US20120060371A1

US20120060371A1 - Method for manufacturing two-phase flow heat sink

Info

Publication number: US20120060371A1
Application number: US12/904,277
Authority: US
Inventors: Shih-Ying Chang; Yen-Huan Lei; Wei-Shen Chen; Ji-Rong Fu
Original assignee: National Yunlin University of Science and Technology
Current assignee: National Yunlin University of Science and Technology
Priority date: 2010-09-14
Filing date: 2010-10-14
Publication date: 2012-03-15
Also published as: TW201211488A

Abstract

The present invention relates to a method for manufacturing a two-phase flow heat sink. The two-phase flow heat sink comprises an evaporation chamber and a capillary layer. The material of the capillary layer, which has at least a porous structure, is cooled and disposed on the inner side of the evaporation chamber from a melted state. The method first sprays the thermally melted material of the capillary layer on the substrate of the evaporation chamber for forming the capillary layer on the substrate. Because the capillary layer is sprayed on the substrate of the evaporation chamber, the capillary layer is distributed irregularly on the substrate and forming irregularly distributed holes. Thereby, the flowing space for fluids in the evaporation chamber is increased, and hence enhancing the heat transfer efficiency of the heat sink.

Description

FIELD OF THE INVENTION

The present invention relates generally to a method for manufacturing a heat transfer apparatus, and particularly to a method for manufacturing a two-phase flow heat sink.

BACKGROUND OF THE INVENTION

With the development of electronic industry, the operating speed and overall performance of electronic devices increase continuously. However, as the performance of electronic devices enhances, power consumption increases accordingly, which brings about heat dissipation problems. Heat pipes, such as fins with heat pipes and heat-sinking module, are extensively applied to heat sinking of electronic devices owing to their small size, capability of transferring a substantial amount of heat using latent heat, uniform temperature distribution, simple structure, light weight, nature of requiring no external force, long lifetime, low thermal resistivity, and capability of long-range heat transfer. The working principle of heat pipes is to use phase changes between gas and liquid phases while the fluids filled in the heat pipes absorb and release heat for transferring heat. In general, heat pipes can be classified as trench type, sintering type, fiber type, and net type. The capillary structure in a trench-type heat pipe is composed by a plurality of trenches. The capillary structure of a sintering-type heat pipe is formed by sintering metal powders. The capillary structure of a fiber-type heat pipe is texturized by fiber bundles. The capillary structure of a net-type heat pipe is formed by weaving a plurality of metal threads.
The advantages of heat pipes include simple structure and operations. Besides, they need no external force to do work on the working fluids in heat pipes for achieving heat transfer and circulation. They use latent heat in the working fluids to produce phase changes and hence transferring heat. Because the temperature difference is smaller when the working fluids absorb latent heat and evaporate into the gas phase and when they release latent heat and condense, heat pipes can have a large thermal conductivity in the operating condition of a smaller temperature difference, which means they can substantially conduct the heat produced by electronic devices. When the temperature difference is within the operating range, the thermal conducting capability of heat pipes can exceed tens of times of the thermal conducting capability of high thermal conducting materials such as copper. The gas-phase working fluids release vaporization latent heat while condensing at the cooling end of heat pipes. The vaporization latent heat passes through the capillary structure and pipe walls in heat pipes to radiators external to heat pipes. The reason why the working fluids evaporate to gas phase when heated is that the working fluids at the heating end form various radiuses of curvature in the capillary structure and thus making the capillary structure produce capillarity, which draws condensed liquids from the cooling end back to the heating end and hence completing a working cycle. Thereby, when the capillarity produced in the capillary structure is greater than the total pressure in the heat pipes, the heat pipes can work normally.
In addition, the thermal conducting efficiency of heat pipes is based on coordination between the capillary structure and working fluids. In particular, the capillary structure provides capillarity for liquid-phase working fluids, which can thereby flow to the cooling end of heat pipes. Then the gas-phase working fluids can release the latent heat of evaporation and condense to liquid phase. The liquid-phase working fluids are recycled to the heating end via capillarity to absorb the latent heat of evaporation conducted from the external of heat pipes to the internal. By this way, the liquid-phase working fluids are changed to gas-phase working fluids, which flow to the cooling end and condense to liquid phase again. Accordingly, the strength of capillarity determines the flow rate of liquid-phase working fluids, and hence further influences the heat-conducting efficiency, namely, heat-sinking efficiency, of heat pipes. This is what manufacturers of the field stress and propose to improve for the hope of enhancing capillarity of the capillary structure and thus increasing the flow rate of liquid-phase working fluids.
Most prior art adopts sintering metal powders on the inner sidewall of heat pipes to form porous capillary structures. The capillary structures formed by metal powders can provide better capillarity for liquid-phase working fluids by means of smaller holes and hence speeding up the flow rate of liquid-phase working fluids flowing back to the cooling end. Nonetheless, bubbles in the capillary structures formed by this way are uneasy to exhaust, which brings flow resistance to gas- and liquid-phase working fluids and hence reducing the flow rate of the working fluids cycling in heat pipes. As a result, the heat-conducting efficiency of heat pipes is reduced. The capillary structure of a trench-type heat pipe is formed by etching or machining pipe parts attached to the inner sidewall, and thereby having better heat-conducting efficiency. However, the holes in the capillary structures of trench-type heat pipes are greater than those in net-type or sintering-type heat pipes. In addition, the amount of the holes in the capillary structures of trench-type heat pipes is fewer than that in net-type or sintering-type heat pipes. Therefore, the capillarity of trench-type heat pipes is inferior to net- and sintering-type heat pipes.
Moreover, the capillary structures of net-type heat pipes have superior permeability, providing better capillarity and hence providing a faster flow rate for liquid-phase working fluids. However, the contact areas between the capillary structures and the inner sidewall of net-type heat pipes are smaller than those of sintering-type heat pipes. Therefore, the heat-conducting efficiency of the inner sidewall of the capillary structures of net-type heat pipes is inferior to that of sintering- and trench-type heat pipes. Thereby, although the heat pipe apparatuses according to the prior art solve the problem of heat conduction, they don't provide solid technique, such as enhancing the flow rate and convection of liquid-phase working fluids, for enhancing heat-conducting efficiency.
Accordingly, the present invention provides a method for manufacturing a two-phase flow heat sink, which uses a porous capillary structure for enhancing the conversion efficiency of working fluids from the liquid phase to the gas phase. In addition, the capillary structure according to the present invention has a greater moistened area, which facilitates producing convection when working fluids are changing from the liquid phase to the gas phase. Thereby, gas-phase working fluids and liquid-phase working fluids can convect in an evaporation chamber with ease.

