US20060162906A1

US20060162906A1 - Heat pipe with screen mesh wick structure

Info

Publication number: US20060162906A1
Application number: US11/164,093
Authority: US
Inventors: Chu-Wan Hong; Jung-Yuan Wu; Ching-Tai Cheng; Chang-Ting Lo
Original assignee: Individual
Current assignee: Foxconn Technology Co Ltd
Priority date: 2005-01-21
Filing date: 2005-11-10
Publication date: 2006-07-27

Abstract

A heat pipe (10) includes a pipe body (20) having an inner wall (22) and a screen mesh (30) disposed on the inner wall of the pipe body. The screen mesh is in the form of a multi-layer structure with at least one layer thereof having an average pore size different from that of the other layers. The layer with large-sized pores is capable of reducing the flow resistance to the condensed fluid to flow back, whereas the layer with small-size pores is capable of providing a relatively large capillary pressure for drawing the condensed fluid from the condensing section to the evaporating section.

Description

FIELD OF THE INVENTION

The present invention relates generally to a heat pipe as a heat transfer device, and more particularly to a heat pipe with a screen mesh wick structure.

DESCRIPTION OF RELATED ART

As electronic industry continues to advance, electronic components such as central processing units (CPUs), are made to provide faster operation 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. Thus 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. During operation of the heat pipe, the working fluid absorbs the heat generated by the CPU or other electronic device and evaporates. Then the vapor moves to the condensing section to release the heat thereof. The vapor cools and condenses at the condensing section. The condensed working fluid returns to the evaporating section and evaporates into vapor again, whereby the heat is continuously transferred from the evaporating section to the condensing section.
In general, movement of the working fluid depends on capillary pressure of the wick structure. Usually the wick structure has following four configurations: sintered power, grooved, fiber and screen mesh. For 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 pore size of the screen mesh. In order to obtain a relatively large capillary pressure for a screen mesh, a mesh screen having a small-sized pores 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 the decrease in 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 pore size often suffers dry-out problem at the evaporating section as the condensed fluid cannot be timely return 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 fluid back from its condensing section to its evaporating section and thereby to avoid the undesirable dry-out problem at the evaporating section. There is also a need for a heat pipe with a screen mesh which has a range of pore sizes so that the heat pipe can operate under different conditions without the undesirable dry-out problem at the evaporating section.

SUMMARY OF INVENTION

A heat pipe in accordance with a preferred embodiment of the present invention comprises a pipe body having an inner wall and a screen mesh disposed on the inner wall of the pipe body. The screen mesh is in the form of a multi-layer structure with at least one layer thereof has an average pore size different from that of the other layers. The layer with large-sized pores is capable of reducing the flow resistance to the condensed fluid to flow back, whereas the layer with small-sized pores is still capable of providing a relatively large capillary pressure for the condensed fluid in the heat pipe.
Other advantages and novel features of the present invention will become more apparent from the following detailed description of preferred embodiment when taken in conjunction with the accompanying drawings, in which:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of a heat pipe in accordance with a first embodiment of the present invention;
FIG. 2 is a view similar to FIG. 1, showing a heat pipe according to a second embodiment of the present invention;
FIG. 3 is a longitudinal cross-sectional view of a heat pipe in accordance with a third embodiment of the present invention;
FIG. 4 is a longitudinal cross-sectional view of a heat pipe in accordance with a fourth embodiment of the present invention;
FIG. 5 is a longitudinal cross-sectional view of a heat pipe in accordance with a fifth embodiment of the present invention;
FIG. 6 is a longitudinal cross-sectional view of a heat pipe in accordance with a sixth embodiment of the present invention;
FIG. 7 is a longitudinal cross-sectional view of a heat pipe in accordance with a seventh embodiment of the present invention;
FIG. 8 is a longitudinal cross-sectional view of a heat pipe in accordance with an eighth embodiment of the present invention;
FIG. 9 is a longitudinal cross-sectional view of a heat pipe in accordance with a ninth embodiment of the present invention; and
FIG. 10 is a longitudinal cross-sectional view of a heat pipe in accordance with a tenth embodiment of the present invention;

