US20070251673A1

US20070251673A1 - Heat pipe with non-metallic type wick structure

Info

Publication number: US20070251673A1
Application number: US11/309,569
Authority: US
Inventors: Chuen-Shu Hou; Chao-Nien Tung; Tay-Jian Liu
Original assignee: Foxconn Technology Co Ltd
Current assignee: Foxconn Technology Co Ltd
Priority date: 2006-04-28
Filing date: 2006-08-24
Publication date: 2007-11-01
Also published as: CN100480612C; CN101063597A

Abstract

A heat pipe includes a casing (100) and a capillary wick (200) received in the casing. The casing has an evaporating section (400), a condensing section (600) and a central section (500) between the evaporating section and the condensing section. The capillary wick arranged at the central section is made of non-metallic material. The capillary wick at the central section of the casing provides a low cost and a lightweight to the heat pipe.

Description

FIELD OF THE INVENTION

The present invention relates generally to a heat transfer apparatus, and more particularly to a heat pipe having a capillary wick made of non-metallic material.

DESCRIPTION OF RELATED ART

As a heat transfer apparatus, heat pipes can transfer heat rapidly and therefore are widely used in various fields for heat dissipation purposes. For example, in the electronics field, heat pipes are commonly used to transfer heat from heat-generating electronic components, such as central processing units (CPUs), to heat dissipating devices, such as heat sinks. A heat pipe in accordance with the related art generally includes a sealed casing made of thermally conductive material with a working fluid contained in the casing. The working fluid is employed to carry heat from one end of the casing, typically called the “evaporating section”, to the other end of the casing, typically called the “condensing section”. Specifically, when the evaporating section of a heat pipe is thermally attached to a heat-generating electronic component, the working fluid receives heat from the electronic component and evaporates. Then, the generated vapor moves towards the condensing section of the heat pipe under the vapor pressure gradient between the two sections. In the condensing section, the vapor is condensed to liquid state by releasing its latent heat to, for example, a heat sink attached to the condensing section. Thus, the heat is removed from the electronic component.
In order to rapidly return the condensed liquid back from the condensing section to the evaporating section to start another cycling of evaporation and condensation, a capillary wick is generally provided on an inner surface of the casing in order to accelerate the return of the liquid. In particular, the liquid is drawn back to the evaporating section by a capillary force developed by the capillary wick. The capillary wick may be a plurality of fine grooves defined in its lengthwise direction of the casing, a fine-mesh wick, or a layer of sintered metal or ceramic powders.
However, these capillary wicks are generally made of metal material. These metallic-type capillary wicks generally cannot provide a low cost and a lightweight advantage to the heat pipes. Besides, the oxidation problem of the metal material may change surface tension of the metallic-type capillary wick, whereby quality of the heat pipes is difficult to control. Moreover, porosity of the metallic-type capillary wick is limited during manufacturing of the metallic-type capillary wick and, accordingly, the heat transfer efficiency of the heat pipe cannot be enhanced to a satisfied level.
In view of the above-mentioned disadvantage of the heat pipe, there is a need for a heat pipe having good heat transfer.

SUMMARY OF THE INVENTION

A heat pipe in accordance with a preferred embodiment of the present invention includes a metal casing and a capillary wick arranged on an inner surface of the casing. The casing has an evaporating section, a condensing section and a central section between the evaporating and condensing sections. The capillary wick arranged at the central section is made of non-metallic material. The capillary wick at the central section of the casing provides a low cost and a lightweight to 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 THE DRAWINGS

Many aspects of the present apparatus and method can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present apparatus and method. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

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 longitudinal cross-sectional view of a heat pipe in accordance with 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; and

