Patent Application
20150204617
The present invention claims the benefit of Japanese Patent Applications No. 2014-007012 filed on Jan. 17, 2014 with the Japanese Patent Office, the disclosures of which are incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to the art of a heat pipe having a wick structure constructed of sintered metal powder arranged in a sealed container.
2. Discussion of the Related Art
Conventional heat pipes are adapted to absorb heat from a heat generating object such as an electronic device in the form of latent heat of working fluid. In the heat pipe, the working fluid is evaporated by an external heat and condensed while radiating heat. Cooling performance of the heat pipe of this kind may be enhanced by increasing mass flow of the working fluid.
In recent years, electronic devices has been downsized and highly improved hence generate higher heat. Therefore, the heat pipes are required to be downsized while enhancing heat transport capacity. For example, given that a flat heat pipe and a cylindrical heat pipe have same widths, the flat heat pipe is thinner than the cylindrical heat pipe. However, an inner space of the flat heat pipe serving as a flow path is smaller than that of the cylindrical heat pipe.
For instance, US2012/0118537 A describes a flattened heat pipe comprising a wick structure attached to an inner flat wall of a container, and vapor flowing passages formed in curves areas of both sides of the container. Working fluid is encapsulated and circulates in the container.
US2011/0303392 A also describes a flat heat pipe comprising a wick formed by bundling a plurality of thin metal wires extending in a longitudinal direction of a container while being contacted to a predetermined portion of an inner face of the container.
In turn, JP-A-2013-2640 describes a wick structure comprising a fiber wick layer formed of a plurality of metal wires laid on an inner surface of a sealed container, and a powder wick layer laid on the fiber wick layer.
Further, JP-A-11-294980 describes a cylindrical heat pipe having a wick structure for increasing a mass flow of the working fluid flowing through a flow path from a condensing portion toward an evaporating portion.
Specifically, according to the teachings of JP-A-11-294980, the wick structure is comprised of a metal net and a sintered metal powder. An inner wall of a container is entirely covered with the metal powder, and the metal net is situated on the metal net or interposed between the container and the metal powder.
However, according to the heat pipe taught by US2012/0118537 A, a pressure loss of the wick structure may be high, and hence it may be difficult to transport the working fluid over a long distance. Although a traveling distance of the working fluid can be extended by the wick taught by US2011/0303392 A, a flow rate of the working fluid per unit of area has to be increased. According to the wick structure taught by JP-A-2013-2640, thermal resistance between the container and the wick may be too large and hence the metal powder may fall from the wick into grooves. According to the wick structure taught by JP-A-11-294980, the sintered metal powder may not be fixed to the metal net firmly thereby increasing thermal resistance.
The present invention has been conceived noting the foregoing technical problems, and it is therefore an object of the present invention is to enhance the heat transfer performance of a heat pipe by efficiently returning working fluid flowing through a wick structure arranged in a sealed container.
The present invention is applied to a heat pipe comprising a container sealed at its both ends, a working fluid encapsulated in the container, and a wick structure covering an inner face of the container. In order to achieve the above-mentioned objectives, according to the present invention, the wick structure is comprised of a porous wick constructed of a sintered metal powder, and a fiber wick extending in a length direction of the container. An outer face of the porous wick exposed to an air passage serves as an evaporating face. Specifically, the fiber wick is formed by bundling a plurality of metal fibers in a manner such that a capillary pressure is reduced to be weaker than that of the porous wick, and that a pressure loss is reduced to be smaller than that of the porous wick. the fiber wick thus structured is entirely buried in the porous wick while being contacted to the inner face of the container.
In addition, the inner surface of the container is entirely covered with the porous wick holding the fiber wick therein.
According to another aspect of the present invention, a flat container having flat portions is used as the container. In this case, an inner flat face of the flat portion contacted to a heat-generating object is covered with the porous wick holding the fiber wick.
Specifically, the flat container is flattened to have a pair of flat portions opposed to each other. According to still another aspect of the present invention, the inner flat face of one of the flat portions is covered with a first porous wick, and the inner flat face of the other flat portion is covered with a second porous wick. In this case, a first fiber wick is buried in the first porous wick while being contacted to the inner flat face of said one of the flat portion, and a second fiber wick is buried in the second porous wick while being contacted to the inner flat face of the other flat portion.
For example, not only a round column-shaped fiber wick but also a rectangular-column shaped fiber wick may be arranged in the porous wick.
