Patent Publication Number: US-2010124022-A1

Title: Thermoelectric cooling apparatus and method for cooling an integrated circuit

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional application number 61/114,846, filed Nov. 14, 2008, which is incorporated by reference in its entirety herein. 
    
    
     BACKGROUND 
     The present application relates to a computer system with a cooling apparatus that cools an integrated circuit. In particular, the present application relates to a computer system with a cooling apparatus that cools an integrated circuit using a pipe and a thermoelectric cooling module. 
     In addition, the present application relates to a method of cooling an integrated circuit. In particular, the present application relates to a method that cools an integrated circuit by circulating fluid in a pipe in thermal contact with the integrated circuit and a thermoelectric cooling module. 
     Integrated circuits, also known as microchips, silicon chips, microcircuits, or chips, have consistently migrated to smaller feature sizes and form factors over the past several years allowing for more transistors to be packaged in a single integrated circuit. Electricity passing through transistors generates heat. Heat dissipation requirements also tend to increase as transistor switching speeds become faster. Because the density of transistors within a single integrated circuit is continuing to increase, as is the operational switching speed of these transistors, an ever-increasing significant amount of heat must be dissipated to reduce the possibility of undesired consequences such as overheating, melting, or system crashes. 
     Heat sinks and fans are commonly used to dissipate heat generated by integrated circuits, however they are subject to mechanical failure and dust build-up after prolonged use. In addition, cooling approaches that employ active mechanisms such as fans tend to have a certain amount of noise associated with their operation. This noise can range from being merely annoying to highly distracting. 
     In addition, heat sinks and fans have limited heat dissipation capacity limited to the surface area of the heat sink and the amount of air circulated by the fan. 
     SUMMARY 
     An advantage of the present application is to provide a computer apparatus with a cooling apparatus and a method capable of cooling an integrated circuit without mechanical moving parts that are subject to mechanical failure or dust build-up after prolonged use. 
     The computer apparatus according to an embodiment combines an integrated circuit with a cooling apparatus. The cooling apparatus includes: a thermoelectric cooling module, a heat sink, a fluid-bearing pipe, a magneto-hydrodynamic pump assembly, a heat exchange attachment and a reservoir for additional fluid. 
     Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a perspective view of a computer system with a cooling apparatus of one embodiment of the present disclosure. 
         FIG. 2  is a perspective view of a heat exchange attachment of one embodiment of the present disclosure. 
         FIG. 3  is a cross sectional view of magneto-hydrodynamic heat pump assembly of one embodiment of the present disclosure. 
         FIG. 4  is a perspective view of a thermoelectric cooling module of one embodiment of the present disclosure 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present application will be described in detail with reference to the accompanying drawings. 
       FIG. 1  shows a computer apparatus  1  according to an embodiment. Computer apparatus  1  as shown in  FIG. 1  includes a case  2 , an integrated circuit  3  and a cooling apparatus  4 . 
     The case  2  further includes a first side  5 , a second side  6 , a third side  7 , a fourth side  8  and a fifth side  9 . While computer system  1  in  FIG. 1  is shown without a sixth side, an embodiment may include a sixth side as well as a wall covering all sides of a computer system including the sixth side. The walls may be solid or hollow, but are commonly metal or plastic or a combination thereof. The first side  5 , as shown in  FIG. 1 , also includes an opening  10  therethrough to allow a portion of the cooling apparatus to extend outside case  2 . 
     In addition, while  FIG. 1  shows the computer apparatus  1  in a horizontal desktop position, a computer apparatus in an embodiment could be in vertical tower position. Furthermore, the form factor for the computer apparatus in an embodiment could be a laptop, a rack-mount server, a desktop or the like. 
     The integrated circuit  3  in  FIG. 1  is a central processing unit (CPU) and is shown as being at least partially enclosed by the case  2 . While this integrated circuit  3  in  FIG. 1  is a CPU, an integrated circuit in an embodiment could be a graphics processing unit (GPU) or any other microchip that requires cooling. 
     The cooling apparatus  4  in the embodiment includes a pipe  11 , a heat exchange attachment  12 , a reservoir  13 , a magneto-hydrodynamic pump assembly  14 , a thermoelectric cooling module  15  and a heat sink  16 . 
