VAPOR CHAMBER WITH IMPROVED WICKING STRUCTURE
The present invention is a vapor chamber including a housing that forms a recess within; at least one wicking structure manufactured from a bundle of wires having capillary voids therebetween that is disposed within the recess; and an amount of working fluid disposed within the recess and in fluid contact with the wicking structure such that fluid may move within the capillary voids in the wicking structures through capillary action.
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This application claims the benefit of priority of United States Provisional Patent Application No. 61/862,625, filed on Aug. 6, 2013.
FIELD OF THE INVENTIONThe present invention relates to vapor chambers for use in spreading heat to be dissipated and, in particular, to a vapor chamber having an improved wicking structure.
BACKGROUNDSemiconductors and other electrical components generate heat as a by-product of their operation. The generated heat can reduce or impede performance of the component if not effectively dissipated. As technology has advanced, the amount of heat to be dissipated from many of these components has risen dramatically, while the acceptable cost of heat dissipating devices has remained constant or dropped. Therefore there is a need for inexpensive products for dissipating heat that are capable of dissipating ever greater amounts of heat from an ever widening array of components and devices.
A heat pipe is a simple vapor chamber type heat-exchange device that can quickly transfer heat from one point to another. Heat pipes provide high thermal conductivity with small temperature differences; have a fast thermal response; are small in size and lightweight; come in a large variety of shapes; require no electrical power supply; are maintenance free; and reduce the overall system size and costs. The three basic components of a common heat pipe are a housing, a working fluid, and a wick or capillary structure. An efficient heat pipe system can be affected by the heat pipe length, the type of working fluid, the return wick type, and the number of bends in the heat pipe.
The housing isolates the working fluid from the outside environment. By necessity, the housing must be leak-proof, maintain the pressure differential across its walls, and enable transfer of heat to take place from and into the working fluid. Selection of the housing's fabrication material depends on many factors including compatibility; strength-to-weight ratio; thermal conductivity; ease of fabrication; porosity, etc. The housing acts to transfer heat contained within the working fluid to the outside environment.
Working fluids are many and varied. The prime consideration is the operating vapor temperature range. Often, several possible working fluids may exist within the approximate temperature band. Various characteristics must be examined in order to determine the most acceptable of these fluids for the application considered such as: thermal stability; compatibility with wick and wall materials; vapor pressure relative to the operating temperature range; latent heat; thermal conductivity; liquid and vapor viscosities; surface tension; and acceptable freezing or pour point. The selection of the working fluid must also be based on thermodynamic considerations that are concerned with the various limitations to heat flow occurring within the heat pipe, including viscous, sonic, capillary, entrainment, and nucleate boiling levels. Most heat pipes use water and methanol/alcohol as working fluid.
The typical wick is a porous structure—made of materials like steel, aluminum, nickel or copper in various pore size ranges—fabricated using metal foams, and more particularly felts, the latter being more frequently used. By varying the pressure on the felt during assembly, various pore sizes can be produced. By incorporating removable metal mandrels, an arterial structure can also be molded in the felt. The prime purpose of the wick is to generate capillary pressure to transport the working fluid from the condenser section of the housing to the evaporator section. It must also be able to distribute the liquid around the evaporator section to any area where heat is likely to be received by the heat pipe. Often these two functions require wicks of different forms. The selection of the wick for a heat pipe depends on many factors, several of which are closely linked to the properties of the working fluid.
In operation, one end of the heat pipe attaches to a heat source. As the heat rises to the desired operating temperature, the tube boils the working fluid and transforms it into a vapor state. As the evaporating fluid fills the hollow center of the wick, it spreads throughout the heat pipe toward to the cold end. Vapor condensation occurs wherever the temperature is even slightly below that of the evaporation area. As it condenses, the vapor releases the heat acquired during evaporation and the now-condensed working fluid then recedes back to the evaporation section. In most cases, the application must have gravity working with the system; that is, the evaporator section (heated) must be lower, with respect to gravity, than the condenser (cooling) section. When a wick structure is present in the heat pipe, the fluid recedes therein; otherwise, the fluid recedes gravimetrically. The above thermodynamic cycle continues and helps maintain constant temperatures.
Heat pipes are effective in a number of applications but, unfortunately, traditional heat pipes have significant drawbacks. First, although heat pipes are good at moving heat from one point to another, they are not particularly effective at spreading heat from multiple inputs on a surface. Second, the wicking structures used in heat pipes are difficult and expensive to manufacture. Finally, although heat pipes may be flattened to increase their surface area, such flattening adds to the overall cost of manufacture and reduces the effective heat dissipating capacity of the heat pipe.