Thus, in the heat pipe according to the present invention, the fiber wick is buried in the porous wick. A pressure drop of the working fluid flowing through the fiber wick is smaller than that of the working fluid flowing through the porous wick. Therefore, the working fluid in the liquid phase is allowed to return to the evaporating portion over the long distance so that the heat transfer capacity of the heat pipe can be enhanced. In addition, the working fluid can be pumped efficiently into the fiber wick by the capillary action of the porous wick so that dry-out of the fiber wick can be prevented.
As described, the fiber wick is entirely buried in the porous wick while being contacted to the inner face of the container. That is, the fiber wick is enclosed by the porous wick exerting strong capillary pressure. Therefore, the working fluid can be spread homogeneously all over the wick structure.
According the present invention, the inner surface of the container may be covered entirely with the porous wick holding the fiber wick. In this case, the working fluid can be spread homogeneously all over the wick structure. In addition, a thermal resistance between the inner face of the container and an outer face of the porous wick can be reduced.
In case of using the flat container, only the inner flat face of the flat portion contacted to the heat-generating object is covered with the porous wick holding the fiber wick. In this case, an air passage can be ensured sufficiently in the container so that the working fluid is allowed to be returned efficiently to the evaporating portion. Consequently, the heat transfer capacity of the heat pipe can be enhanced.
In case of using the flat container, alternatively, the inner flat face of one of the flat portions may be covered with the first porous wick holding the first fiber wick, and the inner flat face of the other flat portion may be covered with the second porous wick holding the second fiber wick. In this case, the working fluid can be returned more efficiently to the evaporating portion, and the heat transfer capacity of the heat pipe can be further enhanced.
In case of using the rectangular-column shaped fiber wick, a cross-sectional area of the fiber wick can be ensured sufficiently in the flat container to allow the working fluid to flow smoothly therethrough.
Features, aspects, and advantages of exemplary embodiments of the present invention will become better understood with reference to the following description and accompanying drawings, which should not limit the invention in any way.
Preferred examples of the present invention will now be explained in more detail with reference to the accompanying drawings. The heat pipe of the present invention is comprised of working fluid encapsulated in a sealed container, a porous wick structure constructed of a sintered metal powder, and a water channel arranged in the porous wick. The water channel is constructed of bundled metal fibers so that fluid flow resistance of the water channel is smaller than that of the porous wick. The working fluid is evaporated when it is heated, and condensed when heat is removed therefrom.
Referring now to
The first example relates to a cylindrical heat pipe having a container 2 whose cross-sectional shape is round. The container 2 is a cylindrical member made of metal such as copper, and although not especially illustrated in
A curvature of an inner face 2a of the container 2 in a circumferential direction is entirely constant, and a thickness of the inner face 2a is also constant. In addition, a surface of the inner face 2a is entirely smooth. Thus, a smooth pipe is employed as the container 2.
The inner face 2a of the container 2 is covered entirely with a wick structure 10 so that the working fluid condensed at a condensing portion is pumped by an capillary action of the wick structure 10 to an evaporating portion. In the heat pipe 1, specifically, the working fluid is evaporated at the evaporating portion by an external heat, and the vaporized working fluid migrates though an internal space serving as an air passage to the condensing portion. The heat of the vaporized working fluid is radiated at the condensing portion so that the working fluid is condensed again and penetrates into the wick structure 10. Then, the working fluid thus condensed at the condensing portion is returned to the evaporating portion by the capillary pumping of the wick structure 10.
As illustrated in
The wick structure 10 may also be constructed of other known material. For example, the fiber wick 12 may also be constructed of other metal fibers or carbon fibers. In the description, reference numeral 12a represents an outer circumference of the bundled fibers forming the fiber wick 12.
The fiber wick 12 is buried in the porous wick 11 while extending in a length direction of the container 2, and both porous wick 11 and fiber wick 12 are adapted to perform capillary pumping. That is, the fiber wick 12 serves as a water channel in the porous wick 11, and the fluid flow resistance of the fiber wick 12 is smaller than that of the porous wick 12.
