer. However, one of ordinary skill in the art can appreciate that embodiments of the electronic system can be within the context of one of several electronic devices containing electrical components.  
       FIG. 1  shows a perspective view of an electronic system  100  according to an embodiment of the present invention. The electronic system  100  resides in an enclosure  102  having a top portion  104 , a base portion  106 , and side walls, for example, a front wall  108 , left and right side walls  110 ,  112 , and a back wall  114 . The base portion  106  supports a circuit board  120  and a liquid cooling system  130  internal to the enclosure  102 .  
      The liquid cooling system  130  includes a motor  132 , an impeller  134  (shown in phantom) enclosed by impeller housing  136 , a plurality of heat sinks  140 ,  142 ,  144 ,  146 , and conduit  148  which carries the liquid cooling medium between heat sinks  140 ,  142 ,  144 , and  146  for example, through conduit portions  150 ,  152 ,  154 ,  156 , and  158 . The conduit  148  can be for example, a continuous tubing that flows through and between the heat sinks  140 ,  142 ,  144 ,  146 . In an alternative embodiment, portions of conduit  148 , for example, portions  150 ,  152 ,  154 ,  156 , and  158  can be formed by the heat sinks  140 ,  142 ,  144 ,  146 , respectively.  
      A heat-generating component, such as heat-generating components  160 ,  162 ,  164 ,  166 , which can be for example an integrated circuit or chip, can generate much heat as it operates to process data at high speeds to perform many functions. During operation the temperature of electronic system  100  becomes elevated and the environment needs to be cooled to ensure the stable operation of heat-generating components and other electrical components. Cooling is facilitated by the cooling system  130  having heat sinks  140 ,  142 ,  144 , and  146 .  
      In one embodiment the liquid cooling medium flows along a closed circulation path  131 . At least a portion of the closed circulation path  131  of the liquid cooling system  130  contacts one or more heat sinks  140 ,  142 ,  144 , and  146 . In an alternative embodiment, the entire closed circulation path  131  can contact the heat sink. The electronic system  100  of  FIG. 1  has a plurality of heat sinks such as heat sinks  140 ,  142 ,  144 , and  146 , however, the electronic system  100  can have a single heat sink that is sized to be in thermal communication with all of the heat-generating components  160 ,  162 ,  164 , and  166 , or the circuit board  120  or both. Portions of the closed circulation path  131 , as shown in  FIG. 1 , are disposed within the heat sinks  140 ,  142 ,  144 , and  146 , however in an alternative embodiment, the closed circulation path  131  of the liquid cooling system  130  can be disposed on the heat sinks or otherwise contact the surface of heat sinks  140 ,  142 ,  144 , and  146 .  
      The flow of the liquid cooling medium through the closed circulation path  131  can initiate from within the impeller housing  136  through conduit portion  150  and into heat sink  140 , through conduit portion  152  through heat sink  142 , through conduit portion  154 , through heat sink  144 , through conduit portion  156  to heat sink  146 , through conduit portion  158  and back to impeller housing  136 . The motor  132  drives the impeller  134  to rotate which forces the flow of liquid cooling medium through the impeller housing  136  and through the conduit  148 .  
      In an alternative embodiment, the liquid cooling medium can flow in the opposite direction, for example, from the impeller  134  through conduit portion  158  to heat sink  146 , and so on through conduit portions  156 ,  154 ,  152 , and  150  which connect to heat sinks  144 ,  142  and  140 , respectively. Regardless of the path of flow, the liquid cooling fluid absorbs heat produced by heat-generating components  160 ,  162 ,  164 ,  166  and the heat diffuses to the plurality of the heat sinks which radiate the heat from their surfaces. While flowing through the closed circulation path  131  the liquid cooling medium releases heat, and can be air cooled as it passes through conduit  148  and before being supplied back into the impeller housing  136 . This cooling cycle is repeated.  
      The motor  132  is external to the closed circulation path and does not come into contact with the liquid cooling medium that flows within the closed circulation path  131 . In this configuration the motor  132  can be removed from the liquid cooling system for repair or replacement without disturbing the liquid cooling medium, as will be further described. In this respect, the integrity of the closed circulation path  131  is maintained while decoupling the motor  132 , thereby advantageously preventing a leak of the liquid cooling medium from the closed circulation path  131  while the motor  132  is decoupled therefrom.  
      The heat sinks  140   142 ,  144 , and  146 , are in thermal communication with heat-generating components (shown in phantom)  160 ,  162 ,  164 , and  166 , respectively. The “heat-generating component” as used herein describes one or more components that produce heat during operation. An electronic module, for example, may contain, but is not limited to, a semi-conductor package, one or more microprocessors, application specific integrated circuits (ASIC), analog circuits, digital circuits, programmed logic devices, memory devices, chips, for example. An electronic module that includes one or more microprocessors may also be referred to, for example, as a processor module.  
