Patent Publication Number: US-2011056669-A1

Title: Heat Transfer Device

Description:
TECHNICAL FIELD OF THE DISCLOSURE 
     This disclosure generally relates to heat transfer devices, and more particularly, to a heat transfer device that is implemented with pins having a reduced width in a direction transverse to the direction of intended airflow. 
     BACKGROUND OF THE DISCLOSURE 
     Heat transfer devices transfer heat from one medium to another. Heat sinks are a particular type of heat transfer device that dissipate heat to air. Heat transfer devices of this type typically include multiple protrusions, such as fins or pins, arranged over a base plate or other similar structure that is thermally coupled to a device to be cooled or heated. The protrusions provide a relatively large amount of surface area for enhanced thermal coupling of the base plate to air. 
     SUMMARY OF THE DISCLOSURE 
     According to one embodiment, a heat transfer device includes an array of elongated pins coupled between a base plate and a cover plate. Each pin has a cross-sectional shape with a major width and a minor width that is perpendicular to the major width, in which the length of the minor width is less than the major width. The cover plate and the base plate forming a plenum for the movement of air across the array of pins along a direction parallel to the major width of each pin. 
     Some embodiments of the disclosure may provide numerous technical advantages. For example, some embodiments of the heat transfer device may be implemented in applications that would otherwise require liquid cooling mechanisms. The pins of the heat transfer device have a cross-sectional shape that is thinner in a direction transverse to the intended direction of airflow. This cross-sectional shape reduces the level of turbulence created, thus providing for relatively higher airflow levels. Thus, the heat transfer device may provide an enhanced level of efficiency due to an increased level of airflow through its plenum. The increased level of efficiency, therefore, may enable their use with applications that have heretofore required liquid cooling mechanisms. 
     Some embodiments may benefit from some, none, or all of these advantages. Other technical advantages may be readily ascertained by one of ordinary skill in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of embodiments of the disclosure will be apparent from the detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of one embodiment of a heat transfer device according to the teachings of the present disclosure; 
         FIG. 2  is a top view of the heat transfer device of  FIG. 1  shown with the cover plate removed in order to reveal the arrangement of pins on the base plate; 
         FIG. 3  is a side view of the heat transfer device of  FIG. 1 ; 
         FIGS. 4A ,  4 B, and  4 C are cross-sectional views of other embodiments of pins that may be configured on the heat transfer device of  FIG. 1 ; 
         FIG. 5  is a graph showing airflow performance plots for circular-shaped pins and elliptical-shaped pins, respectively; and 
         FIG. 6  are test result charts and showing test results for the heat transfer device of  FIG. 1  having elliptical-shaped pins and a known heat transfer device configured with circular-shaped pins, respectively. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     It should be understood at the outset that, although example implementations of embodiments are illustrated below, various embodiments may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the example implementations, drawings, and techniques illustrated below. Additionally, the drawings are not necessarily drawn to scale. 
     Heat transfer devices may includes protrusions, such as fins or pins, for enhanced thermal coupling to air. The fins of some heat transfer devices may be formed from sheet metal using a stamping process and arranged on a base plate at regularly spaced intervals using an assembly process. Heat transfer devices formed with pins, on the other hand, are typically formed using a casting process in which the pins are integrally formed with its associated base plate. 
     Certain heat transfer devices may be more conducive to manufacture using a casting process. For example, the manufacture of heat transfer devices configured on peltier devices are typically performed using a casting process. Peltier devices, which are also referred to a thermoelectric coolers or coldplates, are solid-state devices that move heat from one region to another using electric current. In many cases, the cooling efficiency of peltier devices may be limited by the ability of its associated heat transfer device to dissipate heat to the air. 
       FIGS. 1 ,  2 , and  3  are illustrations showing one embodiment of a heat transfer device  10  according to the teachings of the present disclosure. Heat transfer device  10  includes an array of elongated pins  12  having two ends  14   a  and  14   b . End  14   a  of each pin  12  is coupled to a base plate  16  and end  14   b  is coupled to a cover plate  18 . Each pin  12  has a cross-sectional shape defined by a minor width W minor  that is less than a major width W major . Base plate  16  and cover plate  18  form a plenum for constraining the movement of air across pins  12  along a direction that is generally parallel to the major width W major  of each pin  12 . 
     Certain embodiments of heat transfer device  10  incorporating pins  12  having a reduced minor width W minor  relative to its major width W major  may provide an advantage in that heat transfer may be obtained by the movement of air across pins  12  while exhibiting relatively less pressure drop than may typically experienced by known heat transfer device devices configured with circular-shaped pins. Circular-shaped pins of known heat transfer device devices may generate relatively large amounts of turbulence under high airflow levels. This turbulence often reduces the amount of direct contact with air thus reducing its effective heat transfer coefficient. The heat dissipation capacity, therefore, of known heat transfer device devices implemented with circular-shaped pins, therefore, may be limited. The heat transfer device  10  according to the teachings of the present disclosure may provide enhanced heat dissipation by allowing relatively higher airflow levels without increased turbulence that may be characteristic of those implemented with circular-shape pins. 
