Abstract:
Apparatus for removing thermal energy from PC circuit board devices such as graphics cards and the like, and including a waterblock adapted to be positioned on one side of a graphics cards, or the like, a heat sink adapted to be secured to the opposite side of the card, and a bridge plate adapted to extend over an edge of the card and be sandwiched between the heat sink and waterblock to serve as a means for coupling heat from the heat sink to the waterblock where it can be transferred to a liquid coolant and transported to an external radiator for disposal. The heat sink may include radiating vanes and an associated heat pipe for enhancing transport of thermal energy collected by the heat sink to the bridge plate.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a new device for removing heat from PC circuit board apparatus such as graphics cards, and the like, which generate substantial heat when in operation, and, more particularly, to liquid cooled waterblocks for transferring thermal energy from electronic components to a liquid flowstream. 
       BACKGROUND OF THE INVENTION 
       [0002]    Microprocessors are at the heart of most computing systems, and whether the system is a desktop computer, a laptop computer, a communication system, a television, etc., processors are often the fundamental building block of the system and may be deployed as central processing units (CPU), graphics processing units (GPU), memories, controllers, etc. 
         [0003]    With the advance of computer operating speeds, the thermal energy generated by active components of the computer, such as the processor and memory devices, often becomes significant. Furthermore, in order to enable desktop and other computers to rapidly process graphics and game technology, add-on units generally referred to as “graphics cards” or “VGA” cards” are often installed in computer devices. Such cards include a separate processor, called a GPU, one or more high speed memory devices, and other required circuitry, all mounted to a second circuit board including an edge connector that is adapted to plug into an available slot in the associated computer device. Typically, GPU and/or memory chips generate substantial heat that if not dissipated will adversely affect operation of not only the graphics card, but perhaps the entire computer. 
         [0004]    With the advancement of computing systems, the power of the processors driving these systems has dramatically increased. The speed and power of the processors has bee achieved by using new combinations of materials and by populating the processor with a larger number of processing circuits. As a consequence, the increased circuitry per unit area of the processor as well as the conductive properties of the materials used to build the processors has resulted in the generation of more and more heat. Further, as these computing systems have become more sophisticated, additional processors have been implemented within the computing system and thus contribute additional heat. In addition to the processors, other systems operating within the computing system may also generate significant heat and add to the heat experienced by the processors. 
         [0005]    Many adverse effects may result from the increased heat. At one end of the spectrum, the processor may begin to malfunction and incorrectly process information. For example, when the circuits of a processor are implemented with digital logic devices, the logic devices may incorrectly register a logical zero or a logical one, or logical zeros may be mistaken as logical ones and vice versa. Moreover, when a processor becomes overheated, it may experience a physical breakdown in its structure. For example, the metallic leads or wires connected to the core of the processor may begin to melt, and/or the structure of the semiconductor material itself may breakdown once certain heat thresholds are met. These types of physical breakdowns may be irreversible and render the processor and the computing system inoperable and un-repairable. 
         [0006]    A number of approaches have been implemented to address the issue of processor heating. Initial approaches focused on either cooling the air outside of the computing system, cooling the air inside the computing system, or a combination of both. An early approach was to cool the ambient environment using various types of air conditioning systems. But such solution was costly to build and operate, thus making the cold room impractical for this type of user. 