       FIG. 2  is a cross-sectional view of the electronic system  100  of  FIG. 1  taken along lines  2 - 2 . Heat-generating component  166  is shown attached to a connector  202  which is received by receptor  204  to make electrical connection to the printed circuit board  120 . The heat-generating component can be connected to the circuit board  120  by a connector  202  that may be a pin connector and receptor  204  may be a pin receptor, for example. Alternatively, the connection between the heat-generating component  166  and printed circuit board  120  may be fixed, such as, for example, by a soldered connection, such as a ball grid array. Other types of connectors may also be used. The heat-generating component  166  can also be physically connected to the circuit board  120  by an adhesive or a combination of a connector and an adhesive.  
      Referring back to  FIG. 1  the heat-generating component  166  is disposed between the circuit board  120  and the heat sink  146 , however, in an alternative embodiment, the circuit board  120  can be disposed between the heat- generating component  166  and the heat sink  146 . For example, the heat sink  146  can be located along the surface of the circuit board  120  that is opposite to the surface on which the heat-generating component  166  is mounted. In the embodiments described the liquid cooling system can transfer heat away from the heat-generating components  160 ,  162 ,  164 , and  166  and the circuit board  120 . The liquid cooling system  130  is in thermal communication with the heat-generating components, for example heat-generating component  166 , and is also in thermal communication with the circuit board  120 .  
      Heat sink  146  can have a top portion  208  and a bottom portion  210  that are connected by a plurality of securing devices, for example, securing devices  220 ,  222 . Removal of the top portion  208  of heat sink  146  can allow for easy access of the conduit  148 , for example conduit portion  170 . Referring to  FIGS. 1 and 2 , conduit portion  170  is shaped, for example in a serpentine configuration, such that the flow of liquid cooling medium makes several passes along the surface of heat sink  146  to improve heat transfer from the liquid cooling medium to the heat sink  146 .  
      In another embodiment of the invention, liquid cooling system  130  of the electronic system can further include a heat sink, for example heat sink  180 , that extends radially from closed circulation path  131  of the liquid cooling system  130 . Heat sink  180  can include a plurality of heat radiating plates  181  which can radiate heat from their surfaces to release heat from the liquid cooling medium. The additional surface area can result in greater heat transfer released from the electronic system. Heat sink  180  is shown along conduit portion  158 , however, heat sink  180  can be located along one or more various locations along conduit  148 .  
      Heat sinks  140 ,  142 ,  144 , and  146 , and  180  can be made of one of many thermally conductive materials, for example, materials that contain at least one of aluminum, copper, and graphite, which have a desirable heat transfer coefficient.  
      The conduit  148  for transporting the liquid cooling medium can be made of a thermally conductive material, for example copper, which has a desirable heat transfer coefficient and is corrosion resistant. The conduit  148  can also be made of a polymer, such as, a thermoplastic or thermoset polymer that has a desirable heat transfer coefficient, for example a silicone-based compound. It should be understood, however, that the conduit does not need to made of a thermally conductive material and many other materials may be used.  
      The liquid cooling medium can be any one of a variety of liquids including, but not limited to, water, and ethylene glycol, for example. In one embodiment, the liquid cooling medium has a specific heat that is much greater than air.  
       FIG. 3  is a perspective view of electronic system  100  of  FIG. 1  showing the motor disassembled or removed from the liquid cooling system  130 , according to an embodiment of the invention. The impeller  134  remains at least partially disposed within the closed circulation path  131  and the motor  132  is external to the closed circulation path  131 .  
      In one embodiment of the invention, impeller  134  is driven by motor  132  in a contactless driving arrangement. As shown in  FIGS. 1 and 3  the impeller  134  is magnetically-driven by the motor  132 , for example. The motor  132  can include a rotary bearing  338  which slides around a driving shaft  339  of the impeller  134  to magnetically rotate the impeller  134 . The rotation of the impeller  134  draws the liquid cooling medium into the impeller housing  136  and then discharges the liquid cooling medium through the conduit  148 , for example conduit portion  150 , along the closed circulation path  131  and to the heat sinks  140 , 142 ,  144 , and  146  as described above with respect to  FIGS. 1 and 2 .  
      Securing devices  320 ,  322 ,  324 ,  326 , and support bracket  310  support the motor  132  when it is connected to the printed circuit board  120  ( FIG. 1 ) during operation of the liquid cooling system  130 . Securing devices can be inserted through tab openings  312 ,  314 , of the support bracket  310  and through openings  321 ,  323 ,  325 , and  327  of printed circuit board  120 . Support bracket  310  and securing devices  320 ,  322 ,  324  and  326 , can engage the printed circuit board  120  directly, or to mounting hardware (not shown) which can be attached to the printed circuit board  120 . Securing devices may be threaded to engage threads of the mounting hardware or they may be snap-fitted into a mating component of the mounting hardware or circuit board  120 .  
