Patent Publication Number: US-7724517-B2

Title: Case for a liquid submersion cooled electronic device

Description:
This application is a continuation application of U.S. patent application Ser. No. 11/736,965 filed on Apr. 18, 2007, pending, which claims the benefit of U.S. Provisional Application 60/800,715 filed May 16, 2006, each of which is incorporated by reference herein in its entirety. 

   TECHNICAL FIELD 
   This disclosure relates to a liquid submersion cooling system, and in particular, to a liquid submersion cooling system that is suitable for cooling electronic devices, including computer systems. 
   BACKGROUND 
   A significant problem facing the computer industry is heat. The higher the temperature a component operates at, the more likely it is to fail. Also, high temperatures, while not causing catastrophic failures, can create data processing errors. Operation at high temperatures can cause power fluctuations that lead to these errors within a central processing unit (CPU) or on the motherboard anywhere that data management is handled. Despite efforts at reducing waste heat while increasing processing power, each new CPU and graphics processing unit (GPU) released on the market runs hotter than the last. Power supply and motherboard components required to provide power and handle signal processing also are producing more and more heat with every new generation. 
   The use of liquids in cooling systems to cool computer systems is known. One known method of cooling computer components employs a closed-loop, 2-phase system  10  as illustrated in  FIG. 1 . The 2-phase system  10  is employed to passively cool the north  12  and south  14  bridge chips. The vapor travels through a tube  16  to a cooling chamber  18 , the vapor turns back into liquid, and the liquid is returned by tube  20  to the chips  12 ,  14  for further cooling. In another known liquid cooling system, internal pumps move liquid past a hot plate on a CPU and then the heated liquid is pumped into a finned tower that passively cools the liquid and returns it to the plate. 
   In the case of large-scale, fixed-installation supercomputers, it is known to submerge the active processing components of the supercomputer in inert, dielectric fluid. The fluid is typically allowed to flow through the active components and then it is pumped to external heat exchangers where the fluid is cooled before being returned to the main chamber. 
   Despite prior attempts to cool computer components, further improvements to cooling systems are necessary. 
   SUMMARY 
   A liquid submersion cooling system is described that is suitable for cooling a number of electronic devices, including cooling heat-generating components in computer systems and other systems that use electronic, heat-generating components. Examples of electronic devices to which the concepts described herein can be applied include, but are not limited to, desktop computers and other forms of personal computers including laptop computers, console gaming devices, hand-held devices such as tablet computers and personal digital assistants (PDAs); servers including blade servers; disk arrays/storage systems; storage area networks; storage communication systems; work stations; routers; telecommunication infrastructure/switches; wired, optical and wireless communication devices; cell processor devices; printers; power supplies; displays; optical devices; instrumentation systems, including hand-held systems; military electronics; etc. 
   The electronic device has a portable, self-contained liquid submersion cooling system. The electronic device can include a housing having an interior space. A dielectric cooling liquid is contained in the interior space, and a heat-generating electronic component or a plurality of components are disposed within the space and submerged in the dielectric cooling liquid. The active heat-generating electronic components are in direct contact with the dielectric cooling liquid. Alternatively, the components are indirectly cooled by the cooling liquid. A pump is provided for transporting the cooling liquid into and out of the space, to and from a heat exchanger that is fixed to the exterior of the housing. The heat exchanger includes a cooling liquid inlet, a cooling liquid outlet and a flow path for the cooling liquid from the cooling liquid inlet to the cooling liquid outlet. Either the pump can be placed within the interior space so that it is submerged in the cooling liquid or the pump can be disposed outside the interior space. 
   In another embodiment, an electronic device is provided that relies on convection of the cooling liquid, thereby eliminating the need for a pump. In this embodiment, the heat-generating electronic component is disposed within the interior space that contains the dielectric cooling liquid. Convection causes the cooling fluid to flow out of the interior space to the heat exchanger, and from the heat exchanger back into the interior space. 
   An air-moving device, such as a fan, can be used to move air past the heat exchanger to increase the heat transfer from the heat exchanger. In addition, a filter, for example, a HEPA filter, can be located adjacent to the air-moving device for filtering the air. 
   When the electronic device is a computer, for example, a personal computer, a motherboard is disposed within the interior space. The motherboard includes a number of heat-generating electronic components. Heat-generating components of the computer may include: one or more CPUS, one or more GPUs, one or more memory modules such as random access memory (RAM), one or more power supplies, one or more mechanical storage devices such as hard drives, and other storage devices, including solid-state memory storage units. All of these components can be submerged in the cooling liquid. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a cooling system employing a 2-phase system  10  to passively cool the north and south bridge chips. 
       FIG. 2  is a view of an embodiment of a portable, self-contained liquid submersion cooling system on a personal computer. 
