Abstract:
A device for cooling a heat-dissipating component, including an expansion chamber that is expandable between a first volume and a second volume. The expansion chamber adjusts its surface exposure to ambient air according to the operating conditions of the device.

Description:
BACKGROUND 
   As electronic systems become more compact, there is a continuing desire to increase the rate of heat transfer away from heat-dissipating components. With many heat transfer techniques considered for compact devices, it is difficult to provide sufficient cooling for components within the available space inside the device. 
   Although forced air convection has been used in small electronic devices, such as, for example, laptop computers, forced air convection methods have practical limits. The amount of air required to provide sufficient cooling in a forced air convection system generally creates an undesirable noise level and can consume battery life in portable devices. 
   Another method for cooling heat-dissipating components involves the use of fluids in a thermal transfer bag. Thermal transfer bags are generally made from flexible, durable, and air-impermeable films. The bags are filled with a thermally conductive fluid and are generally placed between a heat-generating component and the environment. 
   Although thermal transfer bags have been used in some cooling systems, the use of thermal transfer bags in small electronic devices, such as, for example, laptop computers has been limited, at least in part, because of the limited amount of available space within the chassis of the computer and their surface area requirements for effective cooling. Accordingly, there is a continuing need to provide inexpensive, quiet, and effective cooling systems for cooling small electronic devices that minimize the use of space within the device. 
   SUMMARY 
   The present invention relates generally to a device for cooling electronic components, and more particularly, to a device that adjusts its surface exposure to ambient air according to the operating conditions of the device. In one aspect, the device functions as thermosyphon. 
   In one aspect of the present invention, the variable position cooling apparatus comprises a substrate and an expansion chamber having at least one sidewall that is substantially impermeable to fluid. The sidewall defines an enclosed volume that is expandable between a first volume and a second volume. The second volume can be the volume of the expansion chamber when it is fully opened, or any other volume between the closed volume and the fully open volume. The sidewall also has a proximal end affixed to the substrate, a distal end opposite the proximal end, an inner surface proximate the enclosed volume, and an outer surface opposite the inner surface. A quantity of heat transfer fluid is disposed within said enclosed volume and the distal end moves from a first position proximate the substrate to a second position as the enclosed volume expands from the first volume to the second volume. 
   In some embodiments, a plurality of expansion chambers are used to form the variable position cooling apparatus. In yet further embodiments, a movable member is affixed to the distal ends of the plurality of expansion chambers. In some embodiments, a biasing element cooperates with the substrate and the movable member to force the distal end to be proximate the substrate at said first volume of said expansion chamber. 
   In some embodiments, the distal end of the sidewall is at least 1 centimeter away from the substrate in the second position. In other embodiments, the distal end of the sidewall is at least 1 centimeter away from the substrate in the second position. In yet further embodiments, the distal end is at least 5 centimeters away from the substrate in said second position. 
   In some embodiments of the present invention, the sidewall of the expansion chamber has a corrugated portion. The sidewall of the expansion chamber can also include an area adaptable for displaying a graphic. The graphic becomes visible when the enclosed volume is at said second volume. The graphic is concealed when the enclosed volume is at the first volume. In some embodiments, the sidewall of the expansion chamber comprises a geometric shape that is visible when the enclosed volume is at the second volume. 
   In some aspects of the present invention, the expansion chamber is in fluid communication with the heat-dissipating component. In some embodiments, the heat transfer fluid used in the expansion chamber comprises at least one of a perfluorocarbon, hydrofluorocarbon, hydrofluoroether, and perfluoroketone. 
   In some embodiments of the present invention, the sidewall of the expansion chamber comprises at least one of a polymer film, a metal foil, and a multilayer barrier film. 
   The variable position cooling apparatus of the present invention can be attached to a computer chassis. The variable position cooling apparatus of the present invention can also be used as a component in a larger cooling system. 
