Abstract:
Presented is a heat sink arrangement, incorporating a fluid media, which transfers heat between stationary and movable objects. Included are pump structures which are designed to be or operate integrally with the fluid-filled heat transfer apparatus, and are adapted to provide optimum and unique cooling flow paths for implementing the cooling of electronic devices, such as computer chips or the like, that require active cooling action. The pumps and heat sink arrangements selectively possess either rotating or stationary shafts, various types of impeller and fluid or cooling media circulation structures, which maximize both the convective and conductive cooling of the various components of the electronic devices or equipment by means of the circulating fluid.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a heat sink arrangement comprising a fluid media, which transfers heat between stationary and movable objects. More particularly, the present invention relates to pump structures which are designed to be or operate integrally with the fluid-filled heat transfer apparatus, and are adapted to provide optimum and unique cooling flow paths for implementing the cooling of electronic devices, such as computer chips or the like, that require active cooling action. 
         [0003]    2. Discussion of the Prior Art 
         [0004]    In particular, pursuant the prior art, as represented by Sri-Jayantha, et al, U.S. Patent Publication 2004/0114327 A1, and U.S. Pat. No. 6,876,550 B2, the latter of which issued on that particular patent publication, each illustrate active heat sinks for high power microprocessors, and which incorporate structures possessing both static and dynamic components. Essentially, in each instance, the structure incorporates a thermal interface material (TIM), which facilitates the conduction of heat from a first modular component to a further component, while concurrently absorbing or compensating for thermally induced variations in the clearances that are present between the operative or structural components. In particular, the prior art, as represented hereinabove, discloses the concept of a kinetic heat sink, in which a rigid heat spreader supports a fluid film on one side thereof and provides a conductive path from a computer chip to the heat spreader through a thermal interface material. There is no disclosure of utilizing the fluid film as an asset for convecting heat to the remaining surfaces of the prior art heat sink system. 
         [0005]    Various other prior art publications relate to diverse types of structures and systems for transmitting fluids or the like, in order to be able to effectuate the cooling of various electronic devices and components. 
         [0006]    Houle, et al., U.S. Patent Publication No. 2005/0068725 A1 disclose a thermal transfer system and method for a self-contained closed-loop microchannel cooling arrangement integrated into a micro-component package. However, the system, as disclosed in this publication, which employs fins for conducting heat from heat-generating components to the surroundings, does not provide for the type of pumping structures analogous with that employed in the present invention for attaining highly efficient flow patterns able to adequately cool the various components. 
         [0007]    Lee, et al., U.S. Patent Publication No. 2005/0024830 A1 discloses a liquid-cooled heat sink assembly utilizing an impeller, and which also does not, in any manner, describe nor even suggest the unique pumping structure for cooling media pursuant to the present invention. 
         [0008]    Gwin, et al., U.S. Patent Publication No. 2004/0125561 A1, disclose a sealed and pressurized liquid cooling arrangement for a microprocessor which, however, does not provide for an optimized heat transfer in both convection and conduction modes pursuant to the present invention. 
         [0009]    Similarly, representing primarily technological background disclosures, Wu, et al, U.S. Patent Publication No. 2004/0052048 A1; Morris, et al., U.S. Pat. No. 6,580,610 B2; Morris, et al., U.S. Pat. No. 6,507,492 B2; Gwin, et al., U.S. Pat. No. 6,890,928 B2, which issued on previously mentioned U.S. Patent Publication No. 2004/0125561A1; and Morris, et al., U.S. Pat. No. 6,377,458 B1 are all limited to various types of systems, which are utilized for cooling the operative and heat-generating components of electronic devices or computer chips, but wherein the systems do not incorporate the type of heat transfer apparatus employing pump structures which are integral to the fluid field components of the heat transfer apparatus in order to obtain maximum or optimized degrees of cooling effects due to both the convection and conduction of heat through and away from the confines of the equipment, which is being cooled. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly, pursuant to the invention, there is provided a novel pumping structure facilitating the incorporating of all possible types of optimized cooling flow paths for effectuating the proficient cooling of a computer chip or other electronic devices, which necessitates the interposition of an active cooling system. 
