US20070240851A1

US20070240851A1 - Heat pipe

Info

Publication number: US20070240851A1
Application number: US11/309,312
Authority: US
Inventors: Tay-Jian Liu; Chao-Nien Tung; Chuen-Shu Hou; Ji-Feng Wang; Qian-Hua He
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: CN101055157A; CN100513973C

Abstract

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

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 which has a heat reservoir for quickly absorbing 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.

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 where 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, 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 by virtue of phase change of the working media taking place therein. Generally, the working media is 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 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, the 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 prematurely changes into condensed liquid before reaching the condensing section. The prematurely condensed liquid is 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 at the evaporating section to become the liquid is increased 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 difference 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 structure is arranged at an inner surface of the hollow metal casing. A sealed heat reservoir is mounted on the evaporating section of the heat pipe to increase heat absorbing area of the heat pipe. The heat pipe is so configured 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 II-II 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; and

FIG. 6 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 structure 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 evaporating section 120. 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 structure 12 so as to guide vapor to flow therein.
The heat reservoir 20 has a hollow cylindrical configuration and 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 evaporating section 120 of the heat pipe extends through the heat reservoir 20, thereby to position 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 structure 22 is formed at an inner surface of the heat reservoir 20 and an outer surface of the evaporating section 120. 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 at 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.
In use, the heat reservoir 20 mounted on the evaporating section 120 of the heat pipe first absorbs heat from heat resource; the heat is transferred to the second working fluid contained in the heat reservoir 20 whereby the second working fluid evaporates into vapor. The vapor condenses and releases the heat. Then the heat is transferred to the first working fluid contained in the evaporating section 120 so that the first working fluid quickly evaporates into vapor. The generated vapor moves towards and carries the heat simultaneously to the condensing section 160 where the vapor is condensed into liquid after releasing the heat into ambient environment. The heat reservoir 20 has a so large heat absorbing area that the heat from the heat resource can be quickly absorbed by the heat reservoir 20. The absorbed heat is then quickly transferred to the evaporating section 120 and released at the condensing section 160, thereby to reduce the heat resistance of the heat pipe and enhance 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 evaporating section 120 of the heat pipe is inserted into the heat reservoir 20 and is interferentially engaged with the inner wall of the heat reservoir 20, whereby the heat reservoir 20 is positioned on evaporating section 120 of the heat pipe. Alternatively, the heat reservoir 20 is positioned on the evaporating section 120 of the heat pipe by solder means or glue 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 first embodiment. However, a heat reservoir 20 a replaces the heat reservoir 20 of the previous 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.
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 structure arranged at an inner surface of the hollow metal casing; and

a sealed heat reservoir mounted on the evaporating section of the heat pipe for absorbing heat generated by a heat source and transferring the heat generated by the heat source to the evaporating section of the metal casing, wherein the heat reservoir has a second working fluid and a second capillary wick structure contained therein.

2. The heat pipe of claim 1, wherein the evaporating section of the heat pipe is inserted into the heat reservoir and is interferentially connected with the heat reservoir.

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

4. The heat pipe of claim 1, wherein the heat reservoir comprises an outer wall and a pair of opposite lateral sides connects 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 evaporating 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 respectively have a circular cross section.

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 each have a quadrilateral cross section.

11. The heat pipe of claim 1, wherein the heat reservoir surrounds the evaporating section of the metal casing.

12. The heat pipe of claim 1, wherein the evaporating section of the metal casing is inserted into the heat reservoir and soldered to the heat reservoir.