      Securing devices  320 ,  322 ,  324 ,  326 , and support bracket  310  are shown disconnected from the circuit board  120  so that the motor  132  can be removed from the liquid cooling system  130  and also from the electronic system  100 , whereas the impeller housing  136  remains connected to the liquid cooling system  130 , and optionally, the printed circuit board  120  by securing devices  302 ,  304 . Once the motor  132  is decoupled from the impeller  134 , the motor  132  can be pulled away from the impeller  134  along the axis of connection  350  while the closed circulation path  131  of the liquid cooling system  130  remains closed. This arrangement facilitates easy repair or replacement of the motor  132 , or a motor component, without breaking the closed circulation path of the liquid cooling system  130 .  
      In one embodiment the method for disassembling a liquid cooling system  131  in electronic system  100  comprises decoupling the motor  132  from the closed circulation path  131  containing liquid cooling medium. The motor  132  can be disconnected by unfastening the securing devices, such as for example, securing devices  320 ,  322 ,  324 , and  326  and pulling the rotary bearing  338  away from the driving shaft  339  of the impeller  134 , for example, such that magnetic attraction is dissipated.  
       FIG. 4  is a perspective view of electronic system  400  showing motor  432  disassembled or removed from the liquid cooling system  430 , according to another embodiment of the invention. The liquid cooling system  430  of electronic system  400  includes closed circulation path  431 , motor  432  and impeller  434  disposed inside housing  436 .  
      Impeller  434  is driven by motor  432  in a mechanical driving arrangement. In one embodiment, the impeller housing  436  can include a shaft  438  that protrudes therefrom having a spline opening  437 , for example an opening having protrusions are arrayed in the circumferential direction and extended in the radial direction. The spline opening  437  of shaft  439  can mate with or receive spline shaft  439  of the motor to mechanically rotate the impeller  434  to circulate the liquid cooling medium within the closed cooling path  431  of the liquid cooling system  430 . The rotation of the impeller  434  driven by motor  432  draws the liquid cooling medium from within conduit, such as conduit portion  450  and into the impeller housing  436  and then discharges the liquid cooling medium through the conduit, for example conduit portion  458 , and along the closed circulation path  431  to the heat sinks (not shown) along the same or similar alternative circulation paths as described above with respect to  FIGS. 1 and 2 .  
      One skilled in the art will recognize several alternative mechanisms are available for rotating the impeller  434 . The impeller  434  may be driven directly from a motor  432  as shown. In an alternative embodiment, a motor  432  may drive a pulley arrangement or a gear arrangement formed on or attached to the impeller  434 . For example, the impeller  434  may include a central axle (not shown) where one end of the axle is attached to a pulley wheel which is driven by a belt from a drive pulley attached to motor  432 .  
      Securing devices  420 ,  422 ,  424 ,  426 , and support bracket  410  are shown disconnected from the circuit board  120  so that the motor  432  can be removed from the liquid cooling system  130  and electronic system  100 , whereas the impeller housing  436  remains connected to the liquid cooling system  130  and the printed circuit board  420  by securing devices  402 ,  404 . Once the motor  432  is decoupled from the impeller  434 , the motor  432  can be pulled away from the impeller  434  while the closed circulation path  431  of the liquid cooling system  430  remains closed.  
      A method for disassembling liquid cooling system  430  of electronic system  400  includes decoupling the motor  432  from the closed circulation path  431  containing liquid cooling medium. The motor  432  can be disconnected by unfastening the securing devices, for example, securing devices  420 ,  422 ,  426 ,  428 , from openings  421 ,  423 ,  425 ,  427 , and then pulling the spline shaft  439  out of the spline opening  437 . The motor  432  can then be repaired or replaced without accessing the closed circulation path  431  and thus avoiding possible damage of components within the electronic system  400  caused by liquid cooling medium. Specifically, the integrity of the closed circulation path  431  is maintained while decoupling the motor  436 , thereby preventing a leak of the liquid cooling medium from the closed circulation path  431  while the motor  436  is decoupled therefrom.  
      In the embodiments of the invention shown and described above, for example in electronic system  100  ( FIG. 1 ), the motor  132  and the impeller  134  are attached to the circuit board  120  inside enclosure  102 , however the enclosure  102  is not necessary. In an alternative embodiment the heat sinks  140 ,  142 ,  144 , and  146  of the liquid cooling system  130  can be located on the circuit board  120 ,  420  and motor  132 ,  432 , and the impeller  134 ,  434 , can be remote from the circuit board  120 .  
      In another embodiment the motor  132  and the impeller  134  are external to enclosure  102  ( FIG. 1 ). In such arrangement the motor  132  and the impeller  134  can be located in a separate enclosure (not shown) and the closed circulation path  131  ( FIG. 1 ) can extend between two or more enclosures.  
      Although the invention is shown and described with respect to certain embodiments, it is obvious that equivalents and modifications will occur to others skilled in the art upon the reading and understanding of the specification. The present invention includes all such equivalents and modifications, and is limited only by the scope of the claims.