METAL WOODPILE CAPILLARY WICK

Abstract

A heat pipe that employs a metal woodpile capillary wick. The heat pipe includes an outer enclosure defining a chamber therein that contains a working fluid, an evaporator section for converting the fluid to vapor in response to being heated from a heat source, and a condenser section for converting the vapor back into the fluid in response to cooling from a heat sink. The wick is positioned within the chamber in contact with the enclosure and extends between the evaporator section and the condenser section. The wick includes a plurality of layers each having spaced apart parallel thermally conductive bars defining channels therebetween, where the bars in adjacent layers are oriented in different directions and where the condensed fluid flows through the channels in the wick from the condenser section to the evaporator section.

Claims

1. A heat pipe comprising: an outer enclosure defining a chamber therein and containing a working fluid; an evaporator section for evaporating the fluid to vapor in response to being heated from a heat source; a condenser section for condensing the vapor back into the fluid in response to cooling from a heat sink; and a capillary wick positioned within the chamber in contact with the enclosure and extending between the evaporator section and the condenser section, wherein the capillary wick has a size to as to create a vapor cavity in the chamber outside of the wick, said wick including a plurality of layers each having spaced apart parallel and straight thermally conductive bars defining channels therebetween where the bars in adjacent layers are oriented in different directions and where the vapor flows through the vapor cavity from the evaporator section to the condenser section and the condensed fluid flows through the wick from the condenser section to the evaporator section.

2. The heat pipe according to claim 1 wherein the bars in adjacent layers are orthogonal to each other.

3. The heat pipe according to claim 1 wherein the bars in every other layer are oriented in the same direction.

4. The heat pipe according to claim 3 wherein the bars that are oriented in the same direction in different layers are aligned with each other.

5. The heat pipe according to claim 3 wherein the bars that are oriented in the same direction in different layers are offset from each other.

6. The heat pipe according to claim 1 wherein some of the bars have a different cross-sectional size than other bars.

7. The heat pipe according to claim 1 wherein some of the bars have a different cross-sectional shape than other bars.

8. The heat pipe according to claim 1 wherein the bars are round in cross-section.

9. The heat pipe according to claim 1 wherein the bars are rectangular in cross-section.

10. The heat pipe according to claim 1 wherein the bars in some layers are round in cross-section and the bars in other layers are rectangular in cross-section.

11. The heat pipe according to claim 1 wherein the wick is designed to provide greater thermal capacity closer to the enclosure and greater evaporation farther from the enclosure.

12. The heat pipe according to claim 1 wherein the bars are copper bars.

13. A heat pipe comprising: an outer enclosure defining a chamber therein and containing a working fluid; an evaporator section for evaporating the fluid to vapor in response to being heated from a heat source; a condenser section for condensing the vapor back into the fluid in response to cooling from a heat sink; and a capillary wick positioned within the chamber in contact with the enclosure and extending between the evaporator section and the condenser section, wherein the capillary wick has a size to as to create a vapor cavity in the chamber outside of the wick, said wick including a plurality of layers each having spaced apart parallel and straight copper rectangular bars defining channels therebetween where the bars in adjacent layers are orthogonal to each other and where the vapor flows through the vapor cavity from the evaporator section to the condenser section and the condensed fluid flows through the wick from the condenser section to the evaporator section.

14. The heat pipe according to claim 13 wherein the bars in every other layer are oriented in the same direction.

15. The heat pipe according to claim 14 wherein the bars that are oriented in the same direction in different layers are aligned with each other.

16. The heat pipe according to claim 14 wherein the bars that are oriented in the same direction in different layers are offset from each other.

17. The heat pipe according to claim 13 wherein some of the bars have a different cross-sectional size than other bars.

18. (canceled)

19. (canceled)

20. (canceled)

21. A heat pipe comprising: an outer enclosure defining a chamber therein and containing a working fluid; an evaporator section for evaporating the fluid to vapor in response to being heated from a heat source; a condenser section for condensing the vapor back into the fluid in response to cooling from a heat sink; and a capillary wick positioned within the chamber in contact with the enclosure and extending between the evaporator section and the condenser section, said wick including a plurality of layers each having spaced apart parallel thermally conductive bars defining channels therebetween where the bars in adjacent layers are oriented in different directions and where the condensed fluid flows through the wick from the condenser section to the evaporator section, wherein the layers in the wick are configured so that layers that are closer to the enclosure have a greater heat conduction than layers that are farther from the enclosure and layers that are farther from the enclosure have a greater evaporation capacity than layers that are closer to the enclosure.