         [0007]    Another conventional cooling technique focused on cooling the air surrounding the processor within the computing system. This approach was implemented initially by providing simple ventilation holes or slots in the chassis of the computing system, and subsequently, by deploying a fan in the housing of the computing system. However, as processors became more densely populated with circuitry and as the number of processors implemented in a computing system increased, simply exchanging the air within the housing could no longer dissipate the necessary amount of heat from the processor or the chassis of the computing system. 
         [0008]    Other conventional methods of cooling computing systems have included the addition of sophisticated heat sink designs that can, in combination with various types of air blowers, remove the vast amounts of heat that can be generated by a modern processor. However, the size of the heat sink is directly proportional to the amount of heat that can be dissipated by the sink, and thus the more heat to be dissipated, the larger the heat sink required. Although larger heat sinks can be utilized, the size of the heat sink can become so large that this solution becomes infeasible. 
         [0009]    Refrigeration techniques and heat pipes have also been used to dissipate heat from a processor. However, these techniques have limitations. Refrigeration requires substantial additional power which drains the battery in a portable computing system. In addition, condensation and moisture, which is damaging to the electronics in computing systems, typically develops when using the refrigeration techniques. Heat pipes provide yet another alternative; however, conventional heat pipes have proven to be ineffective in dissipating the large amount of heat generated by a processor. 
         [0010]    Consequently, the heat produced by processors is quickly exceeding the levels that can be cooled using even specialized combinations of the air-cooling techniques mentioned above. 
         [0011]    More recently, heat removal systems have been implemented wherein a liquid is used to remove heat from heat exchangers disposed within the chassis, and in intimate relationship with the sources of heat, so that it can be dissipated outside of the computer housing. However, because space is limited within the computer housings it is necessary that the heat exchanger be small and highly efficient. Further, as a result of the competitive nature of the electronics industry, the additional cost for any new type of heat dissipation apparatus must be very low or incremental. 
         [0012]    Although a number of designs have been proposed and used to couple thermal energy from processors, such designs have in large part been similar in design to previous embodiments using air as the heat transporting fluid. When such designs are used to transport the more viscous liquid coolants, they do not usually achieve efficient heat transfer and often generate flow resistances that require substantial pumping power to move the fluid through the system. 
         [0013]    There is thus a need in the art for improved fluid handling apparatus for use in cooling computing systems and the processors deployed within the system. There is also a need in the art for optimal, cost-effective apparatus for cooling processors so that they may operate at marketed operating capacities. Moreover, there is a need for improved fluidic heat transfer and removal apparatus that can be deployed within the small footprint available in laptop computers, desktop, and other processing systems. 
       SUMMARY OF THE INVENTION 
       [0014]    Briefly, a presently preferred embodiment of the present invention includes a waterblock adapted to be positioned on one side of a graphics cards, or the like, a heat sink adapted to be secured to the opposite side of the card, and a bridge plate adapted to extend over an edge of the card and be sandwiched between the heat sink and waterblock to serve as a means for coupling heat from the heat sink to the waterblock where it can be transferred to a liquid coolant and transported to an external radiator for disposal. The heat sink may include radiating vanes and an associated heat pipe for enhancing transport of thermal energy collected by the heat sink to the bridge plate. 
         [0015]    A principal objective of the illustrated embodiment is provide a means for exchanging the maximum amount of heat per unit area by generating as much turbulence in the flow stream as possible without contributing material flow resistance. This embodiment utilizes the design of the flow channel and the offset positioning and design of the vanes or fins which extend the surface area of the heat transferring metal into the flow channel to accomplish this purpose. 
     
