FLAT HEAT PIPE AND METHOD FOR MANUFACTURING FLAT HEAT PIPE
An exemplary flat heat pipe includes a hollow, flattened casing and a first wick structure and a second wick structure received in the casing. The casing includes a top plate and a bottom plate opposite to the top plate. The first wick structure is folded by a steel sheet with a plurality of pores, and the second wick structure is made of sintered metal powder. The first and second wick structures are disposed at inner sides of the bottom and top plates of the casing, respectively. The first and second wick structures contact each other. The casing defines two vapor channels at opposite lateral sides of the combined first and second wick structures, respectively.
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This application is related to two co-pending applications respectively entitled “FLAT HEAT PIPE AND METHOD FOR MANUFACTURING THE SAME” (attorney docket number US33318) and “FLAT TYPE HEAT PIPE AND METHOD FOR MANUFACTURING THE SAME” (attorney docket number US34501), both assigned to the assignee of this application. The application entitled “FLAT HEAT PIPE AND METHOD FOR MANUFACTURING THE SAME” was filed on 2010 Jun. 28. The application entitled “FLAT TYPE HEAT PIPE AND METHOD FOR MANUFACTURING THE SAME” is filed on the same date as this application. The two related applications are incorporated herein by reference.
BACKGROUND1. Technical Field
The disclosure generally relates to heat transfer apparatuses, and particularly to a flat heat pipe with high heat transfer 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 heat conductive material, and a working fluid contained in the sealed tube. 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, 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. Due to the difference in vapor pressure between the two sections of the heat pipe, the generated vapor moves, carrying the heat with it, toward the condenser section. At the condenser section, the vapor condenses after transferring the heat to, for example, fins thermally contacting the condenser section. The fins then release the heat into the ambient environment. Due to the difference in capillary pressure which develops in the wick structure between the two sections, the condensate is then drawn back by the wick structure to the evaporator section where it is again available for evaporation.
Wick structures currently available for heat pipes can be fine grooves defined in the inner surface of the tube, screen mesh or fiber inserted into the tube and held against the inner surface of the tube, or sintered powder bonded to the inner surface of the tube by a sintering process. The grooved, screen mesh and fiber wick structures provide a high capillary permeability and a low flow resistance for the working fluid, but have a small capillary force to drive condensed working fluid from the condenser section toward the evaporator section of the heat pipe. In addition, a maximum heat transfer rate of these wick structures drops significantly after the heat pipe is flattened. The sintered wick structure provides a high capillary force to drive the condensed working fluid, and the maximum heat transfer rate does not drop significantly after the heat pipe is flattened. However, the sintered wick structure provides only a low capillary permeability, and has a high flow resistance for the working fluid.
What is needed, therefore, is a flat heat pipe with high capillary permeability and low flow resistance and a method for manufacturing such a flat heat pipe.
Referring to
The casing 11 is made of metal or metal alloy with a high heat conductivity coefficient, such as copper, copper-alloy, or other suitable material. The casing 11 has a width much larger than its height. In particular, the casing 11 has a flattened transverse cross section. To meet the height requirements of common electronic products, the height of the casing 11 is preferably less than or equal to 2 millimeters (mm). The casing 11 is hollow, and longitudinally defines an inner space 110 therein. The casing 11 includes a top plate 111, a bottom plate 112 opposite to the top plate 111, and two side plates 113, 114 extending between the top and bottom plates 111, 112. The top and bottom plates 111, 112 are flat and parallel to each other. The side plates 113, 114 are arcuate and respectively disposed at opposite lateral sides of the casing 11.
The first wick structure 12 is elongated, and extends longitudinally through the evaporator section 101 and the condenser section 102. The first wick structure 12 is flattened during manufacture of the flat heat pipe 10 to form a generally block-shaped structure. In addition, the first wick structure 12 is a multilayer-type structure. The multilayer-type structure is obtained from an elongated steel sheet with a plurality of pores (not labeled). The elongated steel sheet is folded on itself again and again (i.e. concertianed), and then layered on the bottom plate 112. Alternatively, the first wick structure 12 can be a monolayer-type steel sheet with a plurality of pores. The first wick structure 12 provides a large capillary permeability for the working medium and has a low flow resistance to the working medium, thereby promoting the flow of the working medium in the flat heat pipe 10.