     Certain embodiments of heat transfer device  10  may also provide an advantage in that pins  12  may have a greater cross-sectional area than circular-shaped pins with widths similar to the minor widths W minor  of pins  12 . The enhanced cross-sectional area of pins  12  may provide reduced thermal resistance along its extent for improved conduction of heat away from base plate XX. Additionally, pins  12  may provide relatively greater surface area than circular-shaped pins having widths similar to the minor widths W minor  of pins  12  for improved transfer of heat from pins  12  to air in some embodiments. 
     Heat transfer device  10  may be manufactured using any suitable manufacturing technique. In one embodiment, pins  12  are integrally formed with base plate  16  using a casting process. The casting process may be well suited for applications, such as peltier devices, that typically use a casting process for coupling of heat transfer devices to their active regions. Following formation of pins  12  and base plate  16 , cover plate  18  may be coupled to the ends  14   b  of pins  12  using an adhesive or other suitable attachment mechanism. 
     In the particular embodiment shown, pins  12  have a length L of approximately 0.7 inches, a major width W major  of approximately 0.14 inches, a minor width W minor  of approximately 0.07 inches, a transverse spacing T of approximately 0.19 inches, and a streamwise spacing S of approximately 0.17 inches. The transverse spacing T defines an extent between adjacent pins  12  normal to the dominant direction of intended airflow, while the streamwise spacing defines an extent between adjacent pins  12  parallel to the dominant direction of intended airflow. Other embodiments may have a differing length L, major width W major , minor width W minor  transverse spacing T, streamwise spacing S than described above. In one embodiment, for example, the transverse spacing T may vary among differing rows of pins  12  such that the transverse spacing T of each row of pins  12  increases along the direction of intended airflow or decreases along the direction of intended airflow. 
     In the particular embodiment described above, the ratio of the minor width W minor  to the major width W major  is 0.5. Pins  12  having this shape may be relatively easy to manufacture using common casting techniques while providing relatively good laminar airflow across its surface. In other embodiments, pins  12  may have any suitable size ratio of their minor width W minor  to major width W major , such as less than 0.5 or greater than 0.5. 
     The ratio of the length L to the minor width W minor  of each pin  12  forms an important design consideration that is typically used to model the aerodynamic behavior of pins  12  in a constrained environment, such as the plenum formed between base plate  16  and cover plate  18 . This ratio (L/W minor ) generally describes an amount of frontal area impinged upon the movement of airflow through the plenum. In general, pins  12  having ratios (L/W minor ) greater than 10 may be modeled without regard to base plate  16  and/or cover plate  18  effects, and pins  12  having ratios less than 2.5 may be modeled with only minor regard to pin  12  effects. That is, the aerodynamic effects of base plate  16  and cover plate  18  may be effectively negligible when the ratio (L/W minor ) is greater than 10, and the aerodynamic effects pins  12  may be effectively negligible when the ratio (L/W minor ) is less than 2.5. Pins  12  having ratios (L/W minor ) in the range of 3 to 10, however, are typically modeled with regard to the aerodynamic behavior of pins  12 , base plate  16 , and cover plate  18 . Heat transfer devices  10  implemented on peltier devices are typically be configured with pin dimensions in this range. 
     Pins  12  may have any cross-sectional shape with a minor width W minor  that is less than its major width W major . In one embodiment, the cross-sectional shape of each pin may be generally symmetrical about an axis that extends along the major width W major  of each pin  12 . In this manner, the resultant lateral air movement due to airflow across the pin&#39;s surface may be reduced or eliminated. In other embodiments, the cross-sectional shape of each pin  12  may have an airfoil shape that may not necessarily be symmetrical about its major width W major  axis. In the particular embodiment shown, each pin  12  has an elliptical shape. 
       FIGS. 4A ,  4 B, and  4 C are cross-sectional views of other embodiments of pins  12 ′,  12 ″, and  12 ′″ that may be configured on the heat transfer device  10  of  FIG. 1 . Each of the pins  12 ′,  12 ″, and  12 ′″ has a leading edge  20 ′,  20 ″, and  20 ′″ that is adapted to face into the airflow direction  22  and a trailing edge  24 ′,  24 ″, and  24 ′″ that is configured opposite the leading edge  20 ′,  20 ″, and  20 ′″ of its respective pin  12 ′,  12 ″, and  12 ′″. 