    
     
       IN THE DRAWINGS 
         [0016]      FIG. 1  is a schematic perspective view generally showing one side of a thermal energy transfer device, in accordance with the present invention; 
           [0017]      FIG. 2  is a schematic perspective view generally showing the other side of the thermal energy transfer device depicted in  FIG. 1 ; 
           [0018]      FIG. 3  is an elevational view of the thermal energy transfer device as viewed in the direction indicated by the arrows  3 - 3  of  FIG. 2 ; 
           [0019]      FIG. 4  illustrates the outside surface of the main heat transfer plate adapted to engage the electronic components to be cooled; 
           [0020]      FIG. 5  illustrates the interior side and flow channel details of the main heat transfer plate; 
           [0021]      FIG. 5   a  is a partial schematic perspective view generally showing one of the E-shaped vanes formed on the interior surface of the main heat transfer plate; 
           [0022]      FIG. 6  illustrates the finned exterior side of the secondary heat transfer plate; and 
           [0023]      FIG. 7  illustrates the interior side of the secondary heat transfer plate. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Referring now to  FIG. 1  of the drawings, one embodiment of a thermal energy transfer device in accordance with the present invention is depicted at  10  and shown operatively affixed to a graphics card  14  mounted in an expansion slot  16  of a PC “motherboard board”  12  of a computer system. 
         [0025]    In the illustrated embodiment, the device  10  is in the form of an assembly that includes, on one side of the card  14 , a waterblock  19  that includes a main heat transfer plate  18 , typically made of copper or other good thermally conductive material, and a cover plate  20  which, in the illustrated embodiment, is made of DELRIN, and on the other side of the card  14 , a finned secondary heat transfer plate or heat sink  22  made of a good heat conductive material such as aluminum. An upper portion of the heat sink  22  is thermally connected to the plate  18  by means of a bridging connection  28  not clearly shown in this figure. 
         [0026]    The upper portion of the assembly includes a pair of cooling fluid inlet and outlet ports to which flexible conduits  24  and  26  are joined to circulate fluid coolant through the waterblock  19 . The other ends of the conduits are connected to a pump and radiator or other heat exchanger means (not shown) typically mounted outside the chassis or housing of the computer system. Although the term “waterblock” is used herein, it will be appreciated that other coolant fluids besides water may be used in this embodiment. 
         [0027]    Referring now to  FIG. 2 , the opposite side of the assembly is shown to reveal details of the finned exterior of the secondary heat transfer mechanism or heat sink  22 . This view also shows the positioning of the bridging connector between the heat sink  22  and the plate  18 . Note that the connector extends across the top edge of card  14 . As will be more clearly shown and described below, the assembly including the heat sink  22 , bridging connector  28  and waterblock  19  is held together and clamped across the card  14  by three screws or bolts  30 . Other fasteners (not shown) may also be used to fasten the assembly to the card. 
         [0028]      FIG. 3  is an elevational view pictorially showing the relationship between the waterblock  19 , heat sink  22  and bridging connector  28 . Details of these elements will follow below, but briefly, note that the heat sink  22  includes a metal plate  32 , perhaps made of copper or aluminum, that on one side may be adapted to engage the card surface and/or specific sources of heat or board surface areas on one side of the card  14 . Extending across separated upper portions of the plate  32 , and across the entire mid and lower portions of the plate are a plurality of black anodized heat radiating fins  34 . Note also that the bridging connection  28  includes a conductive metal plate  36  and a heat pipe  38 , both of which are sandwiched between heat sink  22  and plate  18 . As indicated above, the assembly is held together by the screws or bolts  30 . 
         [0029]      FIG. 4  illustrates various details of the exterior side or face  40  of the plate  18  including an inlet port  25  to which the tube  24  is secured, and an outlet port  27  to which the tube  26  is secured as shown in  FIGS. 1 and 2 . Also provided on the face  40  are a plurality of raised surface areas  41 ,  43  and  45  for intimately engaging various electronic components on card  14 . The larger region  45  is specifically intended to engage the outer surface of the GPU. A conductive glue or grease may be used to enhance the heat transfer between the respective surfaces. Also shown are a plurality of bolt holes adapted to receive the plurality of bolts used to secure the plate  18  to the outer plate  20 . 
         [0030]      FIG. 5  illustrates the interior side or face of plate  18  and shows the fluid flow channel  40  formed of broadly grooved or recessed regions of the surface of the plate on the side which will face and be covered by and attached to the cover plate  20 . The channel  40  is molded or machined into the plate  18  and is circumscribed by narrow grooves  42  and  44  that are adapted to receive resilient “O-rings” which when engaged by the cover plate  20  form seals about the inner and outer boundaries of the channel  40 . Note that the channel  40  is of a generally diamonded shape to maximize surface contact with the fluid passing therethrough from the inlet aperture  25  to the outlet aperture  27 . Note also that the lower part of the channel  40  is widened at  46 , the portion opposite the region  45  on the other side which will overlie and engage the GPU on the graphics card  14 . 
         [0031]    The channel portion  46  is provided with a plurality of upstanding three-part generally E-shaped vane assemblies  48 , perhaps more clearly illustrated in  FIG. 5   a , that preferably extend through the channel to engage the facing surface of the cover plate  20  when it is attached. It will thus be appreciated that with the DELRIN plate  20  ( FIG. 1 ) secured in place over the plate  18  a continuous flow channel will be created that extends from the inlet port  25  to the outlet port  27 . The vanes  48  serve to disrupt the flow of fluid in the region  46  as it passes therethrough so as to create heat exchange enhancing turbulence in the flow across the GPU without materially increasing the flow resistance in the channel. 
         [0032]    Although turbulent flow may require a slightly higher input of energy from the flow causing pump than would be the case if the flow was laminar it is generally recognized that turbulent flow is essential for good heat transfer. 
         [0033]    The (dimensionless) Reynolds number characterizes whether flow conditions lead to laminar or turbulent flow; e.g. for a flow path of this type, it is believed that a Reynolds number above about 4000 (a Reynolds number between 2100 and 4000 is known as transitional flow) will be turbulent. At very low speeds the flow is laminar, i.e., the flow is smooth (though it may involve small vortices). However, as the flow speed is increased, at some point a transition is made to turbulent flow wherein unsteady vortices appear will interact with each other. 
         [0034]    In this embodiment, with a fluid flowing through the channel the rate of heat transfer between the bulk of the fluid in the channel and the external surface of plate  18  beneath the channel can be roughly calculated as: 
         [0000]    
       