DETAILED DESCRIPTION

FIG. 1 illustrates a heat pipe 10 in accordance with a first embodiment of the present invention. The heat pipe 10 comprises a 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 70 and a condensing section 90 at respective opposite ends thereof, and an adiabatic section 80 located between the evaporating section 70 and the condensing section 90.
The pipe body 20 is typically made of high thermally conductive materials such as copper or copper alloys. The screen mesh 30 is saturated with a working fluid (not shown), which acts as a heat carrier for carry thermal energy from the evaporating section 70 toward the condensing section 90 when undergoing phase change from a fluid state to a vaporous state. The working fluid may be water, alcohol or other material having a low boiling point and the heat pipe 10 is vacuumed; thus, the working fluid can easily evaporate to vapor during operation.
Along a longitudinal direction of the pipe body 20 from the evaporating section 70 to the condensing section 90, the screen mesh 30 has a multi-layer structure, which includes in sequence a first layer 40, a second layer 50 and a third layer 60. In this embodiment, the first, second and third layer 40, 50, 60 correspond to the evaporating, adiabatic and condensing section 70, 80, 90 of the heat pipe 10, respectively. Each layer of the screen mesh 30 has an average pore size different from that of the other layers. The first layer 40 has the smallest average pore size, whereas the third layer 60 has the largest average pore size. That is, the three layers 40, 50, 60 are arranged side by side in such a manner that the average pore sizes thereof gradually increase along the longitudinal direction from the evaporating section 70 toward the condensing section 90. According to the general rule, the capillary pressure of the screen mesh 30 and its flow resistance to the condensed fluid increase due to a decrease in pore size of the screen mesh 30; the multi-layer construction of the screen mesh 30 is thus capable of providing a capillary pressure gradually increasing from the condensing section 90 toward the evaporating section 70, and a flow resistance gradually decreasing from the evaporating section 70 toward the condensing section 90.
FIG. 2 shows a heat pipe 210 according to a second embodiment of the present invention. The heat pipe 210 includes a pipe body 20 and a screen mesh 230 in the form of a three-layer structure arranged in the pipe body 20. The difference between the second embodiment and the first embodiment is that the three layers 240, 250, 260 of this second embodiment are arranged together side by side in such a manner that the average pore sizes thereof gradually decrease along the longitudinal direction from the evaporating section 270 toward the condensing section 290. The first layer 240 corresponding to the evaporating section 270 of the heat pipe 210 has the largest average pore size, whereas the third layer 260 corresponding to the condensing section 290 of the heat pipe 210 has the smallest average pore size. The second layer 250 corresponding to the adiabatic section 280 of the heat pipe 210 has an average pore size larger than that of the first layer 240 and smaller than that of the third layer 260.
FIG. 3 shows a third embodiment of the heat pipe 310. Similar to the first embodiment, the heat pipe 310 also comprises a pipe body 20 and a screen mesh 330 in the form of a three-layer structure disposed in the pipe body 20. The difference of the third embodiment over the first embodiment is that the first and third layer 340, 360 of the this embodiment which are corresponding to the evaporating and condensing section 370, 390 of the heat pipe 310 have the same average pore size. The second layer 350 corresponding to the adiabatic section 380 has an average pore size different from that of the two layers 340, 360.
FIG. 4 illustrates a heat pipe 410 according to a fourth embodiment of the present invention. The heat pipe 410 includes a pipe body 20 and a screen mesh 430 arranged in the pipe body 20. The screen mesh 430 is in the form of a multi-layer structure, which comprises an outer layer 440, an intermediate layer 450 and an inner layer 460. These layers 440, 450, 460 are stacked together along a radial direction of the pipe body 20 with the outer layer 440 abutting the inner wall 22 of the pipe body 20. Each layer of the screen mesh 430 has an average pore size different from that of the other layers, and these layers 440, 450, 460 are stacked together in such a manner that the average pore sizes thereof gradually increase along the radial direction from the inner wall 22 of the pipe body 20 towards a central axis X-X of the pipe body 20.
