|Publication number||US20070006993 A1|
|Application number||US 11/306,422|
|Publication date||Jan 11, 2007|
|Filing date||Dec 28, 2005|
|Priority date||Jul 8, 2005|
|Also published as||CN1892165A, CN100437005C|
|Publication number||11306422, 306422, US 2007/0006993 A1, US 2007/006993 A1, US 20070006993 A1, US 20070006993A1, US 2007006993 A1, US 2007006993A1, US-A1-20070006993, US-A1-2007006993, US2007/0006993A1, US2007/006993A1, US20070006993 A1, US20070006993A1, US2007006993 A1, US2007006993A1|
|Inventors||Jin-Gong Meng, Ching-Bai Hwang|
|Original Assignee||Jin-Gong Meng, Ching-Bai Hwang|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (16), Classifications (10), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates generally to an apparatus for transfer or dissipation of heat from heat-generating components, and more particularly to a flat type heat pipe applicable in electronic products such as personal computers for removing heat from electronic components installed therein.
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. 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 held against the inner wall thereof, or sintered powders combined to the inner wall of the casing by sintering process.
In operation, 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 and carries the heat simultaneously towards the condensing section where the vapor is condensed into condensate 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 condensate is then brought back by the wick structure to the evaporating section where it is again available for evaporation.
In order to draw the condensate back timely, the wick structure provided in the heat pipe is expected to provide a high capillary force and meanwhile generate a low flow resistance for the condensate. Also, the wick structure is expected to provide a high permeability at the condensing section of the heat pipe in order for the condensate resulting from the vapor in that section to enter into the wick structure more easily. However, the wick structure provided in the conventional heat pipe generally has a uniform pore size distribution over its entire length. This uniform-type wick structure cannot satisfy these requirements. If the condensate is not timely brought back from the condensing section, the heat pipe will suffer a dry-out problem at the evaporating section.
Therefore, it is desirable to provide a heat pipe with a wick structure which can draw the condensate back from its condensing section to its evaporating section effectively and timely.
The present invention relates to a flat type heat pipe. The heat pipe includes a metal casing and a wick structure arranged inside the metal casing. The metal casing has an evaporating section and a condensing section. The wick structure extends from the evaporating section towards the condensing section of the metal casing and has a first section in conformity with the condensing section of the metal casing and a second section in conformity with the evaporating section of the metal casing. The first section has a pore size larger than that of the second section of the wick structure.
In the heat pipe, the first section of the wick structure generates a relatively low resistance for the condensate as it flows in the condensing section, and the second section of the wick structure is still capable of maintaining a relatively high capillary force for drawing the condensate back from the condensing section towards the evaporating section. Meanwhile, the condensate in the condensing section is capable of entering into the wick structure easily due to a relatively high permeability of the first section of the wick structure. As a result, the condensate is drawn back to the evaporating section rapidly and timely, thus preventing the potential dry-out problem occurring at the evaporating section.
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:
As shown in
In operation, the evaporating section 123 of the heat pipe 10 is placed in thermal contact with a heat source (not shown), for example, a central processing unit (CPU) of a computer, that needs to be cooled. The working fluid contained in the evaporating section 123 of the heat pipe 10 evaporates into vapor upon receiving the heat generated by the heat source. Then, the generated vapor moves, via the other region of the chamber 14 without being occupied by the wick structure 16, towards the condensing section 124 of the heat pipe 10. After the vapor releases the heat carried thereby and turns into condensate in the condensing section 124, the condensate is brought back by the wick structure 16 to the evaporating section 123 of the heat pipe 10 for being available again for evaporation.
In the present heat pipe 10, the capillary forces and the flow resistances generated by different sections of the wick structure 16 are different. The general rule is that the larger a pore size a wick structure has, the smaller a capillary force and the lower a flow resistance it provides. A first section of the wick structure 16 in conformity with the condensing section 124 of the heat pipe 10 has a pore size larger than that of a second section of the wick structure 16 in conformity with the evaporating section 123 of the heat pipe 10. Thus, the first section of the wick structure 16 generates a relatively low resistance for the condensate as it flows in the condensing section 124, and the second section of the wick structure 16 is still capable of maintaining a relatively high capillary force for drawing the condensate back from the condensing section 124 towards the evaporating section 123. Meanwhile, the condensate resulting from the vapor in the condensing section 124 is capable of entering into the wick structure 16 easily due to a relatively high permeability of the first section of the wick structure 16. As a result, the condensate is drawn back to the evaporating section 123 rapidly and timely, thus preventing a potential dry-out problem occurring at the evaporating section 123.
The metal foam used to form the wick structure 16 may be made of such materials as stainless steel, copper, copper alloy, aluminum alloy and silver. The wick structure 16 may be formed independently of the metal casing 12 and then inserted into the metal casing 12. Typically, the metal foam of the wick structure 16 is fabricated by expanding and solidifying a pool of liquid metal saturated with an inert gas under pressure. The porosity of the foam after solidification may be in a wide range, subject to the levels of pressure applied during the fabrication process. Electroforming is another typical method for fabricating the metal foam, which generally involves steps of providing one kind of porous material such as polyurethane foam, then electrodepositing a layer of metal over the surface of the polyurethane foam and finally heating the resulting product at a high temperature to get rid of the polyurethane foam to thereby obtain the porous metal foam. Still another fabrication method for the metal foam, called die-casting process, is also widely used, which generally includes steps of providing one kind of porous material such as polyurethane foam, filling ceramic slurry into the pores of the porous polyurethane foam and then solidifying the ceramic slurry therein, then heating the resulting product at a high temperature to get rid of the polyurethane foam to obtain a matrix of porous ceramic, thereafter filling metal slurry into the pores of the ceramic matrix and finally getting rid of the ceramic material after solidification of the metal slurry to thereby obtain the porous metal foam. However, there are still some other methods suitable for fabrication of the metal foam. Fox example, the metal foam can be made by steps of filling a kind of bubble-generating material such as metallic hydride into metal slurry to generate a large number of bubbles distributing randomly throughout the metal slurry and solidifying the metal slurry to thereby obtain the metal foam with a plurality of pores therein.
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.
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|U.S. Classification||165/104.26, 257/E23.088|
|Cooperative Classification||H01L23/427, F28D15/046, F28D15/0233, H01L2924/0002|
|European Classification||F28D15/02E, F28D15/04B, H01L23/427|
|Dec 28, 2005||AS||Assignment|
Owner name: FOXCONN TECHNOLOGY CO.,LTD., TAIWAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MENG, JIN-GONG;HWANG, CHING-BAI;REEL/FRAME:016943/0300
Effective date: 20051215