         
           
             Q 
             = 
             
               
                 
                   ( 
                   
                     1 
                     
                       
                         1 
                         h 
                       
                       + 
                       
                         t 
                         
                           k 
                            
                           
                               
                           
                         
                       
                     
                   
                   ) 
                 
                 · 
                 A 
                 · 
                 Δ 
               
                
               
                   
               
                
               T 
             
           
         
       
     
         [0000]    where
       Q=heat transfer rate (W)   h=heat transfer coefficient (W/(m 2 ·K))   t=plate thickness (m)   k=plate thermal conductivity (W/m·K)       
 
         [0039]    The heat transfer coefficient is the heat transferred per unit area per Kelvin. Thus, area is included in the equation as it represents the area over which the transfer of heat takes place. The thermal resistance due to the channel wall and the vane surfaces may be roughly calculated by the following relationship: 
         [0000]    
       
         
           
             R 
             = 
             
               x 
               
                 k 
                 · 
                 A 
               
             
           
         
       
     
         [0000]    where
       x=the plate thickness (m)   k=the thermal conductivity of the material (W/mk)   A=the total area of the channel (m 2 )       
 
         [0043]    This represents the heat transfer by conduction in the channel. 
         [0044]      FIG. 6  shows the outer side of the heat sink  22  with its heat radiating ribs  34 , mounting screw receiving holes  23  and bridge fastening holes  31  for receiving the bolts or screws  30  shown in  FIG. 3 . 
         [0045]      FIG. 7  illustrates at a slightly larger scale the inner side of heat sink  22 , and shows the inverted U-shaped heat pipe  38  and conductive metal bridge plate  36 , as well as bolt holes  23  for securing the heat sink to the card  14 . With the heat sink  22  secured to the waterblock  19 , heat collected by the plate  32  and not radiated into the environment via the vanes  34  will be communicated by the heat pipe  38  to the bridge plate  36  and coupled into the plate  18  where it will be transferred to the fluid in the flow channel and transported through the outlet port  27  and tube  26  to an external radiator for removal. 
         [0046]    Although details of the present invention have been shown and described above in terms of a single embodiment, it will be appreciated that other embodiments can be implemented as well without departing from the true spirit and scope of the invention. For example, in an alternative embodiment, a second finned heat sink plate might be substituted for the DELRIN cover plate  20 . In still another embodiment, another waterblock might be substituted for the heat sink  22  or sandwiched between the heat sink  22  and the card  14 . In yet another embodiment, a single waterblock might be configured to have a medial slot formed therein to receive and thereby surround the card  14 .