The first wick structure 12 is disposed at a middle of one inner side of the casing 11, with a bottom surface of the first wick structure 12 snugly attached to an inner surface of the bottom plate 112 of the casing 11, and a top surface of the first wick structure 12 snugly in contact with the second wick structure 13.
The second wick structure 13 is made of sintered metal powder such as copper powder. The second wick structure 13 provides a large capillary force to drive condensed working medium at the condenser section 102 to flow toward the evaporator section 101 of the flat heat pipe 10. In particular, a maximum heat transfer rate (Qmax) of the second wick structure 13 does not significantly drop after the flat heat pipe 10 is flattened. The second wick structure 13 is disposed at a middle of another inner side of the casing 11 opposite to the first wick structure 12. In other words, the second wick structure 13 directly faces and is aligned with the first wick structure 11. The second wick structure 13 tapers from a top surface thereof farthest away from the first wick structure 12 toward a bottom side thereof in contact with the first wick structure 12. In this embodiment, the second wick structure 13 has a generally triangular prism shape. The top surface of the second wick structure 13 is attached to an inner surface of the top plate 111 of the casing 11 by sintering, and the bottom lateral side of the second wick structure 13 forms a rounded ridge attached to a middle of the top surface of the first wick structure 12.
The first and second wick structures 12, 13 are stacked together in a height direction of the casing 11, and divide the inner space 110 of the casing 11 into two longitudinal vapor channels 118. The vapor channels 118 are disposed at opposite lateral sides of the combined first and second wick structures 12, 13, respectively, and provide passages through which the vapor flows from the evaporator section 101 to the condenser section 102.
The working medium is injected into the casing 11 and saturates the first and second wick structures 12, 13. The working medium usually selected is a liquid such as water, methanol, or alcohol, which has a relatively low boiling point. The casing 11 of the flat heat pipe 10 is evacuated and hermetically sealed after injection of the working medium. The working medium can evaporate when it absorbs heat at the evaporator section 101 of the flat heat pipe 10.
In operation, the evaporator section 101 of the flat heat pipe 10 is placed in thermal contact with a heat source (not shown) that needs to be cooled. The heat source can, for example, be a central processing unit (CPU) of a computer. The working medium contained in the evaporator section 101 of the flat heat pipe 10 vaporizes when it reaches a certain temperature after absorbing heat generated by the heat source. The generated vapor moves from the evaporator section 101 via the vapor channels 118 to the condenser section 102. After the vapor releases its heat and condenses in the condenser section 102, the condensed working medium is returned via the first and second wick structures 12, 13 to the evaporator section 101 of the flat heat pipe 10, where the working medium is again available to absorb heat.
In the flat heat pipe 10, the first wick structure 12 is formed by folding the elongated steel sheet, and is disposed at one inner side (i.e., the inner surface of the bottom plate 112) of the casing 11. The second wick structure 13 is made of sintered metal powder, and is disposed at another opposite inner side (i.e., the inner surface of the top plate 111) of the casing 11. The first and second wick structures 12, 13 contact each other. Therefore, during operation of the flat heat pipe 10, the working medium can be freely exchanged between the first and second wick structures 12, 13. Thus, the flat heat pipe 10 has not only a high capillary permeability and a low flow resistance due to the first wick structure 12 being formed by folding the steel sheet, but also a large capillary force due to the second wick structure 13 being made of sintered powder. Thereby, a heat transfer performance of the flat heat pipe 10 is improved.
Table 1 below shows an average of maximum heat transfer rates (Qmax) and an average of heat resistances (Rth) of thirty-five conventional sintered heat pipes and thirty-five flat heat pipes 10 in accordance with the present disclosure, all of which have a height of 2 mm. Table 2 below shows an average of Qmax and an average of Rth of thirty-five conventional sintered heat pipes and thirty-five flat heat pipes 10 in accordance with the present disclosure, all of which have a height of 1.5 mm. Qmax represents the maximum heat transfer rate of each heat pipe at an operational temperature of 50° C. Rth is obtained by dividing the difference between an average temperature of the evaporator section of the heat pipe and an average temperature of the condenser section of the heat pipe by Qmax. A diameter of the transverse cross section (i.e. a width) and a longitudinal length of each of the conventional sintered heat pipes are 6 mm and 200 mm, respectively, which are equal to the diameter of the transverse cross section (i.e. the width) and the longitudinal length of each of the flat heat pipes 10, respectively. Tables 1 and 2 show that the average of Rth of the flat heat pipes 10 is significantly less than that of the conventional sintered heat pipes, and that the average of Qmax of the flat heat pipes 10 is significantly more than that of the conventional sintered heat pipes.