       FIGS. 3A and 3B  are perspective and end views, respectively, showing components of the liquid submersion cooling system of  FIG. 2 . 
       FIG. 4  is a perspective view of the computer case. 
       FIGS. 5A ,  5 B, and  5 C are perspective, top and side views, respectively, of the lid of the computer case showing the pass-through connector. 
       FIG. 6  is a detailed illustration of the pass-through connector. 
       FIG. 7  is a perspective view of the motherboard or main board of the computer. 
       FIGS. 8A and 8B  are perspective and side views, respectively, showing daughter cards on the motherboard and showing engagement with the lid. 
       FIG. 9  illustrates a subassembly including the case, motherboard and daughter cards in the case, and the lid. 
       FIG. 10  illustrates the subassembly of  FIG. 9  with a pump within the case. 
       FIGS. 11A and 11B  are perspective and end views, respectively, of a subassembly that includes a hard drive within the case. 
       FIGS. 12A and 12B  are perspective and end views, respectively, of a subassembly that includes multiple heat exchangers. 
       FIGS. 13A and 13B  are perspective and end views, respectively, of a subassembly that includes a single heat exchanger. 
       FIG. 14  is an end view similar to  FIG. 12B  showing how convection cooling works. 
       FIG. 15  is an illustration of a prototype computer that incorporates the liquid submersion cooling system, where the video boards and pump are visible in the case and the radiators are visible, mounted on the sides. 
       FIG. 16  is an illustration of the prototype computer of  FIG. 15  showing the front and top of the case. 
       FIG. 17  is a perspective view of another embodiment of a portable, self-contained liquid submersion cooling system on a personal computer. 
       FIG. 18  is a side view of the computer shown in  FIG. 17 . 
       FIG. 19  is an end view of the computer shown in  FIG. 17 . 
       FIG. 20  is a perspective view similar to  FIG. 17  but with the motherboard assembly partially lifted from the interior space. 
       FIG. 21  is an end view of the motherboard assembly removed from the computer. 
       FIG. 22  is a perspective view of the motherboard assembly. 
       FIG. 23  is a side view of the motherboard assembly. 
       FIG. 24  illustrates the motherboard assembly in a raised position. 
       FIG. 25  is a perspective view of the computer case with the motherboard assembly and lid removed. 
       FIG. 26  is a side view of the heat exchanger. 
       FIG. 27  illustrates a pair of heat exchanger plates used to form the heat exchanger. 
       FIG. 28  is a perspective view of the heat exchanger and fan. 
       FIG. 29  illustrates a snorkel attachment for use with a hard drive. 
       FIGS. 30A ,  30 B, and  30 C illustrate use of the snorkel attachment on a hard drive. 
       FIGS. 31A ,  31 B and  31 C illustrate details of the AC current cut-off mechanism associated with the lid. 
   

   DETAILED DESCRIPTION 
   A liquid submersion cooling system is described that is suitable for cooling a number of electronic devices, including cooling heat-generating components in computer systems and other systems that use electronic, heat-generating components. In the case of computer systems, the liquid submersion cooling system permits creation of, for example, desktop-sized computers with scalable architectures where it is possible to produce 32 to 64, or more, processor core systems (8 sockets×8 cores=64 processor). The processing power of these desktop-sized computer systems will rival or surpass supercomputing systems that, until now, would require significant floor space. 
   Examples of electronic devices to which the concepts described herein can be applied include, but are not limited to, desktop computers and other forms of personal computers including laptop computers; console gaming devices, hand-held devices such as tablet computers, wearable computers and personal digital assistants (PDAs); servers including blade servers; disk arrays/storage systems; storage area networks; storage communication systems; work stations; routers; telecommunication infrastructure/switches; wired, optical and wireless communication devices; cell processor devices; printers; power supplies; displays; optical devices; instrumentation systems including hand-held systems; military electronics; etc. The concepts will be described and illustrated herein as applied to a desktop-sized computer. However, it is to be realized that the concepts could be used on other electronic devices as well. 
     FIGS. 2 ,  3 A and  3 B illustrate one embodiment of a desktop-sized computer  20  employing a liquid submersion cooling system  22 . All active components are illustrated submerged in a tank of dielectric liquid. This system uses a dielectric cooling liquid in direct contact with the electronically and thermally active components of a computer system. Dielectric liquids that can be used in this type of immersive cooling system include, but are not limited to:
         Engineered fluids like 3M™ Novec™   Mineral oil   Silicone oil   Natural ester-based oils, including soybean-based oils   Synthetic ester-based oils
 
Many of these dielectric fluids also have the ability to extinguish fires on computer components. By submerging computer components in a dielectric, fire-retardant fluid, the chance of a fire starting due to computer component failure is minimized.