     Pins  12 ′ and  12 ″ have leading edges  20 ′ and  20 ″ and trailing edges  24 ′ and  24 ″ with a generally rounded contour in a similar manner to the elliptical shape of pins  12  as shown in  FIG. 3 . Pins  12 ′ and  12 ″ differ, however, in that their minor widths W minor  are not centrally configured between their respective leading edges  20 ′ and  20 ″ and trailing edges  24 ′ and  24 ″. Specifically, the minor width W minor  of pin  12 ′ is closer to its respective leading edge  20 ′, while the minor width W minor  of pin  12 ″ is closer to its respective trailing edge  24 ″. 
     Pin  12 ′″ has a leading edge  20 ′″ with a generally rounded contour in a similar manner to pins  12 ,  12 ′, and  12 ″. Trailing edge  24 ′″ of pin  12 ′″ differs, however, in that it comprises an angled contour providing a teardrop-like shape for pin  12 ′″. The particular pin  12 ′″ shown has a trailing edge  24 ′″ with an angled contour. In other embodiments, the trailing edge  24 ′″ and the leading edge  20 ′″ may have an angled contour, or the leading edge  20 ′″ may have an angled contour while the trailing edge  24 ′″ has a rounded contour. 
       FIG. 5  is a graph showing airflow performance plots  26  and  28  for circular-shaped pins and elliptical-shaped pins  12 , respectively. Plot  26  shows the pressure drop as a function of volumetric flow rate through an array of circular-shaped pins and plot  28  shows the pressure drop as a function of volumetric flow rate through an array of elliptical-shaped pins  12 . As can be seen, a heat transfer device  10  configured with elliptical-shaped pins  12  has a lower pressure drop relative to the pressure drop experienced by a known heat transfer device having circular-shaped pins. 
     Lower pressure drop across an array of pins  12  may provide enhanced cooling efficiency in certain embodiments. For example, a lower pressure drop across pins  12  may enable airflow rates to be maintained at relatively higher levels for a given size of pins  12  in an heat transfer device  10 . Because airflow rates may be higher, more air may be moved through heat transfer device  10  for enhanced cooling efficiency. The relatively lower pressure drop also tends to indicate that air movement across pins  12  may be generally more laminar than airflow across circular-shaped pins. The relatively greater laminar flow may provide improved air to pin  12  contact for enhanced transfer of heat in some embodiments. 
       FIG. 6  are test result charts  30  and  32  showing test results for a heat transfer device configured with elliptical-shaped pins and an heat transfer device  10  configured with circular-shaped pins  12 , respectively. The values shown in test result chart  30  were obtained from a heat transfer device  10  having dimensions described above with respect to  FIGS. 1 ,  2 , and  3 , while the values shown in test result chart  32  are for a known heat transfer device having circular-shaped pins with a diameter of 0.07 inches. 
     One metric used for calculating heat transfer is a heat transfer coefficient (h) mathematically represented by equation 34. q mdl  represents the heat transferred through heat transfer device  10  or the known heat transfer device configured with circular pins. A ht  represents the combined surface area in contact with air, which includes the surface area of pins  12 , base plate  16 , and cover plate  18 . T wall  shows the temperature of heat transfer device  10  or the known heat transfer device configured with circular pins, and T blk  shows the ambient air temperature. Δp static  shows the static pressure drop through heat transfer device  10 . 
     As shown, the resulting heat transfer coefficient (h) for heat transfer device  10  with elliptical-shaped pins  12  has an approximate 2.5 percent improvement over the heat transfer coefficient (h) for the known heat transfer device with circular-shaped pins. The static pressure drop (Δp static ) for heat transfer device  10  shows an approximate 18.6 percent improvement. Because the combined surface area of heat transfer device  10  is greater, it provides approximately 41 percent improved efficiency over the known heat transfer device with circular-shaped pins. Thus, heat transfer device  10  configured with elliptical-shaped pins  12  may provide improved efficiency while causing less pressure drop to forced airflow through its pins  12 . The elliptical-shaped pins  12  may also provide increased cross-sectional area for reduced thermal resistance along their extent and increased surface area for improved coupling to the surrounding airflow than may be provided by circular-shaped pins having a width similar to the minor width W minor  of pins  12 . 
     Modifications, additions, or omissions may be made to heat transfer device  10  without departing from the scope of the disclosure. The components of heat transfer device  10  may be integrated or separated. For example, pins  12  may be integrally formed with base plate  16 , such as may be provided using a casting process or may be formed separately and combined later in a subsequent manufacturing step. Moreover, the operations of heat transfer device  10  may be performed by more, fewer, or other components. For example, additional elements may be provided within the plenum formed between base plate  16  and cover plate  18  to direct or concentrate airflow to certain regions of pins  12  configured in heat transfer device  10 . As used in this document, “each” refers to each member of a set or each member of a subset of a set. 
     Although the present disclosure has been described with several embodiments, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present disclosure encompass such changes, variations, alterations, transformation, and modifications as they fall within the scope of the appended claims.