Patent Application
20140166244
1. Technical Field
The disclosure generally relates to heat transfer apparatuses such as those used in electronic equipment, and more particularly to a flat heat pipe with stable and reliable 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 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 of the heat pipe in a typical application, 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. The generated vapor moves, carrying the heat with it, toward the condenser section. At the condenser section, the vapor condenses after the heat is dissipated. The condensate is then drawn back by the wick structure to the evaporator section where it is again available for evaporation. For the condensate to be drawn back rapidly, the wick structure located at the evaporator section must have a capillary force larger than that of the wick structure located at the condenser section. However, the capillary force of the wick structure is uniform. Thus, the evaporator section is prone to become dry.
What is needed, therefore, is a heat pipe to overcome the above described shortcomings.
Embodiments of the present flat heat pipe will now be described in detail below and with reference to the drawings.
Referring to
The tube 30 is made of metal or metal alloy with a high heat conductivity coefficient, such as copper, copper-alloy, or other suitable material. The tube 30 is elongated, and has an evaporator section 11, an adiabatic section 13, and a condenser section 15 defined in that order along a longitudinal direction thereof. A transverse section of the tube 30 is oval-shaped (or racetrack-shaped). A longitudinal section of the tube 30 is rectangular.
The wick structure 50 includes a first wick portion 51, a second wick portion 53, and a third wick portion 55. The first wick portion 51 is formed on an inner surface of the evaporator section 11. The second wick portion 53 extends longitudinally from the adiabatic section 13 to the condenser section 15, and is formed on inner surfaces of the adiabatic section 13 and the condenser section 15. The second wick portion 53 contacts and communicates with the first wick portion 51. The third wick portion 53 is enclosed by the first wick portion 51 and the second wick portion 53. The third wick portion 53 extends longitudinally from the evaporator section 11, and through the adiabatic section 13 to the condenser section 15, and communicates with the first wick portion 51 and the second wick portion 53. A capillary force of the second wick portion 53 is larger than that of the third wick portion 55 and less than that of the first wick portion 51. A pore density of the second wick portion 53 is larger than that of the first wick portion 51 and less than that of the third wick portion 55. In one embodiment, sizes of the pores of the first, second and third wick portions 51, 53, 55 are approximately the same. In such case, the pore density can be measured according to the number of pores per unit area/volume. In other embodiments, sizes of the pores of any one or more of the first, second and third wick portions 51, 53, 55 differ. In such cases, the pore density can be measured according to the total volume of pores per unit area/volume.
The first wick portion 51 is sintered metal powder, and has the shape of a flattened annulus. An outer surface of the first wick portion 51 is snugly attached to the inner surface of the evaporator section 11.
The second wick portion 53 is a groove-type wick portion, and a left end thereof connects and communicates with a right end of the first wick portion 51. A length of the second wick portion 53 is larger than that of the first wick portion 51. The second wick portion 53 includes a plurality of ridges (or elongated teeth) 531 and a plurality of grooves 533. Each groove 533 is defined between two corresponding adjacent ridges 531.
In the illustrated embodiment, all the ridges 531 are substantially the same size, and all the grooves 533 are substantially the same size. A transverse cross-section of each ridge 531 is trapezoidal, and a transverse cross-section of each groove 533 is trapezoidal. A size of the transverse cross-section of each ridge 531 is substantially the same as a size of the transverse cross-section of each groove 533. Each ridge 531 tapers from an end thereof far from a center of the tube 30 to an end thereof nearer the center of the tube 30. Each groove 533 tapers from an end thereof nearer the center of the tube 30 to an end thereof far from the center of the tube 30. A transverse width of each groove 533 at the end thereof nearer the center of the tube 30 is larger that of each ridge 531 at the end thereof nearer the center of the tube 30.
The third wick portion 55 is disposed at a middle of one side of the tube 30. A bottom surface of the third wick portion 55 at the evaporator section 11 is snugly attached to an inner surface of the first wick portion 51. A bottom surface of the third wick portion 55 at the adiabatic and condenser sections 13, 15 is snugly attached to an inner surface of the second wick portion 53. A top surface of the third wick portion 55 is spaced from the first wick portion 51 and the second wick portion 53. The third wick portion 55 is formed by weaving a plurality of metal wires such as copper wires and/or stainless steel wires. A length of the third wick portion 55 is equal to a sum of a length of the first wick portion 51 and a length of the second wick portion 53.
In operation, the working fluid at the evaporator section 11 absorbs heat generated by one or more electronic components, and thereby turns to vapor. The generated vapor moves, carrying the heat with it, toward the condenser section 15. At the condenser section 15, the vapor condenses after the heat is dissipated. Because the pore density of the third wick portion 55 is larger than that of the first wick portion 51, the condensate can rapidly permeate into the third wick portion 55. Because the capillary force of the first wick portion 51 is larger than that of the third wick portion 55, the condensate in the third wick portion 55 can be drawn back to the evaporator section 11 rapidly by the first wick portion 51. Therefore, the evaporator section 11 of the flat heat pipe 1 avoids becoming dry. Thus, the flat heat pipe 1 has stable and reliable performance.
Referring to
Referring to
In step S1, the tube 30 with an open end is provided.
In step S2, the inner surfaces of the adiabatic section 13 and condenser section 15 are etched to form the ridges 531 and the grooves 533, and thus the second wick portion 53 is formed.
In step S3, an amount of metal powder and a mandrel are provided. The mandrel is inserted in the evaporator section 11. A gap is defined between an outer surface of the mandrel and the inner surface of the evaporator section 11. The metal powder is filled into the gap. The tube 30 with the mandrel and the metal powder is heated at high temperature until the metal powder sinters to form the first wick portion 51. The mandrel is then drawn out of the tube 30. A particle diameter of each grain of metal powder is larger than the transverse width of each groove 533.
In step S4, a plurality of metal wires is provided and weaved to form the third wick portion 55. Then the third wick portion 55 is disposed at the middle of one side of the tube 30, with the bottom surface of the third wick portion 55 snugly attached to inner surfaces of the first wick portion 51 and the second wick portion 53, and the top surface of the third wick portion 55 spaced from the first wick portion 51 and the second wick portion 53.
In step S5, the working medium is injected into the tube 30, the tube 30 is evacuated, and the open end of the tube 30 is sealed. In this state, the flat heat pipe 1 is manufactured completely.
A method for manufacturing the flat heat pipe 1a is similar to that of the flat heat pipe 1, except that in step S2, the whole of the inner surface of the tube 30 is etched to form the second wick portion 53a. Then the first wick portion 51a is sintered on the inner surface of the second wick portion 53a located at the evaporator section 11, substantially according the third step described above in relation to the flat heat pipe 1.
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 disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201210547166.6 | Dec 2012 | CN | national |
