Patent Publication Number: US-8123386-B2

Title: Shape forming heat sink with flexible heat rod

Description:
TECHNICAL FIELD 
     The present invention relates generally to heat sinks and, more specifically, to a heat dissipating structure that conforms to an irregular surface to which heat is to be transferred. 
     BACKGROUND INFORMATION 
     Light emitting diodes (LEDs) provide an energy-efficient light source and are increasingly being used instead of fluorescent and halogen gas lamps for high capacity lighting needs, such as street lamps. In order to increase the amount of light generated, LEDs are often incorporated into street lamps, which can lead to significant problems of overheating. The performance and lifetime of the LEDs is degraded if the operating temperature exceeds a threshold level. For example, the useful life of an LED street lamp is sometimes specified as the number hours of operation before which the luminous output of the lamp drops to half of its initial output. Empirical data suggests that there is an inverse exponential relationship between the useful life of an LED lamp and the amount by which the average operating temperature exceeds a threshold level, such as 25 degrees Celsius. Thus, dissipating the heat generated by the LEDs in the street lamp is a problem that must be solved. 
     The LEDs of a street lamp are enclosed by a covering. The covering typically has openings to allow the heat generated by the LEDs to escape the covering. However, the openings allow dust, moisture and insects to enter the covering and to block much of the light that is generated. 
       FIG. 1  (prior art) shows an existing LED street lamp  10  that does not permit dust, moisture and insects to obstruct the transparent lower cover  11  through which the generated light shines onto the street. Transparent lower cover  11  is kept free of dust, moisture and insects by completely sealing off the lower compartment below the LEDs. Consequently, most of the heat generated by the LEDs must be dissipated through the upper compartment. The heat is transmitted from the LEDs to a heat conducting plate  12 . The heat then passes on to heat-dissipating fins  13  via a heat guiding piece  14 . Heat is dissipated out of the upper compartment by fans  15  that blow heated air out of venting slots  16  in the upper cover  17 . For additional details on this prior art method of dissipating heat from a street lamp, see U.S. Pat. No. 7,278,761 to Kuan entitled “Heat Dissipating Pole Illumination Device.” 
     This prior art method of dissipating heat from an LED street light has multiple disadvantages. First, although dust, moisture and insects are prevented from entering the lower compartment, they will nevertheless enter the upper compartment through the venting slots  16 . The dust, moisture and insects will likely clog the spaces between the fins  13  and reduce the ability of the fins to dissipate heat. Second, the fans  15  have moving parts and will likely malfunction, especially if they are subjected to the dust, moisture and insects that enter through the venting slots  16 . Moreover, the fans  15  also require a power supply, which might not be able to be shared with the LEDs. Finally, the fins  13  through which the heat guiding piece  14  extends and the fans  15  add to the cost of the street lamp. 
     A method is sought for dissipating heat from an LED street lamp that does not subject the inner compartments of the street lamp to dust, moisture and insects and that does not require fans or fins. 
     SUMMARY 
     A conforming heat dissipating structure transfers heat to a non-planar surface from a heat source mounted to the planar bottom surface of the heat dissipating structure. The heat dissipating structure includes an open container over-filled with metal balls that are interspersed among metallic shavings. The shavings and balls are made of a heat-conductive material, such as copper or aluminum. The upper surface of the shavings and balls is disposed above the upper rim of the open container. A flexible retainer with a copper screen covers the upper surface of the shavings and balls. The shavings and balls are pressed against the non-planar surface and are compressed so as to conform to the shape of the irregular surface. In an embodiment, the heat source is an array of light emitting diodes (LEDs) mounted to the bottom surface of the open container. And the heat sink is a dome-shaped concave surface of the upper cover of a street light. Fasteners attach the open container to the non-planar surface of the street light such that the upper surface of the metallic shavings is pressed against the non-planar surface. The fasteners can be bolts, screws, clamps, rivets or cables. The street light originally configured for gas bulbs can be retrofitted with LEDs by using the non-planar cover of the street light as a heat sink to dissipate the heat generated by the LEDs that are mounted to the bottom of the novel conforming heat dissipating structure. 