         [0011]    In essence, the implementation of fluid dynamics analysis provides a clear indication that a thin film of a fluid of preferably less than 1 mm thickness, which is trapped between a rotating cylinder and a stationary cylinder, is imbued with a specific flow pattern. The face of the rotating cylinder, i.e., the normally disk-like portion, creates a centrifugal force acting on the fluid in closer proximity to its surface, and which forces the fluid to flow radially outwardly at a certain velocity. Inasmuch as the radius of the cylinder is finite and the mass of the fluid is conserved, there is resultingly encountered a return or centripetal radial velocity of the fluid along the stationary portion of the external cylinder. This flow in the fluid film offers an opportunity for enhancing the convective heat transfer. With the centrifugal action being limited to the fluid film, that comes into contact with the rotating cylinder surface, it becomes necessary to actively produce a pumping action in order to enhance or augment the fluid flow and hence the convective heat transfer of the cooling system. 
         [0012]    In order to effectuate the foregoing, pursuant to the present invention, there are provided various types of fluid pumping arrangements, which are operatively located integral to the heat sink and adjacent the electronic device, such as computer chips or the like, which require the application of an optimized cooling action or effect in order to maintain the components which are being cooled at their highest degree of operating efficiencies. 
         [0013]    Accordingly, in order to be able to achieve the foregoing advantages of an optimized cooling and high heat transfer degrees of efficiency in a heat transfer apparatus pursuant to the invention, it is an object to provide unique and highly diverse variations in pump structures, which are integral to the concept of employing a fluid-filled heat transfer apparatus, particularly in the utilization of cooling systems for computer chips or other electronic devices which necessitate maximum degrees of cooling during the operation thereof in order to achieve a lengthy and reliable service life for the electronic devices. 
         [0014]    Furthermore, it is another object of the present invention to provide an availability of diverse and unique types of pumps and heat sink arrangements possessing both rotating and stationary shafts, various types of impeller and fluid or cooling media circulation structures, which propagate both the convective and conductive cooling of the various components of the electronic devices or equipment by means of a fluid-filled heat transfer apparatus and unique pump structures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Reference may now be made to the following detailed description of various and generally diverse types of pump structures, which are integral to a fluid filled heat transfer apparatus and the components thereof, taken in conjunction with the accompanying drawings, in which: 
           [0016]      FIG. 1  diagrammatically illustrates a heat sink for high power microprocessors pursuant to the prior art utilizing heat sink fin structures pursuant to the prior art; 
           [0017]      FIG. 2  illustrates a kinetic heat sink with a fluid dynamic bearing as represented in the prior art; 
           [0018]      FIG. 3  illustrates a kinetic heat sink incorporating a fixed or stationary center shaft structure pursuant to the prior art; 
           [0019]      FIG. 4  illustrates an embodiment of a kinetic heat sink with a rotating center shaft pursuant to the prior art; 
           [0020]      FIG. 5  illustrates a graphical representation of a flow pattern within a fluid film utilizing computational fluid mechanics software; 
           [0021]      FIG. 6  illustrates graphically a radial velocity crossectional profile at various locations along the radial position of the fluid film of  FIG. 5 ; 
           [0022]      FIG. 7  illustrates graphically a radial velocity profile along the radius for an 0.5 mm wide film gap; 
           [0023]      FIG. 8  illustrates diagrammatically a pump structure pursuant to the present invention providing for a radially outward fluid flow driven by impeller action; 
           [0024]      FIG. 9(   a ) illustrates generally diagrammatically a self-pumping impeller with helical fluid flow structure; 
           [0025]      FIG. 9(   b ) illustrates a perspective representation of a detail of the helical geometry showing the shaft rotation of the structure of  FIG. 9(   a ); 
           [0026]      FIG. 9(   c ) illustrates the impeller exit representative of the disk rotation of the structure of  FIG. 9(   a ); 
           [0027]      FIG. 10  illustrates a pump structure showing the fluid circulation limited in the disk plane of the shaft pursuant to the invention; 
           [0028]      FIG. 11  illustrates a pump structure showing fluid circulation in both a disk plane and along a sidewall of a rotating center shaft pursuant to the invention; 
           [0029]      FIG. 12  illustrates a pump structure pursuant to the invention representing a fluid film optimized for conduction and convection heat spreader function; 
           [0030]      FIG. 13  illustrates a pump structure providing for a radially inward fluid flow driven by both impeller and helical action; 
           [0031]      FIG. 14  illustrates a pump structure which discloses a computer chip completely immersed within a fluid flow path providing for an offset pumping action; 
           [0032]      FIG. 15  illustrates a pump structure including a perforated chip which is embedded in a circulating fluid flow; 
           [0033]      FIGS. 16(   a ) and  16 ( b ) illustrate, respectively, various types of perforations formed in a heat generating chip as utilized in the structure of  FIG. 15 ; 
           [0034]      FIG. 17  illustrates a pump structure including radial fins employed for heat transfer with an integrated pump; and 
           [0035]      FIG. 18  illustrates, on an enlarged scale, the partial perforation of the computer chip employed in  FIG. 17 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0036]    One arrangement for providing active cooling action is the kinetic heat sink (KHS). In kinetic heat sinks, a stationary structure is placed in intimate contact with the electronic device and conducts heat away from said device. The heat is then transferred via a fluid interface to a rotating structure where it is dissipated into the cooling medium. The basic concept of providing kinetic heat sinks for high power microprocessors which incorporate heat transfer configurations in the embodiment of a rotating fin structure or through the intermediary of a heat transfer apparatus containing a compliant fluid film interface is already known in the present state-of-the-technology. 