       
   Initial testing has involved the dielectric liquid 3M™ Novec™. However, other dielectric liquids, like mineral oil and ester-based oils, may be used. Other dielectric liquids that have a higher boiling temperature along with greater thermal transfer capability can be employed. These cooling liquids need not change state if they have a high enough thermal transfer capability to handle the amount of heat being generated by components contained in the system. 
   The lid  2  of the case  1  will attach to the connector side of the computer motherboard  30 , shown in  FIGS. 7 ,  8 A and  8 B, allowing motherboard input/output (IO) connections, daughter card  4  IO and power to be passed in and out of the system. Components such as daughter cards  4 , additional processors  6 , power supply card  5 , and memory cards  8  can be added to the system by opening the tank lid  2  and lifting the attached electronics out of the case  1 . In addition, a hard drive  11  can be disposed in the case  1 , with an air line  10  connected to the hard drive breather hole leading from the hard drive to the exterior of the case  1 . 
   At least one pump  13  will pump warm liquid from the top of the case  1  and pass it through surrounding heat exchangers  3 . The pump  13  may be submersed in the liquid as shown in  FIGS. 3B and 10 , or external to the case  1 . Using two external pumps  13  with quick-release hose attachments would allow hot-swapping of a failed pump while the other pump maintains system circulation. Using one external pump  13  with quick-release hose attachments would allow the change-out of a failed pump with only a brief system downtime. 
   The heat exchangers  3  can act as the outside surface and supporting structure of the computer case  1 . The majority of the case wall may act as a radiator surface. Unlike current Advanced Technology Extended (ATX) or Balanced Technology Extended (BTX) cases that push air through fans from the front of the case to the back, the disclosed system will take cold air from the base of the case and, aided by natural convection, pull more air up as intake air is heated and rises. The walls of the heat exchangers  3  may be tapered upward, like a cooling tower on a boiler. This tapering will help accelerate convection currents, making it possible to cool the system without the use of air-moving devices, such as fans. 
   As shown in  FIG. 3A and 3B , the case  1  is large enough to contain all of the active computer components that require cooling. It may also be necessary to leave space for liquid return lines  48  with nozzles over critical components that require cooling. Nozzles may be incorporated to direct the flow of the return liquid at specific, high-temperature areas like the CPUs. 
   As shown in  FIGS. 5A-C ,  6  and  9 , the lid  2  not only provides a liquid- and gas-tight seal for the case  1 , but it also contains a pass-through connector  7  that allows external component IO, storage IO and power to pass into and out of the case  1 , to and from the computer motherboard  30  and its components. The lid  2  will have a gasket that will seal the case  1 . The lid  2  may also contain a fill port  32  for filling the case  1  with coolant. 
   As shown in  FIGS. 7 ,  8 A and  8 B, the motherboard  30  is essentially functionally the same as in current ATX or BTX specification boards, with the exception being that it does not have the same IO and power connectors. Instead, the top edge of the board is lined with a series of conductive pads  34  that are contacts for engaging the pass-through connector  7  that is part of the lid  2 . Multiple motherboards or other circuit boards may be employed to allow stacking of extra processors  6  or other components for additional computing power or to allow for multiple computers within a single tank enclosure. This cooling system would allow for numerous computer systems to be cooled in a single tank or individual tanks which may be interconnected to create a server or workstation rack system. 
   As shown in  FIGS. 8A and 8B , the daughter cards  4  connect to the motherboard  30  as they do with current ATX or BTX specification boards. Daughter cards  4  can include video cards and other PCI or PCIE cards that require  10  pass-through to the outside of the case  1 . These daughter cards  4  will require liquid- and gas-tight gaskets in order to allow external IO connections. 
   Unlike ATX or BTX designs, the power supply  5  may also be a daughter card  4 , with no power supply to motherboard wiring required. The power supply may also be directly integrated into the motherboard. External alternating current (AC) connections would be made through a pass-through connector into the liquid-filled tank with a liquid and gas-tight gasket. 
   As shown in  FIG. 9 , the pass-through connector  7  is integrated into the lid  2  in such a way that it creates a liquid- and gas-tight electrical conduit for IO and power connectivity. It attaches to the motherboard  30  on the inside of the case  1  and leads to a connector break-out  36  on the outside of the tank  1 . 
