US20060169439A1

US20060169439A1 - Heat pipe with wick structure of screen mesh

Info

Publication number: US20060169439A1
Application number: US11/164,094
Authority: US
Inventors: Chu-Wan Hong; Ching-Tai Cheng; Chang-Ting Lo; Jung-Yuan Wu
Original assignee: Individual
Current assignee: Foxconn Technology Co Ltd
Priority date: 2005-01-28
Filing date: 2005-11-10
Publication date: 2006-08-03
Also published as: TW200626862A; TWI271502B

Abstract

A heat pipe (10) includes a hollow pipe body (20) for receiving a working fluid therein and a screen mesh (30) disposed in the pipe body. The screen mesh includes at least two layers. One of the two layers is in the form of a planar layer (50) and the other is in the form of a wave layer (40). A plurality of flowing channels (48) is formed by the wave layer. The channels formed by the wave layer of the screen mesh are capable of reducing the flow resistance for the condensed fluid to flow back while pores in the screen mesh provide a relatively large capillary pressure for drawing the condensed fluid to flow back.

Description

FIELD OF THE INVENTION

The present invention relates generally to heat pipes, and more particularly to a heat pipe with a wick structure of screen mesh.

Description of Related Art

As electronic industry continues to advance, electronic components such as central processing units (CPUs), are made to provide faster operational speeds and greater functional capabilities. When a CPU operates at a high speed, its temperature frequently increases greatly. It is desirable to dissipate the heat generated by the CPU quickly.
To solve this problem of heat generated by the CPU, a cooling device is often used to be mounted on top of the CPU to dissipate heat generated thereby. It is well known that heat absorbed by fluid having a phase change is ten times more than that the fluid does not have a phase change; thus, the heat transfer efficiency by phase change of fluid is better than other mechanisms, such as heat conduction or heat convection. Accordingly, a heat pipe has been developed.
The heat pipe has a hollow pipe body receiving a working fluid therein and a wick structure disposed on an inner wall of the pipe body. Generally the heat pipe is divided into an evaporating section, an adiabatic section and a condensing section along a longitudinal direction thereof. During operation of the heat pipe, the working fluid absorbs the heat generated by the CPU or other electronic device and evaporates into vapor. The vapor moves from the evaporating section to the condensing section to dissipate the heat, whereby the vapor cools and condenses at the condensing section. The condensed working fluid returns to the evaporating section via a capillary force generated by the wick structure. From the evaporating section, the fluid is evaporated again to thereby repeat the heat transfer from the evaporating section to the condensing section.
In general, movement of the working fluid depends on the capillary pressure (force) of the wick structure. Usually the wick structure has following four configurations: sintered powders, grooves, fiber and screen mesh. Since the thickness and pore size of the screen mesh can be easily changed, the screen mesh is widely used in the heat pipe.
It is well recognized that the capillary pressure of a screen mesh increases due to a decrease in the pore size of the screen mesh. In order to obtain a relatively large capillary pressure, a mesh screen having a small-sized pore is usually adopted. However, it is not always the best way to choose a screen mesh having small-sized pores, because the flow resistance to the condensed working fluid also increases due to a decrease in the pore size of the screen mesh. The increased flow resistance reduces the speed of the condensed working fluid in returning back to the evaporating section and therefore limits the heat transfer performance of the heat pipe. As a result, a heat pipe with a screen mesh that has too large or too small a pore size often suffers dry-out problem at the evaporating section as the condensed working fluid cannot be timely sent back to the evaporating section of the heat pipe.
