US20060196641A1

US20060196641A1 - Screen mesh wick and method for producing the same

Info

Publication number: US20060196641A1
Application number: US11/164,457
Authority: US
Inventors: Chu-Wan Hong; Ching-Tai Cheng; Jung-Yuan Wu; Chang-Ting Lo
Original assignee: Individual
Current assignee: Foxconn Technology Co Ltd
Priority date: 2005-01-28
Filing date: 2005-11-23
Publication date: 2006-09-07
Also published as: TW200626863A; TWI275765B

Abstract

A screen mesh wick (14) and a method of making the same are disclosed. The wick is made separately and is adaptive for inserting into a heat pipe as a wick structure. The wick includes a plurality of elongated wires (141, 142) woven together and a plurality of protruding portions (145) formed on the wires. The protruding portions may be small metal powders attached to outer surfaces of the wires. The method includes the steps of weaving a plurality of wires to form a mesh (14′) firstly and then forming a plurality of protruding portions on the mesh, for example, by spreading the metal powders onto the mesh while the mesh is subject to heating. With these protruding portions formed on the wires, the effective pore size defined between the wires is reduced and therefore the wick is capable of providing a larger capillary pressure.

Description

FIELD OF THE INVENTION

The present invention relates generally to an apparatus for transfer or dissipation of heat from heat-generating components such as electronic components, and more particularly to a screen mesh wick applicable in heat pipes and a method for producing such wick.

DESCRIPTION OF RELATED ART

Heat pipes have excellent heat transfer performance due to their low thermal resistance, and therefore are an effective means for transfer or dissipation of heat from heat sources. Currently, heat pipes are widely used for removing heat from heat-generating components such as central processing units (CPUs) of computers. A heat pipe is usually a vacuum casing containing therein a working fluid, which is employed to carry, under phase transitions between liquid state and vapor state, thermal energy from one section of the heat pipe (typically referring to as the “evaporating section”) to another section thereof (typically referring to as the “condensing section”). Preferably, a wick structure is provided inside the heat pipe, lining an inner wall of the casing, for drawing the working fluid back to the evaporating section after it is condensed at the condensing section. Specifically, as the evaporating section of the heat pipe is maintained in thermal contact with a heat-generating component, the working fluid contained at the evaporating section absorbs heat generated by the heat-generating component and then turns into vapor. Due to the difference of vapor pressure between the two sections of the heat pipe, the generated vapor moves towards and carries the heat simultaneously to, the condensing section where the vapor is condensed into liquid after releasing the heat into ambient environment by, for example, fins thermally contacting the condensing section. Due to the difference of capillary pressure developed by the wick structure between the two sections, the condensed liquid is then brought back by the wick structure to the evaporating section where it is again available for evaporation.
The wick structure currently available for heat pipes includes fine grooves integrally formed at the inner wall of the casing, screen mesh or bundles of fiber inserted into the casing and typically held against the inner wall thereof, or sintered powder combined to the inner wall of the casing by sintering process. Among these wicks, the screen mesh wick is preferred to the other wicks due to its economic advantage in manufacturing. The manufacture of a screen mesh wick is comparatively simple and generally involves weaving together a plurality of pliable wires or threads such as metal wires or synthetic fibers. In this sense, the screen mesh wick is formed separately and then inserted into the casing of a heat pipe.
In a heat pipe, the primary function of a wick is to draw condensed liquid back to the evaporating section of the heat pipe under the capillary pressure developed by the wick. Therefore, whether the wick could provide a large capillary pressure is a major consideration that is used to evaluate the performance of the wick. A heat pipe with a wick that has too large a pore size generally cannot provide a large capillary force and therefore 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. Since it is well recognized that the capillary pressure of a wick increases due to a decrease in pore size of the wick, it is thus preferred to have the screen mesh wick woven in a greater density so as to reduce the pore size formed between the wires of the wick and accordingly obtain a relatively large capillary pressure for the wick. However, under current weaving technology, it is difficult to reduce the pore size of the screen mesh wick further due to the restriction of the weaving technology.
Therefore, it is desirable to provide a method for manufacturing a screen mesh wick which can further reduce the pore size of the wick. What is also desirable is to provide a screen mesh wick made from this method and a heat pipe incorporating such wick.

