Abstract:
In one embodiment, there is shown a heat transfer device having at least one ultra-dense heat sink, where the heat sink is maintained in a position to be air flow direction neutral. In another embodiment, there is shown a method of conducting heat away from an electronic device wherein the electronic device is constructed on a circuit board, the method comprises placing a plurality of heat transfer devices in heat transfer relationship with the electronic device and passing air through the heat transfer devices in at least one air flow direction.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to heat transfer devices and more particularly to such devices for use with multi-directional air flow.  
       DESCRIPTION OF RELATED ART  
       [0002]     Electronic circuits tend to generate heat which then must be removed from the circuit for proper operation. A heat sink closely positioned with respect to the electronic circuit is often employed to assist in heat removal. Often, the heat sink size is limited by the available space on a circuit board or other circuit mounting structure.  
         [0003]     Heat sinks operate by removing the heat generated by the electronic circuit. This removal process is aided by allowing the heat from the circuit to pass into “cooling fins” (sometimes using a heat transfer gel) and then passing air across the surface of the fins to transport the heat from the fins to another location. This other location is usually outside of the housing containing the heat generating circuit. Typically, a particular heat sink functions with air moving in one direction with respect to the orientation of the heat sink cooling fins. Thus, in order to avoid the necessity of designing different heat sink configurations for different air flow directional movements, designers have attempted to design heat sinks that are air flow neutral such that they can function with air that can flow from more than one direction.  
         [0004]     Some heat sinks have been designed with their cooling fins cross-cut so that the air can pass both parallel and horizontal to the fins. These arrangements have not been particularly effective. Other heat sinks have been designed using pin fins which allow the air to move past the pins in any direction. These pin fins allow air to flow in multiple directions, but for the equivalent thermal performance of plate fins, the pin fins require higher pressure drop.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     In one embodiment, there is shown a heat transfer device having at least one ultra-dense heat sink where the heat sink is maintained in a position to be air flow direction neutral. In another embodiment, there is shown a method of conducting heat away from an electronic device wherein the electronic device is constructed on a circuit board, the method comprises placing a plurality of heat transfer devices in heat transfer relationship with the electronic device and passing air through the heat transfer devices in at least one air flow direction. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  illustrates one embodiment of an ultra-dense heat sink;  
         [0007]      FIG. 2  illustrates the heat sink of  FIG. 1  superimposed on the footprint of an electronic circuit;  
         [0008]      FIGS. 3A, 3B ,  3 C,  3 D show embodiments of several ultra-dense devices using heat sinks positioned with respect to an electronic circuit; and  
         [0009]      FIGS. 4, 5 ,  6 ,  7  and  8  illustrate embodiments of ultra-dense heat sinks. 
     
    
     DETAILED DESCRIPTION  
       [0010]      FIG. 1  illustrates one embodiment  10  of an ultra-dense heat sink having frame  11  (optional) and a series of heat transfer elements  12   a  and  12   n , and base  13  for contact with a device from which heat is to be removed. Heat transfer elements are, in this embodiment, plate fins. Air is shown flowing from front to back. Elements  12   a - 12   n  are densely packed on the order of at least 30 fins (elements) per inch with element spacings on the order of a few hundred microns. (The illustration is not scale) Proper heat transfer is achieved by managing thermal resistance as a trade off between more cooling area and pressure drop. This trade off is a function of the Reynolds number and, in one embodiment, can follow the principles set forth in U.S. Pat. No. 6,422,307 which patent is hereby incorporated herein. Essentially, the heat transfer co-efficient is increased more than the heat transfer area is decreased. The physical size of heat sink  10  can be designed, if desired, to be no larger than the size of a typical electrical component that it is associated with. As will be discussed herein, this reduced footprint allows denser component possibilities and/or design flexibility within an allocated space. The smaller size also reduces the overall weight of the device by at least fifty percent depending on the materials used in the device, which also would provide cost savings.  
         [0011]      FIG. 2  illustrates ultra-dense heat sink  10  superimposed on footprint  20  of a typical electronic circuit. Footprint  20  is the space allocated in our example for conventionally designed heatsinks. Note that in some cases the original sized heat sink could even be larger than the device to be cooled. Thus, since a heat sink using the concepts discussed herein can be made much smaller, it would be a design choice as to the exact size. One consideration is that if the heat sink were to be designed too narrow (from top to bottom in  FIG. 2 ) then the air could easily flow around the heat sink because of the high impedance of the heat sink. Thus, as shown in  FIG. 2 , heat sink  10  is shown covering the full width of footprint  20 . Air is shown flowing from left to right. Using ultra-dense heat sink  10 , the device has gone from the full dimension of the footprint (as shown by dashed line  20 ) to a much smaller profile, even though it covers the full width of the footprint. One advantage of using an ultra-dense heat sink is the reduction in weight achieved. In some situations, this weight reduction could be in the range of 80%.  