In order to overcome the downsides of traditional heat pipes, other types of vapor chambers have been developed. One common type of vapor chamber includes a flat hollow rectangular housing into which is disposed a wicking structure and a working fluid. The wicking structure is typically a mesh type screen, metal foam, or felts that is specifically fabricated for this purpose and fills substantially all of the inside of the housing. The wicking structure allows the vapor chamber to work against gravity like a wick type heat pipe. These wicking structures are again difficult and expensive to manufacture and the use of these wicking structures limits the versatility of the layout of the heat dissipating components. Further, the use of traditional wicking structures requires the vapor chambers to be fairly thick, which limits their application.
Therefore, there is a need for a vapor chamber that may be easily and inexpensively manufactured, that has substantial versatility in layout of wicking structures, that may be made thinner than current vapor chambers or flattened heat pipes, and that are not limited to transferring heat from one point to another.
SUMMARY OF THE INVENTIONThe present invention is a vapor chamber.
In its most basic form, the present invention is a vapor chamber including a housing that forms a recess within; at least one wicking structure manufactured from a bundle of wires having capillary voids therebetween that is disposed within the recess; and an amount of working fluid disposed within the recess and in fluid contact with the wicking structure such that fluid may move within the capillary voids in the wicking structures through capillary action.
The wicking structure preferably includes a plurality of individual wires, preferably between twenty and forty, but less than twenty or greater than forty may be included. The wicking structures are preferably made of a non-reactive metal, such as copper. Other materials out of which the wicking structures may be manufactured include aluminum, carbon fiber and certain plastics, as well as any material commonly used in the art. In some embodiments, standard off-the-shelf wire ropes may be used. The individual wires have capillary voids between the wires, within the wicking structure. These capillary voids may be three cornered or four cornered depending on the type and orientation of the wires within the bundle. The individual wires within a wicking structure are packed tightly, but not fluid tightly, so that fluid may still traverse within the capillary voids. There are also “v”-shaped vacancies between the individual wires on the surface of the wicking structures. In practice, the working fluid moves through these capillary voids and “v”-shaped vacancies toward the heat source, through capillary action. It is preferred that the wicking structures be twisted so that the distance through a capillary void or “v”-shaped vacancy from one side of the wicking structure to the other is short. More tightly twisted wire bundles will have a shorter distance than more loosely twisted wire bundles. The wires may also be braided, twisted in pairs and then aligned within the bundle, or twisted in pairs or groups and then twisted all together, for example. Herein, the term “twisted” may refer to any of these possibilities. The wicking structures may also be straight, or not twisted, but this is less effective in many applications, and therefore non-preferred. The capillary action occurs regardless of orientation of the vapor chamber and heat source relative to gravitational forces.
The housing is designed to fit its application, but preferably includes a base and a cover and is small and flat. The recess is formed between the base and the cover. The preferred housing is preferably substantially rectangular. Herein, “substantially rectangular” may mean that the housing is rectangular or that it may be rectangular, but with rounded corners. It is understood that some embodiments may also have a shape other than substantially rectangular. When the cover and base are united, the preferred housing is 2.5″×5″×0.125″, but may be of smaller or larger dimensions. The housing is preferably made of copper, but may be made of other materials, such as aluminum, stainless steel, nickel, or refrasil fiber. The working fluid within the recess of the housing is preferably water, but may be other working fluids, such as acetone, ammonia, methanol, or ethylene-based glycol ether products. The base and cover of the housing are preferably sealed together through welding, but may also be sealed using epoxy, screws, o-rings, gaskets, or any other method commonly used in the art.
In some embodiments, the inside of the housing may be sprayed or otherwise coated with polytetrafluoroethylene (“PTFE,” commonly sold under the brand name TEFLON) or other non-reactive hydrophobic materials with similar characteristics to PTFE. With such embodiments, aluminum wire structures, which traditionally have only been usable with non-water working fluids, may be used with water as the working fluid. This is a significant advantage, as water is dramatically more effective, even with the added resistance.
The housing may or may not be vacuum sealed. When the housing is vacuum sealed, the base of the housing may include several separators for maintaining a distance between the cover and base of the housing. The separators are small posts extending upward from the floor of the recess in the base to a height so that the cover rests on the top of the separators. The separators provide mechanical support for the cover so that it does not buckle into the recess under pressure. When the housing is not vacuum sealed, expansion may be a problem. In these embodiments, at least one, and preferably two, locations may be selected to weld the cover and base together from the outside so as to prevent the cover and base from expanding away from one another.