SUMMARY

An objective of the present invention is to provide a method for manufacturing a two-phase flow heat sink, which sprays a capillary layer on a substrate of an evaporation chamber. The capillary layer is thermally bonded to the substrate of the evaporation chamber and hence increasing flow channels in the evaporation chamber.
Another objective of the present invention is to provide a method for manufacturing a two-phase flow heat sink, which sprays the capillary layer using a melting injection process for forming a porous structure rapidly.
The present invention provides a method for manufacturing a two-phase flow heat sink, which sprays a capillary layer on a substrate of an evaporation chamber using the melting injection process, and condensing a porous structure during the cooling process of the capillary layer. Then the two-phase flow heat sink is formed according to the substrate of the evaporation chamber and the capillary layer. Thereby, the two-phase flow heat sink according to the present invention comprises the evaporation chamber and the capillary layer. The capillary layer is disposed at the inner side of the evaporation chamber and has at least a porous structure. The two-phase flow heat sink according to the present invention adopts the melting injection process for increasing flow channels of fluids inside the two-phase flow heat sink. Consequently, the flow rate of the fluids is increased, and hence enhancing the heat transfer efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a cross-sectional view of a two-phase flow heat sink according to a preferred embodiment of the present invention;

FIG. 1B shows a cross-sectional view of a two-phase flow heat sink according to another preferred embodiment of the present invention;

FIG. 1C shows a cross-sectional view of a two-phase flow heat sink according to another preferred embodiment of the present invention;

FIG. 1D shows a cross-sectional view of a two-phase flow heat sink according to another preferred embodiment of the present invention;

FIG. 1E shows a cross-sectional view of a two-phase flow heat sink according to another preferred embodiment of the present invention;

FIG. 2 shows a flowchart according to a preferred embodiment of the present invention;

FIG. 3A shows a structural schematic diagram of a two-phase flow heat sink according to another preferred embodiment of the present invention;

FIG. 3B shows a partial enlarged view of FIG. 3A;

FIG. 4A shows a structural schematic diagram of a two-phase flow heat sink according to another preferred embodiment of the present invention;

FIG. 4B shows a partial enlarged view of FIG. 4A;

FIG. 5A shows a structural schematic diagram of a two-phase flow heat sink according to another preferred embodiment of the present invention; and

FIG. 5B shows a partial enlarged view of FIG. 5A.