   In some embodiments, the variable position cooling apparatus comprises a substrate, a movable member that is movable between a first position and a second position, and an expansion chamber. The expansion chamber has a proximate end affixed to the substrate and a distal end affixed to the movable member. The expansion chamber is filled with a quantity of heat transfer fluid. The movable member moves between the first position and the second position as the vapor pressure of the heat transfer fluid changes. 
   The present invention also provides methods for cooling a heat-dissipating component. The method includes providing an expansion chamber comprising a quantity of heat transfer fluid and at least one sidewall that is substantially impermeable to fluid. The sidewall defines an enclosed volume that is expandable between a first volume and a second volume. The vapor pressure of the heat transfer fluid is increased by heating the heat transfer fluid. The increased vapor pressure causes the sidewall to move as the expansion chamber expands from the first volume to the second volume. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1A  is a perspective view of an exemplary embodiment of the present invention in a closed position; 
       FIG. 1B  is a perspective view of the exemplary embodiment shown in  FIG. 1A  in the open position; 
       FIG. 2A  is a cross-sectional view of an exemplary heat transfer bag of the present invention; 
       FIG. 2B  is a cross-sectional view of the exemplary heat transfer bag shown in  FIG. 2A  showing attachment interface areas, 
       FIG. 3A  is a cross-sectional view of an exemplary embodiment of the present invention in the closed position; 
       FIG. 3B  is a cross-sectional view of the exemplary embodiment shown in  FIG. 3A  in an open position; 
       FIG. 4A  is a perspective view of an exemplary embodiment of the present invention in an open position displaying a heart shape; 
       FIG. 4B  is a perspective view of the exemplary embodiment shown in  FIG. 4A  in the closed position; 
       FIG. 5  is a perspective view of an exemplary embodiment of the present invention in an open position displaying an oval shape; and 
       FIG. 6  is a cross-sectional view of an exemplary embodiment having a folding expansion chamber in an open position. 
   

   These figures, which are idealized, are not to scale and are intended to be merely illustrative of the present invention and non-limiting. 
   DETAILED DESCRIPTION 
     FIG. 1A  shows a perspective view of an exemplary embodiment of the present invention positioned on a laptop computer. As shown in  FIG. 1A , a movable member  12  is connected to a substrate  14 . The substrate  14  is the backside of the viewing screen of the laptop computer  11 . In  FIG. 1A , the movable member  12  is shown in a closed position wherein the movable member  12  is proximate the substrate  14 . 
     FIG. 1B  shows a perspective view of the exemplary embodiment shown in  FIG. 1A  with the movable member  12  shown in an open position wherein the movable member  12  is positioned a distance from substrate  14 . Also shown in  FIG. 1B  is a heat transfer bag  30  having a plurality of expansion chambers  16  connecting the movable member  12  to the substrate  14 . A change in pressure within the expansion chambers  16  causes the movable member  12  to move relative to the substrate  14 . The movable member  12  generally moves toward the substrate  14  as pressure within the expansion chambers  16  is reduced. Likewise, the movable member  12  generally moves away from the substrate  14  as pressure within the expansion chambers  16  is increased. 
   In some embodiments, the distance between the movable member and the substrate in the closed position is less than about 1 centimeter. In other embodiments, the distance between the movable member and the substrate in the closed position is less than about 0.5 centimeter. In yet further embodiments, the distance between movable member and the substrate in the closed position is less than about 0.2 centimeter. 
   In some embodiments, the distance between the movable member and the substrate in an open position is more than about 1 centimeter. In other embodiments, the distance between the movable member and the substrate in an open position is more than about 2 centimeters. In yet further embodiments, the distance between movable member and the substrate in an open position is more than about 5 centimeters. 
     FIG. 2A  is a cross-sectional view of an exemplary heat transfer bag of the present invention. As shown in  FIG. 2A , the heat transfer bag  230  comprises a plurality of expansion chambers  216 . Sealing two films together forms the expansion chambers  216 . Each expansion chamber  216  has a seal  232  and cut line  234  around a majority of the perimeter of the expansion chamber  216 . 
