US20070107878A1

US20070107878A1 - Heat pipe with a tube therein

Info

Publication number: US20070107878A1
Application number: US11/309,263
Authority: US
Inventors: Chuen-Shu Hou; Tay-Jian Liu; Chao-Nien Tung; Chih-Hsien Sun; Ji-Feng Wang
Original assignee: Foxconn Technology Co Ltd
Current assignee: Foxconn Technology Co Ltd
Priority date: 2005-11-17
Filing date: 2006-07-20
Publication date: 2007-05-17
Also published as: CN100480611C; CN1967129A

Abstract

A heat pipe includes a metal casing (100) filled with a working fluid therein, a capillary wick (200) provided inside of the metal casing and a tube (300) contacting with a surface of the capillary wick. The capillary wick extends in an axial direction of the casing and has a middle portion separated from an inner wall of the metal casing. A vapor passage (700) is formed between an outer wall of the tube and the inner wall of the casing and a liquid channel (800) is defined by the capillary wick. The working fluid in vapor state flows along the vapor passage and the working fluid in liquid flows along the liquid channel. The tube separates the vapor from the liquid at a place where the tube is located.

Description

DESCRIPTION

1. Field of the Invention
The present invention relates generally to heat pipes as heat transfer/dissipating device, and more particularly to a heat pipe with a tube therein.
2. Description of Related Art
Heat pipes have excellent heat properties, and therefore are an effective means for heat transfer or dissipation from heat sources. Currently, heat pipes are widely used for removing heat from heat-generating components such as central processing units (CPUs) of computers. FIG. 6 shows an example of a related heat pipe. The heat pipe includes a vacuum casing 10 containing a working fluid therein (not shown) and a capillary wick 20 attached to an inner surface of the casing 10. The casing 10 includes an evaporating section 40 at one end and a condensing section 60 at the other end. An adiabatic section 50 is provided between the evaporating and condensing sections 40, 60. The adiabatic section 50 is typically used for transport of the generated vapor from the evaporating section 40 to the condensing section 60. A vapor channel 70 is formed in the central of an inside of the casing 10 and a liquid channel 80 is defined by the capillary wick 20. As the evaporating section 40 of the heat pipe is maintained in thermal contact with a heat-generating component, the working fluid contained in the evaporating section 40 absorbs heat generated by the heat-generating component and then turns into vapor. Due to the difference of vapor pressure between the evaporating and condensing sections 40, 60 of the heat pipe, the generated vapor moves towards and carries the heat simultaneously to the condensing section 60 along the vapor channel 70. The vapor is condensed into liquid at the condensing section 60 after releasing the heat into ambient environment. FIG. 7 is a diagrammatically longitudinal cross-sectional view showing opposite flowing paths between vapor and condensed liquid of the working fluid in the casing 10 of the heat pipe. Because of contacts of the vapor and the condensed liquid, an entrainment limit caused by the opposite flowing between the vapor and the condensed liquid prevents circulations of the vapor and condensed liquid. The condensed liquid is heated before it reaches the evaporating section 40. Accordingly, heat-transferred ability of the heat pipe is weakened and heat dissipation efficiency of the heat pipe is lowered.
In view of the above-mentioned disadvantage of the conventional heat pipe, there is a need for a heat pipe having a good heat transfer effect.

