US20070240856A1

US20070240856A1 - Heat pipe

Info

Publication number: US20070240856A1
Application number: US11/309,309
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: 2006-04-14
Filing date: 2006-07-25
Publication date: 2007-10-18
Also published as: CN100529640C; CN101055156A

Abstract

A heat pipe includes a hollow metal casing (10). The casing has an evaporating section (120) and a condensing section (160) at opposite ends thereof, and an adiabatic section (140) located between the evaporating section and the condensing section. A capillary wick (12) is arranged at an inner surface of the hollow metal casing. A working fluid is received in the metal casing. A sealed heat reservoir (20) is mounted on the condensing section of the heat pipe to increase heat dissipation area of the heat pipe. The heat reservoir has a capillary wick structure (22) and a working fluid therein.

Description

1. 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 which has a heat reservoir for quickly dissipating heat received from an electronic component such as a central processing unit (CPU) to increase the maximum heat transfer capacity and reduce the temperature differential across the length of the heat pipe.

2. DESCRIPTION OF RELATED ART

It is well known that a heat pipe is essentially a vacuum-sealed pipe with a porous wick structure provided on an inner face of the pipe, and where the pipe is filled with at least a phase changeable working media employed to carry heat. Generally, according to the direction from which heat is input or output, the heat pipe has three sections, namely, 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 through 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 flows along two opposing 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. At the same time, the condensing section has a relatively small heat dissipating area. As a result, the heat pipe often suffers dry-out problems at the evaporating section as the condensed liquid cannot be quickly 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 may be dissipated during transmission of the vapor and a part of the vapor may change 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 wick structure of the heat pipe has uniform thickness and a vapor channel of uniform dimensions for passage of the vapor so that speed of the vapor transferring from the evaporating section to the condensing section is reduced, and the temperature difference (ΔT) between the evaporating section and the condensing section is increased as a result.
A conventional method for increasing the maximum heat transfer capacity of the heat pipe consists of 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 slowed and the temperature difference between the evaporating section and the condensing section is increased accordingly.
A 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 differential across the length of the heat pipe.

SUMMARY OF THE INVENTION

The present invention relates to a heat pipe. A heat pipe includes a hollow metal casing. The casing has 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. A capillary wick is arranged at an inner surface of the hollow metal casing. A sealed heat reservoir is mounted on the condensing section of the heat pipe to increase heat dissipation area of the heat pipe. The heat pipe is configured so as to simultaneously reduce heat resistance and enhance 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 longitudinally cross-sectional view of a heat pipe in accordance with a first embodiment of the present invention;

FIG. 2 is a transversely cross-sectional view taken along lines 11-11 of FIG. 1;

FIG. 3 is a transversely cross-sectional view of a heat pipe in accordance with a second embodiment of the present invention;

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

FIG. 5 is a transversely cross-sectional view of a heat pipe in accordance with a fourth embodiment of the present invention;

FIG. 6 is a transversely cross-sectional view of a heat pipe in accordance with a fifth embodiment of the present invention; and