         [0037]    Referring in particular detail to the various heat sink structures shown in  FIGS. 1-4  of the drawings, these illustrate the prior art static and dynamic heat sink structures and pumps, as represented in Sri-Jayantha, et al., U.S. Patent Publication No. 2004/0114327A1 and U.S. Pat. No. 6,876,550 B2. 
         [0038]    In particular, as illustrated in these known embodiments, the structures generally disclose a thermal interface material (TIM)  10 , which facilitates a heat conduction from one modular component, such as a chip or die  12 , to a heat spreader  15 , while absorbing or compensating for a thermally-induced variation in clearances between the components, as in  FIG. 1 .  FIG. 2  shows a kinetic heat sink (KHS)  16  where a rigid heat spreader  15  supports a fluid film  20  on one side and provides a thermal conduction path from the chip  12  to itself through a TIM  10 . This prior art does not envisage using the fluid film  20  as an asset for convecting heat to any remaining surfaces of the heat sink system. A rotating shaft  22  is encompassed by the fluid film  20 , and supports a metallic blade  24  providing a heat sink arrangement.  FIGS. 3 and 4  show variations in the prior art corresponding to  FIG. 2 . In each configuration, the method of supporting a rotational blade is varied, wherein  FIG. 3 , a fixed center shaft is employed. The heat flux from a source is conducted through a TIM to a fixed shaft  26 , wherein the shaft diameter is optimized for maximum surface area providing for heat conduction, while constituting a structure for supporting the rotatable components. As previously mentioned, all of these features and arrangements are disclosed in the above-referenced publications. 
         [0039]    Referring to  FIG. 5  of the drawings, this shows a plot of an estimate of a flow pattern within a fluid film (spun or rotated at 3000 RPM with 0.5 mm thick film) using a computational fluid mechanics software. The total velocity of the fluid is mainly composed of two components; i.e., a dominant tangential and a weak radial vector. The tangential component in cylindrical coordinates is driven by the rotational speed of the shaft, such that the fluid attached to the shaft (or disk) face has the maximum tangential velocity. The fluid that is attached to the stationary external cylinder has a no-slip condition, thus, resulting in a zero velocity. The fluid velocity inbetween the stationary and rotating surface of the structure has a velocity gradient along the axis of rotation (z-axis). The net effect of the tangential velocity is to generate a centrifugal force in the form of body force on the fluid. Since the fluid film attached to the rotating surface of the shaft has the largest centrifugal force with a gradually decreasing centrifugal force nearer the stationary surface, a radial flow component is resultingly generated. The flow is directed radially outwardly at the rotating surface and inwardly at the stationary surface, thereby satisfying the principle of conservation of mass. 