     A method of manufacturing the conforming heat dissipating structure involves the steps of filling an open container with metallic shavings and metal balls, covering the upper surface of the shavings and balls with a flexible retainer, and fastening a frame gasket to the open container in order to hold the flexible retainer in place over the shavings. The metal balls are interspersed among the metallic shavings. The open container is filled with copper shavings and balls beyond the upper rim of the open container to form an upper surface of the shavings. The frame gasket is fastened to the upper rim of the open container so as to hold the flexible retainer in place between the upper rim and the frame gasket. A heat source such as an array of LEDs is attached to the planar bottom surface of the open container. The open container is then attached to a non-planar surface such that the upper surface of the metallic shavings is pressed against the non-planar surface and assumes the irregular shape of the non-planar surface. 
     A novel conforming heat dissipating structure includes an open container and a heat source attached to the planar bottom surface of the structure. In addition, the heat dissipating structure includes a means for transmitting heat generated by the heat source to a non-planar surface above the upper rim of the open container. The means is disposed inside the open container as well as above the upper rim of the open container, and the means is adapted to be compressed between the open container and the non-planar surface. The means acquires the shape of the non-planar surface when the means is compressed. 
     A novel flexible heat rod enables heat to be transferred over a flexible path from a heat source to a heat sink. The flexible heat rod is made from a cable with many strands. One end of the flexible heat rod passes through a hole in the bottom of an open container, and the strands are spread out inside the open container. The open container is filled with metallic shavings and metal balls both above and below the strands. The open container, the metallic shavings, the metal balls and the flexible heat rod are made of copper. As the mixture of shavings and balls is compressed, the strands are pressed between the metallic shavings forming a good thermal contact between the flexible heat rod and the shavings. A retaining cover is fastened to the upper rim of the open container and retains the shavings and balls inside the open container. 
     In an embodiment, the other end of the flexible heat rod passes through a hole in the bottom of a second open container. Strands from the other end of the flexible heat rod are spread out inside the second open container. The second open container is filled with additional shavings and balls around the strands as well as above the upper rim of the second open container. A flexible retainer covers the upper surface of the additional metallic shavings. The shavings and balls are pressed against a non-planar surface so as to conform to the shape of the surface. Fasteners attach the second open container to the non-planar surface such that the upper surface of the additional metallic shavings is pressed against the non-planar surface. 
     In one application, the heat source is LEDs mounted to the bottom surface of the first open container. The second open container is pressed against the inside cover of a street light such that the upper surface of the metallic shavings conforms to the shape of the street light cover. The flexible heat rod provides a means for transmitting heat generated by the LEDs on a first heat dissipating structure to the irregular-shaped street light cover that is pressed against the over-filled shavings in a second conforming heat dissipating structure. The flexible heat rod can easily bend to avoid obstacles in the path between the heat source and the heat sink. In another application, the flexible heat rod is used to conduct the heat generated by a field programmable gate array (FPGA) chip out from between cramped computer components to a location where a fan can blow air through fins attached to a second heat dissipating structure. The flexible heat rod can also be used to conduct heat away from other electronic components, such as a complex programmable logic device (CPLD), a central processing unit (CPU) or a stacked memory device. 
     Further details and embodiments and techniques are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention. 
         FIG. 1  (prior art) is a perspective view of an existing LED street lamp that dissipates heat by blowing hot air out of venting slots. 
         FIG. 2  is an exploded perspective view of a conforming heat dissipating structure that includes an open container covered by a flexible retainer. 
         FIG. 3  is an exploded side view of the heat dissipating structure of  FIG. 2  filled with metallic shavings and metal balls. 
         FIG. 4  is a side perspective view of the heat dissipating structure of  FIG. 2  in which the metallic shavings are covered by a flexible retainer. 
         FIG. 5  is a perspective view of the heat dissipating structure of  FIG. 2  being fit against the inside upper cover of a street light. 
         FIG. 6  is a flowchart of steps for manufacturing the conforming heat dissipating structure of  FIG. 2 . 
         FIG. 7  is a perspective view of a heat dissipating structure with a flexible heat rod. 
         FIG. 8  is a perspective view of the flexible heat rod and heat dissipating structure of  FIG. 7  filled with metallic shavings and metal balls. 
         FIG. 9  is a perspective view of the flexible heat rod of  FIG. 7  connecting heat dissipating structures in a street light. 
         FIG. 10  is a perspective view of a flexible heat rod used on a printed circuit board to transfer heat away from a field programmable gate array chip. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 2  is an exploded top perspective view of a conforming heat dissipating structure  19  that includes an open container  20  and a flexible retainer  21 . In an embodiment, open container  20  is a rectangular half box that is about ten inches long, six inches wide and one inch tall. Open container  20  has a bottom  22  and walls  23  that are about one-quarter inches thick. The bottom  22  of open container  20  has a planar bottom surface  24 . The walls form an upper rim  25 . Open container  20  is made of a material with a high thermal conductivity, such as copper, aluminum or a metal alloy such as aluminum 6061. Flexible retainer  21  includes a copper screen or wire mesh  26  that is held in place by a frame gasket  27 . Alternatively, instead of a metal screen, a graphite sheet can be used as the mesh  26 . Frame gasket  27  fits over upper rim  25  and is attached to open container  20  with fasteners  28  that screw into threaded holes  29 . In  FIG. 2 , fasteners  28  are bolts. When frame gasket  27  is attached to open container  20 , a portion of wire mesh  26  is held between frame gasket  27  and upper rim  25 . 
       FIG. 3  is an exploded side perspective view of conforming heat dissipating structure  19  that includes flexible retainer  21 , open container  20  filled with metallic shavings  30  and a platform  31  upon which a heat source is mounted.  FIG. 3  shows an array of nine individual light emitting diodes (LEDs)  32  mounted to the bottom surface of platform  31 . In other embodiments, an individual LED or an LED array are mounted to platform  31 . Platform  31  in turn is attached to bottom surface  24  of open container  20 . In an embodiment, platform  31  is made of soft aluminum to which the LEDs  32  are attached via a dielectric layer. In another embodiment, platform  31  is thermally conductive, yet electrically nonconductive. For example, platform  31  can be made of aluminum oxide (Al 2 O 3 ) or aluminum nitride (AlN). Open container  20  is over-filled with the metallic shavings  30  such that the shavings are disposed in the open container as well as above upper rim  25 . 
     Interspersed among the metal shavings  30  are metal balls  33 . The metal balls add mass and thereby make the heat sink of structure  19  more efficient. The metal shavings  30  hold the metal balls  33  in place and form a malleable compress. In an embodiment, both metal shavings  30  and metal balls  33  are made of copper. The metal shavings  30  can be purchased from recycling companies that obtain the shavings from machine shops. Balls intended for bead blasting can be used as the metal balls  33 . For example, copper balls are used for bead blasting where a blasting medium that is softer than steel is required. Copper balls with a diameter of 3/16 inch can be dispersed among the copper shavings  30 . Balls of other sizes can also be used, for example, balls with a diameter of 1/16 inch (small), 5/64 inch (medium) or 3/32 inch (large). Flexible retainer  21  is then fastened down over upper rim  25  and holds the metal shavings  30  and metal balls  33  in place in open container  20 . 
     In another embodiment, a graphite powder is mixed in with the shavings  30  and balls  33 . The graphite powder fills in some of the air pockets between the shavings and balls and enhances the ability of the mixture to transfer heat. A graphite powder with good thermal conductivity is used, such as Primary Synthetic Graphite Powder GP55-B manufactured by GrafTech International of Clarksburg, W. Va. The graphite powder fills in more of the air pockets as the mixture of shavings, balls and powder is later compressed. In yet another embodiment, graphite balls are mixed into graphite powder instead of using metal shavings and balls. The graphite powder and ball mixture is then covered with a graphite sheet and compressed into open container  20  in a later step. 
       FIG. 4  is a side perspective view of conforming heat dissipating structure  19  that includes flexible retainer  21 , open container  20  filled with metallic shavings  30  and platform  31  upon which LEDs  32  are mounted. The shavings  30  and balls  33  have been compressed into open container  20  using an arbor press such that the air pockets between the shavings and balls comprise less than 50% of the volume of the mixture of shavings and balls. Nevertheless, the upper surface of the compress of shavings and balls still protrudes well above upper rim  25  of open container  20 . Flexible retainer  21  is fastened down over upper rim  25  such that the upper surface  34  of the metallic shavings  30  and metal balls  33  is pillow shaped. Four fasteners  28  pass through holes in frame gasket  27  of flexible retainer  21  and screw into holes  29  in the walls  23  of open container  20 . The pillow top of conforming heat dissipating structure  19  acts like a sand bag and molds to any shape that upper surface  34  is pushed against. 