As depicted in
According to the first example of the heat pipe 1, there are two fiber wicks 12 are arranged parallel to each other in the porous wick 11. Specifically, a first fiber wick 12A penetrates through the lowest portion of the porous wick 11 in
Specifically, the porous wick 11 is formed by sintering copper powder, and according the examples, average diameter of the copper powder is approximately 125 μm. In the porous wick 11, clearances among the copper powders serve as flow passages, however, structures of the flow passages are rather complicated. As described, the inner face 2a of the container 2 is entirely covered with the porous wick 11. Therefore, the flow passages are created not only among the copper powders forming the porous wick 11 but also between an outer circumference of the porous wick 11 and the inner face 2a of the container 2. The working fluid condensed at the condensing portion is returned to the evaporating portion by the capillary pumping of the porous wick 11 through the flow passages thus formed.
As also described, each fiber wick 12A and 12B is individually buried in the porous wick 11 while being contacted to the inner face 2a of the container 2. That is, the fiber wick can be kept to be bundled by the porous wick 11 and fixed to the inner face 2a without using a bundling wire or the like. In addition, the flow passages are also created between the copper fibers of the fiber wick 12 and the copper powders of the porous wick 11.
According to the examples, specifically, the fiber wick 12 is formed by bundling the copper fibers whose diameters are within the range including 50 to 100 μm, and each clearance among the bundled fibers serves as linear flow passages extending in the length direction of the heat pipe 1. Such linear flow passages are also formed on both sides of a contact portion between the fiber wick 12 and the inner face 2a of the container 2. The working fluid condensed at the condensing portion is returned to the evaporating portion by the capillary pumping of those linear flow passages.
The capillary pumping of the flow passage is enhanced by reducing radius of capillary. According to the preferred examples, the clearance among the copper powders, that is, the radius of capillary of the porous wick 11 is smaller than the clearance among the copper fibers of the fiber wick 12. Namely, the capillary pumping of the porous wick 11 is stronger than that of the fiber wick 12.
However, in the wick structure 10 thus structured, a pressure loss is caused depending on configurations of the flow passages. According to the preferred example, specifically, the flow passages in the porous wick 11 are complicated as a maze but the flow passages in the fiber wick 12 extend straight. That is, the pressure loss of the fiber wick 12 is smaller than that of the porous wick 11.
Thus, in the wick structure 10, the fiber wick 12 in which the pressure loss is smaller is buried in the porous wick 11 whose capillary pumping is stronger. This means that the porous wick 11 has the fiber wicks 12 functioning as the water channels where the working fluid is allowed to flow smoothly therethrough.
In the wick structure 10, therefore, the porous wick 11 mainly exerts capillary pumping and the fiber wick 12 mainly serves as the water channel so that the working fluid can be returned to the evaporating portion over the long distance.
Thus, according to the first example of the present invention, the wick structure 10 has independent sections such as the porous wick 11 to exert strong capillary pumping and the fiber wick 12 to allow the working fluid to flow smoothly therethrough. Therefore, a distance between the condensing portion and the evaporating portion can be extended so that the heat transfer capacity of the heat pipe 1 can be enhanced.
As described, since the inner face 2a of the container 2 is covered substantially entirely with the wick structure 10, the working fluid is allowed to penetrate into the wick structure 10 entirely and homogeneously. In addition, thermal resistance between the inner face 2a of the container 2 and the wick structure 10 can be reduced.
As also described, the fiber wick 12 is entirely buried in the porous wick 11. That is, an evaporating face of the wick structure 10 facing to the air passage is formed only by the copper powders of the porous wick 11 so that the capillary pressure is also exerted by the evaporating face. Therefore, the working fluid will not be dried out at the evaporating portion by also pumping the working fluid by the capillary action of the evaporating face to the evaporating portion. That is, the pressure loss of the porous wick 11 can be covered by the capillary pumping of the evaporating face thereof. In addition, since only the porous wick 11 is exposed to the air passage, scattering of the condensed working fluid caused by the countercurrent of the vaporized working fluid can be reduced. Therefore, heart transfer capacity of the heat pipe can be enhanced in comparison with that of the case in which the fiber wick is exposed to the air passage. Besides, given that the fiber wick is exposed to the air passage, the pressure loss of the porous wick 11 cannot be covered by the capillary pumping of the evaporating face and the working fluid in the evaporating portion would be dried out. In addition, the working fluid flowing through the fiber wick may be scattered by the countercurrent of the vapor.
Further, heat transfer efficiency of the wick structure 10 can be enhanced under the top heat mode where the evaporating portion is situated above the condensing portion. In addition, the heat transfer capacity of the wick structure 10 will not be impaired even if the posture of the heat pipe 1 is changed. According to the first example of the present invention, the heat transfer capacity of the heat pipe 1 can be enhanced approximately 150 to 200 present in comparison with those of the conventional heat pipes.