         [0040]    Referring to  FIG. 6 , this shows a graphical plot of the radial velocity profile, across the fluid thickness, at various locations along the radial position. A progressively increasing velocity profile can be observed with the radial velocity vector reversing its direction near the middle plane. The volume flow rate increases as the radius increases.  FIG. 7  shows the effect of Z-distance from the wall, as well as the radius. The further it is away from the wall, the higher is the radial velocity, while proximate the wall, the fluid is stagnant in the radial direction, but rotates along with the shaft in the tangential direction.  FIG. 6  indicates that the radial flow is significant in the disk-like face of the rotating shaft, but it is mostly negligible in the gap contained in the sidewall. Since the stagnant fluid can produce high thermal resistance, it is important to reduce the film thickness where conduction can be more advantageous than convection, while in regions where conduction is not as effective, the convection features can be maximized to improve the heat-spreading capability of the fluid film. In order to move the heat flux from the disk-like face to the sidewall, flow direction elements can be added so that fluid traverses the maximum surface area. With these concepts, which are provided by the fluid dynamic simulation, various advantageous embodiments can be developed in this connection to facilitate improved heat transfer phenomena. 
         [0041]    Fluid circulation, due to a plain or flat shaft face, produces only a limited forced convection; however, by adding an impeller feature to the shaft face, and by providing a return path for the fluid, as illustrated in  FIG. 8 , there is demonstrated the maximum forced convection effect that can be designed and implemented. By having an (centrifugal) impeller  30  so arranged at the lower face of the disk or shaft  32 , there is attained a radially outward flow resultingly augmenting the natural flow direction of the fluid  34  due to centrifugal force. A part of the shaft  32  has axial passageways  36  and radial passageways  38  to complete the fluid path  40 .  FIG. 9(   a ),  9 ( b ) and  9 ( c ) each disclose a representative geometry for an impeller  30 , as well as for helical surface structures  42  to help generate pressure in the desired direction of the fluid flow path  40 . 
         [0042]      FIG. 10  shows a structure  50  including a solid rotating shaft  52  with a fluid circulation path  54 , where said path is confined to the face of the shaft  52 , but not along its sides by the provision of a fluid flow-separator  56 . The flow separator  56  divides the fluid volume into two fluid flow regions, i.e., a radial outward and a radial inward. The fluid flow separator  56  can also be designed with features (not shown) that would generate turbulent mixing of the fluid in order to enhance the heat transfer capability of the structure. Hereby, the fluid film present in the sidewall is not actively used for cooling in this embodiment.  FIG. 11  shows a modified fluid flow separator  60  that extends the radial fluid flow into the sidewall region  62  about the shaft  52 , with all other features being identical with the structure of  FIG. 10 , where the upper end of the shaft  52  supports a heat dissipating finned element  66 . 
         [0043]    The film thickness contributes in a non-linear way to the radial convective velocity, whereby  FIG. 12  illustrates an embodiment of a structure  70  where the heat conduction through the fluid film  72  is maximized directly above a heat source  74  by maintaining an ultra thin fluid film (less than 50 μm thick) in which the convective velocity is by an order of magnitude lower compared to its tangential velocity. However, as the distance from heat source  74  increases, it is advantageous to maintain a good heat spreading capability, so that in order to increase the radial convective velocity, the fluid film thickness is increased accordingly. The embodiment in  FIG. 12  shows how conductive and convective capability can be maximized in a thermal cooling application. 
         [0044]    The remaining embodiments in  FIGS. 13 through 18  are primarily variations on flow generation capability with flow paths and heat transfer geometry. Elements and structure components, which are similar to or identical with those disclosed in the preceding embodiments, are designated with the same reference numerals.  FIG. 13  shows a reverse flow pattern by having an impeller  80  mounted on the top surface of the rotating disk or shaft  82 .  FIG. 14  represents a modification where a semiconductor chip  90  along with its solder bumps  92  is immersed in the circulating fluid  94 . In order to facilitate the return of the fluid flow, a pressure-generating pump mechanism  96  is offset from the center of the chip  90 . It is noted that in this embodiment, the heat transfer to the rotating fin structure  100  is dominated by convection, whereby in order to avoid such a rather complex offset design, the semiconductor chip may require to be imparted a perforation; of which an embodiment is shown in  FIG. 15 . 
         [0045]    Variations in the pattern of the perforation, which can be a single opening  102  in the center of the chip  90  or of a distributed multiple configuration  104 , are shown in  FIGS. 16(   a ) and  16 ( b ), respectively. Under this fluid flow condition, the heat transfer surface can further be enhanced by means of radial fins  106 , as shown in  FIGS. 17 and 18 . 
         [0046]    While the present invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made without departing from the scope and spirit of the present invention. It is therefore intended that the present invention not be limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims.