Abstract:
According to some embodiments, an enhanced heat exchanger may be provided. The enhanced heat exchanger may comprise, for example, a heat transfer portion to receive heat from a heat source and to transfer heat from the heat source, and a remote heat sink adjacent to the heat transfer portion to remove heat from the heat transfer portion. In some embodiments, the remote heat sink may comprise a solid metal portion that extends away from the heat transfer portion, and a porous medium coupled to the solid metal portion. According to some embodiments, the porous medium may extend away from the solid metal portion such that a thermal boundary layer exists in substantially the entire porous medium.

Description:
BACKGROUND 
   Heat generated by electronic devices and other equipment may be dissipated to allow for efficient operation and to prevent damage to components. In some applications, a heat exchanger or heat sink may be used to effectuate the dissipation of heat. Forced convection may also be employed to enhance the performance of the heat exchanger. 
   The amount of heat that can be dissipated may increase with the size and/or surface area of the heat exchanger. Where space constraints limit the size of a heat exchanger, the efficiency of the heat exchanger may become important. Some devices, for example, might be limited in speed or functionality because higher power components would generate more heat than could be effectively dissipated by a heat exchanger of a given size. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of an apparatus. 
       FIG. 2  is a block diagram of a heat sink. 
       FIG. 3  is a block diagram of a heat exchanger according to some embodiments. 
       FIG. 4  is a block diagram of a method according to some embodiments. 
       FIG. 5  is a flow diagram of an apparatus according to some embodiments. 
       FIG. 6  is a block diagram of a system according to some embodiments. 
   

   DETAILED DESCRIPTION 
   Some embodiments described herein are associated with a “heat exchanger” or a “heat sink”. As used herein, the terms “heat exchanger” and “heat sink” may be used interchangeably and generally refer to any apparatus, device, system, or object for dissipating, removing, and/or otherwise eliminating heat. By way of example, a heat exchanger may be a longitudinal finned metal heat sink used to cool a processor or another electronic device component. 
   In addition, some embodiments are associated with a “heat transfer device.” As used herein, the phrase “heat transfer device” may refer to any device adapted to move, transfer, and/or otherwise relocate heat. Examples of heat transfer devices may include, but are not limited to, heat pipes, pumped loops, and/or refrigeration loops. In some embodiments for example, a heat exchanger may be a heat pipe for transferring heat from a processor to a heat sink. 
   Although a heat transfer device may also act as a heat exchanger or heat sink, as used herein the term “heat transfer device” generally refers to a device, apparatus, component, and/or object that is primarily used to move or relocate heat within an electronic or other device. The actual or majority of heat dissipation might be accomplished, for example, by a finned heat sink attached to the heat transfer device. 
   Referring first to  FIG. 1 , a block diagram of an apparatus  100  for dissipating heat is depicted for use in explanation, but not limitation, of described embodiments. Upon reading this disclosure, those skilled in the art will appreciate that different types, shapes, and configurations of apparatus and systems may be used. 
   In electronic systems such as notebook or portable computers, heat may need to be dissipated from various electronic components. For example, a heat source  102  may generate heat that must be dissipated from a notebook computer. Because vertical or head space may be limited in the casing of a notebook computer, there might not be enough room to place a heat sink directly on or attached to the heat source  102 . Because a heat transfer device  104  may take up less vertical space than a heat sink, the heat transfer device  104  may be used to transfer heat generated by the heat source  102  to a different location within, adjacent, or even external to the notebook computer. The alternate location may, for example, contain sufficient vertical space in which to locate a remote heat sink  106 . Air may be forced toward, through, and/or over the remote heat sink  106  by a fan  108  to enhance the heat dissipation of the remote heat sink  106 . The fan  108  may also or alternatively expel heat and/or heated air from, for example, the notebook computer. 
   The heat source  102  may be any device, element, object, and/or area that produces, emanates, and/or contains heat. In the case of a notebook computer, for example, the heat source  102  may be or include a processor such as a Mobile Intel® Pentium® 4 Processor or a Mobile Intel® Pentium® 4 Processor—M coupled with a Mobile Intel® 845 family chipset. The heat transfer device  104  may be any device for transferring heat away from the heat source  102  that is known, available, and/or described herein. The heat transfer device  104  may, for example, be a heat pipe. The remote heat sink  106  may generally be a metal finned heat sink of various sizes, shapes, and/or configurations. The remote heat sink  106  may be attached to a remote end and/or portion of the heat transfer device  104 . The fan  108  may be any type of device for causing air to flow toward and/or over the remote heat sink  106 . The fan  108  may, for example, be a standard axial-flow fan or a blower fan. 
     FIG. 2  shows an exemplary remote heat sink  106  that may be used, for example, in the apparatus  100 . The remote heat sink  106  is shown in  FIG. 2  as a longitudinal finned metal heat sink having multiple metal fins  110  protruding longitudinally from a heat sink base  112 . The fins  110  are oriented in parallel to each other and are arranged to provide a uniform lateral spacing or gap  114 . The remote heat sink  106  may have fewer or more parallel fins than shown in  FIG. 2 , and the fins may also be arranged in various orientations known to those skilled in the art. The fins  110  may be composed of any known or available thermally conductive material including metals such as copper. The base  112  of the remote heat sink  106  may be a solid metal surface attached to and/or placed adjacent to the remote end and/or portion of the heat transfer device  104 . The base  112  may also be or include the remote end and/or portion of the heat transfer device  104 . 
   Heat generally flows into the base  112  from the heat transfer device  104 . The heat may then travel upward through the parallel fins  110 . The fins  110  provide extensive surface area over which the remote heat sink  106  may release heat into the surrounding environment. The fan  108  described with respect  FIG. 1  may be used to force air between the fins  110 , expelling heated air and promoting greater remote heat sink  106  efficiency. 
   Turning to  FIG. 3 , a block diagram of a heat exchanger  120  in accordance with some embodiments is shown. The heat exchanger  120  may, according to some embodiments, have a base  112  and fins  110  similar to those described with respect to the remote heat sink  106  herein. Fewer or more fins  110  than shown in  FIG. 3  may be used in some embodiments. The heat exchanger  120  may also have a porous medium  122  attached and/or otherwise located between adjacent fins  110 . The porous medium  122  may be any known or available type of porous medium including, but not limited to, cellular or porous metals, metal foams, and metal sponges. Generally, any thermally conductive material that contains voids may be used as the porous medium  122 . 
   In some embodiments, the porous medium  122  may be forced, under compressive load, between adjacent fins  110 . Forcing the porous medium  122  into the space between adjacent fins  110  may result in good thermal contact and/or thermal coupling between the porous medium  122  and each of the metal fins  110 . Another method of providing good thermal contact between the porous medium  122  and the fins  110  may be to heat the fins  110  and/or the heat exchanger  120  (without the porous medium  122 ), place the porous medium  122  between adjacent fins  110 , and allow the fins  110  and/or heat exchanger  120  to cool. The heating of the fins  110  and/or heat exchanger  120  widens the gap  124  between adjacent fins  110 , permitting a properly sized portion of porous medium  122  to be placed between the fins  110 . The cooling allows the gap  124  to narrow, compressing the porous medium  122  between adjacent fins  110 . Other attachment methods such as using thermally conductive adhesive to bond the porous medium  122  to the fins  110  may also be employed to assemble the heat exchanger  120 . In some embodiments, the porous medium may be attached and/or thermally coupled to a single fin  110 . Also according to some embodiments, the porous medium  122  may be thermally coupled to and/or otherwise attached to the base  112 . 
   The porous medium  122  may generally have a very large surface area and therefore may provide very efficient heat dissipation. The tortuous path that heat may need to take to travel through the porous medium  122  may however generally limit the thermal conductivity from one end of the porous medium  122  to the other. For example, heat traveling from the base  112  into the porous medium  122  may only be able to travel a short distance into the porous medium  122  proximate to the base  112  prior to being dissipated. This may thermally isolate the remaining portions of the porous medium  122  that are distal from the base  112 , rendering them ineffective for heat dissipation. 
   According to some embodiments however, the thermal conductivity of the metal fins  110  is very high, allowing heat to travel easily to the tips of the fins  110 . Good thermal contact and/or thermal coupling between the fins  110  and the porous medium  122  may allow heat to flow into the porous medium  122  from any point along the length of the fins  110 , including from the tips of the fins  110  into the portions of the porous medium  122  most distal from the base  112 . The majority of or all of the porous medium  122  may therefore be utilized to greatly enhance the efficiency of the heat exchanger  120 . 
   In some embodiments, the use of the porous medium  122  may provide a gap  124  that may be optimally sized for thermal dispersion. For example, a heat sink  106  such as depicted in  FIG. 2  may generally have an optimal fin spacing  114 . The optimal lateral spacing  114  may often be too small to effectively manufacture (e.g., smaller than the manufacturing tolerances and/or capabilities). This may occur, for example, where the fin spacing  114  is required to be reduced below manufacturing capabilities in order to minimize resistance in systems using forced convection. In such circumstances, the heat sink  106  can not be manufactured in an optimal configuration for increased heat dissipation efficiency. In some embodiments however, the porous medium  122  may provide an optimal spacing  124  for the heat exchanger  120  that is larger than the optimal spacing  114  for a heat sink  106 . 
   For example, the thermal boundary layers within the porous medium  122  may be larger than those possible when air flows in a free stream between fins  110  (i.e., as in a heat sink  106 ). Optimal fin  110  spacing may generally be considered to have a direct relationship with the thickness of the thermal boundary layer. Thus, use of a porous medium  122  between fins  110  may provide for an optimal spacing  124  that may be within manufacturing limits. Further, increased lateral spacing  124  may reduce the total number of fins  110  required for a heat sink of a given size. As shown in  FIGS. 2 and 3  for example, the heat sink  106  and the enhanced heat exchanger  120  are the same size, yet the heat sink  106  has six fins  110 , while the enhanced heat exchanger  120  has only four fins  110 . Fewer fins  110  may result in more simplified manufacturing and thus may reduce manufacturing costs. Some embodiments therefore provide an enhanced heat exchanger  120  that may be manufactured with a fin spacing  124  optimized for heat dissipation efficiency. Such an enhanced heat exchanger  120  may also be more easily and more cheaply manufactured than standard heat sinks. Those skilled in the art will recognize that various known and/or available fin  110  types and orientations may be used in conjunction with the porous medium  122  to provide an enhanced heat exchanger  120 . 
     FIG. 4  is a flowchart of a method  150  in accordance with some embodiments. The method  150  may be practiced, for example, by the apparatus  200  or by the system  250  described in conjunction with  FIGS. 5 and 6  herein. In some embodiments, other systems and/or apparatus may be used to process the method  150 . The method  150  may begin at  152  by transferring heat from a heat source using a heat transfer device. For example, the heat generated by a microprocessor in a notebook computer may be taken up by a heat pipe attached to the processor. The heat may then be transferred from the end of the heat pipe adjacent to the processor to a remote end of the pipe. Attached to the remote end of the heat pipe may be one or more remote heat exchangers utilizing a porous medium. In some embodiments, the remote heat exchanger may be an enhanced heat exchanger  120  as described herein in conjunction with  FIG. 3 . At  154  the remote heat exchanger may take up the heat from the heat transfer device and dissipate it into the surrounding environment. In a notebook computer application for example, the remote heat exchanger may dissipate heat from the heat transfer device into the air within the notebook casing. 
   In some embodiments, forced convection may be used to increase the heat dissipation of the remote heat exchanger, at  156 . For example, a blower fan may be mounted within a notebook casing near the remote heat exchanger. According to some embodiments, a blower fan may be used to reduce the amount of vertical space needed and/or taken up within the notebook casing. Axial-flow fans, for example, may be required to be mounted above the remote heat exchanger (taking up vertical space within the notebook casing) in order to force air through or withdrawal air from the remote heat exchanger. The blower fan may direct air through the porous medium of the remote heat exchanger, expelling heated air from the remote heat exchanger and thus enhancing the efficiency of the remote heat exchanger. The blower fan may also be used, for example, to expel heated air from the casing of the notebook computer. 
   Referring now to  FIG. 5 , a block diagram of an apparatus  200  according to some embodiments is shown. The apparatus  200  may include a heat source  102 , a heat transfer device  104 , an enhanced remote heat exchanger  120  having a porous medium  122  sandwiched between adjacent fins  110 , and a fan  108  for blowing air through the porous medium  122 . In some embodiments the components  102 ,  104 ,  108 ,  120  of the apparatus  200  may be components as described herein in conjunction with  FIGS. 1–3 . Also according to some embodiments, fewer or more components may be included in and/or attached to the apparatus  200 . For example, one or more heat sources  102 , heat transfer devices  104 , enhanced remote heat exchangers  120 , fans  108 , and/or any combination thereof may be parts of the apparatus  200 . 
   The heat source  102  generally gives off and/or otherwise generates heat that requires dissipation. The heat may travel into a heat transfer device  104  attached and/or adjacent to the heat source  102 . In some embodiments, the heat may then travel along and/or through the heat transfer device  104  to a location remote from the heat source  102 . The heat may then flow into the base  112  of an enhanced remote heat exchanger  120 , and into the fins  110  and porous medium  122  of the enhanced remote heat exchanger  120 . Heat may then emanate from the various surface areas of the fins  110  and porous medium  122 . In some embodiments a fan  108  may be used to blow air between the fins  110  and through the porous medium  122 , to remove heated air from the enhanced remote heat exchanger  120 . The fan  108  in  FIG. 5  is shown located behind the enhanced remote heat exchanger  120  and may generally be oriented to blow air in a direction parallel to the fins  110  and through the porous medium  122 . The apparatus  200  may, according to some embodiments, be an enhanced heat exchanger for removing heat from portable electronic devices such as notebook computers. 
   The porosity of the porous medium  122  may generally be very high. Some metal foams, for example, may have porosities of around ninety percent or even as high as ninety-five percent. Porous mediums  122  may therefore generally weigh very little. The use of porous mediums  122  in an enhanced heat exchanger  120  may, according to some embodiments, provide a lighter-weight heat exchanger than would otherwise be possible. Notebook computers and other portable electronics are weight-sensitive devices that could benefit from the reduced weight of an enhanced heat exchanger  120 . Also according to some embodiments, the pore size of the porous material  122  may be selected to provide enhanced heat dispersion without changing the porosity. For example, a metal foam  122  may have a pore size of between five and twenty pores per inch (PPI). In some embodiments, a metal foam with a pore size of twenty PPI may, for example, be chosen because it provides for enhanced heat dispersion. 
   The fan  108  may be or include one or more blower fans located in a notebook computer or other portable computing device. Blower fans are generally characterized as providing low air flows, but being able to create high pressure differentials (or pressure head). Blower fans may generally save vertical space when used in portable electronics such as notebook computers because their configuration allows them to be mounted adjacent to, instead of on top of, a component (such as a heat exchanger) requiring air flow. In some embodiments, the pressure differential created by a blower fan  108  may assist in dispersing heat from the enhanced remote heat exchanger  120 . For example, the pressure differential created by the blower fan  108  may cause the formation of eddies and/or flow vortices on the trailing edge of the enhanced remote heat exchanger  120 . The eddies and/or vortices may, according to some embodiments, promote thermal dispersion by dissipating heated air adjacent to the enhanced remote heat exchanger  120 . 
     FIG. 6  shows a block diagram of a system  250  according to some embodiments. The system  250  may generally include a motherboard  252 , a processor  102  attached to the motherboard  252 , a heat pipe  104  for removing heat from the processor  102 , and an enhanced remote heat exchanger  120  utilizing a porous medium  122  for dissipating heat from the heat pipe  104 . The system  250  may also include a blower fan  108  for forcing air through the enhanced remote heat exchanger  120 , a battery adapter  256  to provide battery power to the system  250 , and a casing  254  for housing the system components. In some embodiments the system  250  may be or include a notebook computer or other portable electronic device or any other type or configuration of computing or electronic device including, but not limited to, a desktop computer and a computer server. For example, the motherboard  252  may be the system board of a notebook computer, the processor  102  may be a Mobile Intel® Pentium® 4 Processor as described herein, the battery adapter  256  may be an adapter that allows the notebook computer to be powered by a rechargeable or non-rechargeable battery, and the casing  254  may be the chassis of the notebook computer. The system  250  may be used, for example, to dissipate heat in accordance with the method  150  described herein in conjunction with  FIG. 4 . 
   According to some embodiments, heat generated by the processor  102  is removed from the processor  102  by the heat pipe  104 . The remote end of the heat pipe  104  may, for example, form the base  112  of the enhanced remote heat exchanger  120 . Heat may therefore flow through the base  112  into the fins  110  and porous medium  122  of the enhanced remote heat exchanger  120  where it is dissipated into the air within the casing  254 . The blower fan  108  may force air over and through the enhanced remote heat exchanger  120 , creating a pressure differential across the enhanced remote heat exchanger  120 . The heated air surrounding the enhanced remote heat exchanger  120  is expelled by the blower fan  108  and, in some cases, is forced through a vent or other opening in the casing  254 . 
   Larger and/or more powerful blower fans  108  may, in some embodiments, be used to create higher pressure differentials across the enhanced remote heat exchanger  120  and promote further thermal dispersion efficiency. Higher air flows may generally increase acoustic noise however, and the size of the fan  108  that may be employed in a notebook computer, for example, may be limited based on the amount of noise that is acceptable to produce. According to some embodiments however, the flow of air through the porous medium  122  may produce noise in the broad band range (acoustic energy distributed over a wide range of frequencies). As compared to the noise that may be produced by blowing air through a heat sink  106  (from  FIG. 2 ), the broad band noise created by blowing air through the enhanced remote heat exchanger  120  may be less irritating to the human ear. Some embodiments may therefore allow larger fans  108  to be used than would normally be acceptable, further increasing the effectiveness of the enhanced remote heat exchanger  120 . 
   The several embodiments described herein are solely for the purpose of illustration. Persons skilled in the art will recognize from this description that other embodiments may be practiced with modifications and alterations limited only by the claims.