   The pump  13  (or pumps) is either internally-mounted within the case  1 , submersed in the liquid as shown in  FIG. 10 , or externally mounted. The pump is used to circulate warm coolant from inside the tank  1  to outside of the tank  1  within the heat exchangers  3 . Liquid may also be circulated through external hard drive cooling plates as well. The pump  13  can be wired such that it can be turned on to circulate liquid even if the computer is off. Or the pump  13  can be wired to turn on only when the computer is on. After the computer is shut off, there is more than sufficient thermal capacity in the liquid within the case  1  to remove residual heat from the submerged components. This would ensure that there is no post-shut down thermal damage. Also, if a flow sensor or pump monitor indicates that flow of coolant has stopped or has slowed below a minimum required rate, a controlled shutdown of the computer could be completed well before any damage is done to the submerged components. This embodiment avoids the possibility of a fan failure, resulting in catastrophic failure of a computer that relies on air cooling. 
   As shown in  FIG. 10 , the pump  13  is illustrated in the lower left corner of the case  1 . Warm coolant is pumped from the top of the tank  1  to outside of the tank  1  into the heat exchangers  3 . The pump(s)  13  may alternatively be attached to the lid  2  of the computer. This would allow for direct intake of fluids from the warmest region of the tank  1  and make maintenance and replacement of warn-out pumps much easier. 
   As shown in  FIGS. 11A and 11B , the hard drives or other internal storage systems  11  can also be submerged. In the case of current platter-based, mechanical storage systems that require breather holes, the air line  10  could be fixed over the breather hole, allowing an open-air connection to the outside of the tank  1 . The rest of the drive  11  would be sealed as to be gas and liquid impermeable. 
   The processors  6  mount to the motherboard  30  via normal, vender-specified sockets. Testing has shown that no heat sinks or other appliances need to be attached to the processors  6  in order to cool them sufficiently for normal, vendor-specified temperatures. However, if lower operating temperatures or a higher level of heat transfer is required for processor  6  over-clocking, heat sinks, which greatly increase the exposed surface area of heat conduction from the processor(s)  6 , may be employed. 
   As shown in  FIGS. 12A and 12B , the heat exchangers  3  or heat exchanger surfaces may serve as the external shell or case of the computer  20 . When warm cooling liquid is pumped from within the case  1  to the heat exchangers  3 , the liquid is cooled to ambient temperature. Cooling of liquids utilizing a heat exchanger  3  can be accomplished by one of several means:
         A compressor, as is the case with typical refrigeration systems   Peltier effect cooling   Active air cooling of the radiator surface using a fan or other air-moving mechanism   Passive cooling by exposing as large of a thermally conductive heat exchange surface as possible to lower ambient temperatures       

   As shown in  FIGS. 12A ,  12 B,  13 A and  13 B, the heat exchangers  3  are designed such that they angle inward and upward, creating a cooling tower effect, as seen on industrial boilers. This taper will serve to create thermal conduction that draws more cool air from near the bottom of the case  1  and allows it to migrate naturally upward and out of the top of the heat exchangers  3 . Cool-air inlet ports (not shown) at the base of the heat exchangers can be covered with filter material in order to keep dust and other foreign matter out of the heat exchangers, while allowing air to enter. A fan or multiple fans may be used to aid in the upward flow of air through the cooling system. 
   As the cooled liquid is pumped back into the case  1 , it may be sent through tubes or other deflection/routing means to injector head assemblies that serve to accelerate coolant across the most thermally active components. This accelerated liquid would help to create turbulent flow of coolant across the heated surface. This turbulent flow would break down natural laminate flow, which is poor at conducting heat through a liquid because only the first few molecules of liquid that are in contact with the heated surface can actually take heat energy away from the heated surface. 
   The computer  20  can also include external, removable storage drives such as CD, DVD, floppy and flash drives (not illustrated). In addition, external IO, power button and other human interface controls (not shown) would attach to the pass-through connector  7  and be mounted on a rigid circuit board or flex circuit. 
     FIG. 12B  illustrates one possible flow path of liquid through the multiple heat exchangers  3 :
         1. Liquid is pumped out of the case  1  from the warm upper area of the case  1  by the pump  13  through an inlet pipe  40  and out a discharge pipe  42  (see  FIG. 10 ); the discharge pipe  42  is connected to an inlet  44  of the heat exchanger  3 .   2. Liquid flows through and is cooled by the heat exchanger  3  that is also one side wall of the computer case.   3. A connection  46  allows liquid to pass through from the heat exchanger  3  on one side of the case  1  to the heat exchanger  3  on the other side of the computer case  1 .   4. Coolant flows through the heat exchanger  3  on the other side of the case  1 .   5. Cooling liquid flows from the heat exchanger through a passageway  48  back into the case  1  near the bottom thereof where it is warmed by the heat-generating electronics and components and rises back to the top of the case  1  and the cycle begins again.       
   Alternatively, a single heat exchanger  3  as shown in  FIGS. 13A and 13B  can be used in the cooling system through the following steps.