22. The heat pipe according to claim 21 wherein the bars in adjacent layers are orthogonal to each other.

23. The heat pipe according to claim 21 wherein the bars in every other layer are oriented in the same direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is an isometric view of a metal woodpile capillary wick;

[0011] FIG. 2 is a top view of the woodpile capillary wick shown in FIG. 1;

[0012] FIG. 3 is a cross-sectional type side view of a heat pipe incorporating the woodpile capillary wick;

[0013] FIG. 4 is an illustration of a metal woodpile capillary wick employing offset rectangular beams;

[0014] FIG. 5 is an illustration of a metal woodpile capillary wick employing rectangular beams of different sizes; and

[0015] FIG. 6 is an illustration of a metal woodpile capillary wick employing round and rectangular beams.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] The following discussion of the embodiments of the disclosure directed to a heat pipe employing a metal woodpile capillary wick is merely exemplary in nature, and is in no way intended to limit the disclosure or its applications or uses.

[0017] As will be discussed in detail below, this disclosure proposes a heat pipe employing a metal woodpile capillary wick. As used herein, a woodpile is a three-dimensional grid of aligned and orthogonal thermal conductor bars that are uniform in cross-section either rectangular or circular. By aligning the bars, the woodpile wick straightens both the heat conduction and fluid delivery pathways, which reduces both resistances. The straight fluid flow channels minimizes the hydraulic resistance and allows a direct line-of-sight for mass transport to occur. The cross-section shape, pitch and volume fraction of the bars can be independently tuned to provide maximum control of the precise material structure for optimizing the transport properties of the heat pipe. Fabrication techniques exist that can form the bars to have very small cross-sections, such as on the order of 100 nanometers.

[0018] FIG. 1 is an isometric view and FIG. 2 is a top view of a metal woodpile capillary wick 10 of the type proposed above. The wick 10 includes a number of layers 12 of spaced apart parallel round conductor bars 14 defining flow channels 16 therebetween. The bars 14 are oriented so that they are orthogonal to each other from one layer 12 to an adjacent layer 12. The bars 14 can be made out of any suitable thermally conductive material, such as copper. The cross-sectional size, the cross-sectional shape, the pitch (spacing) and the orientation of the bars 14 can be selected for a particular application. Heat flows along the bars 14 in a straight direction and fluid flows through the channels 16 in a straight direction.

[0019] FIG. 3 is a cross-sectional type side view of a heat pipe 20 including an outer conductive enclosure 22 defining an internal chamber 24 therein and having end walls 26 and 28, where the enclosure 22 can have any suitable cross-sectional shape and be made of any suitable material for a particular application. The heat pipe 20 also includes an evaporator section 30 provided adjacent to the wall 26, where a heat source 32, such as an electronic device, is provided in thermal contact with the enclosure 22 in the section 30, and an condenser section 34 provided adjacent to the wall 28, where a heat sink 36, such as a metal block, is provided in thermal contact with the enclosure 22 in the section 34. A metal woodpile capillary wick 40 including conductor bars 42 configured in the manner discussed above is positioned within the chamber 24 in thermal contact with the enclosure 22. Heat from the heat source 32 is conducted into the wick 40 and the heat evaporates a working fluid, such as water, therein to vapor that is transported through a vapor cavity 44 in the chamber 24 outside of the wick 40 towards the condenser section 34. Heat is drawn out of the vapor in the condenser section 34 and is condensed back into the fluid and is wicked along the bars 42 in the wick 40 by the capillary action towards the evaporator section 30 to be reheated into vapor. Thus, the heat pipe 20 controls the temperature of the heat source 32. It is noted that although the wick 40 is only shown on one side of the enclosure 22, it can be provide all of the way around and in contact with the enclosure 22.

[0020] As mentioned above, the cross-sectional shape, pitch, volume fraction, etc. of the conductor bars 42 can be independently tuned for a particular heat pipe and its application. Each layer in the wick 40 can be configured differently than other layers to provide different characteristics so that it is not uniform, such as providing increased heat conduction near the enclosure 22 and increased evaporation near the vapor cavity 44.

[0021] FIG. 4 is a side illustration of a metal woodpile capillary wick 50 having rectangular conductor bars 52 that have varying sizes and are offset from each other in layers 54 having the bars 52 going in the same direction. FIG. 5 is a side illustration of a metal woodpile capillary wick 60 employing round conductor bars 62 going in one direction and rectangular conductor bars 64 going in an orthogonal direction in adjacent layers 66. FIG. 6 is a side illustration of a metal woodpile capillary wick 70 employing rectangular conductor bars 72 of different sizes in adjacent layers 74. In all of these embodiments, the conductor bars in adjacent layers are orthogonal to each other. However, in other designs the bars in adjacent layers can be angled other than 90° relative to each other.

[0022] Any suitable fabrication technique can be used to fabricate a heat pipe including a metal woodpile capillary wick as described herein. For example, soft lithography or layer-by-layer templating and electroplating can be employed where the wick is built up layer-by-layer on a substrate and then the substrate is rolled to form the heat pipe.

[0023] The foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the disclosure as defined in the following claims.