     Conforming heat dissipating structure  19  can be used as a heat transfer element to retrofit street lights by replacing halogen lights with LEDs. Typically, the retrofitted street lights do not have adequate vents or heat sinks to dissipate the heat produced by the LEDs. If the heat generated by the LEDs is to be transferred to the housing of the street light, there should be a large area of contact between the structure holding the LEDs and the housing in order to convey the heat generated by the LEDs to the outside surface of the street light housing. It is difficult to obtain the exact measurements of the concave surface of the street light housing in order to construct a solid metal heat sink that fits up against the inside of the upper cover of the street light housing. Constructing the solid metal heat sink would typically require a solid model to be made. In addition, a different solid metal heat sink to have to be constructed to match the specific shape of each type of street light. Alternatively, a malleable thermal compound could be molded like putty to an irregular surface. But with time and heat, thermal compounds tend to dry out, turn into powder and lose their thermal conductivity. Conforming heat dissipating structure  19  is the solution to making a tight, long-term contact between a heat dissipating structure and a large area of a non-planar surface that can absorb heat from the dissipating structure. For example, the pillow top of conforming heat dissipating structure  19  molds against any shape of the inside upper cover of a street light housing. Even though the mixture of shavings  30  and balls  33  has already been compressed once into open container  20  by the arbor press, the remaining air pockets between the shavings and balls are compressed further and permit the compress of shavings and balls to conform to the shape of the non-planar surface of the street light housing. Thereafter, the compress of copper shavings and balls maintains its shape when exposed to extreme heat over time. 
       FIG. 5  shows conforming heat dissipating structure  19  being fit against the dome-shaped concave surface  35  of the upper cover  36  of a street light  37 . Upper surface  34  of the metallic shavings  30  and metal balls  33  is pressed against concave surface  35  of street light  37 . In an embodiment, an arbor press is used to press structure  19  against upper cover  36  and thereby compress the metallic shavings  30  and metal balls  33  and decrease the size of the air pockets between the shavings and balls. The volume occupied by air allows the copper shavings  30  and copper balls  33  to conform to the non-planar surface  35  as the shavings and balls are compressed. As the size of the air pockets decreases, the density of the shavings and balls increases. In an embodiment, a density is achieved in which the air pockets comprise less than 50% of the volume of the compress of shavings and balls. A compress of copper shavings and balls having less than 50% air pockets has a thermal conductivity that is greater than solid aluminum 6061, considering that copper has a thermal conductivity of 390 W/mK and aluminum 6061 has a thermal conductivity of 180 W/mK (Watts per meter-Kelvin). In an embodiment in which a graphite powder is added to the mixture of shavings and balls, air pockets comprise much less than 50% of the volume of the compress. In the embodiment in which graphite balls are mixed into graphite powder, there are practically no large air pockets remaining after the mixture is compressed. 
     After conforming heat dissipating structure  19  is pressed against upper cover  36 , structure  19  is fastened to upper cover  36  by bolts  38  that pass through structure  19  and screw into holes in upper cover  36 . Either the holes in upper cover  36  are threaded, or nuts on used to secure bolts  38  on the outside of upper cover  36 . Bolts  38  act as fasteners to attach open container  20  to the non-planar surface  35  such that upper surface  34  of the metallic shavings  30  remains pressed against non-planar surface  35 . By maintaining a large area of contact between structure  19  and upper cover  36 , the heat generated by the LEDs  32  is dissipated out of the body of street light  37  without using fins, fans or venting slots. The LEDs  32  are able to achieve a longer service life because the heat they generated is dissipated out of the street light  37  through the upper cover  36 . 
     In addition to retrofitting street lights, conforming heat dissipating structure  19  can be used to dissipate heat from a heat source to a non-planar cover of other lamps, such as traffic lights, yard lamps, bay lights and spot lights. 
       FIG. 6  is a flowchart illustrating steps  39 - 45  of a method of manufacturing conforming heat dissipating structure  19 . 
     In a first step  39 , open container  20  made of metal is machined. For example, open container  20  is machined from a solid rectangular piece of copper. Four threaded holes  29  are drilled into open container  20  to accept the four fasteners  28 , such as bolts. 