         1. Liquid is pumped out of the case  1  from the warm upper area of the tank as in the embodiment in  FIG. 12B .   2. Liquid flows through and is cooled by the heat exchanger  3  that is on one side wall of the computer case  1 .   3. Cooling liquid flows back to the bottom area of the tank  1  through a passageway  50  where it is warmed and rises back to the top of the case  1 , and the cycle begins again.       

   The computer system can be cooled via active or passive convection cooling, as shown in  FIG. 14 . Rather than forcing air from the front of the case to the back of the case, as seen in conventional designs, air is allowed to travel vertically. Heat rises, and the cooling system  22  design takes advantage of this, as described in the following steps.
         1. Cool air from underneath the computer is drawn upward as shown by arrows  52 .   2. The heat exchangers  3  are designed to allow the cool air to flow upward between the heat exchangers and the outside of the case  1 . As heat is dissipated from the coolant inside the heat exchangers  3 , the cooler air around the heat exchangers  3  is heated and rises.   3. The air flows through the heat exchangers  3  and is expelled at the sides and top of the system. This rising air helps to pull more cool air into the system, much like a cooling tower for a boiler.       

   Air flow may be aided by the use of an air-moving device or devices such as one or more fans mounted on the top or bottom of the cooling stack. However, for some applications only passive, convection-induced air flow may be required. 
     FIGS. 15-16  illustrate a prototype computer  80  that incorporates the liquid submersion cooling system  22 . Due to the clear case, the video boards and pump are visible in the case and the heat exchangers are visible, mounted on the sides of the case. 
     FIGS. 17-19  illustrate another embodiment of a personal computer  100  employing an alternative liquid submersion cooling system  102 . The computer  100  includes a case  104  that has a liquid-tight interior space  106  ( FIG. 20 ) designed to be leak-proof so that it can be filled with a coolant liquid. As used herein, the word “case” is meant to include a housing, an enclosure, and the like. In the illustrated embodiment, the side wall  107  of the case defines at least one side of the interior space  106 , and a portion  109  of the side wall  107  is made of translucent, preferably transparent, material to allow viewing inside the space  106 . The material used for the portion  109  can be any material suitable for forming a leak-proof container and, if viewing of the internal computer components is desired, the material should be translucent or transparent. An example of a suitable material is a polycarbonate. 
   The case  104  also includes non-liquid tight space  111  next to the liquid-tight interior space  106  in which components of the computer  100  and the cooling system  102  are disposed as described below. 
   With reference to  FIGS. 17 and 20 , the case  104  includes a lid  108  that closes the top of the case  104 , but which can be removed to permit access to the spaces  106 ,  111 . The lid  108  includes a seal  113  (shown in  FIGS. 21 and 22 ) for forming a liquid-tight seal with the interior space  106  of the case when the lid  108  is in position closing the case. In addition, the lid  108  includes a handle  110  that facilitates grasping of the lid  108  and lifting of any internal computer components connected thereto out of the interior space  106 . The lid  108  also includes a pass-through connector  112  (partially visible in  FIG. 22 ), similar in function to the pass-through connector  7 , to which a motherboard  114  assembly is connected, and which permits pass-through connections such as USB ports, video card connections, etc., through the lid  108  to the inside of the space  106  and to the outside of the space  106 . 
   For safety, an AC current cut-off mechanism  115  is also provided, as shown in  FIGS. 31A-C , such that when the lid  108  is opened, electrical power in the computer is shut off, preventing operation of any electrical components. For example, the mechanism  115  may be accomplished by routing AC power through a bridge board  400  that is contained in, or otherwise connected to, the lid  108 . The board  400  is connected to the motherboard assembly  114  comprised of a motherboard  302  and a support  300  member. 
   The board  400  includes an AC power socket  402  for receiving AC power. A neutral line  404  and a ground line  406  leads from the power socket  402  to a pass-through connector  112  leading to the interior space  106 . In addition, a hot or live wire  408  leads from the socket  402  to a second pass-through connector  112  leading to the space  111 , passes under the board  400  and back to the top of the board  400  to a return portion  410  that connects to the pass through connector  112  to pass AC power into the interior space  106 . 
   An external board  412 , illustrated in  FIG. 31C , is fixed in the space  111 . The board  402  includes a u-shaped connector  414  at the top thereof, one end of which connects to the hot wire  408  and the other end of which connects to the return portion  410  when the lid  108  is in place. 
   When the case is opened by removing the lid  108 , the hot wire  408  becomes disengaged from the connector  414  on the external board  412 , opening the electrical circuit and disconnecting AC power from the interior space. The current cut-off mechanism  115  may also be accomplished by routing AC power through two pins on the bridge board  400 . These pins would be shorted, passing current back to the external board  412 . When the case is opened, the bridge board  400  becomes disengaged from the connector  414  on the external board  412 . 
