US20080105406A1

US20080105406A1 - Heat pipe with variable grooved-wick structure and method for manufacturing the same

Info

Publication number: US20080105406A1
Application number: US11/556,613
Authority: US
Inventors: Chang-Shen Chang; Juei-Khai Liu; Chao-Hao Wang; Hsien-Sheng Pei
Original assignee: Foxconn Technology Co Ltd
Current assignee: Foxconn Technology Co Ltd
Priority date: 2006-11-03
Filing date: 2006-11-03
Publication date: 2008-05-08

Abstract

A heat pipe (10) includes a casing (11), a plurality of grooves (12, 13) defined in the casing, and working fluid contained in the casing. The casing includes a first portion (14) and a second portion (15) having a smaller diameter than the first portion. The grooves (12) at the first portion of the casing have greater apex angles and smaller groove width than those of the grooves (13) at the second portion. A method for manufacturing the heat pipe includes the steps of: providing a casing with a plurality of grooves defined in an inner wall thereof; shrinking a diameter of one portion of the casing to enable the portion to function as an evaporator section of the heat pipe; vacuuming and placing a predetermined quantity of working fluid in the casing; sealing the casing to obtain the heat pipe.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates generally to a heat pipe for transfer or dissipation of heat from heat-generating components, and more particularly to a heat pipe with variable grooved-wick structure defined therein for increasing heat transfer capability thereof.
2. Description of Related Art
Nowadays, thermal modules are widely used in notebook computers to dissipate heat generated by CPUs. The thermal module includes a blower, a fin assembly, and a heat pipe. The heat pipe has an evaporator section and a condenser section respectively connected with a CPU and the fin assembly so as to transfer heat generated by the CPU to the fin assembly. The fin assembly is arranged at an air outlet of the blower to dissipate heat absorbed from the condenser section of the heat pipe to the surrounding environment.
In the thermal module, the evaporator section of the heat pipe usually has a smaller area than the condenser section. Accordingly, a contacting area between the evaporator section of the heat pipe and the CPU is smaller than that between the condenser section of the heat pipe and the fin assembly. Therefore, the radial power density which the evaporator section of the heat pipe undergoes is greater than that the condenser section of the heat pipe needs to undergo.
In a conventional grooved heat pipe, grooves at the evaporator section thereof have similar groove shapes to grooves at the condenser section thereof. This means the evaporator section of the conventional grooved heat pipe has the same radial power density as the condenser section thereof, which limits the increase of the heat transfer capability of the conventional grooved heat pipe and further limits the increase of the heat dissipating efficiency of the thermal module. Thus, it can be seen that improvement of the radial power density of the evaporator section of the heat pipe is key to improve the heat dissipation efficiency of the thermal module.

SUMMARY OF THE INVENTION

The present invention relates to a heat pipe for removing heat from heat-generating components and a method for manufacturing the same. The heat pipe includes a casing, a plurality of grooves defined in the casing, and working fluid contained in the casing. The casing includes a first portion and a second portion having a smaller diameter than the first portion. The grooves at the first portion of the casing have smaller groove width than that of the grooves at the second portion. The method includes the steps of: providing a casing with a plurality of tiny grooves defined in an inner wall thereof; shrinking a diameter of one portion of the casing to function the portion as an evaporator section of the heat pipe; vacuuming and placing a predetermined quantity of working fluid in the casing; sealing the casing to obtain 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 invention 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 invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views:

FIG. 1 is a heat pipe in accordance with a preferred embodiment of the present invention;

FIG. 2 is an enlarged transverse cross-sectional view of the heat pipe of FIG. 1, taken along line II-II;

FIG. 3 is an enlarged transverse cross-sectional view of the heat pipe of FIG. 1, taken along line III-III;

FIG. 4 is a flow chart showing a preferred method for manufacturing the heat pipe of FIG. 1;