         [0012]      FIG. 3A  shows one embodiment of device  30  utilizing a plurality of ultra-dense heat sinks, such as heat sinks  10   a  to  10   n . The heat sinks are tilted, for example, 45 degrees with respect to the air flow so as to accommodate any air flow direction, thereby making device  30  air flow directionally neutral. In the embodiment shown, the air zig zags briefly as it passes through the various heat sinks  10   a - 10   n . The air can flow in direction A (left to right) or in direction B (top to bottom), or both, or reverse therefrom, if desired. Advantage has been taken of the relatively small size of each ultra-dense heat sink  10  to position a plurality of such devices angularly with respect to the anticipated air flow direction. While multiple elements are shown in  FIG. 3A , a single element can be positioned at an angle spanning the entire width of space  20  as shown in  FIG. 7 . One or more or all of heatsinks  10   a - 10   n  can be tilted in the opposite direction, if desired.  
         [0013]      FIG. 3B  illustrates embodiment  31  in which heat sinks  10   a  and  10   c  have cooling air moving there through in the A direction. Heat sinks  10   b  and  10   d , which are angularly displaced (in the embodiment shown they are displaced 90 degrees) with respect to heat sinks  10   a  and  10   n , have cooling air moving there through in the B direction. As shown, the heat sinks faced in the A direction form a multi pass heat sink device while those positioned in the B direction form a single pass heat sink device. In the embodiment shown, air flowing in direction A will pass through multiple devices  10 , while air flowing in direction B passes through a single device. Note that in  FIG. 3A , only four heat sinks are shown, but any number could be used. Accordingly, to prevent air from flowing around the heat sink it may be necessary to duct the air flow tightly. Additional fans are an alternative for solving the high impedance problem.  
         [0014]      FIG. 3C  illustrates embodiment  32  constructed with a plurality, (in this case four) ultra-dense heat sinks  10   a - 10   d  around a central core area  301  to be cooled. Air can flow in both the A and B directions, or in any direction in between, if desired. Note that embodiment  32  can be, if desired a single assembly.  
         [0015]      FIG. 3D  illustrates embodiment  33  in which an air movement device, such as fan (or blower)  34 , is positioned within central (core) space  301 . Fan (or blower)  34  can blow air out, or suck air in. Also, the air could be blown upward (out of the page) or, the air could flow in from the top and be blown out radially through heat sinks  10   a - 10   d . A fan would typically be above the core while a blower could be positioned within the core.  
         [0016]      FIG. 4  illustrates embodiment  40  having, for example, carbon nanotubes  42  or fibers, or any other highly conductive material, if desired, could form the nucleus of a covered fin (as shown in  FIG. 1 ) supported by frame top  41  and frame base  43 . These elements, nanotubes  42  (or other material) are shown greatly expanded, but would be sized and spaced so that there would be 30 or more fins (tubes) per inch spaced apart in the micron range.  
         [0017]      FIG. 5  illustrates embodiment  50  where more than one row of fins  52  form the heat sink device. Embodiment  50  is a nanotube array, (for example, carbon nanotubes) but many other materials could be employed for heat transfer. Also, if desired, structure  50  can be within a frame. This structure could stand alone, or could be imbedded in a plate fin device.  
         [0018]      FIG. 6  illustrates embodiment  60  in which the cooling “fins” consist of mesh  601  woven from carbon nanotubes  62  (or other material) and webbing  61 . Webbing  61  can be nanotubes, if desired. Of course, any combination of heat transfer materials can be used, all designed to provide an ultra dense heat sink. For example, carbon fibers, graphite, copper, aluminum, gold or diamond can be used. Also, foils in the range of one tenth of a millimeter can be used.  
         [0019]      FIG. 7  illustrates one embodiment of heat sink transfer device  70  using at least one ultra-dense heat sink  10 . Heat sink  10  (shown without its top frame support) is positioned angularly with respect to the air flow direction so as to be air flow direction made neutral. Base  13  of heat sink  10  is positioned on heat transfer plate  74  with thermal contact (bolted, soldered, brazed, etc.), which in turn is positioned to receive heat from electronic device  72 . Note that base  13  could, if desired, be positioned to receive heat directly from electronic device  72  and thus could replace heat transfer plate  74 . Or, alternatively, fins  12   a - 12   n  could be in continuous direct thermal contact with plate  74 . Electronic device  72  is shown mounted to circuit board  71  in any well-known manner. If desired, thermal interface material  73  is positioned between plate  74  and electronic device  72  to facilitate heat transfer. Plate  74  is optional and its dimensions would be tailored to the size of the heat sinks used and their positioning. The phantom lines around plate  74  show a traditional size heat transfer plate, and the plate of this embodiment can be any dimension up to the phantom line. Using the embodiments discussed an omni-directional heat sink becomes available with a reduced weight.  
         [0020]      FIG. 8  illustrates one embodiment  80  of a high density heat sink having heat pipe  81  built as part of the frame of the heat sink. The inside of heat pipe  81  is constructed with a wicking structure, such as structure  82 , which serves to move liquid (or other heat transfer substances) around the frame of heat sink  80 . The advantage of a heat pipe is that it has an effectively infinite thermal conductivity. Thus, it is possible to transfer heat from a device (not shown) at the bottom of the heat pipe to the top of the heat pipe with barely a temperature drop. Since the top surface would be at the same temperature as the base, the fin length is effectively cut in half, yielding even higher thermal efficiency by the uni-temperature nature of device  80 .  
         [0021]     Materials generally used in heat sink designs are aluminum and copper, but as discussed above, many other materials including carbon nanotubes, graphite, gold and diamond can be used to advantage.  
         [0022]     It should be understood that the FIGURES herein are for illustrative purposes only and not drawn to scale.