Heat exchange – Intermediate fluent heat exchange material receiving and... – Liquid fluent heat exchange material
Reexamination Certificate
1999-09-02
2001-09-25
Lazarus, Ira S. (Department: 3743)
Heat exchange
Intermediate fluent heat exchange material receiving and...
Liquid fluent heat exchange material
C165S104330, C029S890032, C361S700000, C257S715000
Reexamination Certificate
active
06293333
ABSTRACT:
RIGHTS OF THE GOVERNMENT
The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
BACKGROUND OF THE INVENTION
The present patent application document is somewhat related to the copending and commonly assigned patent application document “MICRO CHANNEL HEAT PIPE HAVING CORRUGATED FIN ELEMENTS AND METHOD OF FABRICATION”, AFD 00384, Ser. No. 09/389,270, filed on even date herewith. The contents of that even filing date application are hereby incorporated by reference herein.
The present invention relates generally to heat dissipating devices and more particularly to a micro channel heat pipe and method of fabrication.
As is well known in the art, heat pipes are closed, self contained devices that contain a volatile working fluid designed to transport thermal energy efficiently. In general, heat pipes have an inner cavity lined with a wick or grooves designed to provide a capillary structure for the transport of the working fluid.
In operation, the heat pipe takes advantage of the latent heat of vaporization of the working fluid. Heat is applied to one portion of the device, causing evaporation of the fluid in that portion of the chamber. The fluid vapor moves to a cooler portion of the device whereupon it condenses. The condensed fluid returns, and the action repeats itself.
As can be imagined, this vaporization and condensation action is continuous and provides for a very efficient means of transportation of thermal energy. The heat pipe is a sealed unit and requires no additional energy input to enable operation. Thus it is very efficient and is useful in a wide array of applications.
A current trend towards micro miniaturization of electronic components and high power devices gives rise to the desirability of correspondingly miniaturized cooling devices. As a result, attempts have been made to miniaturize heat pipes. However, as heat pipes are miniaturized, it becomes increasingly difficult to fabricate an effective wick structure to provide acceptable heat transfer operation. For example, forming of very narrow rectangular channels, 0.2 mm×0.9 mm or similar sizes and shapes within the internal walls of tubes with hydraulic diameter in the range of 5-10 mm is difficult. Appropriate groove cutting tools, extrusion dies and the like, necessary for cutting such small channels often provide unsatisfactory results and are expensive.
A need exists therefore for a micro channel heat pipe which provides high efficiency operation while simultaneously eliminating the difficulties encountered in fabrication heretofore encountered to date.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to provide a micro channel heat pipe and method of fabrication overcoming the limitations and disadvantages of the prior art techniques.
It is another object of the invention to provide a micro channel heat pipe that can be readily manufactured from known techniques.
It is still another object of the present invention to provide an improved micro channel heat pipe for efficient utilization in micro-miniature applications.
It is yet another object of the present invention to provide an improved micro channel heat pipe having a wire cloth wick for efficient heat transfer in micro-miniature applications.
These and other objects of the invention will become apparent as the description of the representative embodiments proceeds.
In accordance with the foregoing principles and objects of the invention, a micro channel heat pipe and method of fabrication are described. The method includes forming micro channels in a fine mesh wire cloth wick. The wick is inserted into the heat pipe housing and preferably includes a compression or shrink fit.
Micro channel heat pipes are characterized as having at least one capillary channel such that r
c
/r
h
≧1 where r
c
is the capillary radius and r
h
is the hydraulic radius of the flow channel. In order to provide efficient operation, the capillary channels in micro channel heat pipes are quite small, for example, 0.2 mm or less. The known groove forming methods such as rolling, dicing saw cutting, electrodischarge machining, etc. are difficult to enact properly, can provide unsatisfactory results and are expensive to perform.
As stated, the micro channel heat pipe of the present invention includes a wick formed from wire cloth. There are many benefits realized by utilizing wire cloth to form the wick of the present invention. By forming the wick from wire cloth, micro capillary channels can be easily formed therein by the ready application of known fin making processes. Since the wick thus formed is porous to the working fluid, the number of capillary channels available for heat transfer is doubled to incorporate both open and closed channels. As can be appreciated, this greatly enhances the operational efficiency of a micro channel heat pipe fabricated according to the teachings of the present invention. Moreover, the capillary action of the wick is greatly enhanced by the tight mesh of the wire cloth. Also, the wire cloth enables circumferential fluid distribution within the channels due to capillary action. This is not possible with the solid wall channels of the prior art.
Good mechanical contact between the wick and the heat pipe housing is assured by a shrink fit insertion process. More specifically, the housing is heated prior to insertion of the wick. When the housing cools and the assembly reaches an equilibrium temperature, a net compressive force will be exerted on the wick assuring good thermal contact, enhancing overall effectiveness.
By the avoidance of the complicated groove machining of the known techniques, another advantage of the present invention becomes apparent. More specifically, in order to machine the micro capillary channels within the housing, the housing correspondingly would have to be split longitudinally in order to provide access for machining purposes. However, by utilizing the teachings of the present invention, the housing need not be split because the wick is formed separately and then inserted into the housing. Advantageously, this contributes to low cost mass production.
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Leland John E.
Ponnappan Rengasamy
Kundert Thomas L.
Lambert Richard A.
Lazarus Ira S.
McKinnon Terrell
Scearce Bobby D.
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