The housing preferably includes a fluid input for introducing the working fluid into the recess. The fluid input is preferably disposed within the height of the base, so that the base remains flat. The fluid input is preferably a small hole within the height of the base with a removable cap that fits snugly within the hole and prevents leakage of the working fluid when in place. The cap may be welded or otherwise permanently attached, or may be removable to allow the working fluid to be recharged. Alternatively, any art recognized means of sealing the hole may be utilized. References herein to a “side” of the housing always refer to the larger, flat sides of the cover or base of the housing. The height of the housing, which is on all four sides of the housing, will be referred to as the “height” rather than a “side,” so as to avoid confusion.
In operation, at least one heat source is applied to the outside of the base or cover of the housing. The wicking structures are preferably wire bundles that act as wicks so that the working fluid moves toward the heat source through the wicking structures by capillary action.
In a preferred embodiment, heat is absorbed on one side of the housing, either the base or the cover depending on where the heat source is located, and is emitted on the other side of the housing, therefore moving through the height of the housing. The operation of the heat chamber takes advantage of similar physical properties used with heat pipes, described, for example, in Wallin, Per. “Heat Pipe, selection of working fluid.” Project Report MVK160 Heat and Mass Transfer, 7 May 2012, hereby incorporated by reference. The traditional heat pipe generally moves heat from one end of the heat pipe to the other end. In some embodiments of the vapor chamber of the present invention, heat is moved similarly to a traditional heat pipe where the heat is moved through the length or width of the housing, rather than through the height of the housing, as described above. Distinctions between the traditional heat pipe and the vapor chamber of the present invention will be evident to one of ordinary skill in the art.
The preferred housing is as described above. It is understood, however, that the housing may also be of the type used traditionally with heat pipes. Heat pipe housings may take any of a variety of forms, such as sealed metal tubes. Such a heat pipe housing used in combination with the wicking structure of the present invention would have significant differences from a traditional heat pipe. Where a traditional heat pipe typically includes some sort of porous or sponge-like material as its wick, a heat pipe housing in combination with the wicking structure of the present invention would use the wicking structure as its wick. The wicking structure is unique as a wick because although the individual wire strands are not porous, the bundle of wire strands together is porous, after a fashion, in that it includes the capillary voids, and “v”-shaped vacancies, as discussed above. A heat pipe housing used in combination with a wicking structure of the present invention would also move heat via the working fluid in multiple dimensions.
Moreover, a traditional heat pipe typically moves heat via the working fluid from one end of the heat pipe to the other. A heat pipe housing used in combination with a wicking structure of the present invention, on the other hand, would move heat via the working fluid not only from one end of the wicking structure to the other, but also from one side of the wire bundle to the other through the twists in the wire bundle, as discussed above. A traditional tube-like heat pipe housing used in combination with a wicking structure of the present invention would preferably have twisted wire bundle wicking structures aligned around the inner surface of the tube, parallel with one another, and stretching from one end of the heat pipe to the other. In this way, the wicking structure moves heat via the working fluid from one end of the heat pipe to the other, as in a traditional heat pipe, but also from the inside cavity of the heat pipe to the outer surface of the heat pipe through the twists in the wire bundles of the wicking structure.
The wicking structures may be oriented within the recess in any pattern. Patterns of the wicking structures include expanding out from the middle like a star, in a big swirl, in parallel lines, or in any other configuration that makes sense considering where the heat sources will be applied to the vapor chamber.
If we consider the side of the vapor chamber on which a heat source is applied the “hot side” and the other side the “cold side,” liquid working fluid present in the recess of the housing will move toward the hot side through the capillary voids and “v”-shaped vacancies. On the hot side, the working fluid will evaporate and move back toward the cold side, where it will then condense and be drawn back toward the heat, et cetera. In some embodiments, some sort of additional heat sink or “cold source” may be applied to the cold side of the housing.
In addition to their utility as described in detail above, most embodiments of the vapor chamber of the present invention are relatively easy and inexpensive to manufacture. It is understood, however, that some embodiments may include complex machining details that may increase the ease and price of manufacture.
These aspects of the present invention are not meant to be exclusive and other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description and accompanying drawings.
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In addition to the heat moving from the hot side to the cold side of the housing 10, the heat may also move toward cooler portions of the vapor chamber along the length of the wicking structures 20. In
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Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions would be readily apparent to those of ordinary skill in the art. Therefore, the spirit and scope of the description should not be limited to the description of the preferred versions contained herein.
Claims
1. A vapor chamber comprising:
- a housing;
- a recess within said housing;
- at least one wicking structure disposed within said recess, wherein: said at least one wicking structure comprises a plurality of individual wires; capillary voids are formed between said plurality of wires within said at least one wicking structure; and v-shaped vacancies are formed between said plurality of wires on a surface of said at least one wicking structure; and
- an amount of working fluid disposed within said recess and in fluid contact with said at least one wicking structure such that said working fluid is capable of moving through said capillary voids and said v-shaped vacancies of said at least one wicking structure through capillary action.
