US20140166244A1

US20140166244A1 - Flat heat pipe and method for manufacturing the same

Info

Publication number: US20140166244A1
Application number: US13/850,268
Authority: US
Inventors: Sheng-Liang Dai; Jia-Hong Wu
Original assignee: Furui Precise Component Kunshan Co Ltd; Foxconn Technology Co Ltd
Current assignee: Furui Precise Component Kunshan Co Ltd; Foxconn Technology Co Ltd
Priority date: 2012-12-17
Filing date: 2013-03-25
Publication date: 2014-06-19
Also published as: CN103868386A; TWI589830B; TW201428225A

Abstract

An exemplary flat heat pipe includes a hollow tube and a wick structure lining an inner surface of the tube. The tube includes an evaporator section, an adiabatic section and a condenser section defined in turn along a longitudinal direction thereof. The wick structure includes a first wick portion located in the evaporator section, a second wick portion located in the condenser section, and a third wick portion extending longitudinally from the evaporator section, through the adiabatic section to the condenser section and communicating with the first wick portion and the second wick portion. A capillary force of the first wick portion is larger than that of the third wick portion, and a pore density of the first wick portion is less than that of the third wick portion.

Description

BACKGROUND

1. Technical Field
The disclosure generally relates to heat transfer apparatuses such as those used in electronic equipment, and more particularly to a flat heat pipe with stable and reliable performance.
2. Description of Related Art
Heat pipes are widely used in various fields for heat dissipation purposes due to their excellent heat transfer performance. One commonly used heat pipe includes a sealed tube made of thermally conductive material with a working fluid contained therein. The working fluid conveys heat from one end of the tube, typically referred to as an evaporator section, to the other end of the tube, typically referred to as a condenser section. Preferably, a wick structure is provided inside the heat pipe, lining an inner wall of the tube, and drawing the working fluid back to the evaporator section after it condenses at the condenser section.
During operation of the heat pipe in a typical application, the evaporator section of the heat pipe maintains thermal contact with a heat-generating electronic component. The working fluid at the evaporator section absorbs heat generated by the electronic component, and thereby turns to vapor. The generated vapor moves, carrying the heat with it, toward the condenser section. At the condenser section, the vapor condenses after the heat is dissipated. The condensate is then drawn back by the wick structure to the evaporator section where it is again available for evaporation. For the condensate to be drawn back rapidly, the wick structure located at the evaporator section must have a capillary force larger than that of the wick structure located at the condenser section. However, the capillary force of the wick structure is uniform. Thus, the evaporator section is prone to become dry.
What is needed, therefore, is a heat pipe to overcome the above described shortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal, cross-sectional view of a flat heat pipe according to a first embodiment of the present disclosure.

FIG. 2 is a transverse, cross-sectional view of an evaporator section of the flat heat pipe of FIG. 1, corresponding to line II-II thereof.

FIG. 3 is a transverse, cross-sectional view of a condenser section of the flat heat pipe of FIG. 1, corresponding to line thereof.

FIG. 4 is a longitudinal, cross-sectional view of a flat heat pipe according to a second embodiment of the present disclosure.

FIG. 5 is a transverse, cross-sectional view of an evaporator section of the flat heat pipe of FIG. 4, corresponding to line V-V thereof.

FIG. 6 is a flowchart showing an exemplary method for manufacturing the flat heat pipe of FIG. 1.