Therefore, there is a need for a heat pipe with a screen mesh which can provide simultaneously a relatively large capillary pressure and a relatively low flow resistance so as to effectively and timely bring the condensed working fluid back from the condensing section to the evaporating section of the heat pipe and thereby to avoid the undesirable dry-out problem at the evaporating section.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, a heat pipe comprises a hollow pipe body for receiving a working fluid therein and a screen mesh disposed in the pipe body. The screen mesh comprises at least two layers. One of the two layers is in the form of a planar layer and the other of the two layers is in the form of a wave layer. The wave layer forms a plurality of flowing channels for the working fluid to flow from a condensing section to an evaporating section of the heat pipe. The channels formed by the wave layer of the screen mesh is capable of reducing the flow resistance to the condensed fluid to flow back while pores in the screen mesh are capable of providing a relatively large capillary pressure for drawing the condensed fluid to flow back.
Other advantages and novel features of the present invention will be drawn from the following detailed description of a preferred embodiment of the present invention with attached drawings, in which:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a transverse cross-section view of a heat pipe in accordance with a preferred embodiment of the present invention;
FIG. 2 is an isometric, unfurled view of a planar layer of a mesh screen of the heat pipe of FIG. 1;
FIG. 3 is an isometric, unfurled view of a wave layer of the mesh screen of the heat pipe of FIG. 1;
FIG. 4 is a transverse cross-section view of the heat pipe in accordance with a second embodiment of the present invention;
FIG. 5 is an isometric, unfurled view of the wave layer of the mesh screen of the heat pipe of FIG. 4;
FIG. 6 is a transverse cross-section view of the heat pipe in accordance with a third embodiment of the present invention;
FIG. 7 is an isometric, unfurled view of the wave layer of the mesh screen of the heat pipe of FIG. 6;
FIG. 8 is a transverse cross-section view of the heat pipe in accordance with a fourth embodiment of the present invention;
FIG. 9 is a transverse cross-section view of the heat pipe in accordance with a fifth embodiment of the present invention, and
FIG. 10 is a transverse cross-section view of the heat pipe in accordance with a sixth embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIG. 1, a heat pipe 10 according to a preferred embodiment of the present invention comprises a hollow pipe body 20 and a screen mesh 30 disposed on an inner wall 22 of the pipe body 20. The heat pipe 10 comprises an evaporating section and a condensing section at respective opposite ends thereof, and an adiabatic section located between the evaporating section and the condensing section. The heat pipe 10 is vacuumed and two ends of the heat pipe 10 are sealed.
The pipe body 20 is made of high heat conductivity material such as copper or copper alloys. The screen mesh 30 has a plurality of pores and is saturated with a working fluid (not shown). The working fluid may be water, alcohol or other material having a low boiling point; thus, the working fluid can easily evaporate to vapor during operation when the evaporating section receives heat from a heat-generating electronic device, such as a CPU.
The screen mesh 30 comprises a wave layer 40 and a planar layer 50 arranged along circumferential and axial directions of the pipe body 20. The wave layer 40 is staked on the inner wall 22 of the pipe body 20 while the planar layer 50 is stacked on the wave layer 40 along a radial direction of the heat pipe 10 from a center to a periphery thereof. The wave layer 40 is directly attached to the inner wall 22 of the pipe body 20. The planar layer 50 is disposed on an inner side of the wave layer 40.
As best seen in FIG. 2, which shows the planar layer 50 in an unfurled state, outer surfaces of the planar layer 50 are flat.
FIG. 3 shows the wave layer 40 in an unfurled state. The wave layer 40 is square-wave shaped and comprises alternate upper and lower horizontal sections 42 and vertical sections 46 between the horizontal sections 42. When the wave layer 40 is rolled and inserted into the pipe body 20, the upper horizontal sections 42 abut against the inner wall 22 of the pipe body 20. Thus, a flow channel 48 is formed between two adjacent vertical sections 46 of the wave layer 40 of the screen mesh 30 and the inner wall 22. Each flow channel 48 extends along the longitudinal direction and entire length of the pipe body 20, and has a trapezoid-shaped cross section (as shown in FIG. 1).