2. The vapor chamber as claimed in claim 1, wherein said capillary voids are shaped as one of a group consisting of three cornered and four cornered.
3. The vapor chamber as claimed in claim 1, wherein said plurality of individual wires are twisted.
4. The vapor chamber as claimed in claim 1, wherein said housing comprises a base, a cover and a seal disposed between said base and said cover and, wherein said base and said cover are removable attached.
5. The vapor chamber as claimed in claim 1, wherein an interior of said housing and each of said wires is coated with polytetrafluoroethylene, and wherein said working fluid is water.
6. The vapor chamber as claimed in claim 1, wherein said working fluid is water.
7. The vapor chamber as claimed in claim 1, wherein said housing is vacuum sealed and said vapor chamber further comprises at least one separator disposed within said recess between said cover and said base so as to maintain a separation between said cover and said base while said housing is under vacuum.
8. The vapor chamber as claimed in claim 1, wherein at least one location on said housing, said cover and said base are affixed together so as to prevent expansion of said cover and said base away from one another.
9. The vapor chamber as claimed in claim 1, further comprising a fluid input disposed on said housing, wherein said fluid input allows for deposit of said working fluid into said recess.
10. The vapor chamber as claimed in claim 1, wherein said at least one wicking structure is disposed within said recess in a star-like pattern, expanding outward from a middle of said recess.
11. The vapor chamber as claimed in claim 1, wherein said at least one wicking structure is disposed within said recess in a swirled pattern
12. The vapor chamber as claimed in claim 1, wherein said plurality of individual wires comprises wires all of the same size.
13. The vapor chamber as claimed in claim 1, wherein said plurality of individual wires comprises one larger wire surrounded by a plurality of smaller wires.
14. A vapor chamber comprising:
- a housing comprising a base, a cover, and a recess formed between said base and said cover; and
- at least one wicking structure disposed within said recess, wherein: said at least one wicking structure comprises at least three individual wires; and capillary voids are formed between said wires within said at least one wicking structures; and
- an amount of working fluid disposed within said recess and in fluid contact with said at least one wicking structure such that said working fluid is capable of moving through said capillary voids through capillary action.
15. The vapor chamber as claimed in claim 14, wherein an interior of said housing and each of said at least three wires are coated with polytetrafluoroethylene and wherein said working fluid is water.
16. The vapor chamber as claimed in claim 14, wherein said housing is vacuum sealed and said vapor chamber further comprises at least one separator disposed within said recess between said cover and said base so as to maintain a separation between said cover and said base while said housing is under vacuum.
17. The vapor chamber as claimed in claim 14, wherein at least one location on said housing, said cover and said base are affixed together so as to prevent expansion of said cover and said base away from one another.
18. A vapor chamber system comprising:
- a vapor chamber comprising: a housing comprising a base and a cover; a recess formed between said base and said cover when said base and said cover are united; at least one wicking structure disposed within said recess, wherein: said at least one wicking structure comprises a plurality of individual wires; capillary voids are formed between said wires within said at least one wicking structures; and v-shaped vacancies are formed between said wires on a surface of said at least one wicking structure; and an amount of working fluid disposed within said recess and in fluid contact with said at least one wicking structure such that said working fluid is capable of moving through said capillary voids and said v-shaped vacancies through capillary action; and
- at least one heat source disposed proximate to one of said base and said cover of said housing of said vapor structure such that heat from said at least one heat source is transferred through said housing into said working fluid disposed within said housing.
19. The vapor chamber system as claimed in claim 18, further comprising at least one cold source disposed at a different position proximate to one of said base and said cover of said housing of said vapor structure than said at least one heat source, such that heat from said working fluid disposed within said housing is transferred from said heat source through said housing into said at least one cold source.
20. The vapor chamber system as claimed in claim 19, wherein said at least one wicking structure is disposed within said recess of said housing of said vapor chamber such that:
- a portion of said at least one wicking structure is proximate to said at least one heat source such that said working fluid in fluid contact with said at least one wicking structure evaporates and moves away from said at least one heat source through said capillary voids and v-shaped vacancies in said at least one wicking structure; and
- a portion of said at least one wicking structure is far enough away from said at least one heat source and any other heat source such that said working fluid that evaporated near said at least one heat source and moved away from said at least one heat source through said capillary voids and v-shaped vacancies condenses.
Type: Application
Filed: Aug 5, 2014
Publication Date: Feb 12, 2015
Applicant: AALL POWER HEATSINKS, INC. (Clearwater, FL)
Inventors: Richard F. Kiley (Louisville, CO), Simone Bush (Pinellas Park, FL)
Application Number: 14/451,905
International Classification: F28D 15/04 (20060101);