SUMMARY OF INVENTION

The present invention relates in one aspect, to a screen mesh wick for a heat pipe. The screen mesh wick is made separately and is adaptive for inserting into a heat pipe as a wick structure. The screen mesh wick comprises a plurality of elongated wires woven together and a plurality of protruding portions formed on the wires. In one preferred embodiment, the protruding portions are small metal powders attached to outer surfaces of the wires. With these protruding portions formed on the wires, the effective pore size defined between the wires is reduced and as a result, the wick is capable of providing a larger capillary pressure for drawing liquid condensed at a condensing section of the heat pipe towards an evaporating section of the heat pipe.
The present invention relates in another aspect, to a method for manufacturing a screen mesh wick for a heat pipe, wherein the method comprises steps of forming a mesh firstly by weaving technology and then forming a plurality of protruding portions on the mesh. By using this method, the capillary force that the wick could develop is increased as a result of a reduce in pore size of the mesh due to the presence of the protruding portions, even though the weaving density of the mesh is not increased.
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 DRAWINGS

FIG. 1 is a cross-sectional view of a heat pipe having a screen mesh wick in accordance with one embodiment of the present invention;
FIG. 2 is an isometric view of the screen mesh wick of FIG. 1, being in an expanded status;
FIG. 3 is a top plan view of the screen mesh wick of FIG. 2;
FIG. 4 is an enlarged view of the circled portion IV of FIG. 3;
FIG. 5 is a flow chart showing a preferred method for manufacturing the screen mesh wick of FIG. 2; and
FIGS. 6-7 are isometric views showing the steps of the preferred method of FIG. 5 in manufacturing the screen mesh wick of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 illustrates a heat pipe 10 in accordance with a preferred embodiment of the present invention. The heat pipe 10 includes a casing 12 and a screen mesh wick 14 arranged against an inner wall of the casing 12. The casing 12 is made of high thermally conductive material such as copper or aluminum. Although the casing 12 as illustrated is in a round shape, it should be recognized that other shapes, such as rectangle or the like, may also be suitable. The screen mesh wick 14 is a porous structure and is saturated with a working fluid (not shown), which acts as a heat carrier when undergoing a phase transition from liquid state to vaporous state. The working fluid is usually selected from liquids—such as water or alcohol—that have a low boiling point and are compatible with the wick 14. In order to maintain the wick 14 to tightly engage the inner wall of the casing 12, retaining means such as a helical spring (not shown) may be used to hold the wick 14 against the casing 12.
The screen mesh wick 14 is typically made separately and then is rolled and inserted into the heat pipe 10 as a wick structure. Referring to FIGS. 2-4, the screen mesh wick 14 is formed by weaving together a plurality of flexible wires or threads such as metal wires or synthetic fibers. As illustrated in this embodiment, the wick 14 is constructed by weaving a first wire 141 and a second wire 142 together, wherein the first wire 141 has plate-type configuration while the second wire 142 has a rod configuration. The wires 141, 142 have sufficient flexibility so that they can be woven together easily. Each of the wires 141, 142 has a preferred diameter or width of 45 micrometers (μm), and may be constructed from a material with excellent thermal conductivity such as copper, aluminum, or stainless steel. The wires 141, 142 may be constructed from a single material or different materials, and also may have identical configurations or different configurations.
As shown in FIG. 4, a pore 143 is illustrated as defined between a pair of adjacent first wires 141 and a pair of adjacent second wires 142. In order to reduce the size of the pores 143 and ultimately gain a relatively large capillary pressure for the screen mesh wick 14, a plurality of micron-sized protruding portions 145 is combined to outer surfaces of the wires 141, 142. Some the protruding portions 145 protrude into the pores 143 to reduce the size thereof. These protruding portions 145 may be small particles such as metal powders that are attached to the wires 141, 142 after the wires 141, 142 are heated to a temperature near one-third to two-third of their melting point. These particles may be such materials as copper, aluminum, stainless steel or combination thereof, and may have an average particle size that is about one-fifth to one-third of the diameter or width of the wires 141, 142. Preferably, the melting points of these particles are not higher than those of the wires 141, 142. More preferably, the protrusions 145 and the wires 141, 142 are made of the same metal.
With reference to FIG. 5, a preferred method 100 for constructing such wick 14 is shown. The preferred method 100 generally includes two steps, i.e., the first step 101 and the second step 102. The first step 101 is to form a mesh 14′ by weaving together a plurality of the first and second wires 141, 142, as shown in FIG. 6. The second step 102 is to form a plurality of the protruding portions 145 on the outer surfaces of the mesh 14′ formed by the foregoing first step 101, to thereby obtain the screen mesh wick 14 as illustrated in FIG. 2. As with the second step 102, if these protruding portions 145 to be formed on the mesh 14′ are small metal powders, a nozzle 20 is typically used to spread these metal particles onto the mesh 14′ while the mesh 14′ is heated, for example, to a temperature substantially equal to one-third to two-third of the melting point of the mesh 14′, thus combining these particles to the mesh 14′ after these particles and the mesh 14′ are cooled. For combining these particles to the mesh 14′, some other methods may also be suitable. For example, the metal particles to be formed as the protruding portions 145 of the wick 14 may be spread on a flat surface evenly to form a “bed of powder” in advance, and then the mesh 14′, after it is heated, is applied to the bed of powder, optimally with a downward pressing force, to thereby adhere the particles to the mesh 14′ and form the screen mesh wick 14.
In the above-illustrated embodiment, the wick 14 is formed firstly by weaving technology and is then processed to further reduce the effective pore size thereof by means of forming a plurality of the protruding portions 145 thereon. The wick 14 is thus capable of providing a larger capillary force than the mesh without the protruding portions thereon, thereby effectively solving the dry-out problem as experienced by the prior art.
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 screen mesh wick being made separately and adaptive for inserting into a heat pipe as a wick structure, the screen mesh wick comprising a plurality of elongated wires woven together and a plurality of protruding portions formed on the wires.