     In step  40 , metal balls  33  are mixed in with metal shavings  30 . Larger metal balls  33  are used for larger dimensioned open containers. 
     In step  41 , open container  20  is filled with the mixture of metal shavings  30  and metal balls  33 . Optionally, a final layer of just metal shavings is added on top of the mixture. Open container  20  is filled beyond upper rim  25  to form upper surface  34  of a mound of metallic shavings. 
     In step  42 , the shavings  30  and balls  33  are compressed into open container  20  using an arbor press such that the air pockets between the shavings and balls comprise less than 50% of the volume of the mixture of shavings and balls. Nevertheless, upper surface  34  of the compress of shavings and balls still protrudes well above upper rim  25  of open container  20 . 
     In step  43 , upper surface  34  of metallic shavings  30  is covered with flexible retainer  21 . Copper screen  26  is pulled down over the mound of metal shavings  30  and metal balls  33  and forms a pillow top. 
     In step  44 , frame gasket  27  is fastened to upper rim  25  of open container  20  so as to hold copper screen  26  in place between upper rim  25  and frame gasket  27 . Frame gasket  27  is fastened to upper rim  25  by screwing the bolts  28  into the threaded holes  29 . Performing steps  39 - 43  produces conforming heat dissipating structure  19 . 
     In step  45 , an array of LEDs  32  is attached to the planar bottom surface  24  of open container  20 . An aluminum platform  31  upon which the LEDs  32  are mounted is attached using thermal glue to bottom surface  24 . Power wires used to provide the LEDs  32  with current are then attached to platform  31 . 
     In step  46 , heat dissipating structure  19  and the mounted LEDs  32  are attached to a non-planar surface to which the heat generated by the LEDs is to be transferred. For example, open container  20  is pressed against the inside dome-shaped concave surface  35  of the upper cover  36  of street light  37  (as shown in  FIG. 5 ). An arbor press is used to press open container  20  against surface  35  so that the size of the air pockets between the shavings  30  and the balls  33  is reduced. In an embodiment, the mixture of shavings  30  and balls  33  is compressed between open container  20  and surface  35  until the air pockets between the shavings and balls occupy less than 50% of the volume of the space between open container  20  and surface  35 . As the mixture is compressed, the metal shavings  30  at upper surface  34  mold to the contour of concave surface  35 . When street light  37  is operating, heat generated by the LEDs  32  flows through bottom  22  of open container  20 , through shavings  30  and balls  33 , through copper screen  26  and to upper cover  36  of street light  37 . The heat then escapes into the atmosphere from the outer, upper surface of upper cover  36 . 
       FIG. 7  is a perspective view of a heat dissipating structure  47  that is adapted to transfer heat over a flexible path from a heat source to a heat sink. The heat source is often located some distance away from where the heat is to be dissipated. For example, structural beams or walls may be located between the dome-shaped surface  35  of upper cover  36  of street light  37  and the most desirable location to place the LEDs  32 . Or it may be necessary to locate the ac/dc driver block for the LEDs  32  between the LEDs and upper cover  36 . A means is needed to direct the flow of heat around obstacles from a heat source, such as LEDs  32 , to a heat sink, such as surface  35 . A flexible heat rod  48  is used to transfer heat from heat dissipating structure  47  to heat dissipating structure  19 . Heat dissipating structure  19  is located at the opposite end of flexible heat rod  48  from structure  47 , but is not shown in  FIG. 7 . 
     Flexible heat rod  48  is a thick copper wire made of many strands  49 . Flexible heat rod  48  can be made using a high-power transmission cable or the wire used to ground the lightning rod on a building. In the embodiment of  FIG. 7 , flexible heat rod  48  has a diameter of about one inch. One end of flexible heat rod  48  passes through a hole  50  in bottom  22  of heat dissipating structure  47 . Hole  50  is formed to have the same diameter as the diameter of flexible heat rod  48 . The other end of flexible heat rod  48  passes through another hole in the bottom of the open container of heat dissipating structure  19 .  FIG. 7  shows that the ends of the strands  49  are spread apart in a circular pattern inside open container  20 . The strands  49  are dispersed throughout the volume of open container  20 . Then the volume of open container  20  is filled around the strands  49  with a mixture of metallic shavings  30  and metal balls  33 . 