     FIG. 2B  is a cross-sectional view of the exemplary heat transfer bag shown in  FIG. 2A  showing attachment interface areas. The substrate attachment interface  236  is located on one side of the heat transfer bag  230  and affixes a portion of each expansion chamber to the substrate. The movable member attachment interface  238  is located on the opposite side of the heat transfer bag  230  and affixes a portion of each expansion chamber to the movable member. The attachment interfaces  236 ,  238  can be affixed to the substrate  214  and movable member  212  with adhesive, mechanical fasteners, welding, or any other means known to those skilled in the art. In certain embodiments, the substrate attachment interface  236  and the movable member attachment interface  238  comprise a double-sided adhesive tape. 
   Materials suitable for use as the sidewall of heat transfer bag include, for example, metal foils, plastic, polymeric films, and multilayer barrier films such as those commonly used in food packaging, particularly those lined with a polyamide or polyimide. 
   The term multilayer barrier film refers to any combination of metal, plastic, or cellulosic layers (e.g., foils, films, and paper). The combination of metal, plastic, or cellulosic layers can include multiple layers of different materials, such as, for example, a metal combined with a plastic layer. The combination of metal, plastic, or cellulosic layers can also include multiple layers of similar materials, such as, for example, two layers of plastic. 
   Multilayer barrier films useful in the present invention include multilayer films with layers that are affixed to one another, for example, by coating, laminating, coextrusion, or deposition. Multilayer barrier films useful in the present invention can comprise layers of low-density polyethylene, high-density polyethylene, polypropylene, polyester, nylon, polyethylene-co-vinyl acetate, polyvinylidene chloride, polyamide, or polyimide. In some embodiments, a multilayer barrier composite having a layer of metal, such as, for example, aluminum is used. Multilayer barrier films and other films useful for the sidewall of the present invention are described in U.S. Pat. No. 4,997,032 (Danielson et al.) and U.S. Pat. No. 5,411,077 (Tousignant), incorporated by reference. 
   In some embodiments, the heat transfer bag is welded to form the seal  232 . In other embodiments, seal  232  is formed with adhesive or a mechanical fastener. Other suitable methods for sealing films known to those skilled in the art can also be employed. 
   A quantity of heat transfer fluid is disposed within the heat transfer bag  230  prior to completely sealing the heat transfer bag. The heat transfer fluid useful in the present invention can be any fluid capable of transferring heat, including water, volatile fluids, such as, for example, alcohols, and electronic cooling fluids known to those skilled in the art. In certain embodiments, the heat transfer fluid is dielectric, non-flammable, and provides a significant vapor pressure at the operating temperature of the heat-dissipating component. 
   In certain embodiments, the heat transfer fluid is thermally conductive, chemically inert, essentially gas-free, and thermally stable. In other embodiments, the heat transfer fluid has a boiling point that is at or below the operating temperature of the heat-dissipating component such that portions of the liquid adjacent the heat-dissipating component will vaporize when conducting heat. The heat transfer fluid can be selected from the representative class of fluorinated linear, branched or cyclic alkanes, ethers, ketones, tertiary amines, and aminoethers, and mixtures thereof. In some embodiments, perfluorinated fluids are used in this invention, though partially fluorinated fluids can also be used. The perfluorinated fluids can be straight chain, branched chain, cyclic, or a combination thereof. In some embodiments, the perfluorinated fluids can be saturated, that is, free of ethylenic, acetylenic, and aromatic unsaturation. The skeletal chain can include catenary oxygen and/or trivalent nitrogen heteroatoms providing stable links between fluorocarbon groups and not interfering with the inert character of the compound. In some embodiments, hydrofluoroethers, either segregated or non-segragated are used. In other embodiments, perfluorinated ketones are used. 