FIG. 7 is a transversely cross-sectional view of a heat pipe in accordance with a fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show a heat pipe in accordance with one embodiment of the present invention. The heat pipe has a cylindrical configuration and includes a metal casing 10 made of highly thermally conductive materials such as copper or copper alloys, a first working fluid (not shown) contained in the casing 10 and a first capillary wick 12 arranged in an inner surface of the casing 10. The casing 10 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 sealed heat reservoir 20 is mounted on the condensing section 160. A vapor channel 14 is defined along an axial direction of the heat pipe and is located at a center of the casing 10. The vapor channel 14 is surrounded by an inner surface of the first capillary wick 12 so as to guide vapor to flow therein.
The heat reservoir 20 has a hollow cylindrical configuration and is made of highly thermally conductive materials such as aluminum or copper or copper alloys. The heat reservoir 20 has a bigger radius than that of the heat pipe. The condensing section 160 of the heat pipe extends through the heat reservoir 20, thereby positioning the heat reservoir 20 thereon. The heat reservoir 20 comprises an outer wall 211 and a pair of lateral sides 221 connecting with two opposite ends of the outer wall 211 to form a sealed chamber. A second capillary wick 22 is formed on an inner surface of the heat reservoir 20 and an outer surface of the condensing section 160. A second working fluid (not shown) is contained in the heat reservoir 20. A vapor channel 24 is defined along an axial direction of the heat reservoir 20 and is located in a center of the heat reservoir 20 to guide vapor to flow therein. The heat reservoir 20 is vacuum-exhausted to make the second working fluid easy to evaporate.
As the evaporating section 120 of the heat pipe absorbs heat from a heat source, the first 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. Then, the heat is carried by the first working fluid in the form of vapor to the condensing section 160 where the heat is transferred to the heat reservoir 20. The second working fluid contained in the heat reservoir 20 absorbs the heat and evaporates. The heat reservoir 20 has a so large heat dissipating area that the heat at the condensing section 160 can be quickly absorbed and dissipated by the heat reservoir 20, thereby reducing the heat resistance of the heat pipe and enhancing the maximum heat transfer capacity of the heat pipe.
Alternatively, a cylinder inner wall (not shown) is formed in the heat reservoir 20. The inner wall interconnects the two opposite lateral sides 221. The condensing section 160 of the heat pipe is inserted into the heat reservoir 20 and engages with the inner wall of the heat reservoir 20, whereby the heat reservoir 20 is positioned on condensing section 160 of the heat pipe. Alternatively, the heat reservoir 20 is positioned on the condensing section 160 of the heat pipe by metallurgical or adhesive means.
FIG. 3 illustrates a heat pipe according to a second embodiment of the present invention. The heat pipe of the second embodiment is similar to that of the previous embodiment. However, a heat reservoir 20 a replaces the heat reservoir 20 of the first embodiment. In the second embodiment, the heat reservoir 20 a has a square cross section.
FIG. 4 illustrates a heat pipe according to a third embodiment of the present invention. In this embodiment, the heat pipe has a similar structure to the heat pipe of the previous first embodiment. However, a casing 10 b of the heat pipe replaces the casing 10 of the previous first embodiment. In the third embodiment, the casing 10 b has a square cross section.
FIG. 5 illustrates a heat pipe according to a fourth embodiment of the present invention. In this embodiment, the heat pipe has a similar structure to the heat pipe of the previous first embodiment. However, a heat reservoir 20 c replaces the heat reservoir 20 of the previous first embodiment. In the fourth embodiment, the heat reservoir 20 a has a triangular cross section.
FIG. 6 illustrates a heat pipe according to a fifth embodiment of the present invention. In this embodiment, the heat pipe has a similar structure to the heat pipe of the previous third embodiment. However, a heat reservoir 20 d replaces the heat reservoir 20 of the previous third embodiment. In the fifth embodiment, the heat reservoir 20 a has a square cross section.
FIG. 7 illustrates a heat pipe according to a sixth embodiment of the present invention. The heat pipe has a similar structure to the heat pipe of the first embodiment. In this embodiment, a plurality of fins 26 are mounted on the outer wall 211 of the heat reservoir 20 to increase the heat dissipating area of the heat pipe.
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 for receiving heat and a condensing section for releasing the heat, and an adiabatic section located between the evaporating section and the condensing section;

a first working fluid contained in the metal casing;

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

a sealed heat reservoir mounted on the condensing section of the heat pipe for increasing heat dissipation area, the heat reservoir having a second wick capillary wick structure and a second working fluid contained therein.

2. The heat pipe of claim 1, wherein the condensing section of the heat pipe is inserted into the heat reservoir and engages with the heat reservoir.

3. The heat pipe of claim 1, wherein the second capillary wick is arranged at an inner surface of the heat reservoir and an outer surface of the condensing section.

4. The heat pipe of claim 1, wherein the heat reservoir comprises an outer wall and a pair of opposite lateral sides connect with two opposite ends of the outer wall.

5. The heat pipe of claim 4, wherein an inner wall is formed in the heat reservoir, and the condensing section of the heat pipe is inserted into the heat reservoir and engaged with the inner wall of the heat reservoir.

6. The heat pipe of claim 1, wherein the heat pipe and the heat reservoir both have circular cross sections.

7. The heat pipe of claim 1, wherein the heat pipe has a circular cross section and the heat reservoir has a quadrilateral cross section.

8. The heat pipe of claim 1, wherein the heat pipe has a quadrilateral cross section and the heat reservoir has a circular cross section.

9. The heat pipe of claim 1, wherein the heat pipe has a circular cross section and the heat reservoir has a triangular cross section.

10. The heat pipe of claim 1, wherein the heat pipe and the heat reservoir both have quadrilateral cross sections.

11. The heat pipe of claim 1, wherein a plurality of fins are mounted on an outer surface of the heat reservoir.

12. The heat pipe of claim 1, wherein the heat reservoir surrounds the condensing section of the metal casing.

13. The heat pipe of claim 1, wherein the condensing section of the heat pipe is inserted into the heat reservoir and soldered to the heat reservoir.