   The lid  108  also includes an opening  116  through which liquid can be added into the space  106 . The opening  116  is closed by a removable cap which is removed when liquid is to be added. The lid  108  can also include a lock mechanism (not shown) that locks the lid in place. 
   With reference to  FIG. 20 , the case  104  can include a drain valve  118  (shown schematically) that can be opened in order to drain liquid from the case. The valve  118  can be any type of valve that can be opened and closed, preferably manually, for draining the case. The valve  118  is illustrated as being positioned at the bottom of the interior space at the bottom of the case  104 . However, the valve can be positioned at any other suitable location on the case. The front portion of the case  104  can have a touch screen display that allows users to run the computer  100  from the front without plugging in a monitor. 
   The motherboard assembly  114  acts as a support for many of the internal components of the computer  100 . The motherboard assembly  114  is removable and disposed in the interior space  106  to permit the motherboard assembly to be lifted from the case when the lid  108  is lifted upward. With reference to  FIGS. 20-22 , the motherboard assembly  114  includes a support member  300  on which is disposed a motherboard  302  that supports the submerged components. 
   The motherboard assembly  114  is fixed to the lid  108  via flanges  122  at the top end of the motherboard  114 , shown in  FIG. 24 , that connect to the pass-through connector  112 . In addition, a pair of tabs  123  that are fixed to the support member  300  are connected to the lid  108 . 
   An exemplary layout of the motherboard components is illustrated in  FIG. 23 . The layout is designed to render the motherboard nearly or completely  302  wire-free and facilitate movement of cooling liquid in the interior space  106 . The motherboard  302  is illustrated as having mounted thereto four CPUs and/or GPUs  124 , video/motherboard memory cards  126 , memory cards  127 , power supply  128 , and controller chips  130 . These components are laid out relative to each other to define a number of vertical and horizontal liquid flow channels that aid in the flow of liquid. For example, vertical channels include channel  132 A between the CPUs/GPUs  124 , channels  132 B between the controller chips  130 , and channels  132 C between the CPUs/GPUs and the memory cards  126 ,  127 . Horizontal channels include, for example, channel  134 A between the CPUs/GPUs, channel  134 B between the CPUs/GPUs and the controller chips  130 , and channel  134 C between the CPUs/GPUs and the power supply  128 . A plurality of sets of light-emitting diodes (LEDs)  136 , that can produce a desired color/wavelength of light, such as ultraviolet, can also be mounted to the motherboard  114  at dispersed locations. When illuminated, the LEDs  136  give the liquid in the interior space  106  a luminescent glow. 
   To help dissipate heat, heat sinks can be affixed to some or all of the heat-generating components on the motherboard  302 . The use of heat sinks will depend on the amount of heat generated by a particular component and whether it is determined that additional heat dissipation than that provided by direct contact with the liquid is necessary for a particular component. 
   As shown in  FIGS. 20-23 , heat sinks  140  are shown attached to the CPUs/GPUs  124  and the controller chips  130 . The heat sinks  140  each comprise a plurality of elongated fins  142  that extend from a base plate  144  fixed to the component. The fins  142  and plate  144  conduct heat away from the component. In addition, the fins  142  define flow channels therebetween that allow the cooling liquid to flow through and past the plurality of fins to transfer heat to the liquid. 
   Heat sinks  150  are also attached to the memory cards  126 ,  127  and the power supply  128 . The heat sinks  150  are similar to the heat sinks  140 , including fins  152  connected to a base plate  154  fixed to the component. However, the fins  152  are short, having an axial length significantly less than the fins  142 . Nonetheless, the fins  152  define flow channels therebetween which allow the cooling liquid to flow through and past the plurality of fins to transfer heat to the liquid. 
   As described above, the motherboard assembly  114  is removable and disposed in the interior space  106  to permit the motherboard assembly to be lifted from the space when the lid  108  is lifted upward. With reference to  FIG. 24 , the interior space  106  of the case  104  includes a pair of channels  160  at opposite ends of the walls that define the interior space. Each channel  160  extends from the top of the walls to the bottom, and are continuous from top to bottom. As shown in  FIGS. 22 and 24 , the side edges of the motherboard assembly are provided with slides  162  that are sized and configured to slide within the channels  160 . The channels  160  and the slides  162  help guide the motherboard assembly  114  when it is lifted upward from the case and when it is lowered back into the interior space. 
   With reference to  FIGS. 21-24 , one or more slide locking mechanisms  170  can be provided to retain the motherboard assembly  114  at a raised position outside the interior space  106 . Two slide locking mechanisms  170  are illustrated. However, a single slide locking mechanism could be used if found sufficient to retain the motherboard assembly at the raised position. By keeping the motherboard assembly raised, maintenance and/or replacement of motherboard components is facilitated, while also allowing liquid to drain down into the interior space  106  when the assembly  114  is lifted upward. 