     Pipe  11  as shown in  FIG. 1  is arranged to circulate fluid in order to carry heat away from the integrated circuit  3  to the thermoelectric cooling module  15 . A portion of this pipe  11  extends through the aforementioned opening  10  (and hence the pipe  11  is partially outside of the case  2 ) thereby allowing for more efficient heat dissipation. While  FIG. 1  shows a single pipe having a 1 inch diameter, an embodiment may include a single pipe having other diameters or even multiple pipes of uniform or varying diameters. In addition, in an embodiment the pipe may be completely enclosed by the case  2  rather than partially extending therefrom as shown here. This pipe  11  could be metal, glass, plastic or any other material of choice. Depending on the fluid within the pipe, metal may be preferred because of the expansive characteristic of many liquids when heated. 
     The heat exchange attachment  12 , as shown in  FIG. 1 , is connected to the pipe  11 . As further shown in  FIG. 2 , the heat exchange attachment  12  includes a fluid-containing reservoir  22  wherein the pipe  11  enters and exits the reservoir  22 . So configured, fluid within the pipe  11  can similarly enter the reservoir  22  and then exit accordingly. 
     A planar surface of reservoir  22  comprises a heat-exchange medium that is in direct physical contact with the integrated circuit  3  and hence there is good thermal contact between the reservoir  22  and the integrated circuit  3 . This reservoir  22 , at least at this point of physical contact, may be made of a heat conductive material such as a suitable metal. While the embodiment shows the heat exchange attachment  12  as comprising a reservoir  22 , there are other possibilities. For example, the heat exchange attachment  12  could be a fin heat sink, or a portion of the pipe  11  that is shaped and disposed to be in thermal contact with an integrated circuit  3 . 
     Referring again to  FIG. 1 , the early-mentioned reservoir  13  contains additional fluid. As shown in  FIG. 1 , this reservoir  13  is connected to the pipe  11  and is in direct physical and thermal contact with the thermo-electric cooling module  15 . This reservoir  13  may be metal or plastic, or a combination thereof. In an embodiment, the additional fluid in this reservoir  13  increases the heat-absorption capacity of the cooling apparatus  4 . This reservoir  13  is optional and in an embodiment, this reservoir  13  for additional fluid need not be part of the cooling apparatus. 
     The magneto-hydrodynamic pump assembly  14  as shown in  FIG. 1  connects to a portion of the pipe  11 . Magneto-hydrodynamics generally refers to the behavior of a plasma, or, in general, any electrically-conducting fluid in the presence of electric and magnetic fields. Accordingly, this magneto-hydrodynamic pump assembly utilizes such fields to effect the movement of an electrically-conductive fluid of choice. This fluid, in turn, serves as a carrier to move heat from the integrated circuit to the thermoelectric cooling module  15 . 
     While  FIG. 1  shows this magneto-hydrodynamic pump assembly  14  to be connected to a portion of the pipe  11  between the heat-exchange attachment  12  and the thermoelectric cooling module  15 , a pump in an embodiment could be located at any portion of the pipe  11 . In addition, an embodiment could use an ordinary fluid pump instead of a magneto-hydrodynamic pump assembly. It will also be understood that more than one such pump assembly could be employed if desired. 
       FIG. 3 . is a cross section of a magneto-hydrodynamic pump assembly according to an embodiment. In this illustrative example, the magneto-hydrodynamic pump assembly  14  includes a pair of mutually attractive magnets  32 ,  33  positioned to create a magnetic field  34  across the pipe  11 , and a pair of electrodes  36 ,  37  used to generate an electric current  38  through the aforementioned magnetic field  34 . These magnets  32 ,  33  may be permanent magnets or electromagnets. Generally speaking, for many application settings, the permanent magnet (such as a neodymium magnet) may be preferred since an electromagnet might interfere with the perpendicular electric field needed to effectively circulate the fluid. 