Referring also to
The first wick structure preform 15 is obtained from an elongated steel sheet with a plurality of pores. The elongated steel sheet is folded on itself repeatedly, and then inserted into the tube 16. A transverse cross section of the first wick structure preform 15 is arch-shaped once the first wick structure preform 15 is received in the mandrel 14. In particular, an outer curvature of the first wick structure preform 15 substantially matches an outer curvature of the mandrel 14, and an inner curvature of the first wick structure preform 15 substantially matches an inner curvature of the mandrel 14 in the notch 141.
The first wick structure preform 15 is horizontally inserted into the notch 141 of the mandrel 14. Then the mandrel 14 with the first wick structure preform 15 is inserted into the tube 16. An amount of metal powder is filled into the cutout 142 of the mandrel 14 in the tube 16. The tube 16 is vibrated until the metal powder is evenly distributed along the length of the tube 16 in accordance with its particle size. In particular, smaller particles of the metal powder migrate to a lower end of the cutout 142 in the tube 16, and larger particles of the metal powder migrate to an upper end of the cutout 142 in the tube 16. The tube 16 with the mandrel 14, the metal powder and the first wick structure preform 15 is heated at high temperature until the metal powder sinters to form a second wick structure preform 17. In this process, a bottom of the first wick structure preform 15 becomes joined to the tube 16. A transverse cross section of the second wick structure preform 17 is in the shape of a segment on a chord. In particular, the transverse cross section includes a straight line 171 and an arcuate line 172 connecting the straight line 171. The arcuate line 172 represents the part of the second wick structure preform 17 which is attached to the inner surface of the tube 16.
Referring to
Advantages of the method include the following. The cutout 142 of the mandrel 14 has a planar inmost extremity. Thus, the cutout 142 can be easily formed by directly milling the mandrel 14 using a milling machine (not shown). This reduces the cost of manufacturing the flat heat pipe 10.
Referring to
During manufacture of the flat heat pipe 20, the first wick structure preform 15 obliquely faces the second wick structure preform 17 (rather than directly facing the second wick structure preform 17 as is illustrated in
Referring to
Referring to
Referring to
During manufacture of the flat heat pipe 40, the first wick structure preform 15 obliquely faces the second wick structure preform 17a (rather than directly facing the second wick structure preform 17a as is illustrated in
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 invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Claims
1. A flat heat pipe comprising:
- a hollow, flattened casing, comprising a top plate and a bottom plate opposite to the top plate; and
- a first wick structure and a second wick structure received in the casing, the first wick structure being made of a folded steel sheet with a plurality of pores, the second wick structure being made of sintered metal powder, the first and second wick structures disposed at inner surfaces of the bottom and top plates of the casing, respectively, the first and second wick structures contacting each other, the casing defining two vapor channels at opposite lateral sides of the combined first and second wick structures, respectively.
2. The flat heat pipe of claim 1, wherein a bottom of the first wick structure is attached to the bottom plate, a top of the second wick structure is attached to the top plate, and a top of the first wick structure not in contact with the bottom plate is attached to a bottom of the second wick structure not in contact with the top plate.
3. The flat heat pipe of claim 1, wherein the first wick structure is aligned with the second wick structure, and the second wick structure is attached to a middle of the first wick structure.
4. The flat heat pipe of claim 3, wherein the second wick structure tapers from the top thereof farthest away from the first wick structure toward the bottom thereof in contact with the first wick structure, and the bottom of the second wick structure in contact with the first wick structure forms a rounded ridge attached to the middle of the first wick structure.
5. The flat heat pipe of claim 3, wherein the bottom of the second wick structure is attached to the top of the first wick structure, and the second wick structure is generally cuboid.
6. The flat heat pipe of claim 1, wherein a center of the first wick structure and a center of the second wick structure are offset from each other as would be viewed in transverse cross section of the casing.
7. The flat heat pipe of claim 6, wherein the second wick structure tapers from a top thereof farthest away from the first wick structure toward a bottom thereof attached to the first wick structure.