During operation of the heat pipe 10, when the working fluid saturated in the screen mesh 30 at the evaporating section of the heat pipe 10 evaporates to vapor due to heat absorbed from the CPU, the vapor moves toward the condensing section of the heat pipe 10 due to the difference of vapor pressure to perform heat transport. The vapor then cools and condenses at the condensing section to perform heat dissipation. In this case, the condensed working fluid is absorbed into the screen mesh 30 at the condensing section, and then returns to the evaporating section through the screen mesh 30. The pores of the screen mesh 30 can provide a relatively large capillary pressure to the working fluid while the flow channels 48 can provide a relatively small flow resistance to the working fluid. The screen mesh 30 accordingly can increase the speed of the condensed working fluid in returning back to the evaporating section and therefore promotes the heat transfer performance of the heat pipe 10. As a result, a dry-out problem of the heat pipe 10 can be avoided.
Referring to FIGS. 4-5, they illustrate the heat pipe 410 in accordance with a second embodiment of the present invention. Similar to the first embodiment, the heat pipe 410 also comprises a pipe body 20 and a screen mesh 430 arranged in the pipe body 20. The screen mesh 430 comprises a wave layer 440 directly attached to the pipe body 20 and a planar layer 50 disposed on an inside of the wave layer 440. Flow channels 448 are formed by the wave layer 440 between it and the pipe body 20 and between it and the planar layer 50. The difference of the second embodiment over the first embodiment is that the wave layer 440 is consisted of a plurality of continuous serrations as viewed from the transverse cross-sectional view of the heat pipe 410. Thus, each flow channel 448 has a triangle-shaped cross section. Upper tips of the serrations of the wave layer 440 abut against the inner wall of the pipe body 20, while lower tips thereof abut against the planar layer 50.
FIGS. 6-7 illustrate the heat pipe 610 in accordance with a third embodiment of the present invention. Except for the screen mesh 630 and flow channels 648, 648′, other parts of the heat pipe 610 in accordance with the third embodiment are substantially the same as the heat pipe 410 of the previous embodiment. The screen mesh 630 also comprises a wave layer 640. The wave layer 640 comprises a plurality of horizontal sections 642 and a plurality of serrate sections 646 each interconnecting two neighboring horizontal sections 642. The serrate sections 646 are equally spaced from each other. When the screen mesh 630 is rolled and installed in the pipe body 20, the wave layer 640 defines triangle-shaped first flow channels 648 and trapezoid-shaped second flow channels 648′ alternately arranged along the circumferential direction of pipe body 20. Tips of the serrate sections 646 abut against the inner wall of the pipe body 20, and the horizontal sections 642 abut against planar layer 50.
It is to be understood that the screen mesh 30, 430, 630 is used to provide capillary pressure to force the working fluid returning back to the evaporating section. The screen mesh 30, 430, 630 may be in the form of a multi-layer structure more than two layers. Referring to FIG. 8, the screen mesh 830 has three layers stacked on each other along the radial direction of the pipe body 20. The three layers comprise a wave layer 40 and two planar layers 50 sandwiching the wave layer 40 therebetween. FIG. 9 shows a screen mesh 930 also having three layers stacked on each other along the radial direction of the pipe body 20. These three layers comprise a planar layer 50 and two wave layers 40 sandwiching the planar layer 50 therebetween.
FIG. 10 also illustrates the heat pipe having a screen mesh 130 comprising three layers. The three layers comprise a planar layer 150 and two wave layers 140, 140′ sandwiching the planar layer 150 therebetween. The difference of this embodiment over that of FIG. 9 is that the planar layer 150 has a pore size different from that of the wave layers 140, 140′. In this embodiment, the wave layers 140, 140′ have the same pore size. Although it is not shown in the drawings, it is apparent to those skilled in the art that the embodiment of FIG. 10 can be further modified that the two wave layers 140, 140′ have different pore sizes, whereby the heat pipe can be used in an environment with a broader range of parameters regarding heat-dissipation requirement.
It is understood that the invention may be embodied in other forms without departing from the spirit thereof. Thus, the present example and embodiment is to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.