       FIG. 8  shows that metallic shavings  30  and metal balls  33  are disposed both beneath and over the strands  49 . Heat dissipating structure  47  includes a planar retaining cover  51  upon which platform  31  and an array of LEDs  32  are mounted. Platform  31  is attached to retaining cover  51  using thermal glue. Retaining cover  51  is fastened to upper rim  25  of open container  20  and retains metallic shavings  30  and metal balls  33  inside open container  20 . Open container  20  is first over-filled with the mixture of shavings and balls, and then the mixture is compressed between retaining cover  51  and bottom  22  such that the air pockets between the shavings and balls occupy less than 50% of the volume of the space between retaining cover  51  and bottom  22 . In the compressed state, the metallic shavings  30  make contact with flexible heat rod  48  all along the sides of the individual strands  49  that are spread out inside open container  20 . A much larger contact surface between the shavings and the sides of the multiple strands  49  allows a larger heat transfer than would be achievable by routing a solid rod of the same diameter as flexible heat rod  48  through the shavings. Retaining cover  51  is fastened to open container  20  by threaded bolts  28  that screw into holes  29  in open container  20 , as shown in  FIG. 7 . 
     The second end  52  of flexible heat rod  48  passes through a hole in the bottom  22  of an open container  20  of a heat dissipating structure of the type shown in  FIG. 2 . The ends of the strands  49  are spread apart in a circular pattern inside the open container  20  of structure  19 . Inside structure  19 , metallic shavings  30  and metal balls  33  are also filled in around the strands  49  such that metallic shavings  30  make contact all along the sides of the individual strands  49  when the shavings and balls are compressed. Open container  20  of structure  19  is also over-filled with the mixture of shavings beyond upper rim  25  of the open container  20  of structure  19 . Flexible retainer  21  covers the upper surface  34  of the shavings and balls. 
       FIG. 9  is a perspective view of the heat dissipating structures  19  and  47  being mounted in street light  37 . As with the structure  19  of  FIG. 5  that does not include flexible heat rod  48 , the heat dissipating structure  19  of  FIG. 9  that is attached to flexible heat rod  48  is also pressed against a non-planar surface to which heat is to be transferred. The shavings and balls that are held in place in structure  19  by copper screen  26  are pressed against concave surface  35  of street light  37  and assume the contour of surface  35 . Bolts  38  act as fasteners to attach the open container  20  of structure  19  to non-planar surface  35 . Flexible heat rod  48  allows an LED, an LED array, or an array of individual LEDs  32  to be positioned lower in street light  37  and closer to the glass lens  53 . Flexible heat rod  48  could easily be bent to go around obstructions inside street light  37  between structures  47  and  19 . 
     Flexible heat rod  48  is used in other applications besides retrofitting street light  37 . For example, flexible heat rod  48  is used to lower the location of the LEDs in a bay light such that light is generated at the optimal position in the parabolic curve of the bay light. Yet the heat generated by the LEDs can be transmitted to the covering of the bay light, where it is dissipated into the atmosphere. 
       FIG. 10  shows flexible heat rod  48  used in an application in which the heat source is not related to lighting. In an electronics application, flexible heat rod  48  is attached to a micro heat dissipating structure  47  that covers the top of a computer processing element, such as a large field-programmable gate array (FPGA)  54  mounted on a printed circuit board  55 . Flexible heat rod  48  conducts the heat generated by FPGA  54  out from between cramped computer components to a location at which a fan can blow air through fins  56  attached to a heat dissipating structure at the opposite end of flexible heat rod  48 . Flexible heat rod  48  can also be used to conduct heat away from other electronic components, such as a complex programmable logic device (CPLD), a central processing unit (CPU) or a stacked memory device. 
     Although certain specific embodiments are described above for instructional purposes, the teachings of this patent document have general applicability and are not limited to the specific embodiments described above. Although open container  20  of the heat dissipating structures is described above as having a rectangular box shape, open container  20  can have other shapes, such as an open oval box shape or a circular open box shape. Moreover, bottom  22  of open container  20  is described above as having one hole  50  through which one flexible heat rod  48  passes. In order to transfer more heat from each heat dissipating structure  47 , multiple heat rods can be attached to the structure  47  through multiple holes. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.