Metal working – Method of mechanical manufacture – Heat exchanger or boiler making
Reexamination Certificate
1999-09-02
2001-04-17
Cuda, Irene (Department: 3726)
Metal working
Method of mechanical manufacture
Heat exchanger or boiler making
C029S890030
Reexamination Certificate
active
06216343
ABSTRACT:
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 WIRE CLOTH WICK AND METHOD OF FABRICATION”, AFD 00344, Ser. No. 09/389,269 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 capillary channel 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 corrugated fin elements for efficient heat transfer in micro-miniature applications.
Still another object of the present invention is to provide a method of fabrication of an improved micro channel heat pipe having corrugated fin elements wherein the closed channels are opened during fabrication to create enhanced localized heat transfer.
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 micro channel heat pipe includes a pair of corrugated fin elements attached to the inner walls of the tubular heat pipe housing. The heat pipe housing is enclosed by a pair of end caps and a working fluid is introduced therein.
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 of the prior art, 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 pair of corrugated fin elements attached to the inner surfaces of the heat pipe housing. The corrugated fin elements have a plurality of adjacent open and closed micro capillary grooves or channels formed therein. According to an important aspect of the present invention, material is removed from a portion of the closed micro capillary channels at each end of the heat pipe during fabrication. This creates sections comprised entirely of open micro capillary channels, doubling the number of channels available to the working fluid. This has the advantage of providing maximum heat transfer in the areas of high heat flux and can be used to create, for example, evaporator and condenser sections. Moreover, machining time is minimized because material is removed only in these areas, reducing fabrication time and costs.
Good mechanical contact is established between the corrugated fin elements and the heat pipe housing by brazing. This is readily accomplished by the use of brazing foil, assuring good thermal contact, and enhancing overall effectiveness.
The corrugated fin elements are fabricated by folding techniques, avoiding the complex and problematic micro groove machining of the prior art. Advantageously, this contributes to low cost mass production.
REFERENCES:
patent: 4353415 (1982-10-01), Klaschka et al.
patent: 4846263 (1989-07-01), Miyazaki et al.
patent: 6070654 (2000-06-01), Ito
patent: 6077566 (2000-06-01), Henne et al.
“Micro/Miniature Heat Pipe Technology for Electronic Cooling”, by Faghri et al., WL-TR-97-2083, Wright Laboratory, Wright-Patterson AFB, OH (Jul. 1997).
Leland John E.
Ponnappan Rengasamy
Cuda Irene
Kundert Thomas L.
Lambert Richard A.
Scearce Bobby D.
The United States of America as represented by the Secretary of
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