Claims

1. A heat pipe comprising:

a hollow pipe body for receiving a working fluid therein;

a screen mesh furled and disposed in the pipe body, the screen mesh comprising at least two layers, one of the at least two layers is in the form of a planar layer and another of the at least two layers in the form of a wave layer; and

a plurality of flowing channels being formed by the wave layer for the working fluid received in the heat pipe to flow.

2. The heat pipe as claimed in claim 1, wherein the wave layer comprises a horizontal section and a vertical section alternately arranged along a circumferential direction of pipe body, and each flowing channel has a trapezoid-shaped cross section.

3. The heat pipe as claimed in claim 1, wherein the wave layer comprises a plurality of continuous serrations, and each flowing channel has a triangle-shaped cross section.

4. The heat pipe as claimed in claim 1, wherein the wave layer comprises a plurality of horizontal sections and a plurality of serrations each interconnecting two horizontal sections, and the flowing channels comprises a triangle-shaped first flow channel and a trapezoid-shaped second flow channel alternately arranged along a circumferential direction of pipe body.

5. The heat pipe as claimed in claim 1, wherein the wave layer of the at least two layers is directly attached to the pipe body.

6. The heat pipe as claimed in claim 1, wherein the screen mesh comprises three layers stacked on each other along a radial direction of the pipe body.

7. The heat pipe as claimed in claim 6, wherein the three layers comprise two planar layers and a wave layer sandwiched between the two planar layers.

8. The heat pipe as claimed in claim 6, wherein the three layers comprise two wave layers and a planar layer sandwiched between the two wave layers.

9. The heat pipe as claimed in claim 8, wherein the wave layers have a pore size different from that of the planar layer.

10. The heat pipe as claimed in claim 8, wherein each layer of the screen mesh has a pore size different from that of the other layers.

11. A heat pipe comprising:

a pipe body having an inner wall;

working fluid received in the pipe body;

a screen mesh rolled and installed in the pipe body and abutting against the inner wall thereof, the screen mesh having a plurality of pores therein for drawing the working fluid from a first section to a second section the pipe body, the screen mesh forming circumferentially distributed flowing channels in pipe body, the flowing channels being larger than the pores in the screen mesh, the flowing channels extending along a longitudinal direction of the pipe body.

12. The heat pipe of claim 11, wherein the screen mesh comprises a wave layer and a planar layer, the wave layer abutting against the inner wall of the pipe body.

13. The heat pipe of claim 12, wherein the wave layer is square-wave shaped, and comprises alternate upper and lower horizontal sections and vertical sections between the horizontal sections, the upper horizontal sections abutting against the inner wall of the pipe body, and the vertical sections together with the inner wall forming the channels.

14. The heat pipe of claim 12, where the wave layer comprises of a plurality of continuous serrations.

15. The heat pipe of claim 12, wherein the wave layer includes a plurality of horizontal sections and a plurality of serrations each interconnecting two horizontal sections, the serrations being equally spaced from each other and tips thereof abutting the inner wall of the pipe body, the wave layer forming a plurality of trapezoid-shaped flowing channels with the inner wall of the pipe body, and a plurality of triangle-shaped flowing channels with the planar layer.

16. The heat pipe of claim 11, wherein the screen mesh comprises two planar layers and a wave layers sandwiched between the two planar layers, one of the two planar layers abutting against the inner wall of the pipe body.

17. The heat pipe of claim 11, wherein the screen mesh comprises two wave layers and a planar layer sandwiched between the two wave layers, one of the two wave layers abutting against the inner wall of the pipe body.

18. The heat pipe of claim 17, wherein the two wave layers have a pore size which is different from that of the planar layer.

19. The heat pipe of claim 17, wherein the two wave layers have different pore sizes which are different from that of the planar layer.

20. A heat pipe comprising:

a pipe body having an inner wall;

a screen mesh disposed in the pipe body and abutting against the inner wall of the pipe body, the screen mesh comprising a plurality of layers stacked on each other along a radial direction of the pipe body, wherein two neighboring layers have different configurations with one of which having a wave-like configuration.