SUMMARY OF THE INVENTION

A heat pipe in accordance with a preferred embodiment includes a metal casing containing a working fluid therein and a capillary wick provided in an inside of the casing. The capillary wick extends in an axial direction of the casing and has a middle portion separated from an inner wall of the metal casing. A tube is provided to contact with a surface of the capillary wick to separate the capillary wick from a vapor passage in the heat pipe.
Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present apparatus and method 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 apparatus and method. 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 radial cross-sectional view of the heat pipe in accordance with the first embodiment, taken along line II-II of FIG. 1;
FIG. 3 is a longitudinal cross-sectional view of a heat pipe in accordance with a second embodiment of the present invention;
FIG. 4 is a radial cross-sectional view of a heat pipe in accordance with a third embodiment of the present invention;
FIG. 5 is a radial cross-sectional view of a heat pipe in accordance with a fourth embodiment of the present invention;
FIG. 6 is a longitudinal cross-sectional view of a heat pipe in accordance with related art; and
FIG. 7 is a diagrammatically longitudinal cross-sectional view showing vapor and liquid moving paths of the related heat pipe of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-2 show a heat pipe in accordance with a first embodiment of the present invention. The heat pipe comprises a metal casing 100 made of high thermally conductive materials such as copper or copper alloys, a working fluid (not shown) contained in the casing 100 and a capillary wick 200 arranged inside of the casing 100. The casing 100 comprises an evaporating section 400 at one end, a condensing section 600 at the other end and an adiabatic section 500 arranged between the evaporating section 400 and the condensing section 600. The capillary wick 200 comprises first capillary wicks 220 disposed in opposite ends of the casing 100, respectively, and a second capillary wick 240 interconnecting with the first capillary wicks 220. The first capillary wicks 220 are arranged on the evaporating and condensing sections 400, 600 of the casing 100. The second capillary wick 240 extends in an axial direction of the casing 100. A tube 300 surrounds the second capillary wick 240 so that an inner surface of the tube 300 is attached with an outer surface of the second capillary wick 240 in the casing 100. The first capillary wicks 220 contact with the casing 100, while the second capillary wick is separated from the casing 100. A vapor passage 700 is provided between the tube 300 and an inner wall of the casing 100 and a liquid channel 800 is defined by the first and second capillary wicks 220, 240. The vapor passage 700 is separated from the second capillary wick 240 by the tube 300 at the adiabatic section 500. The tube 300 can reach the evaporating and condensing sections 400, 600 of the casing 100 with a proper range.
As the evaporating section 400 of the heat pipe is maintained in thermal contact with a heat-generating component (not shown), the working fluid contained in the evaporating section 400 absorbs heat generated by the heat-generating component and then turns into vapor. Due to the difference of vapor pressure between the evaporating and condensing sections 400, 600 of the heat pipe, the generated vapor moves along the vapor passage 700 and carries the heat simultaneously to the condensing section 600. The vapor is condensed into liquid at the condensing section 600 after releasing the heat into ambient environment. Because of an arrangement of the tube 300 attached on the second capillary wick 240 at the adiabatic section 500, the vapor flows only along the vapor passage 700 toward the condensing section 600 and the liquid flows only in the liquid channel 800 towards the evaporating section 400 when they flow in the adiabatic section 500. The vapor and the liquid in the adiabatic section 50 are separated by the metal tube 300, which can avoid the adverse contact between the vapor and liquid. Thus, the condensed working fluid from the condensing section 600 can smoothly reach the evaporating section 400 and is prevented from being heated by the high temperature vapor at the adiabatic section 500. Abilities of heat-absorption and heat-dissipation of the working fluid of the heat pipe is enhanced and heat-transfer efficiency of the heat pipe is accordingly improved.
FIG. 3 illustrates a heat pipe according to a second embodiment of the present invention. Main differences between the second and first embodiments are that in the second embodiment the capillary wick 200 further comprises a third capillary wick 230 attached on the inner wall of the casing 100 at the evaporating section 400. The third capillary wick 230 is a thin layer extending from an end of the first capillary wick 220 at the evaporating section 400 of the casing 100. The third capillary wick 230 is so thin that it can guide the vapor at the evaporating section 400 into the vapor passage 700 quickly. Portions of the first capillary wicks 220 near the second capillary wick 240 each have a graduated thickness: the thickness at the evaporating section 400 is gradually decreased along a direction from the evaporating section 400 toward the adiabatic section 500, and at the condensing section 600 is gradually increased from the adiabatic section 500 toward the condensing section 600. The third capillary wick 230 is much thinner than that of the first and second capillary wicks 220, 240. As the evaporating section 400 of the heat pipe absorbs the heat generated by the heat-generating component, the heated working fluid can turn into vapor quickly and then flow into the vapor passage 700 towards the condensing section 600 of the casing 100. The vapor passage 700 is separated from the second capillary wick 240 by the tube 300. A liquid channel 820 is defined by the first, second and third capillary wicks 220, 240 and 230. The condensed liquid in the condensing section 600 flows along the liquid channel 820 and is drawn back to the evaporating section 400 under capillary pressure developed by the first and second capillary wicks 220, 240 to achieve a thermal circulation.
FIG. 4 illustrates a heat pipe according to a third embodiment of the present invention. Four spaced ribs 310 are disposed between an outer wall of the tube 300 and the inner wall of the casing 100 so as to reinforce the heat pipe. The other structure of the heat pipe of the third embodiment is similar to that of the first embodiment.
FIG. 5 illustrates a heat pipe according to a fourth embodiment of the present invention. Four-spaced small pipes 320 are disposed surrounding the tube 300 and an inner surface of each small pipe 320 is filled with a supplementary second capillary wick 240. Each small pipe 320 extends in a longitudinal direction of the casing 100 and is sandwiched between an outer wall of the tube 300 and the inner wall of the casing 100. The vapor passage 700 is enclosed by the inner wall of the casing 100 and defined between the tube 300 and the small pipes 320. The supplementary second capillary wick 240 interconnects the first wick structures at the evaporating section and at the condensing section. The other structure of the heat pipe of the fourth embodiment is similar to that of the first embodiment.
The tube 300 and the pipes 320 in the preferred embodiments are made of metal sheet. Alternatively, they can be made of metal mesh. The tube 300 and the pipes 320 are made of metal materials such as copper or aluminum. Alternatively they can be made of non-metal material such as plastics or resin. A cross-sectional area of the tube 300 or the pipes 320 can also be square or rectangular, according to the shape of heat pipe.
It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.