     Together, the electric current  38  and the magnetic field  34  exert a force on a fluid within the pipe  11  that is perpendicular to the electric current  38  and the magnetic field  34 , thereby circulating the fluid through the pipe  11 . The amount of the force depends on the strength of the magnetic field  34  and the electric current  38 . Generally, the greater the strength of the magnetic field  34  or the electric current  38 , the greater the force exerted on the fluid in the pipe  11 . 
     The movement and circulation of an electrically conductive liquid by use of a magneto-hydrodynamic pump is achieved through the effects of Lorentz Force. The Lorentz Force can be represented as F=qE+qv×B, where F is the magnitude and direction of force, qE is the magnitude and direction of the electric current  38 , qv is the velocity of the current, and B is the magnitude and direction of the magnetic field  34 . In an embodiment, the magneto-hydrodynamic pump assembly could include a plurality of electrodes as well as a plurality of magnets. 
     A magneto-hydrodynamic pump assembly works well with an electrically conductive fluid such as a liquid metal (for example, mercury (Hg)), but in an embodiment the fluid could be water, salt-water (such as water having 2% or so salinity), or any other thermally and electrically conductive fluid. Depending upon the application setting, one could also consider employing ionized gas as the electrically conductive fluid. In an embodiment, a magneto-hydrodynamic pump assembly could include magnets that are coated in a magnetic-shielding material such as Mu-metal to reduce the likelihood of interfering with other magnetically-sensitive components of the computer system. 
     As noted above, the thermo-electric cooling module  15  as shown in  FIG. 1  is in thermal contact with a surface of reservoir  13  which extends outside case  2  through opening  10 . Generally speaking, a thermoelectric cooler is a device that allows for the transfer of thermal energy from one of its sides to another, resulting in one cold side and one hot side. Accordingly, the basic design of a thermoelectric cooler typically comprises two main sides. Both of these sides are often made of ceramic plating. In between these two sides there are usually anywhere from two to over one hundred metal semiconductor cubes, also known as pellets. These cubes are attached to thin copper strips that alternate vertically, each containing two cubes. This chain forms a complete circuit and allows electricity to pass through the thermoelectric cooler. 
     Typically, half of these semiconductor cubes are P-type semiconductors and the other half are N-type semiconductors. Both the P-type and N-type semiconductor crystals in their entirety are electrically neutral. These materials, however, have impurities that result in an excess or deficit of electrons. When a direct current is applied to a thermoelectric cooler, electrons flow from the negative side of the circuit, through the N-type cube, through the opposite copper strip, through the P-type cube in the other direction, and back to the positive side of the circuit. As electrons are passing through the N-type cubes, thermal energy is transferred in the direction opposite of the current flow from one ceramic plate to the other. When these electrons reach the P-type cubes, they easily flow through the holes and thermal energy is transferred along with them. Those skilled in the art will recognize this as a practical application of the Peltier effect. 
     As shown in  FIG. 4 , by one approach this thermo-electric cooling module  15  consists of a plurality of n-type  45  and p-type  46  semiconductors connected in a series circuit. As current travels through the corresponding p-type and n-type junctions  40 ,  41 ,  42 ,  43  of these semiconductors, electrons lose or gain energy depending on the direction of the current. This results in cooling or heating at these junctions  40 ,  41 ,  42 ,  43 . These junctions  40 ,  41 ,  42 ,  43  are arranged such that there is a cold side  50  and a hot side  51 . The cold side  50  is in thermal contact with the reservoir  13 , and the hot side  51  is in thermal contact with the heat sink  16 . While  FIG. 4  shows this cold side  50  as comprising a surface of the reservoir  16 , in an embodiment the cold side of the thermo-electric cooling module could be separate layer. 
     As further shown in  FIG. 4 , the heat sink  16  is a common fin-based heat sink allowing for the absorption and dissipation of heat from the thermoelectric cooling module into the surrounding air. This thermoelectric cooling module  15  therefore serves to pump heat from the pipe  11  to the heat sink  16 . 
     So configured, an increased quantity of heat can be ready dissipated in application settings where the heat-generating components are typically small (and getting smaller). It will be appreciated that these teachings also yield an essentially silent approach to heat-dissipation. These approaches are highly scalable and can be usefully employed in a wide variety of application settings. 
     It should be understood that various changes and modifications to the embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.