   The slide locking mechanisms  170  can have a number of configurations. The illustrated embodiment is shown to include a stop member  172  that forms part of the slide  162 . The stop member  172  is pivotally connected to the motherboard assembly so that it can rotate between the position shown in  FIGS. 21-23  and the position shown in FIG.  24 . The stop member  172  is biased by a spring (not shown) to bias the stop member in a counterclockwise direction (when viewing  FIG. 21 ) so that when the motherboard assembly is lifted upward, the stop member(s) automatically rotate to the position shown in  FIG. 24  when the stop members  172  clear the channels  160 . 
   At the position shown in  FIG. 24 , the stop member  172  is prevented from further rotation in the counterclockwise direction to prevent the motherboard assembly from falling back down into the interior space  106  due to interference between the stop member(s)  172  and the structure forming the channels  160 . To release the slide locking mechanisms  170 , the motherboard assembly is lifted further upward, and the stop member(s) manually rotated in a clockwise direction to the position shown in  FIGS. 21-23 . The assembly is then lowered down into the case. 
   With reference to  FIGS. 17 and 20 , the submersion cooling system  102  includes a heat exchanger  180  mounted in the space  111  within the case  104 , a pump  210  mounted on the motherboard  302  inside the interior space  106 , and a dielectric cooling liquid within the interior space  106 . The interior space should contain enough dielectric cooling liquid to submerge the components that one wishes to be submerged. For example, the cooling liquid may substantially fill the interior space  106 , whereby all heat-generating components on the motherboard are submerged. The cooling system  102  is designed to direct heated dielectric liquid from inside the space  106  and into the heat exchanger  180  outside the space  106  where the liquid is cooled. The cooled liquid is then returned to the space  106 . 
   The heat exchanger  180  is positioned outside of the space and substantially forms an outer wall of the computer  100  as shown in  FIG. 18 . The heat exchanger  180  is configured to allow passage therethrough of the liquid for cooling. In the illustrated embodiment, the heat exchanger  180  is of a size to form substantially one wall of the case  104 . With reference to  FIG. 26 , the heat exchanger  180  includes an inlet  182  through which cooling liquid enters, an outlet  184  through which cooling liquid exits, and at least one flow path for cooling liquid through the heat exchanger extending from the inlet  182  to the outlet  184 . 
   The heat exchanger  180  can take on a number of different configurations, as long as it is able to cool the liquid down to an acceptable temperature prior to being fed back into the space  106 . An exemplary configuration of the heat exchanger  180  is shown in  FIGS. 26 and 27 . In this embodiment, the heat exchanger  180  comprises a plurality of identical plates  186  that are connected together. Each plate  186  includes a hole  188 ,  190  at each end that during use form plenums that receive the dielectric liquid. The plate  186  also includes a first plurality of holes  192  defined by bosses that extend in one direction, and a second plurality of holes  194  defined by bosses that extend in the opposite direction. The holes  188 ,  190  are also defined by bosses that extend in the same direction as the bosses defining the holes  192 . In addition, a central portion  196  of the plate  186  is bulged in the direction of the bosses of the holes  188 ,  190 ,  192 , so that the opposite side of the plate  186  is recessed  198  below a surrounding rim  200 . 
   To form the heat exchanger  180 , a first plate  186 A is flipped over as shown in  FIG. 27 , and the two plates  186 A,  186 B then secured together such as by soldering along the rim  200 . The two holes  188  are aligned at the top, and the two holes  190  are aligned at the bottom. In addition, the bosses that define the holes  194  engage with each other to form a number of air passages between the two plates  186 A,  186 B. The recesses  198  allow liquid to flow downward from the holes  188 , past the engaged bosses of the holes  194 , and down to the holes  190 . 
   A third plate  186  is then connected to one of the plates  186 A,  186 B, with the third plate being flipped over relative to the plate to which it is connected. The bosses that define the holes  188 ,  190  will engage each other, as will the bosses that define the holes  192 . This will create a series of air flow paths  202  on the outside of the heat exchanger as shown in  FIG. 26 . This process of adding plates  186  is repeated to create the size of heat exchanger needed. For the two plates at opposite ends of the heat exchanger  180 , the holes  192 ,  194  will be closed off to prevent escape of liquid. In addition, an inlet fitting  204  defining the inlet  182  will be connected to the boss defining the opening  188 , while an outlet fitting  206  defining the outlet  184  will be connected to the boss defining the opening  190 . At the opposite end of the heat exchanger, the openings  188 ,  190  are closed by suitable caps  208 . 