   Representative examples of suitable fluorinated fluids or mixtures thereof useful for the present invention are commercially available from 3M Company, St. Paul, Minn., and marketed under various trade designations, including, for example, “3M BRAND FLUORINERT ELECTRONIC LIQUIDS” and “3M BRAND NOVEC ENGINEERED FLUIDS”, described in 3M Company product bulletin No. 98-0212-2249-7, issued January 2003. Other commercially available fluorochemicals useful in the present invention are those available from Solvay Solexis S.p.A, Bollate, Italy, under the trade designation “GALDEN PFPE: HEAT TRANSFER FLUIDS” and their hydrofluoroethers available under the trade designation “H-GALDEN ZT HEAT TRANSFER FLUID”. Heat transfer fluids useful in the present invention also include hydrofluorocarbon compounds such as those sold under the trade designations “VERTREL SPECIALTY FLUIDS” and “SUVA REFRIGERANTS” available from DuPont, Wilmington, Del. 
   Also shown in  FIGS. 2A and 2B  is a reservoir  240  within the heat transfer bag  230 . The reservoir  240  is in fluid communication with the expansion chambers  216 . Within the reservoir  240 , is a thermal via  242 . The thermal via  242  can be metallic and can be used to enhance the transfer of heat from a heat-dissipating component to the heat transfer fluid within the heat transfer bag  230 . Thermal vias useful for the heat transfer bag of the present invention are described in U.S. Pat. No. 5,000,256 (Tousignant), incorporated by reference. 
   Reservoir  240  can be used as a conduit between the expansion chamber and the heat-dissipating component. In other embodiments, a fluid conduit external to the heat transfer bag, such as, for example, a pipe or tube, is affixed to the heat transfer bag. In yet further embodiments, a combination of a reservoir within the heat transfer bag and a fluid conduit external to the heat transfer bag is used between the expansion chamber and the heat-dissipating component. In another embodiment, a plurality of expansion chambers are independently connected by a common manifold and are in fluid communication with one another. 
   The heat dissipating component cooled with the present invention can be a semiconductor, such as, for example, a central or graphics processing unit, an insulated gate bipolar transistor (IGBT), memory module, or an application specific integrated circuit (ASIC). In other embodiments, the heat dissipating component can be a hard disk drive, power supply, transformer, laser diode array, light emitting diode (LED) array, halogen bulb, or any other heat-dissipating component known to those skilled in the art. The heat dissipating component can also be a non-heat generating structure, such as, for example, an integrated heat spreader (IHS) that is connected to a heat-generating device, such as, for example, a semiconductor. 
     FIG. 3A  is a cross-sectional view of an exemplary embodiment of the present invention in the closed position. As shown in  FIG. 3A , an expansion chamber  316  is positioned between a substrate  314  and a movable member  312 . The expansion chamber  316  comprises a sidewall  318  that defines an enclosed volume. A quantity of heat transfer fluid  348  is disposed within the enclosed volume. 
   The expansion chamber  316  has a proximal end  322  with a substrate attachment interface  336  affixed to the substrate  314 . The expansion chamber  316  also has a distal end  324  with a movable member attachment interface  338  affixed to the movable member  312 . The attachment interfaces  336 ,  338  of the proximal and distal ends  322 ,  324  can be affixed using an adhesive  352 . 
     FIG. 3B  is a cross-sectional view of the exemplary embodiment shown in  FIG. 3A  in an open position. As shown in  FIG. 3B , the distal end  324  of the expansion chamber  316  has moved away from the substrate  314 . The movement of the expansion chamber  316 , in turn, has caused the movable member  312  to move away from the substrate  314 . In doing so, the outer surface  328  of the sidewall  318  is exposed to ambient air  354  surrounding the cooling assembly  310 . 
   The level of exposure of the side  318  to the ambient air  354  varies with pressure within enclosed volume  320 . When the pressure in the enclosed volume  320  is low (e.g., the heat-dissipating component is operating at low power), the cooling assembly  310  will close as shown in  FIG. 3A  and the outer surface  328  of the sidewall  318  will be substantially insulated from ambient air  354 . As the pressure in the enclosed volume  320  is increased (e.g., the heat-dissipating component is operating at low power), the cooling assembly  310  will open as shown in  FIG. 3B  and the outer surface  328  of the sidewall  318  will be exposed to ambient air  354  surrounding the cooling apparatus  310 . Likewise, as the pressure in the enclosed volume  320  is decreased (e.g., the heat-dissipating component is operating at low power), the cooling assembly  310  will return to the closed position. 