The structure of the heat pipe 1 according to the first example may be modified according to need within the spirit of the present invention. For example, a thickness of the porous wick may be altered arbitrarily unless the fiber wicks are not exposed to the air passage formed in an inner circumferential side of the porous wick. In other words, the thickness of the porous wick may be altered arbitrarily within the range thicker than the diameter of the fiber wick but possible to maintain the air passage.
Likewise, particle diameter of the copper powder forming the porous wick may also be altered to change a size of the clearances created among the particles. In addition, the diameters of the first fiber wick and the second fiber wick are not necessarily to be identical to each other but may be differentiated arbitrarily, and diameters of the fibers forming the fiber wick may also be altered to change a size of the clearance created among the fibers.
Next, the second example of the present invention will be explained with reference to
As shown in
The inner face 6a of the flat container 6 is entirely covered with a wick structure 20 comprised of the porous wick 11 and fiber wicks 22 constructed of the copper fibers. According to the second example, each fiber wick 22 is formed into a rectangular-column shape and also buried entirely in the porous wick 11. Specifically, each fiber wick 22 is individually formed into a rectangular-column shape whose width is longer than a thickness while extending in the length direction of the heat pipe 5. The fiber wick 22 also functions as the water channel where the fluid flow resistance is smaller than that of the porous wick 11.
As described, the inner face of the flat container 6, specifically, the lower flat face 61a, the upper flat face 62a, and the curved faces 63a are entirely covered with the porous wick 11.
The fiber wick 22 includes a first fiber wick 22A attached to a width center of the lower flat face 61a of the flat container 6, and a second fiber wick 22B attached to a width center of the upper flat face 62a of the flat container 6. Specifically, a long face 22a of the first fiber wick 22A is contacted to the lower flat face 61a, and a long face 22a of the second fiber wick 22B is contacted to the upper flat face 62a. A thickness of each fiber wick 22A and 22B falls within a thickness of the porous wick 11 to be buried entirely therein.
A width of each fiber wick 22A and 22B individually falls within a predetermined range on both sides of the width center of the flat container 6, and sintered at a predetermined temperature to be fixed to the lower flat face 61a and to the upper flat face 62a.
Thus, the thickness of the porous wick 11 is thicker than thicknesses of the fiber wicks 22A and 22B to enclose those fiber wicks entirely. Therefore, side faces 22b of the fiber wicks 22A and 22B are also contacted to the porous wick 11.
Here, it is to be noted that the diameter of the fibers used to form the fiber wick 22 may also be altered arbitrarily to change the clearances among the fibers. In addition, the thicknesses and widths of the fiber wicks 22A and 22B are also not necessarily to be identical to each other but may be differentiated arbitrarily.
Thus, according to the second example, each fiber wick 22A and 22B is individually formed into a rectangular-column shape in which the width thereof is wider than the thickness thereof. Therefore, even if the thickness of the flat container 5 is restricted, a cross-sectional area of the fiber wick 22 functioning as the water channel can be ensured sufficiently to allow the working fluid to flow smoothly therethrough. In addition, since the inner face of the heat pipe 5 is entirely covered with the porous wick holding the fiber wicks therein, the heat transfer capacity of the heat pipe 5 can be enhanced.
In turn, here will be explained the third example of the present invention with reference to
As shown in
The wick structure 30 is arranged only on the lower flat portion 61 of the flat container 6 at the width center. Specifically, a width of the wick structure 30 is narrower than that of the lower flat face 61a, and a height of the wick structure 30 is shorter than the clearance between the upper and lower flat faces 61a and 62a. Thus, according to the third example, the upper flat face 62a is not covered with the wick structure. In addition, the porous wick 31 is heaped to be higher than a middle level of the clearance between the upper and lower flat faces 61a and 62a.
Specifically, the porous wick 31 is heaped on the lower flat face 61a in a manner to have a hemioval cross-sectional shape while extending in the length direction of the heat pipe 5. The fiber wick 12 is also buried entirely in the porous wick 31 thus structured while being contacted with the lower flat face 61a.