DETAILED DESCRIPTION

In order to make the structure and characteristics as well as the effectiveness of the present invention to be further understood and recognized, the detailed description of the present invention is provided as follows along with embodiments and accompanying figures.
FIG. 1A shows a cross-sectional view of a two-phase flow heat sink according to a preferred embodiment of the present invention. As shown in the figure, the two-phase flow heat sink 10 according to the present invention comprises an evaporation chamber 12 and a first capillary layer 16. The first capillary layer 16 is disposed on the inner side of the evaporation chamber 12, and has at least a porous stricture (not shown in the figure). The material of the evaporation chamber 12 is a metal material, such as copper (Cu) or aluminum (Al), or a nonmetal material, such as silicon oxide or polymers, with superior heat conductivity. Besides, the two-phase flow heat sink 10 according to the present invention further comprises a working fluid 18 sealed in the evaporation chamber 12. According to the present embodiment, the working fluid 18 is in the gas phase. Because the working fluid 18 is changed from the liquid phase (not shown in the figure) to the gas-phase working fluid 18 by absorbing the latent heat of evaporation. and the working fluid 18 flows on an inner surface of the first capillary layer 16 and flows in the first capillary layer 16 after changing to the liquid phase by releasing heat, the liquid-phase working fluid filled in the evaporation chamber 12 is generally a liquid substance, such as water, ethanol, and acetone, with high heat of evaporation, good fluidity, and low boiling point.
As shown in FIG. 1B, the porous structure 164 according to the present invention is net structured. As shown in FIG. 1C, the porous structure 166 according to the present invention is fiber bundles. As shown in FIG. 1D, the porous structure 168 according to the present invention is trenches. As shown in FIG. 1E, the porous structure 170 according to the present invention is powders. Thereby, the porous structure according to the present invention can be nets, fiber bundles, trenches, or powders. The porous structure 164 is formed by weaving a plurality of thin threads. The material of the plurality of thin threads includes copper (Cu), aluminum (Al), or stainless steel. The porous structure 166 can be a structure formed by fiber bundles chosen of the group consisting of metal fiber bundles, carbon fiber bundles, glass fiber bundles, and ceramic fiber bundles. The porous structure 168 is formed by cutting or etching. The material of the porous structure 170 is chosen from the group consisting of copper (Cu), aluminum (Al), zinc (Zn), tin (Sn), nickel (Ni), gold (Au), silver (Ag), silicon oxide, and aluminum oxide. In addition to round tube, the shape of the two-phase flow heat sink 10 according to the present invention can be a plate for attaching to electronic devices, such as flat-panel displays, various processors, and circuit boards, with a flat appearance.
FIG. 2 shows a flowchart according to a preferred embodiment of the present invention. As shown in the figure, the method for manufacturing a two-phase flow heat sink 10 according to the present invention comprises steps of:

- Step S10: Providing a substrate;
- Step S20: Spraying a capillary layer on a surface of the substrate;
- Step S30: Thermally bonding the capillary layer and the substrate;
- Step S40: Forming a two-phase flow heat sink according to the substrate and the capillary layer;
- Step S50: Vacuuming the two-phase flow heat sink;
- Step S60: Filling a working fluid to the two-phase flow heat sink; and
- Step S70: Sealing the two-phase flow heat sink.