   In some embodiments, the sidewall is convectively cooled. In certain embodiments, the sidewall, the substrate, and the moveable member form a channel that permits buoyancy driven convection. In yet further embodiments, forced air may be used to further cool the sidewall. 
   In addition to increasing the exposed surface of the sidewall as the expansion chamber expands from a closed position to an open position, the exposed surface areas of the substrate and moveable member generally increase as the expansion chamber opens. The increased surface area exposure of the substrate or movable member can be used to provide additional cooling surfaces. 
   In certain embodiments, the type and quantity of heat transfer fluid is selected to create a pressure in the enclosed volume of the expansion chambers that causes the expansion chambers to fully open when the heat-dissipating component is operating at high power. In other embodiments, the type and quantity of heat transfer fluid is selected to create a pressure in the enclosed volume of the expansion chambers that causes the expansion chambers to fully open at the maximum operating power of the heat-dissipating device under expected environmental conditions. 
   In some embodiments, a biasing element (not shown) cooperates with the substrate and the movable member to create a force on the movable member toward the substrate. The biasing element can comprise a spring, elastic material, or any other mechanism known to those skilled in the art for applying a retractive force. In some embodiments, the biasing member is a spring connecting the substrate and the movable member. The retractive force of the biasing member assists the movable member in moving from an open position to a closed position. In some embodiments, the retractive force of the biasing element is selected to allow the expansion chamber to fully open at the normal operating temperature of the heat-dissipating device. 
     FIG. 4A  is a perspective view of an exemplary embodiment of the present invention in an open position displaying a heart shape.  FIG. 4B  is a perspective view of the exemplary embodiment shown in  FIG. 4A  in the closed position. As shown in  FIG. 4A , two expansion chambers  416  are mounted on opposing sides of a substrate  414 . The substrate  414  can be any member that allows the expansion chambers to be in thermal communication with a heat-dissipating device. In some embodiments, the substrate is a portion of a computer chassis, such as, for example, the backside of the screen portion of a laptop computer or the sidewall of a desktop. In other embodiment, the substrate can be a sidewall of a monitor or the sidewall of a monitor support member. 
   The expansion chambers  416  shown in  FIG. 4A  have a sidewall  418  that is generally corrugated. The expansion chamber  416  defines an enclosed volume and has a proximal end  422  affixed to the substrate  414  and a distal end  424 . As shown in  FIG. 4A , in an open position, the distal end  424  of the expansion chamber  416  is a distance away from the substrate. As shown in  FIG. 4B , in a closed position, the distal end  424  of the expansion chamber  416  is proximate the substrate. 
   In some embodiments, the distance between the distal end and the substrate in the closed position is less than about 1 centimeter. In other embodiments, the distance between the distal end and the substrate in the closed position is less than about 0.5 centimeter. In yet further embodiments, the distance between distal end and the substrate in the closed position is less than about 0.2 centimeter. 
   In some embodiments, the distance between the distal end and the substrate in an open position is more than about 1 centimeter. In other embodiments, the distance between the distal end and the substrate in an open position is more than about 2 centimeters. In yet further embodiments, the distance between distal end and the substrate in an open position is more than about 5 centimeters. 
   In some embodiments, the sidewall of the expansion chamber is undulated and forms a corrugated pattern with substantially flat surfaces. The corrugated sidewall allows the expansion chamber to be collapsed in an accordian-like fashion. In other embodiments, the sidewall of the expansion chamber forms a corrugated pattern with curvilinear surfaces that form a scallop-type pattern. In some embodiments, the undulations of a sidewall are substantially constant over the width of the sidewall. In other embodiments, the undulations vary and may appear larger or smaller near the substrate relative to the undulations near the distal end of the expansion chamber 
   In yet further embodiments, the sidewall of the expansion chamber forms a roll that is coiled in the closed position and at least partially unrolls to expose a portion of the sidewall to ambient air. Other collapsible geometric configurations known in the art can also be used to form the sidewall of the expansion chamber. 