DETAILED DESCRIPTION

Embodiments of the present flat heat pipe will now be described in detail below and with reference to the drawings.
Referring to FIGS. 1-3, a flat heat pipe 1 in accordance with a first embodiment of the present disclosure is shown. The flat heat pipe 1 includes a sealed, flat tube 30, a wick structure 50 lining an inner surface of the tube 30, and working fluid (not shown) contained in the wick structure 50.
The tube 30 is made of metal or metal alloy with a high heat conductivity coefficient, such as copper, copper-alloy, or other suitable material. The tube 30 is elongated, and has an evaporator section 11, an adiabatic section 13, and a condenser section 15 defined in that order along a longitudinal direction thereof. A transverse section of the tube 30 is oval-shaped (or racetrack-shaped). A longitudinal section of the tube 30 is rectangular.
The wick structure 50 includes a first wick portion 51, a second wick portion 53, and a third wick portion 55. The first wick portion 51 is formed on an inner surface of the evaporator section 11. The second wick portion 53 extends longitudinally from the adiabatic section 13 to the condenser section 15, and is formed on inner surfaces of the adiabatic section 13 and the condenser section 15. The second wick portion 53 contacts and communicates with the first wick portion 51. The third wick portion 53 is enclosed by the first wick portion 51 and the second wick portion 53. The third wick portion 53 extends longitudinally from the evaporator section 11, and through the adiabatic section 13 to the condenser section 15, and communicates with the first wick portion 51 and the second wick portion 53. A capillary force of the second wick portion 53 is larger than that of the third wick portion 55 and less than that of the first wick portion 51. A pore density of the second wick portion 53 is larger than that of the first wick portion 51 and less than that of the third wick portion 55. In one embodiment, sizes of the pores of the first, second and third wick portions 51, 53, 55 are approximately the same. In such case, the pore density can be measured according to the number of pores per unit area/volume. In other embodiments, sizes of the pores of any one or more of the first, second and third wick portions 51, 53, 55 differ. In such cases, the pore density can be measured according to the total volume of pores per unit area/volume.
The first wick portion 51 is sintered metal powder, and has the shape of a flattened annulus. An outer surface of the first wick portion 51 is snugly attached to the inner surface of the evaporator section 11.
The second wick portion 53 is a groove-type wick portion, and a left end thereof connects and communicates with a right end of the first wick portion 51. A length of the second wick portion 53 is larger than that of the first wick portion 51. The second wick portion 53 includes a plurality of ridges (or elongated teeth) 531 and a plurality of grooves 533. Each groove 533 is defined between two corresponding adjacent ridges 531.
In the illustrated embodiment, all the ridges 531 are substantially the same size, and all the grooves 533 are substantially the same size. A transverse cross-section of each ridge 531 is trapezoidal, and a transverse cross-section of each groove 533 is trapezoidal. A size of the transverse cross-section of each ridge 531 is substantially the same as a size of the transverse cross-section of each groove 533. Each ridge 531 tapers from an end thereof far from a center of the tube 30 to an end thereof nearer the center of the tube 30. Each groove 533 tapers from an end thereof nearer the center of the tube 30 to an end thereof far from the center of the tube 30. A transverse width of each groove 533 at the end thereof nearer the center of the tube 30 is larger that of each ridge 531 at the end thereof nearer the center of the tube 30.
The third wick portion 55 is disposed at a middle of one side of the tube 30. A bottom surface of the third wick portion 55 at the evaporator section 11 is snugly attached to an inner surface of the first wick portion 51. A bottom surface of the third wick portion 55 at the adiabatic and condenser sections 13, 15 is snugly attached to an inner surface of the second wick portion 53. A top surface of the third wick portion 55 is spaced from the first wick portion 51 and the second wick portion 53. The third wick portion 55 is formed by weaving a plurality of metal wires such as copper wires and/or stainless steel wires. A length of the third wick portion 55 is equal to a sum of a length of the first wick portion 51 and a length of the second wick portion 53.
In operation, the working fluid at the evaporator section 11 absorbs heat generated by one or more electronic components, and thereby turns to vapor. The generated vapor moves, carrying the heat with it, toward the condenser section 15. At the condenser section 15, the vapor condenses after the heat is dissipated. Because the pore density of the third wick portion 55 is larger than that of the first wick portion 51, the condensate can rapidly permeate into the third wick portion 55. Because the capillary force of the first wick portion 51 is larger than that of the third wick portion 55, the condensate in the third wick portion 55 can be drawn back to the evaporator section 11 rapidly by the first wick portion 51. Therefore, the evaporator section 11 of the flat heat pipe 1 avoids becoming dry. Thus, the flat heat pipe 1 has stable and reliable performance.
Referring to FIGS. 4-5, a flat heat pipe 1 a in accordance with a second embodiment of the present disclosure is shown. The flat heat pipe 1 a is similar to the flat heat pipe 1 of the first embodiment. However, in the flat heat pipe 1 a, a second wick portion 53 a is formed on the whole of the inner surface of the tube 30; and a first wick portion 51 a is located at the evaporator section 11 and is snugly attached to an inner surface of the second wick portion 53 a.
Referring to FIG. 6, an exemplary method for manufacturing the flat heat pipe 1 includes the following steps:
In step S1, the tube 30 with an open end is provided.
In step S2, the inner surfaces of the adiabatic section 13 and condenser section 15 are etched to form the ridges 531 and the grooves 533, and thus the second wick portion 53 is formed.
In step S3, an amount of metal powder and a mandrel are provided. The mandrel is inserted in the evaporator section 11. A gap is defined between an outer surface of the mandrel and the inner surface of the evaporator section 11. The metal powder is filled into the gap. The tube 30 with the mandrel and the metal powder is heated at high temperature until the metal powder sinters to form the first wick portion 51. The mandrel is then drawn out of the tube 30. A particle diameter of each grain of metal powder is larger than the transverse width of each groove 533.
In step S4, a plurality of metal wires is provided and weaved to form the third wick portion 55. Then the third wick portion 55 is disposed at the middle of one side of the tube 30, with the bottom surface of the third wick portion 55 snugly attached to inner surfaces of the first wick portion 51 and the second wick portion 53, and the top surface of the third wick portion 55 spaced from the first wick portion 51 and the second wick portion 53.
In step S5, the working medium is injected into the tube 30, the tube 30 is evacuated, and the open end of the tube 30 is sealed. In this state, the flat heat pipe 1 is manufactured completely.
A method for manufacturing the flat heat pipe 1 a is similar to that of the flat heat pipe 1, except that in step S2, the whole of the inner surface of the tube 30 is etched to form the second wick portion 53 a. Then the first wick portion 51 a is sintered on the inner surface of the second wick portion 53 a located at the evaporator section 11, substantially according the third step described above in relation to the flat heat pipe 1.
It is to be further understood that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, 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 disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