2. The wick of claim 1, wherein the protruding portions are small powders attached to outer surfaces of the wires.

3. The method of claim 2, wherein the wires are flexible and are constructed from a single material or different materials.

4. The wick of claim 3, wherein the protruding portions are formed from materials including copper, aluminum, stainless steel and combinations thereof.

5. The wick of claim 4, wherein the melting points of the wires are higher than those of the small powders.

6. The wick of claim 3, wherein the wires are formed from materials including copper, aluminum, stainless steel and combinations thereof.

7. The wick of claim 2, wherein the small powders have an average particles size that is substantially one-fifth to one-third of a diameter or a width of the wires.

8. The wick of claim 1, wherein the wires includes a first wire having a plate-type configuration and a second wire having a rod configuration.

9. A method for manufacturing a screen mesh wick for a heat pipe comprising the steps of: forming a mesh by weaving technology; and forming a plurality of protruding portions on the mesh.

10. The method of claim 9, wherein the mesh is formed by weaving a plurality of flexible wires that are constructed from a single material or different materials.

11. The method of claim 10, wherein the protruding portions are formed by spreading small powders onto the mesh while the mesh is heated.

12. The method of claim 11, wherein the melting points of the wires are higher than those of the small powders.

13. The method of claim 10, wherein the protruding portions formed on the mesh are small powders, and the small powders are combined to the mesh by applying the mesh to the small powders after the mesh is heated.

14. The method of claim 13, wherein the melting points of the wires are higher than those of the small powders.

15. A screen mesh wick being inserted into a heat pipe for transmitting heat from one end to another end thereof, comprising: a mesh made of wires woven together, the mesh defining a plurality of pores between the wires; and a plurality of protrusions having a size smaller than that of the wires, secured to the wires and protruding into the pores prior to insertion into the heat pipe.

16. The screen mesh wick of claim 15, wherein the protrusions are made of powders.

17. The screen mesh wick of claim 15, wherein the wires have a rod-shaped configuration and a flat-plate configuration.

18. The screen mesh wick of claim 16, wherein the powders are made of a metal of one of copper, aluminum and stainless steel.

19. The screen mesh wick of claim 16, wherein the powders have a diameter which is about one-fifth to one-third of a diameter of the wires.

20. The screen mesh wick of claim 15, wherein the protrusions are secured to outer surfaces of the wires.