In the step S10, the substrate is provided for the evaporation chamber 12. Because the evaporation chamber 12 of the two-phase flow heat sink 10 needs sufficient thermal conductivity and low thermal resistance, a preferred choice of the substrate is oxygen-free copper. In the step S20, the melting injection process is used for spraying the material of the first capillary layer 16 onto the substrate of the evaporation chamber 12. Because the melting injection process adopts electricity or thermal power to melt the material of the first capillary layer 16 and injects the melted material to the processing surface, the melted material of the first capillary layer 16 will be distributed irregularly on the surface of the substrate. Next, in the step S30, cooled by external air, the material of the first capillary layer 16 condenses on the surface of the substrate. The melting injection process adopts techniques including plasma melting injection, arc melting injection, fire melting injection, and high-speed fire melting injection. In the step S40, The substrate of the evaporation chamber 12 is rolled to form the evaporation chamber 12, and thereby the evaporation chamber 12 and the first capillary layer 16 form the two-phase flow heat sink. The evaporation chamber 12 is located at the outer most side, while the capillary layer 16 is in the inner most. In the step S50, the two-phase flow heat sink 10 is vacuumed. In other words, the evaporation chamber 12 is in the vacuum condition. In the step S60, guide the working fluid of the two-phase heat sink into the evaporation chamber 12. Finally, in the step S70, seal the evaporation chamber 12.
The present invention adopts the melting injection process to form the capillary layer on the substrate of the evaporation chamber 12. Thereby, the number of flow channels of the liquid-phase working fluid in the evaporation chamber 12 is increased, and hence increasing capillarity as well as the flow rate of the liquid-phase working fluid in the evaporation chamber 12. Consequently, the speed of the liquid-phase working fluid changing to the gas-phase working fluid 18 by absorbing the latent heat of evaporation is increased, speeding up the flow rate of the gas-phase working fluid 18. Accordingly, the heat transfer efficiency of the two-phase flow heat sink 10 is enhanced as a result of faster cycles of phase changes between gas and liquid phases therein. In addition. the capillary layer 16 formed by the melting injection process has a greater moistened area, facilitating convection of the liquid- and gas-phase working fluids in the two-phase flow heat sink 10.
Moreover, the structure of the substrate of the evaporation chamber 12 according to the present invention can be a trench-shaped, needle-shaped, or grid-shaped structure, as shown in FIGS. 3A, 4A, and 5A. Because the capillary layer is disposed according to the shape of the substrate of the evaporation chamber 12, the capillary layer will be a trench-shaped, needle-shaped, or grid-shaped structure. As shown in FIG. 3A, a second capillary layer 20 is disposed on a trench-shaped substrate 124. In FIG. 3B, the second capillary layer 20 forms a trench-shaped structure following the shape of the trench-shaped substrate 124. Thereby, the two-phase flow heat sink 10 can use the trench-shaped structure to enhance the speed of changing the gas-phase working fluid 18 to the liquid phase. The difference between FIG. 3A and FIG. 4A is that the second capillary layer 20 according to FIG. 3A is disposed on the trench-shaped substrate 124 and a third capillary layer 22 according to FIG. 4A is disposed on a needle-shaped substrate 126. Besides, as shown in FIG. 4B, the third capillary structure 22 forms a needle-shape structure following to the shape of the needle-shaped substrate 126. Thereby, the present invention can use the third capillary layer 22 of the needle-shaped structure to increase the contact areas of the gas-phase working fluid 18. The difference between FIG. 4A and FIG. 5A is that the third capillary layer 22 according to FIG. 4A is disposed in the needle-shaped substrate 126, and a fourth capillary layer 24 according to FIG. 5A is disposed on a grid-shaped substrate 128 and thus forming a grid-shaped structure following the grid-shaped substrate 128. Thereby, the contact areas of the gas-phase working fluid 18 are increased, and hence increasing the conversion efficiency of the gas-phase working fluid 18 to the liquid phase. Furthermore, the capillary layers described above. including the first, second, third, and fourth capillary layers 16, 20, 22, 24, can have multiple holes for enhancing circulation of two-phase flow, which means increasing the conversion efficiency of the liquid-phase working fluid to the gas-phase working fluid 18.
To sum up, the present invention provides a method for manufacturing a two-phase flow heat sink, which uses the melting injection process to spray the material of capillary layer to the substrate of the evaporation chamber. The capillary layer is arranged irregularly on the substrate of the evaporation chamber owing to the influence of spraying and thus increasing multiple holes therein as the flow channels of the liquid-phase working fluid. Thereby, the flow rate the liquid-phase working fluid is increased. The present invention can increase the number of multiple holes in the heat sink, and hence enhancing the circulation effect of two-phase flow.
Accordingly, the present invention conforms to the legal requirements owing to its novelty, nonobviousness, and utility. However, the foregoing description is only embodiments of the present invention, not used to limit the scope and range of the present invention. Those equivalent changes or modifications made according to the shape, structure, feature, or spirit described in the claims of the present invention are included in the appended claims of the present invention.

Claims

1. A method for manufacturing a two-phase flow heat sink, comprising steps of:

providing a substrate;

spraying a capillary layer on a surface of said substrate using a melting injection process, and said capillary layer having at least a porous structure; and

forming a two-phase flow heat sink according to said substrate and said capillary layer.

2. The method for manufacturing a two-phase flow heat sink of claim 1, and further comprising steps of:

vacuuming said two-phase flow heat sink;

filling a working fluid to said two-phase flow heat sink; and

sealing said two-phase flow heat sink.

3. The method for manufacturing a two-phase flow heat sink of claim 2, and further comprising a step of bonding said capillary layer and said substrate after said step of spraying said capillary layer on said surface of said substrate using said melting injection process.

4. The method for manufacturing a two-phase flow heat sink of claim 1, wherein said melting injection process includes plasma melting injection, arc melting injection, fire melting injection, and high-speed fire melting injection.

5. The method for manufacturing a two-phase flow heat sink of claim 1, wherein said porous structure is a net structure.

6. The method for manufacturing a two-phase flow heat sink of claim 1, wherein said porous structure is a fiber-bundle structure.

7. The method for manufacturing a two-phase flow heat sink of claim 1, wherein said porous structure includes a plurality of trenches.

8. The method for manufacturing a two-phase flow heat sink of claim 1, wherein said porous structure includes a plurality of powders.

9. The method for manufacturing a two-phase flow heat sink of claim 1, wherein said capillary layer is a trench-shaped, needle-shaped, or grid-shaped structure.