US20070235165A1

US20070235165A1 - Heat pipe

Info

Publication number: US20070235165A1
Application number: US11/309,290
Authority: US
Inventors: Tay-Jian Liu; Chao-Nien Tung; Chuen-Shu Hou; Chih-Hsien Sun
Original assignee: Foxconn Technology Co Ltd
Current assignee: Foxconn Technology Co Ltd
Priority date: 2006-04-07
Filing date: 2006-07-21
Publication date: 2007-10-11
Also published as: CN100491889C; CN101050928A

Abstract

A heat pipe (10) includes a hollow metal casing (110). The casing has an evaporating section (120) and a condensing section (160) at opposing ends thereof, and an adiabatic section (140) located between the evaporating section and the condensing section. A capillary wick structure (130) is arranged at an inner surface of the hollow metal casing. A vapor channel (150) is defined along an axial direction of the heat pipe and surrounded by the capillary wick structure. The vapor channel includes a nozzle (154) defined at a boundary between the evaporating section and the adiabatic section, wherein the nozzle has a cross section which gradually reduces towards the condensing section.

Description

FIELD OF THE INVENTION

The present invention relates generally to a heat pipe as heat transfer/dissipating device, and more particularly to a heat pipe having a structure configured to increase the maximum heat transfer capacity and reduce temperature differential across the heat pipe.

DESCRIPTION OF RELATED ART

It is well known that a heat pipe is generally a vacuum-sealed pipe. A porous wick structure is provided on an inner face of the pipe, and the pipe is filled with at least a phase changeable working media employed to carry heat. Generally, according to positions from which heat is input or output, the heat pipe has three sections, an evaporating section, a condensing section and an adiabatic section between the evaporating section and the condensing section.
In use, the heat pipe transfers heat from one place to another place mainly by virtue of phase change of the working media taking place therein. Generally, the working media is a liquid such as alcohol, water and the like. When the working media in the evaporating section of the heat pipe is heated up, it evaporates, and a pressure difference is thus produced between the evaporating section and the condensing section in the heat pipe. As a result vapor with high enthalpy flows to the condensing section and condenses there. Then the condensed liquid reflows to the evaporating section along the wick structure. This evaporating/condensing cycle continues in the heat pipe; consequently, heat can be continuously transferred from the evaporating section to the condensing section. Due to the continual phase change of the working media, the evaporating section is kept at or near the same temperature as the condensing section of the heat pipe.
However, during the phase change of the working media, the resultant vapor and the condensed liquid flow along two opposite directions, which reduces the speed of the condensed liquid in returning back to the evaporating section and therefore limits the maximum heat transfer capacity (Qmax) of the heat pipe. As a result, a heat pipe often suffers dry-out problem at the evaporating section as the condensed liquid cannot be timely sent back to the evaporating section of the heat pipe. Furthermore, the heat pipe has a high ratio of length to radius so that the heat is dissipated during transmission of the vapor and a part of the vapor in advance changes into condensed liquid mixed in the vapor to block transfer of the vapor. Thus, thermal resistance of the heat pipe is accordingly increased and the maximum heat transfer capacity of the heat pipe is reduced. In addition, the heat pipe has a uniform thickness of the wick structure and a uniform vapor channel for passage of the vapor so that a speed of the vapor transferring from the evaporating section to the condensing section is reduced, whereby the temperature difference (ΔT) between the evaporating section and the condensing section is increased.
A conventional method for increasing the maximum heat transfer capacity of the heat pipe is increasing the total thickness of the wick structure of the heat pipe to increase the quantity of the working media contained in the wick structure. However, by this method, the response time of the heat pipe for the liquid to become the vapor at the evaporating section is increased and the temperature difference between the evaporating section and the condensing section is increased accordingly.
Another conventional method for reducing the temperature difference between the evaporating section and the condensing section is reducing the total thickness of the wick structure of the heat pipe to reduce the quantity of the working media contained in the wick structure. However, by this method, the maximum heat transfer capacity of the heat pipe is reduced accordingly.
Therefore, it is desirable to provide a heat pipe which can simultaneously increase the maximum heat transfer capacity and reduce the temperature difference of the heat pipe.