FIG. 5 is an explanatory view of a manufacturing method of the heat pipe of FIG. 1;

FIG. 6 an enlarged transverse cross-sectional view of FIG. 5, taken along line VI-VI;

FIG. 7 is an explanatory view of another manufacturing method of the heat pipe of FIG. 1;

FIG. 8 an enlarged transverse cross-sectional view of FIG. 7, taken along line VIII-VIII; and

FIG. 9 is a heat pipe in accordance with a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 through 3, a heat pipe 10 in accordance with a preferred embodiment of the present invention is shown. The heat pipe 10 includes a casing 11, a plurality of tiny grooves 12, 13 axially defined in an inner wall of the casing 11, and a predetermined quantity of bi-phase working fluid (not shown) contained in the casing 11.
The casing 11 is a metallic hollow tube having a ring-like transverse cross section and a uniform thickness T along a longitudinal direction thereof. The casing 11 includes an evaporator section 15 disposed at an end thereof, a condenser section 14 disposed at the other end thereof, and an adiabatic section 17 disposed between the evaporator and the condenser sections 15, 14. A diameter of the evaporator section 15 is smaller than that of the condenser section 14. A transition section 16 is formed between the evaporator section 15 and the adiabatic section 17. A diameter of the transition section 16 is gradually decreased from the adiabatic section 17 towards the evaporator section 15 so that the transition section 16 has a taper-shaped configuration.
The working medium is usually selected from a liquid which has a low boiling point and is compatible with the casing 11, such as water, methanol, or alcohol. Thus, the working medium can easily evaporate to vapor when it receives heat in the evaporator section 15 and condense to liquid when it dissipates heat in the condenser section 14.
The grooves are coextensive with a central longitudinal axis of the casing 11. Grooves 12 at the evaporator section 15 of the casing 11 have substantially similar heights H to the grooves 13 at the condenser section 14 thereof. An apex angle A1 of each of the grooves 12 at the evaporator section 15 is greater than an apex angle A2 of each of the grooves 13 at the condenser section 14. A top width W₁of each of the grooves 12 at the evaporator section 15 is smaller than a top width W₃of each of the grooves 13 at the condenser section 14, whilst a bottom width W₂of each of the grooves 12 at the evaporator section 15 is smaller than a bottom width W₄of each of the grooves 13 at the condenser section 14. This means a middle width (groove width) of each of the grooves 12 at the evaporator section 15 is smaller than that of each of the grooves 13 at the condenser section 14.
Referring to FIG. 4, the heat pipe 10 is manufactured by such steps: providing a metal casing 11 with a uniform diameter along a longitudinal direction thereof; forming a plurality of grooves in the inner wall of the casing 11; shrinking the diameter of one portion of the casing 11 so as to allow the portion of the casing 11 to function as the evaporator section 15 of the heat pipe 10; vacuuming and placing the predetermined quantity of the working fluid into the casing 11; sealing the casing 11 to obtain the heat pipe 10.
Referring to FIGS. 5 and 6, the evaporator section 15 of the heat pipe 10 can be shrunk by high speed spinning tube shrinkage treatment. A high speed spinning tube shrinkage tool 20 is a hollow tube which includes a tapered portion 21 corresponding to the transition section 16 of the heat pipe 10, and guiding and diminished portions 22, 23 corresponding to the respective condenser and evaporator sections 14, 15 of the heat pipe 10. The guiding portion 22 connects with a front end of the transition section 16, and the diminished portion 23 connects with a rear end of the transition section 16. A diameter of an inner wall of the guiding portion 22 of the high speed spinning tube shrinkage tool 20 is substantially equal to a diameter of an outer wall of the condenser section 14. A diameter of an inner wall of the diminished portion 23 of the high speed spinning tube shrinkage tool 20 is substantially equal to a diameter of an outer wall of the evaporator section 15 of the heat pipe 10. The tapered portion 21 enables to gradually diminish the diameter of the outer wall of the evaporator section 15 so as to form the transition section 16. In shrinkage of the original evaporator section of the casing 11, the casing 11 of the heat pipe 10 is fixed to a work table 40 via two fixing members 50; the high speed spinning tube shrinkage tool 20 is propelled to move from the original evaporator section towards the condenser section 14 of the casing 11 along the central longitudinal axis thereof to a predetermined length. In movement of the tool 20, the guiding portion 22 guides the movement of the tool 20. Meanwhile, the tapered portion 21 compresses the outer wall of the evaporator section 15 so as to shrink the diameter thereof and thereby obtaining the needed heat pipe 10.