According to the above-mentioned general rule, the capillary pressure of a wick and its flow resistance to the condensed fluid increase due to a decrease in pore size of the wick; the inner layer 460 and the intermediate layer 450 have a relatively larger average pore size and therefore are capable of providing a relatively low resistance to the condensed working fluid to flow back. The outer layer 440, however, has a relatively smaller average pore size and therefore is capable of having a relatively high capillary pressure for drawing the condensed working fluid back to the evaporating section. Thus, the multi-layer construction of the screen mesh 430 is capable of providing between these layers, along the radial direction of the pipe body 20 a gradient of capillary pressure gradually increasing from the central axis X-X of the pipe body 20 toward the inner surface of the pipe body 20, and a gradient of flow resistance gradually decreasing from the inner surface of the pipe body 20 toward a central axis X-X of the pipe body 20. Furthermore, the outer layer 440 with small-sized pores is also capable of maintaining an increased contact surface area with the inner surface of the pipe body 20, as well as a large contact surface with the working fluid saturated in the screen mesh 430, to thereby facilitate heat transfer between the working fluid in the heat pipe 410 and a heat source outside the heat pipe 410 that needs to be cooled.
FIG. 5 illustrates a heat pipe 510 according to a fifth embodiment of the present invention. Similar to the fourth embodiment, the heat pipe 510 also has a multi-layer pore-based capillary screen mesh 530 arranged at an inner wall 22 of the heat pipe 510. The screen mesh 530 includes an outer layer 540, an intermediate layer 550 and an inner layer 560, which are stacked together along a radial direction of the heat pipe 510 with the outer layer 540 being connected to the inner wall 22 of the heat pipe 510. These layers 540, 550, 560 have different pore sizes to each other. Conversely from the previous embodiment, these layers 540, 550, 560 are arranged in such an order that the pore sizes thereof gradually decrease from the inner wall 22 of the heat pipe 510 towards a central axis Y-Y of the heat pipe 510. Therefore, the large-sized outer layer 540 has a relatively large pore size and accordingly develops a relatively low resistance to the condensed fluid to return back. However, this construction of the screen mesh 530 is suitable for a heat pipe with a relatively short length.
Also the layers can be arranged variably according to the heat flux of the heat source. As shown in FIG. 6, the screen mesh 630 of the heat pipe 610 comprises three layers 640, 650 660 arranged along a radial direction of the pipe body 20. The outer and inner layer 640, 660 arranged at respective opposite sides of the intermediate layer 650 have the same average pore size, the intermediate layer 650 located between the two layers 640, 660 have an average pore size larger than that of the other two layers 640, 660.
FIG. 7 illustrates a heat pipe 710 according to a seventh embodiment of the present invention. The heat pipe 710 comprises a screen mesh 730 having the outer, intermediate and inner layer 740, 750, 760 arranged along a radial direction of the pipe body 20. Each layer comprises three sections arranged along the longitudinal of the heat pipe 710. The outer layer 740 is divided into a first section 67, a second section 68 and a third section 69 corresponding to the evaporating, adiabatic and condensing section 770, 780, 790 of the heat pipe 710, respectively. Similar to the outer layer 740, the inner layer 760 comprises a first, second and third section 47, 48, 49, and the intermediate layer 750 comprises a first, second and third section 57, 58, 59. Each section of a specific layer has an average pore size different from that of the other sections of the specific layer. Thus the screen mesh 730 is in the form of multi-layer structure either along the longitudinal direction or along the radial direction of the pipe body 20. As a result, the screen mesh 730 can provide a variable capillary pressure and flow resistance along either the longitudinal or the radial direction of the heat pipe 710.
FIG. 8 illustrates an eighth embodiment of the heat pipe 810. Similar to the seventh embodiment, the screen mesh 830 of the heat pipe 810 comprises three layers 840, 850, 860 arranged along a radial direction of the heat pipe 810. The difference of this embodiment over the previous embodiment is that only the intermediate layer 850 comprising three sections along a longitudinal direction of the heat pipe 810. The outer and inner layer 840, 860 has the same average pore size throughout all the three sections of the heat pipe 810, i.e., the evaporating, adiabatic and condensing sections.
Each layer or section of the screen mesh as shown above has the same length or thickness along the longitudinal or the radial direction of the heat pipe 10. It is to be understood that the thickness or length of each layer or section can be changed and different from the others. As shown in FIG. 9, the inner layer 960 of the screen mesh 930 has the smallest thickness, whereas the intermediate layer 950 has the largest thickness along a radial direction of the heat pipe 910. The layer 940 is the outer layer of the screen mesh 930. Another embodiment of the heat pipe 110 as shown in FIG. 10 illustrates a screen mesh 130 comprises three layer arranged in the pipe body (not labeled) along a radial direction of the pipe body. Each layer divided into three sections along a longitudinal direction. The sections arranged corresponding to the evaporating section 170 and the condensing section 190 of the heat pipe 110 have a larger length along the longitudinal direction of the heat pipe 110 than the section corresponding to the adiabatic section 180 thereof.
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 pipe body having an inner wall; and