SUMMARY OF THE INVENTION

The present invention relates to a heat pipe. The heat pipe includes a hollow metal casing. The casing has an evaporating section and a condensing section at opposing ends thereof, and an adiabatic section located between the evaporating section and the condensing section. A capillary wick structure is arranged at an inner surface of the hollow metal casing. A vapor channel is defined along an axial direction of the heat pipe and surrounded by the capillary wick structure. The vapor channel includes a nozzle defined at a boundary between the evaporating section and the adiabatic section, wherein the nozzle has a cross section which gradually reduces towards the condensing section. The nozzle is capable of reducing heat resistance of the heat pipe and enhancing the maximum heat transfer capacity of 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 device 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 device. 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; and

FIG. 4 is a longitudinal cross-sectional view of a heat pipe in accordance with a fourth embodiment of the present invention;

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a heat pipe 10 in accordance with one embodiment of the present invention. The heat pipe 10 includes a metal casing 110 made of highly thermally conductive materials such as copper or copper alloys, a working fluid (not shown) contained in the casing 110 and a capillary wick structure 130 arranged in an inner surface of the casing 110. The capillary wick structure 130 may be a plurality of fine grooves defined in its lengthwise direction of the casing 110, a fine-mesh wick, or a layer of sintered metal or ceramic powders, or combinations thereof. In this embodiment, the casing 110 includes an evaporating section 120 at one end, a condensing section 160 at the other end and an adiabatic section 140 arranged between the evaporating section 120 and the condensing section 160.
A vapor channel 150 is defined along an axial direction of the heat pipe 10 and is located at a center of the casing 110. The vapor channel 150 is surrounded by an inner surface of the capillary wick structure 130 so as to guide vapor to flow therein. The vapor channel 150 has a cross section which varies across its length. The vapor channel 150 comprises a nozzle 154, a diffusing channel 156 and a pair of straight channels 152, 158. The nozzle 154 is defined at a boundary between the evaporating section 120 and the adiabatic section 140. The cross section of the nozzle 154 gradually reduces towards the adiabatic section 140 to increase vapor velocity. Thickness of the capillary wick structure 130 corresponding to the nozzle 154 gradually increases towards the adiabatic section 140. The diffusing channel 156 extends from the minimum end of the nozzle 154 to a boundary between the adiabatic section 140 and the condensing section 160. The cross section of the diffusing channel 156 gradually increases towards the condensing section 160. The thickness of the capillary wick structure 130 corresponding to the diffusing channel 156 gradually reduces accordingly towards the condensing section 160. The straight channel 152 is defined at the evaporating section 120 and connects with the nozzle 154. The straight channel 158 extends from the maximum end of the diffusing channel 156 to the condensing section 160. Each straight channel 152, 158 has a uniform cross section. The thickness of the capillary wick structure 130 corresponding to the straight channel 152, 158 is uniform and of the same thickness as the straight channels 152, 158.
As the evaporating section 120 of the heat pipe 10 absorbs heat from a heat source, the working fluid contained in the evaporating section 120 absorbs the heat and evaporates, and then carries the heat to the condensing section 160 in the form of vapor. When the vapor flows through the nozzle 154, the vapor velocity is gradually increased due to the configuration of the nozzle 154. When the vapor flows through the diffusing channel 156, flow resistance of the vapor is gradually reduced due to the configuration of the diffusing channel 156, whereby the vapor can be quickly arrive at the condensing section 160 where the vapor is condensed into liquid after releasing the heat into ambient environment. Due to the difference of capillary pressure developed by the capillary wick structure 130, the condensed liquid is then sent back by the capillary wick structure 130 towards the evaporating section 120. The thickness of the capillary wick structure 130 at the adiabatic section 140 gradually increases along the flowing direction of the condensed liquid so that the flow resistance of the condensed liquid is gradually reduced. As a result, the condensed liquid can be quickly and timely sent back to the evaporating section 120. Thus, the heat resistance of the heat pipe 10 is reduced and the maximum heat transfer capacity of the heat pipe 10 is effectively enhanced.
FIG. 2 illustrates a heat pipe 10 a according to a second embodiment of the present invention. In this embodiment, a tube 155 is attached to the inner surface of the capillary wick structure 130 to form a vapor-liquid isolation structure for providing passage of the vapor. The tube 155 is made of a metal slice or a metal thin-walled tube, for isolating the liquid of the capillary wick structure 130 from the vapor of the vapor channel 150. The tube 155 extends from the nozzle 154 to the condensing section 160 a. The tube 155 is so configured as to reduce the temperature difference between the evaporating section 120 a and the condensing section 160 a and increase the velocity of the vapor and the condensed liquid.
FIG. 3 illustrates a heat pipe 10 b according to a third embodiment of the present invention. In this embodiment, the heat pipe 10 b has a similar structure to the heat pipe 10 a of the second embodiment. However, the thickness of the capillary wick structure 130 of the condensing section 160 b is larger than that of the evaporating section 120 b such that the cross section of the vapor channel 150 of the evaporating section 120 b is larger than that of the condensing section 160 b.
FIG. 4 illustrates a heat pipe 10 c according to a fourth embodiment of the present invention. In this embodiment, the heat pipe 10 c has a similar structure to the heat pipe 10 a of the second embodiment. However, the thickness of the capillary wick structure 130 of the evaporating section 120 c is larger than that of the condensing section 160 c such that the cross section of the vapor channel 150 of the condensing section 160 c is larger than that of the evaporating section 120 c.
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 hollow metal casing having 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 evaporating section being for receiving heat and the condensing section being for releasing the heat;