   In use of the heat exchanger  180 , liquid to be cooled flows into the inlet  182  and into the plenum at the top of the heat exchanger defined by the holes  188 . The liquid is able to flow downward in the recesses  198  past the bosses of the holes  194 . As it does, the liquid transfers heat to the bosses. At the same time, air can flow into the aligned bosses of the holes  194  to pick up heat. Air also flows into the flow paths  202  for additional heat exchange with the bulged central portion  196 . The cooled liquid collects in the plenum defined by the aligned holes  190 , and is pumped through the outlet  184  and back into the space  106  by the pump  210 . 
   Referring to  FIGS. 20 ,  22  and  23 , the pump  210  is mounted on the motherboard  302  and in use is submerged in the dielectric liquid. The pump  210  is sized to be able to circulate liquid to outside the space, through the heat exchanger, and back into the space. The pump  210  is illustrated as a centrifugal pump having an inlet  212  and an outlet  214 . The inlet  212  receives liquid therethrough from the space  106 , and pumps it through the outlet  214  connected to an outlet port  218  formed on the lid  108 . The outlet port  218  extends through the lid  108  and is fluidly connected to the heat exchanger inlet  182  by suitable tubing. The heat exchanger outlet  184  is fluidly connected by suitable tubing to an inlet port  222  formed through the lid to direct liquid back into the space  106 . 
   In areas where there is significant heat, direct impingement cooling can be used to provide localized cooling. In particular, as shown in  FIGS. 20 ,  22 , and  23 , a spray bar assembly  230  is connected to the inlet port  222 . The spray bar assembly  230  includes a central passageway  231  extending along the vertical channel  132 A, and plurality of branches or vents  232  that extend along the horizontal channels  134 A-C (and at the bottom of the space  106 ). The branches  232  include holes  234  ( FIG. 20 ) to direct cooled liquid directly onto the components  124 ,  126 ,  127 ,  128 ,  130 . The holes  234  are in the top of the branches  232  to direct liquid upwardly. However, holes could also be provided at the bottom of the branches to directed liquid downwardly onto the components. 
   An air-moving device can be provided to create a flow of air past the heat exchanger. A number of different air-moving devices can be used, for example, a fan or an ionization device. The drawings illustrate the use of a fan  240  to create air movement past the heat exchanger  180 . The fan  240  is best seen in  FIGS. 20 ,  25 , and  28 . The fan  240  is positioned at the bottom of the computer  100  at the base of the heat exchanger  180 . In the illustrated embodiment, the fan is a squirrel-cage type fan with an air outlet  241  that extends substantially across the entire length of the heat exchanger in order to create air flow across the entire heat exchanger. An air filter  242  is located in front of the inlet of the fan  240  in order to filter the air. The air filter  242  can be any suitable type of air filter, for example, a high-efficiency particulate air (HEPA) filter. The filter  242  is mounted so as it is able to slide and be removable from the case  104  by pulling on a handle  243 . This permits the filter  242  to be cleaned or replaceable with a replacement filter. Air is drawn into the filter and the fan via a series of air vents  244  ( FIG. 18 ) on the side of the computer. 
   The computer  100  can also include additional features, such as a drive mechanism  250  external to the case  104 . The drive mechanism  250  can be a DVD drive, a floppy drive, a CD drive, a Blu-ray drive, HD drive, and the like. In addition, one or more hard drives  252  are accessible from the opposite side of the case  104 . The hard drives  252  can be mounted so as to permit easy replacement with replacement hard drives. 
   In some embodiments, the hard drive  252  may be disposed within the interior space  106  of the case, submerged in the dielectric liquid. In these embodiments, it is necessary to equalize air pressure within the hard drive and the exterior of the space  106 . FIGS.  29  and  30 A-C illustrate a snorkel attachment  260  that can be connected to a breather hole  261  (see  FIG. 30A ) on a hard drive to aid in achieving the pressure equilibrium. The snorkel attachment  260  includes a circular cap  262  that is designed to fit around the breather hole  261  (see  FIG. 30B ) and form a liquid tight seal with the hard drive  252  to prevent entry of liquid. A fitting  264  extends from the cap  262 , and a breather conduit  266  connects to the fitting  264 . The breather conduit  266  can be directed to the outside of the space  106 , or the conduit  266  can connect to a fitting extending through the lid  108 . The snorkel attachment  260  permits achievement of pressure equilibrium between the hard drive and outside air pressure, allowing the hard drive to function properly while submerged in the dielectric liquid. 
   The dielectric liquid that is used in the computer  100  can be any of the dielectric liquids discussed above. In addition, a soy-based dielectric liquid can be used. If desired, a colorant material can be added to the dielectric liquid to make the liquid a particular color. Because the portion  109  of the side wall  107  is clear, adding a colorant to the liquid will change the visual impact of the computer.