Patent Application
20110174464
1. Technical Field
The disclosure generally relates to a heat transfer apparatus, and particularly to a flat heat pipe with high heat transfer efficiency.
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 thermally conductive material with a working fluid contained therein. 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.
In ordinary use, the heat pipe is flattened to increase a contact area with the electronic component and enable smaller electronic products to incorporate the heat pipe. However, this may result in damage to the wick structure of the heat pipe. When the wick structure of the heat pipe is damaged, the flow resistance of the wick structure is liable to be considerably increased. In such case, the condensate may not be retrieved from the condenser section in a timely manner, and the heat pipe eventually dries out at the evaporator section.
What is needed, therefore, is a flat heat pipe and a method for manufacturing the heat pipe which can overcome the described limitations.
Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the various views, and all the views are schematic.
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 is elongated, and has an evaporator section 111 and an opposite condenser section 113 along a longitudinal direction thereof. The casing 11 has a width larger than its height. In particular, the casing 11 has a flattened transverse cross section. To meet the weight requirements of common electronic products, the height of the casing 11 is preferably less than 2 millimeters (mm) The casing 11 is hollow, and includes a top plate 114, a bottom plate 115 opposite to the top plate 114, and two side plates 116, 117 interconnecting the top and bottom plates 114, 115. The top and bottom plates 114, 115 are flat and parallel to each other. The side plates 116, 117 are arcuate and respectively disposed at opposite lateral sides of the casing 11.
The first wick structures 12, 13 are elongated hollow tubes, and extend longitudinally from the evaporator section 111 to the condenser section 113. An inner space 140 is longitudinally defined in each of the first wick structures 12, 13. The first wick structures 12, 13 are monolayer-type structures, formed by weaving a plurality of metal wires such as copper or stainless steel wires. The first wick structures 12, 13 thus have a plurality of pores therethrough. Alternatively, the first wick structures 12, 13 can be multilayer-type structures layered along a radial direction thereof by weaving a plurality of metal wires. Each first wick structure 12, 13 has a flattened transverse cross section, similar in principle to the flattened transverse cross section of the casing 11. In particular, each first wick structure 12, 13 includes a top wall 121, a bottom wall 122 opposite to the top wall 121, and two sidewalls 123, 124 interconnecting the top and bottom walls 121, 122. The top and bottom walls 121, 122 are flat and parallel to each other. The top and bottom walls 121, 122 contact the top and bottom plates 114, 115 of the casing 11, respectively. The sidewalls 123, 124 are arcuate and respectively disposed at opposite lateral sides of each first wick structure 12, 13.
The first wick structures 12, 13 are spaced from each other, and also from the side plates 116, 117 of the casing 11. The sidewall 123 of the first wick structure 12 and the side plate 116 adjacent to the first wick structure 12 cooperatively define a first vapor channel 141 therebetween. The sidewall 123 of the first wick structure 13 and the side plate 117 adjacent to the first wick structure 13 cooperatively define a second vapor channel 142 therebetween. The two first wick structures 12, 13 cooperatively define a third vapor channel 143 therebetween. The third vapor channel 143 is located at a center of the casing 11. The first, second and third vapor channels 141, 142, 143, provide passages through which the vapor flows from the evaporator section 111 to the condenser section 113.
The second wick structure 14 is disposed along a center axis of the evaporator section 111, and contacts the top and bottom plates 114, 115 of the casing 11. The second wick structure 14 occupies a portion of the third vapor channel 143 at the evaporator section 111 of the casing 11. The second wick structure 14 is a solid wick structure made of sintered copper powder. The second wick structure 14 is joined to the sidewalls 124 of the first wick structures 12, 13 via sintering. The first and second wick structures 12, 13, 14 cooperatively form a composite wick structure 17 in the casing 11. The first and second channels 141, 142 are defined between opposite lateral sides of the composite wick structure 17 and the side plates 116, 117 of the casing 11, respectively.