a capillary wick structure arranged at an inner surface of the hollow metal casing; and

a vapor channel defined along an axial direction of the heat pipe and surrounded by the capillary wick structure, the vapor channel including a nozzle defined at a boundary between the evaporating section and the adiabatic section, wherein the nozzle has a cross section which gradually reduces towards the condensing section.

2. The heat pipe of claim 1, wherein the vapor channel further comprises a diffusing channel extending from a minimum end of the nozzle to a boundary between the adiabatic section and the condensing section, the diffusing channel has a cross section which gradually increases towards the condensing section.

3. The heat pipe of claim 2, wherein the vapor channel further comprises a pair of straight channels, one of the straight channels is located at the evaporating section and the other of the straight channels is located at the condensing section.

4. The heat pipe of claim 3, wherein thickness of the capillary wick structure corresponding to the pair of straight channels is uniform and of the same thickness as the straight channels.

5. The heat pipe of claim 2, wherein thickness of the capillary wick structure of the evaporating section is larger than that of the condensing section.

6. The heat pipe of claim 2, wherein thickness of the capillary wick structure of the condensing section is larger than that of the evaporating section.

7. The heat pipe of claim 1, wherein a tube is attached to the inner surface of the capillary wick structure to form a vapor-liquid isolation structure.

8. The heat pipe of claim 1, wherein the tube extends from the nozzle to the condensing section.

9. A heat pipe comprising:

a vapor channel defined along an axial direction of the heat pipe and surrounded by the capillary wick structure, the vapor channel including a nozzle having a cross section and a diffusing channel having a cross section, wherein the cross section of the nozzle gradually reduces towards the condensing section and the cross section of the diffusing channel gradually increases towards the condensing section, the nozzle being located between the evaporating section and the diffusing channel.

10. The heat pipe of claim 9 wherein the diffusing channel is defined at a boundary between the evaporating section and the adiabatic section.

11. The heat pipe of claim 10, wherein diffusing channel extends from a minimum end of the nozzle to a boundary between the adiabatic section and the condensing section.

12. The heat pipe of claim 9, wherein the vapor channel further comprises a pair of straight channels, one of the straight channels is located at the evaporating section and the other of the straight channels is located at the condensing section.

13. The heat pipe of claim 12, wherein thickness of the capillary wick structure corresponding to the pair of straight channels is uniform and of the same thickness as the straight channels.

14. The heat pipe of claim 12, wherein thickness of the capillary wick structure of the evaporating section is larger than that of the condensing section.

15. The heat pipe of claim 12, wherein thickness of the capillary wick structure of the condensing section is larger than that of the evaporating section.

16. The heat pipe of claim 9, wherein a tube is attached to the inner surface of the capillary wick structure to form a vapor-liquid isolation structure.

17. The heat pipe of claim 16, wherein the tube extends from the nozzle to the condensing section.