What is claimed is:

1. A flat heat pipe for removing heat from a heat-generating component in thermal contact therewith, the flat heat pipe comprising:

a hollow tube comprising an evaporator section, an adiabatic section and a condenser section defined in turn along a longitudinal direction thereof; and

a wick structure lining an inner surface of the tube, the wick structure comprising a first wick portion located in the evaporator section, a second wick portion located in the condenser section, and a third wick portion extending longitudinally from the evaporator section, through the adiabatic section to the condenser section and communicating with the first wick portion and the second wick portion;

wherein a capillary force of the first wick portion is larger than that of the third wick portion, and a pore density of the first wick portion is less than that of the third wick portion.

2. The flat heat pipe of claim 1, wherein a capillary force of the second wick portion is larger than that of the third wick portion and less than that of the first wick portion, and a pore density of the second wick portion is larger than that of the first wick portion and less than that of the third wick portion.

3. The flat heat pipe of claim 1, wherein the third wick portion is enclosed by the first wick portion and the second wick portion.

4. The flat heat pipe of claim 3, wherein the third wick portion is disposed at a middle of one side of the tube, a bottom surface of the third wick portion at the evaporator section is snugly attached to an inner surface of the first wick portion, a bottom surface of the third wick portion at the adiabatic and condenser sections is snugly attached to an inner surface of the second wick portion, and a top surface of the third wick portion is spaced from the first wick portion and the second wick portion.

5. The flat heat pipe of claim 1, wherein the second wick portion extends longitudinally from the adiabatic section to the condenser section, and is formed on inner surfaces of the adiabatic section and the condenser section.

6. The flat heat pipe of claim 5, wherein the first wick portion is formed on an inner surface of the evaporator section, and an inner end of the first wick portion contacts and communicates with an inner end of the second wick portion.

7. The flat heat pipe of claim 1, wherein the second wick portion is formed on the whole of the inner surface of the tube, and the first wick portion is formed on an inner surface of the second wick portion.

8. The flat heat pipe of claim 1, wherein the first wick portion comprises sintered metal powder.

9. The flat heat pipe of claim 1, wherein the second wick portion is a groove-type wick portion.

10. The flat heat pipe of claim 9, wherein the second wick portion includes a plurality of elongated ridges and a plurality of grooves, and each groove is defined between two corresponding adjacent ridges.

11. The flat heat pipe of claim 1, wherein the third wick portion is formed by weaving a plurality of metal wires.

12. The flat heat pipe of claim 1, wherein a length of the third wick portion is equal to a sum of a length of the first wick portion and a length of the second wick portion.

13. A method for manufacturing a flat heat pipe, the method comprising:

providing a hollow tube comprising an evaporator section, an adiabatic section and a condenser section defined in turn along a longitudinal direction thereof;

etching an inner surface of the condenser section to form a plurality of ridges and a plurality of grooves, each groove defined between two corresponding adjacent ridges, the ridges and the grooves cooperatively forming a second wick portion;

providing an amount of metal powder and a mandrel, inserting the mandrel in the evaporator section such that a gap is defined between an outer surface of the mandrel and the inner surface of the evaporator section, filling the metal powder in the gap, heating the tube with the mandrel and the metal powder until the metal powder sinters to form a first wick portion, and then drawing the mandrel out of the evaporator section; and

providing a plurality of metal wires and weaving the metal wires to form a third wick portion, the third wick portion extending longitudinally from the evaporator section, through the adiabatic section to the condenser section and communicating with the first wick portion and the second wick portion;

14. The method of claim 13, wherein when the inner surface of the condenser section is etched to form the plurality of ridges and the plurality of grooves, inner surfaces of the adiabatic section and condenser section are also etched, such that the plurality of ridges and the plurality of grooves are formed in the condenser section, the adiabatic section and condenser section.

15. The method of claim 14, wherein the first wick portion is directly formed on the inner surface of the evaporator section.

16. The method of claim 14, wherein the whole of the inner surface of the tube is etched.

17. The method of claim 16, wherein the first wick portion is formed on an inner surface of the second wick portion.

18. The method of claim 17, wherein a particle diameter of each grain of metal powder is larger than the transverse width of each groove.