FIG. 5 is a longitudinal cross-sectional view of a heat pipe in accordance with a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a heat pipe in accordance with a first embodiment of the present invention. The heat pipe comprises a metallic casing 100 and a capillary wick 200 arranged on an inner wall of the casing 100. A column-shaped vapor passage 300 is enclosed by an inner surface of the capillary wick 200 in a center of the casing 100. The casing 100 comprises an evaporating section 400 at one end, a condensing section 600 at an opposite end thereof, and a central section (i.e., adiabatic section) 500 located between the evaporating section 400 and the condensing section 600. The casing 100 is made of highly thermally conductive materials such as copper or copper alloys and filled with a working fluid (not shown) therein, which acts as a heat carrier for carrying thermal energy from the evaporating section 400 to the condensing section 600. Heat that needs to be dissipated is first transferred to the evaporating section 400 of the casing 100 to cause the working fluid therein to evaporate. Then, the heat is carried by the working fluid in the form of vapor to the condensing section 600 where the heat is released to ambient environment, thus condensing the vapor into liquid. The condensed liquid is then brought back via the capillary wick 200 to the evaporating section 400 where it is again available for evaporation.
The capillary wick 200 is a composite wick and comprises a first wick segment 240 arranged at the evaporating section 400, a second wick segment 250 located at the central section 500 which is made by organic material with macromolecule and a third wick segment 260 arranged at the condensing section 600. The first wick segment 240 and the third wick segment 260 each are a sintered-type wick or a mesh-type wick. The capillary pore size of the first wick segment 240 is smaller than that of the third wick segment 260 and the porosity of the first wick segment 240 is larger than that of the third wick segment 260 so that the first wick segment 240 can contain more working fluid than the third wick segment 260. The second wick segment 250 is made of non-metallic material such as plastics, resin or a combination of plastics and resin so as to reduce weight of the heat pipe and enable the heat pipe to have a low cost. The capillary pore size of the second wick segment 250 can be effectively controlled during manufacturing of the second wick segment 250. The porosity of the second wick segment 250 can be increased to increase the total porosity of the capillary wick 200. Since more working fluid can be received in the heat pipe in accordance with the present invention, heat exchange between the heat pipe and a heat-generating electronic component such as a CPU can be improved and the heat transfer efficiency of the heat pipe can be enhanced, accordingly.
In this embodiment, the capillary wick 200 has different characteristics at different sections of the heat pipe. The third wick segment 260 has a relatively larger capillary pore size and therefore provides a relatively lower flow resistance to the condensed liquid to flow therethrough, and meanwhile, the first wick segment 240 has a relatively smaller average capillary pore size and accordingly develops a relatively larger capillary force to the liquid. As a result, the third wick segment 260 reduces the flow resistance the condensed liquid encounters when flowing through the condensing and central sections 600, 500, and the first wick segment 240 has a large capillary force and therefore the liquid is then rapidly drawn back to the evaporating section 400 from the central section 500 as the liquid reaches to a position adjacent to the evaporating section 400. The condensed liquid is returned back from the condensing section 600 in an accelerated manner. After the condensed liquid is returned back to the evaporating section 400, another phase-change cycle of the working fluid will then begin. Thus, as a whole, the thermal transfer cycle of the working fluid is accelerated and therefore the total heat transfer capacity of the heat pipe is enhanced. Alternatively, other organic material, such as wood fiber or cotton is feasible to make the second wick segment 250.
FIG. 2 illustrates a heat pipe in accordance with a second embodiment of the present invention. Main differences between the first and second embodiments are that a whole of the capillary wick 210 in the second embodiment is made of non-metallic material. As a result, the heat pipe can be very light. Additionally, formation of the capillary wick 210 does not require a high temperature process such as sintering; thus, oxidation of the metal casing can be avoided. The other structure of the heat pipe of the second embodiment is similar to that of the first embodiment.
FIG. 3 illustrates a heat pipe in accordance with a third embodiment of the present invention. Main differences between the third and second embodiments are that in the third embodiment a tube 700 is attached with an inner surface of the capillary wick 210 at the central section 510 of the casing 110. The vapor passage 310 is separated from the capillary wick 210 by the tube 700. Because of an arrangement of the tube 700 attached on the capillary wick 210 at the central section 510 of the casing 110, the vapor flows only along the vapor passage 310 toward the condensing section 610 and the liquid flows only in the capillary wick 210 towards the evaporating section 410 when they flow in the central section 510. The vapor and the liquid in the central section 510 are separated by the tube 700, which can avoid the adverse contact between the vapor and liquid, wherein the vapor and the liquid flow in opposite directions. Thus, the condensed working fluid from the condensing section 610 can smoothly reach the evaporating section 410 and is prevented from being heated by the high temperature vapor at the central section 510. Abilities of heat-absorption and heat-dissipation of the working fluid of the heat pipe is further enhanced and heat-transfer efficiency of the heat pipe is accordingly further improved.
FIG. 4 illustrates a heat pipe in accordance with a fourth embodiment of the present invention. Main differences between the fourth and second embodiments are that in the fourth embodiment a thickness of the capillary wick 220 from the central section 520 to the condensing section 620 of the casing 120 is gradually decreased along a longitudinal direction of the casing 120 and the vapor passage 320 enclosed by the capillary wick 220 corresponding to the central section 520 and the condensing section 620, is gradually increased in the longitudinal direction of the casing 120. The thinnest part of the capillary wick 220 is at the condensing section 620 of the casing 120 so as to provide a low flow resistance for the condensed liquid. The working fluid in vapor at the condensing section 620 is quickly condensed and enters the capillary wick 220. The thickness of the capillary wick 220 at the evaporating section 420 is uniform. The capillary wick 220 at the evaporating section 420 provides a large capillary wick force and absorbs more of the working fluid at the evaporating section 420.
FIG. 5 illustrates a heat pipe in accordance with a fifth embodiment of the present invention. Main differences between the fifth and fourth embodiments are that in the fifth embodiment a thickness of the capillary wick 230 at the central and condensing sections 530, 630 of the casing 130 is uniform and thinner than that at the evaporating section 430 of the casing 130. The thickness of the capillary wick 230 at the evaporating section 430 is also uniform. The vapor passage 330 enclosed by the capillary wick 230 at the central section 530 and the condensing section 630 has a diameter which is larger than that at the evaporating section 430.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

