US20110056669A1

US20110056669A1 - Heat Transfer Device

Info

Publication number: US20110056669A1
Application number: US12/554,575
Authority: US
Inventors: James A. Pruett; Byron E. Short, Jr.; William G. Wyatt
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 2009-09-04
Filing date: 2009-09-04
Publication date: 2011-03-10
Also published as: WO2011028389A3; WO2011028389A2

Abstract

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.

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, 4B, and 4C 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_minorthat 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_majorof each pin 12.
Certain embodiments of heat transfer device 10 incorporating pins 12 having a reduced minor width W_minorrelative to its major width W_majormay 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_minorof 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_minorof 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_majorof approximately 0.14 inches, a minor width W_minorof 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_minortransverse 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_minorto the major width W_majoris 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_minorto 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_minorof 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_minorthat 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_majorof each pin 12. In this manner, the resultant lateral air movement due to airflow across the pin'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_majoraxis. In the particular embodiment shown, each pin 12 has an elliptical shape.
FIGS. 4A, 4B, and 4C 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_minorare not centrally configured between their respective leading edges 20′ and 20″ and trailing edges 24′ and 24″. Specifically, the minor width W_minorof pin 12′ is closer to its respective leading edge 20′, while the minor width W_minorof 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_mdlrepresents the heat transferred through heat transfer device 10 or the known heat transfer device configured with circular pins. A_htrepresents the combined surface area in contact with air, which includes the surface area of pins 12, base plate 16, and cover plate 18. T_wallshows the temperature of heat transfer device 10 or the known heat transfer device configured with circular pins, and T_blkshows the ambient air temperature. Δp_staticshows 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_minorof 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.

Claims

1. A heat transfer device comprising:

an array of elongated pins each having a first end and a second end that is coupled to a base plate configured on a peltier device, each pin having an elliptical shape with a major width and a minor width that is perpendicular to the major width, the length of the minor width being less than the major width, each pin has a height that extends from its first end to its second end, the height to the minor width comprising a ratio that is in the range of 3 to 10; and

a cover plate coupled to the first end of each of the array of pins, 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.

2. A heat transfer device comprising:

an array of elongated pins each having a first end and a second end that is coupled to a base plate, each pin having a cross-sectional shape with a major width and a minor width that is perpendicular to the major width, the length of one of the minor width or the major width being less than the other; and

3. The heat transfer device of claim 2, wherein the cross-sectional shape comprises an elliptical shape.

4. The heat transfer device of claim 2, wherein the major width extends from a leading edge to a trailing edge, the minor width being closer to the leading edge than the trailing edge.

5. The heat transfer device of claim 2, wherein the major width extends from a leading edge to a trailing edge, the minor width being closer to the trailing edge than the leading edge.

6. The heat transfer device of claim 2, wherein the major width extends from a leading edge to a trailing edge, the leading edge or the trailing comprising an angled contour.

7. The heat transfer device of claim 2, wherein each pin has a height that extends from its first end to its second end, the height to the minor width comprising a ratio that is in the range of 3 to 10.

8. The heat transfer device of claim 2, wherein the base plate is configured on a peltier device.

9. The heat transfer device of claim 2, wherein the array of pins are integrally formed with the base plate using a casting process.

10. The heat transfer device of claim 2, wherein the cover plate is coupled to the first end of each of the array of pins using an adhesive.

11. The heat transfer device of claim 2, wherein the length of the minor width is less than 0.5 of the major width.

12. A method for manufacturing a heat transfer device comprising:

forming an array of elongated pins and a base plate, each pin having a first end and a second end that is coupled to the base plate, each pin having a cross-sectional shape with a major width and a minor width perpendicular to the major width, the length of one of the minor width or the major width being less than the other; and

coupling a cover plate to the first end of each of the array of pins, 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.

13. The method of claim 12, wherein the cross-sectional shape comprises an elliptical shape.

14. The method of claim 12, wherein the major width extends from a leading edge to a trailing edge, the minor width being closer to the leading edge than the trailing edge.

15. The method of claim 12, wherein the major width extends from a leading edge to a trailing edge, the minor width being closer to the trailing edge than the leading edge.

16. The method of claim 12, wherein the major width extends from a leading edge to a trailing edge, the leading edge or the trailing comprising an angled contour.

17. The method of claim 12, wherein each pin has a height that extends from its first end to its second end, the height to the minor width comprising a ratio that is in the range of 3 to 10.

18. The method of claim 12, further comprising coupling the base plate to a peltier device.

19. The method of claim 12, wherein the array of pins are integrally formed with the base plate using a casting process.

20. The method of claim 12, wherein the cover plate is coupled to the first end of each of the array of pins using an adhesive.

21. The method of claim 12, wherein the length of the minor width is less than 0.5 of the major width.