The working medium is saturated in the first and second wick structures 12, 13, 14. The working medium is usually selected from a liquid such as water, methanol, or alcohol, which has a low boiling point. The casing 11 of the heat pipe 10 is evacuated and hermetically sealed after the working medium is injected into the casing 11 and saturated in the first and second wick structures 12, 13, 14. Thus, the working medium can easily evaporate when it receives heat at the evaporator section 111 of the heat pipe 10.
In operation, the evaporator section 111 of the 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 111 of the heat pipe 10 is vaporized when receiving heat generated by the heat source. The generated vapor moves from the evaporator section 111 via the vapor channels 141, 142 to the condenser section 113. After the vapor releases its heat and condenses in the condenser section 113, the condensate is returned by the first and second wick structures 12, 13, 14 to the evaporator section 111 of the heat pipe 10, where the condensate is again available for evaporation.
In the present heat pipe 10, the second wick structure 14 is solid, and contacts the top and bottom plates 114, 115 of the casing 11. Therefore, the second wick structure 14 provides support for the casing 11 during flattening of the heat pipe 10. This prevents blockage of the vapor channels 141, 142, 143, promoting vapor flow through the heat pipe 10. In addition, the first wick structures 12, 13 are not easily damaged during the flattening. Furthermore, the first and second wick structures 12, 13, 14 cooperatively form the composite wick structure 17 at the evaporator section 111 of the heat pipe 10. This increases capillary force, and reduces flow resistance and heat resistance. As a result, the condensate is returned to the evaporator section 111 of the heat pipe 10 rapidly, thus preventing potential drying out at the evaporator section 111. Moreover, the second wick structure 14 is not disposed in the condenser section 113 of the heat pipe 10. This enlarges the vapor channels in the condenser section 113, and further promotes the flow of the working medium in the heat pipe 10.
In alternative embodiments, the quantity of first and second wick structures in the heat pipe 10 can vary. The following embodiments include examples of such variations.
Referring to
Referring to
Referring also to
The first wick structures 16, 17 are horizontally inserted into the slots 152, 153 of the mandrel 15, respectively. The mandrel 15 with the first wick structures 12, 13 is inserted into the tube 18. An amount of metal powder is filled into the cutout 154 of the mandrel 15 in the tube 18. The tube 18 with the mandrel 15, the metal powder and the first wick structures 16, 17 is heated at high temperature until the metal powder sinters to form a second wick structure 19. The second wick structure 19 is thereby attached to an inner surface of the tube 18, and joins the first wick structures 16, 17. The mandrel 18 is then drawn out of the tube 18. Subsequent processes such as injecting a working medium into the tube 18, and evacuating and sealing the tube 18, can be performed using conventional methods. Thereby, a straight circular heat pipe 40 is attained. Finally, the circular heat pipe 40 is flattened until the second wick structure 19 contacts the flattened tube 18 at opposite sides thereof, thus forming the flat heat pipe 10 as illustrated in
Advantages of the method include the following. The cutout 154 is defined in a portion of the circumferential surface of the front end of the mandrel 15. As a result, the second wick structure 19 is attached to a portion of the inner surface of the tube 18 between the two first wick structures 16, 17. Thus, the second wick structure 19 is not easily damaged during the flattening operation.
It should be understood that the cutout 154 and the slots 152, 153 of the mandrel 15 are adapted for forming the first and second wick structures 12, 13, 14. The configurations and arrangements of the cutout 154 and the slots 152, 153 can be changed according to the particular wick structures needed to for another kind of desired flat heat pipe.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201010300331.9 | Jan 2010 | CN | national |
This application is related to two co-pending applications respectively entitled “FLAT HEAT PIPE WITH VAPOR CHANNEL” (attorney docket number US32037) and “FLAT HEAT PIPE” (attorney docket number US32038), assigned to the same assignee of this application and filed on the same date as this application. The two related applications are incorporated herein by reference.