1. A heat pipe comprising:

a metal casing containing a working fluid therein, the casing comprising an evaporating section at one end and a condensing section at an opposite end thereof, and a central section located between the evaporating section and the condensing section;

a capillary wick arranged on an inner wall of the casing and comprising a first wick segment corresponding to the evaporating section, a second wick segment corresponding to the central section and a third wick segment corresponding to the condensing section; and

a vapor passage formed inside of the casing and enclosed by the capillary wick; wherein the second wick segment arranged at the central section of the casing is made of non-metallic material.

2. The heat pipe of claim 1, wherein the non-metallic material is an organic material.

3. The heat pipe of claim 1, wherein the non-metallic material is one of plastics, resin, wood fiber and cotton.

4. The heat pipe of claim 1, wherein the first wick segment arranged at the evaporating section is a sintered-type wick and the third wick segment arranged at the condensing section is one of a sintered-type wick and a mesh-type wick.

5. The heat pipe of claim 4, wherein a capillary pore size of the first wick segment at the evaporating section is smaller than that of the third wick segment at the condensing section.

6. The heat pipe of claim 1, wherein the first and third wick segments arranged at the evaporating and condensing sections of the casing are also made of non-metallic material.

7. The heat pipe of claim 1, further comprising a tube attached with an inner surface of the second wick segment at the central section of the casing.

8. The heat pipe of claim 6, wherein thicknesses of the second and third wick segments from the central section to the condensing section of the casing are gradually decreased and a diameter of the vapor passage is gradually increased therealong.

9. The heat pipe of claim 6, wherein thicknesses of the second and third wick segments corresponding to the central and condensing sections of the casing are thinner than a thickness of the first wick segment corresponding to the evaporating section of the casing.

10. The heat pipe of claim 9, wherein the vapor passage corresponding to the central and condensing sections of the casing has a diameter which is larger than that corresponding to the evaporating section of the casing.

11. The heat pipe of claim 10, wherein the thicknesses of the second and third wick segments corresponding to the central and condensing sections of the casing are uniform.

12. A heat pipe comprising:

a metallic, tubular casing having an evaporating section for receiving heat, a condensing section for releasing the heat and an adiabatic section between the evaporating and condensing sections; and

a capillary wick arranged on an inner wall of the casing;

wherein at least a part of the capillary wick corresponding to one of the evaporating, condensing and adiabatic sections of the casing is made of non-metallic material.

13. The heat pipe of claim 12, wherein the part of the capillary wick is correspondent to the adiabatic section of the casing.

14. The heat pipe of claim 12, wherein a whole the capillary wick is made of non-metallic material.

15. The heat pipe of claim 14, wherein a tube is attached to an inner face of the capillary wick at a portion thereof corresponding to the adiabatic section.

16. The heat pipe of claim 14, wherein the capillary wick at the adiabatic and condensing sections has a gradually decreased thickness along a direction from the adiabatic section toward the condensing section.

17. The heat pipe of claim 14, wherein the capillary wick at the adiabatic and condensing sections has a thickness smaller than that at the evaporating section.

18. The heat pipe of claim 12, wherein the non-metallic material is chosen from one of plastics and resin.

19. The heat pipe of claim 12, wherein the non-metallic material is chosen from one of wood fiber and cotton.