8. The flat heat pipe of claim 6, wherein one side of the second wick structure is attached to the first wick structure, and the second wick structure is generally cuboid.
9. The flat heat pipe of claim 1, wherein the second wick structure is substantially triangular prism-shaped or cuboid, and a bottom of the second wick structure not in contact with the casing is attached to the first wick structure.
10. The flat heat pipe of claim 1, wherein the first wick structure is a flattened structure.
11. A method for manufacturing a flat heat pipe, the method comprising:
- providing a cylindrical mandrel, a hollow cylindrical tube and a steel sheet with a plurality of pores, the mandrel defining an elongated notch and an elongated cutout in a circumferential surface thereof, the notch and the cutout located opposite each other across a center axis of the mandrel, and an inner diameter of the tube being substantially equal to an outer diameter of the mandrel;
- folding the steel sheet to form a first wick structure;
- inserting the mandrel and the first wick structure into the tube, wherein the first wick structure is received in the notch of the mandrel;
- filling an amount of metal powder into the cutout of the mandrel in the tube, and sintering the metal powder to form a second wick structure;
- drawing the mandrel out of the tube, wherein the first and second wick structures remain attached to portions of an inner surface of the tube, and face each other;
- injecting a working medium into the tube, and evacuating and sealing the tube; and
- flattening the tube until the first wick structure becomes flattened and the second wick structure contacts the first wick structure, thus forming a flat heat pipe, wherein the flat heat pipe defines two vapor channels at opposite lateral sides of the combined first and second wick structures, respectively.
12. The method for manufacturing a flat heat pipe of claim 11, wherein the cutout defines a generally arcuate cross section, and after the mandrel is drawn out of the tube, the second wick structure has a generally arcuate cross section.
13. The method for manufacturing a flat heat pipe of claim 12, wherein after the tube is flattened, the second wick structure is generally cuboid.
14. The method for manufacturing a flat heat pipe of claim 11, wherein an inmost extremity of the cutout is planar, and after the mandrel is drawn out of the tube, a transverse cross section of the second wick structure comprises a straight line and an arcuate line connecting the straight line, with the arcuate line corresponding to a portion of the second wick structure attached to the inner surface of the tube.
15. The method for manufacturing a flat heat pipe of claim 14, wherein after the tube is flattened, the second wick structure generally tapers from one side thereof farthest away from the first wick structure toward another side thereof in contact with the first wick structure.
16. The method for manufacturing a flat heat pipe of claim 11, wherein the notch defines an arcuate cross section, and the first wick structure defines an arcuate cross section before the tube is flattened.
17. The method for manufacturing a flat heat pipe of claim 11, wherein the first wick structure is pulled by the tube into a flattened shape during the flattening of the tube.
18. The method for manufacturing a flat heat pipe of claim 11, wherein the first wick structure directly faces or obliquely faces the second wick structure before the tube is flattened.
19. A flat heat pipe comprising:
- a hollow, flattened casing, comprising a top plate and a bottom plate opposite to the top plate; and
- a first wick structure and a second wick structure attached to inner sides of the bottom and top plates of the casing, respectively, the first wick structure comprising a folded steel sheet with a plurality of pores, the second wick structure comprising sintered metal powder, the first and second wick structures snugly contacting each other, the casing defining two separate vapor channels at opposite lateral sides of the combined first and second wick structures, respectively;
- wherein the flat heat pipe has an evaporator section and a condenser section respectively located at opposite ends thereof along a longitudinal direction thereof, and the first wick structure extends longitudinally through the evaporator section and the condenser section.
20. The flat heat pipe of claim 19, wherein the first wick structure obliquely faces or is aligned with the second wick structure.
Type: Application
Filed: Dec 21, 2010
Publication Date: May 10, 2012
Applicants: FOXCONN TECHNOLOGY CO., LTD. (Tucheng City), FURUI PRECISE COMPONENT (KUNSHAN) CO., LTD. (KunShan City)
Inventors: SHENG-LIANG DAI (KunShan City), SHENG-GUO ZHOU (KunShan City), JIN-PENG LIU (KunShan City), YUE LIU (KunShan City), SHENG-LIN WU (Tu-Cheng), YU-LIANG LO (Tu-Cheng)
Application Number: 12/973,924
International Classification: F28D 15/04 (20060101); B21D 53/02 (20060101);