Claims

1. A heat pipe comprising:

a casing containing a working fluid therein;

a capillary wick arranged inside of the casing and extending in an axial direction of the casing; and

a tube surrounding the capillary wick and an inner surface of the tube contacting with a surface of the capillary wick in the casing;

wherein a vapor passage is formed between an outer wall of the tube and an inner wall of the casing and a liquid channel is defined by the capillary wick, and wherein the vapor passage is separated from the capillary wick by the tube, the working fluid in vapor and liquid states respectively flowing along the vapor passage and the liquid channel from one end towards an opposing end of the casing in opposite directions.

2. The heat pipe as claimed in claim 1, wherein the capillary wick comprises first capillary wicks provided in opposite ends of the casing and a second capillary wick interconnecting the first capillary wicks and extending in the axial direction of the casing, the tube surrounding the second capillary wick.

3. The heat pipe as claimed in claim 2, wherein the capillary wick further comprises a third capillary wick having a thinner thickness than that of the first and second capillary wicks, the third capillary wick extending from one of the first capillary wicks into the vapor passage and functioning to guide the working fluid in vapor into the vapor passage.

4. The heat pipe as claimed in claim 1, wherein the casing comprises a rib disposed between the outer wall of the tube and the inner wall of the casing.

5. The heat pipe as claimed in claim 2, wherein the casing further comprises a plurality of spaced pipes surrounding the tube and a supplementary capillary wick is filled in each of the pipes and interconnecting the first capillary wicks.

6. The heat pipe as claimed in claim 5, wherein the vapor passage is enclosed by the casing and defined between the tube and the pipes.

7. The heat pipe as claimed in claim 1, wherein the tube is made of metal.

8. The heat pipe as claimed in claim 1, wherein the tube is made of one of plastics and resin.

9. A heat pipe comprising:

a metal casing having an inner wall therein and defining an evaporating section for receiving heat, a condensing section for releasing the heat and an adiabatic section between the evaporating and condensing sections;

a working fluid received in the metal casing and evaporated into vapor in the evaporating section and condensed into liquid in the condensing section;

a capillary wick extending in an axial direction of the casing from the evaporating section through the adiabatic section to the condensing section and having a middle portion spaced from the inner wall of the metal casing;

a tube contacting with a surface of the middle portion of the capillary wick; and

a vapor passage formed inside of the metal casing and between the metal casing and the middle portion of the capillary wick and a liquid channel defined by the capillary wick;

wherein the vapor at the evaporating section flows towards the condensing section of the casing along the vapor passage and the liquid at the condensing section of the casing returns to the evaporating section along the liquid channel, the tube separating the vapor passage and the liquid at a place wherein the tube is located.

10. The heat pipe as claimed in claim 9, wherein the capillary wick comprises first capillary wicks arranged in the evaporating and condensing sections and a second capillary wick interconnecting the first capillary wicks and extending in the axial direction of the casing, the inner surface the tube contacting with the surface of the second capillary wick.

11. The heat pipe as claimed in claim 10, wherein the vapor passage is formed between an outer wall of the tube and the inner wall of the casing and the liquid channel is defined by the second capillary wick.

12. The heat pipe as claimed in claim 9, wherein the metal casing further comprises a rib arranged between an outer wall of the tube and the inner wall of the casing.

13. The heat pipe as claimed in claim 9, wherein the metal casing further comprises a plurality of spaced pipes surrounding the tube, a supplementary capillary being filled in each of the pipes and interconnecting the capillary wick at the evaporating and condensing sections.

14. The heat pipe as claimed in claim 10, wherein the first capillary wick at the evaporating section has a thickness gradually decreased along a direction from the evaporation section toward the adiabatic section, and the first capillary wick at the condensing section has a thickness gradually increased along a direction from the adiabatic section toward the condensing section.

15. The heat pipe as claimed in claim 14, further comprising a third capillary wick extending from the first capillary wick at the evaporating section into the vapor passage.