Referring to FIGS. 7 and 8, the evaporator section 15 of the heat pipe 10 can also be shrunk using spinning stamping tube shrinkage treatment. A spinning stamping tube shrinkage tool 30 includes three sub-tools 31 with arc-shaped inner surfaces 32 thereof evenly distributed around an imaginary circle 33 which is coaxial with and surrounds the casing 11. The tool 30 includes a tapered portion 34 corresponding to the transition section 16 of the heat pipe 10, and enlarged and diminished portions 35, 36 corresponding to the respective condenser and evaporator sections 14, 15 of the heat pipe 10. A diameter of the tapered portion 34 is gradually increased from the diminished portion 36 towards the enlarged portion 35. A diameter of the diminished portion 36 of the tool 30 at the imaginary circle 330 is greater than that of the evaporator section 15 of the casing 11 before the shrinkage operation, whilst a diameter of the diminished portion 36 of the tool 30 is decreased to a predetermined value which is substantially equal to the diameter of the evaporator section 15 of the casing 11 after the shrinkage process. During shrinkage of the evaporator section 15 of the casing 11, the casing 11 of the heat pipe 10 is fixed to a work table 40 via a fixing member 50; the three sub-tools 31 are rotated and at the same time are controlled to move towards the evaporator section 15 of the casing 11 along a radial direction of the casing 11 so as to shrink the diameter of the evaporator section 15. Meanwhile, the sub-tools 31 may be controlled to move towards the evaporator section 15 of the casing 11 along the central longitudinal axis of the heat pipe 10 in order to obtain a predetermine length for the evaporator section 15. In shrinkage of the evaporator section 15 of the casing 11, the diameter of the imaginary circle 33 is gradually decreased to the predetermined value.
In the present heat pipe 10, each of the grooves 12 at the evaporator section 15 has smaller groove width and greater apex angle than that of each of the grooves 13 at the condenser section 14. This increases the density of the grooves 12 at the evaporator section 15 of the heat pipe 10. The radial power density the evaporator section 15 of the heat pipe 10 can undergo is therefore increased, and the thermal resistance of the evaporator section 15 of the heat pipe 10 is decreased. Thus, the heat transfer capability of the heat pipe 10 is improved. In addition, the capillary action generated by the grooves 12 at the evaporator section 15 of the heat pipe 10 is increased, which increases the heat transfer capabilities of the heat pipe 10. The heat transfer capability of the heat pipe 10 is improved according to the shrinkage of the evaporator section 15 of the heat pipe 10, which simplifies the manufacturing of the heat pipe 10. In this way the present heat pipe 10 is adapted for mass production.
In the present heat pipe 10, the evaporator section 15 and the condenser section 14 are respectively disposed at two ends of the casing 11. Alternatively, referring to FIG. 9, the casing 11 a may include two condenser sections 14 a disposed at two ends thereof, and an evaporator section 15 a arranged at a middle portion thereof. Two transition sections 16 a are respectively disposed between the evaporator section 15 a and the condenser sections 14 a. Under this status, the evaporator section 15 a of the casing 11 a is shrunk by spinning stamping tube shrinkage treatment. In order to manufacture this kind of the heat pipe 10, the tool 30 may include a diminished portion 36, two enlarged portions 35 disposed at two sides of the diminished portion 36, and two tapered portions 34 respectively formed between the diminished portion 36 and the enlarged portions 35. Furthermore, the heat pipe 10 can be bent to L-shaped or U-shaped to satisfy different need for the heat pipe. The heat pipe 10 can also be flattened so as to decrease the size thereof for benefiting the heat pipe to be used in a size-limited room such as an inner side of a laptop computer.
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 casing comprising a first portion and a second portion having a smaller diameter than the first portion;