That is, the porous wick 31 is comprised of a flat face 31a contacted to the lower flat face 61a of the flat container 6, and a curved face 31b bulging toward the upper flat face 62a. The curved face 31b is exposed to the air passage of the flat container 6 to serve as the evaporating face. A peak 30a of the curved face 31b is situated higher than the fiber wick 12 buried in the porous wick 31 without being contacted to the upper flat face 62a. Thus, only the porous wick 31 is exposed to the vaporized working fluid flowing through the air passage.
The wick structure 30 thus structured is sintered in the flat container 6, and the flat face 31a of the porous wick 31 is fixed to the lower flat surface 61a of the flat container 6. Consequently, the fiber wick 12 is held and bundled in the porous wick 31 while being contacted to the lower flat surface 61a with or without being fixed thereto.
Alternatively, the rectangular-column shaped fiber wick 22 of the second example shown in
Thus, according to the third example, the porous wick 31 is heaped to have a hemioval cross-sectional shape without being contacted to the upper flat surface 62a of the flat container 6 so that the inner space functioning as the air passage can be sufficiently ensured especially on both sides of the porous wick 30. Therefore, fluid puddle will not be caused even at the peak 30a where the clearance between the porous wick 31 and the upper flat surface 62a is narrowest so that the strongest capillary pumping is exerted. That is, since the clearance between the porous wick 31 and the upper flat surface 62a is getting wider on both sides of the porous wick 31, the capillary pressure acting therebetween is weakened on both sides of the porous wick 31 so that such fluid puddle can be prevented. Consequently, the heat transfer capacity of the heat pipe can be enhanced.
In addition, in case of using the rectangular-column shaped fiber wick 22, the cross-sectional area of the fiber wick serving as the water channel can be ensured sufficiently even if the thickness of the wick structure is thinned to be fitted into the flat container. Therefore, the working fluid is allowed to flow through the fiber wick smoothly so that the heat transfer capacity of the heat pipe can be enhanced.
Next, the fourth example of the present invention will be explained with reference to
As illustrated in
As described, the second wick structure 40B is formed on the width center of the upper flat face 62a of the flat container 6. Specifically, a width of the second wick structure 40B is narrower than that of the upper flat face 62a, and a height of the second wick structure 40B is also lower than a middle level of the clearance between the upper and lower flat faces 61a and 62a. Thus, according to the fourth example, the wick structure 40 is arranged on both upper and lower flat faces 61a and 62a of the flat container 6. As the third example, the fiber wick 12 is buried in each porous wick 41 constructed of the sintered copper powder.
The porous wick 41 is also heaped on each flat face 61a and 62a in a manner to have a hemioval cross-sectional shape while extending in the length direction of the heat pipe 5. The fiber wick 12 is also buried entirely in each porous wick 41 thus structured while being contacted with the flat face 61a or 62a.
The porous wick 41 is also comprised of a flat face 41a contacted to the flat face 61a or 62a of the flat container 6, and a curved face 41b bulging from the flat face. Each curved face 41b is also exposed to the air passage of the flat container 6 to serve as the evaporating face, and a peak 40a of the first wick structure 40A and a peak 40a of the second wick structure 40B are isolated from each other. Thus, according to the fourth example, only the porous wicks 41 are exposed to the vaporized working fluid flowing through the air passage.
Each wick structure 30 thus structured is sintered in the flat container 6, and the flat face 41a of the porous wick 41 is fixed to individually to the upper and lower flat surfaces 61a and 62a of the flat container 6. Consequently, the fiber wick 12 is held and bundled in the porous wick 41 while being contacted to the flat surface 61a or 62a with or without being fixed thereto. That is, the fiber wick 12 can be bundled without using a bundling wire or the like.
Alternatively, the rectangular-column shaped fiber wick 22 of the second example shown in
According to the heat pipe of the fourth example, therefore, the heat of the cooling object can be transported efficiently even if the cooling object is attached to the upper plate of the heat pipe. In addition, a contact area between the evaporating face contacted to the liquid flow and the air passage for the vapor flow is smaller than that of the second example shown in
In addition, in case of using the rectangular-column shaped fiber wick 22, the cross-sectional area of the fiber wick serving as the water channel can be ensured sufficiently even if the thickness of the wick structure is thinned to be fitted into the flat container. Therefore, the working fluid is allowed to flow through the fiber wick smoothly so that the heat transfer capacity of the heat pipe can be enhanced.
It is understood that the invention is not limited by the exact construction of the foregoing first to fourth examples, but that various modifications may be made without departing from the scope of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-007012 | Jan 2014 | JP | national |