     FIG. 5  is a perspective view of an exemplary embodiment of the present invention in an open position displaying an oval shape. As shown in  FIG. 5 , the expansion chamber  516  affixed to a substrate  514 . The expansion chamber  516  comprises a sidewall  518  that defines an enclosed volume. The expansion chamber has a distal end  524  and a proximal end  522 . 
   As shown in  FIG. 5 , in an open position, the distal end  524  of the expansion chamber  516  is a distance away from the substrate. In the closed position (not shown), the distal end  524  is proximate the substrate  514  and the oval geometric shape is not visible. In other embodiments, the expansion chamber can be configured to form other geometric shapes, including, for example, circles, squares, and rectangles. In yet further embodiments, the expansion chamber is configured to form an emblem or trademark, such as, for example, an apple or a heart. 
   Also shown in  FIG. 5  is a graphic  556  located on the outer surface  528  of the sidewall  518 . The graphic  556  can be comprise any text or pictures, including, for example, an emblem, trademark, drawing, or design. As shown in  FIG. 5 , the graphic  556  is visible in an open position. In the closed position (not shown), the distal end  524  is proximate the substrate  514  and the graphic is not visible. 
     FIG. 6  is a cross-sectional view of an exemplary embodiment having a folding expansion chamber in an open position. The sidewall  618  of the expansion chamber  616  comprises a fold between the distal end  624  and the proximal end  622 . The sidewall  618  also comprises a stiffening member  670 . 
   As shown in  FIG. 6 , the distal end  624  of the expansion chamber  616  has moved away from the substrate  614 . The movement of the expansion chamber  616 , in turn, has caused the movable member  612  to move away from the substrate  614 . In doing so, the outer surface  628  of the sidewall  618  is exposed to ambient air  654  surrounding the cooling assembly  610 . In some embodiments, the fold in the sidewall can be used to increase the surface area of the sidewall  618  exposed to ambient air  654  surrounding the cooling assembly. In other embodiments, the fold in the sidewall can be used to control the lateral displacement of the movable member  612  as the expansion chamber is expanded and contracted. In yet further embodiments, the sidewall comprises more than two folds between the distal end  624  and the proximal end  622 . 
   Stiffening members  670  are affixed to at least a portion of the sidewall  618 . The stiffening members  670  can be used to control the shape of the expansion chamber  616  as it expands from a closed volume to an open volume. Materials suitable for use as a stiffening member include, for example, metal, glass, ceramic, plastic, or any other material known to those skilled in the art. In some embodiments, the stiffening member is welded to the sidewall. In other embodiments, the stiffening member is affixed with adhesive or a mechanical fastener. Other suitable methods for attaching materials known to those skilled in the art can also be employed. 
   The level of exposure of the side  618  to the ambient air  654  varies with pressure within enclosed volume  620 . When the pressure in the enclosed volume  620  is low (e.g., the heat-dissipating component is operating at low power), the cooling assembly  610  will close and the outer surface  628  of the sidewall  618  will be substantially insulated from ambient air  654 . As the pressure in the enclosed volume  620  is increased (e.g., the heat-dissipating component is operating at high power), the cooling assembly  610  will open as shown in  FIG. 6  and the outer surface  628  of the sidewall  618  will be exposed to ambient air  654  surrounding the cooling apparatus  610 . Likewise, as the pressure in the enclosed volume  620  is decreased (the heat-dissipating component is operating at low power), the cooling assembly  610  will return to the closed position. 
   It is to be understood that even in the numerous characteristics and advantages of the present invention set forth in above description and examples, together with details of the structure and function of the invention, the disclosure is illustrative only. Changes can be made to detail, especially in matters of shape, size and arrangement of the expansion chamber and methods of use within the principles of the invention to the full extent indicated by the meaning of the terms in which the appended claims are expressed and the equivalents of those structures and methods.