a screen mesh disposed on the inner wall of the pipe body;

wherein the screen mesh comprises several layers, at least one of the several layers has an average pore size different from that of the other layers.

2. The heat pipe of claim 1, wherein each layer of the several layers has an average pore size different from that of a neighboring layer thereof.

3. The heat pipe of claim 1, wherein the several layers are stacked together along a radial direction of the pipe body.

4. The heat pipe of claim 3, wherein the several layers are stacked in such a manner that the average pore sizes thereof increase along the radial direction of the pipe body.

5. The heat pipe of claim 3, wherein the several layers comprise three layers, two layers of the three layers disposed at respective opposite sides of the other layer have the same average pore size, the other layer located between the two layers have an average pore size different from that of the two layers.

6. The heat pipe of claim 3, wherein at least one of the several layers comprises several sections along a longitudinal direction of the pipe body.

7. The heat pipe of claim 6, wherein the heat pipe is divided into an evaporating section, a condensing section, and an adiabatic section along a longitudinal direction of the pipe body, the several sections of at least one of the several layers locate corresponding to the three sections of the heat pipe, respectively.

8. The heat pipe of claim 7, wherein each layer comprises three sections corresponding to the three sections of the heat pipe respectively.

9. The heat pipe of claim 6, wherein one of the sections of the at least one layer has an average pore size different from that of a neighboring section of the at least one layer.

10. The heat pipe of claim 6, wherein each section of the at least one layer has an average pore size different from the other sections of the at least one layer.

11. The heat pipe of claim 3, wherein along the radial direction of the heat pipe, at least one of the several layers has a thickness different from that of the other layers.

12. The heat pipe of claim 1, wherein the several layers are arranged side by side along a longitudinal direction of the pipe body.

13. The heat pipe of claim 12, wherein the several layers are arranged in such a manner that the average pore sizes thereof increase along the longitudinal direction of the pipe body.

14. The heat pipe of claim 13, wherein the heat pipe is divided into an evaporating section and a condensing section at respective opposite ends thereof, and a heat insulating section located between the evaporating section and the condensing section, the several layers comprises three layers at the three sections of the heat pipe, respectively.

15. The heat pipe of claim 14, wherein the three layers of the screen mesh are arranged in such a manner that the average pore sizes thereof decrease from the evaporating section to the condensing section of the heat pipe.

16. The heat pipe of claim 12, wherein along the longitudinal direction of the heat pipe, at least one of the layers has a thickness different from that of the other layers.

17. A heat pipe comprising:

a pipe body having an inner wall and defining an evaporating section and a condensing section;

working fluid received in the pipe body;

a mesh screen attached on the inner wall of the pipe body for drawing the working fluid in a condensed state from the condensing section to the evaporating section, the mesh screen including different layers arranged along one of longitudinal direction and radial direction of the pipe body, pores in the different layers having different pore sizes.

18. The heat pipe of claim 17, wherein the pore sizes decrease along a direction from a center of the pipe body toward the inner wall of the pipe body.

19. The heat pipe of claim 17, wherein the pore sizes increase along a direction from the evaporating section toward the condensing section.

20. The heat pipe of claim 17, wherein the different layers are arranged side by side when the different layers are arranged along the longitudinal direction of the pipe body.