a plurality of grooves defined in an inner wall of the casing; and

a predetermined quantity of bi-phase working fluid contained in the casing;

wherein the grooves at the first portion of the casing have smaller groove width than that of the grooves at the second portion.

2. The heat pipe of claim 1, wherein the grooves extends along a central axis of the casing.

3. The heat pipe of claim 1, wherein the grooves at the first portion of the casing have greater apex angles than that of the grooves at the second portion.

4. The heat pipe of claim 1, wherein the first portion is an evaporator section of the heat pipe, whilst the second section is a condenser section of the heat pipe.

5. The heat pipe of claim 4, wherein the evaporator section is disposed at an end of the heat pipe.

6. The heat pipe of claim 4, wherein the evaporator section is disposed at a middle portion of the heat pipe.

7. The heat pipe of claim 1 further comprising a transition section disposed between the first portion and the second portion, a diameter of the transition section being gradually decreased from the second portion towards the first portion.

8. The heat pipe of claim 1, wherein the casing of the heat pipe is flat in profile.

9. A method for manufacturing a heat pipe with variable grooved-wick structure comprising the steps of:

providing a casing with a plurality of tiny grooves defined in an inner wall thereof;

shrinking a diameter of one portion of the casing via a shrinkage tool to enable it to function as an evaporator section of the heat pipe;

vacuuming and placing a predetermined quantity of working fluid in the casing; and

sealing the casing to obtain the heat pipe.

10. The method as described in claim 9, wherein the grooves are axially carved in the inner wall of the casing.

11. The method as described in claim 9, wherein the shrinkage tool is a high speed spinning tube shrinkage tool, the shrinkage process of the evaporator section comprises the step of controlling the high speed spinning tube shrinkage tool to move towards the evaporator section of the casing along a central longitudinal axis thereof so as to shrink the diameter thereof.

12. The method as described in claim 11, wherein the high speed spinning tube shrinkage tool comprises a tapered portion which enables to compress an outer wall of the evaporator section so as to shrink the diameter thereof and a guiding portion which guides the movement of the high speed spinning tube shrinkage tool.

13. The method as described in claim 12, wherein the high speed spinning tube shrinkage tool further comprises a diminished portion, the tapered portion being disposed between the guiding portion and the diminished portion.

14. The method as described in claim 9, wherein the shrinkage tool is a spinning stamping tube shrinkage tool, the shrinkage process of the evaporator section comprises the step of controlling the spinning stamping tube shrinkage tool to move towards the evaporator section of the casing along a radial direction of the casing so as to shrink the diameter of the evaporator section.

15. The method as described in claim 14, wherein the shrinkage process of the evaporator section further comprises the step of controlling the spinning stamping tube shrinkage tool to move towards the evaporator section of the casing along a central longitudinal axis of the heat pipe in order to obtain a predetermine length for the evaporator section.

16. The method as described in claim 14, wherein the spinning stamping tube shrinkage tool includes more than two sub-tools with arc-shaped inner surfaces thereof distributed around an imaginary circle which is coaxial with and surrounds the casing.

17. The method as described in claim 16, wherein each of the sub-tools comprises diminished portion and a tapered portion connecting with the diminished portion at an end thereof, a diameter of the tapered portion being gradually increased from the end towards an opposite end thereof.

18. The method as described in claim 17, wherein each of the sub-tools further comprises an enlarged portion connecting with the tapered portion at the opposite end thereof.