Flexible heat pipes of an improved type are fabricated as layers of different materials laminated together into vacuum-tight sheets or tapes. In comparison with prior flexible heat pipes, these flexible heat pipes are less susceptible to leakage. Other advantages of these flexible heat pipes, relative to prior flexible heat pipes, include high reliability and greater ease and lower cost of fabrication. Because these heat pipes are very thin, they are highly flexible. When coated on outside surfaces with adhesives, these flexible heat pipes can be applied, like common adhesive tapes, to the surfaces of heat sinks and objects to be cooled, even if those surfaces are curved.

A Flexible Heat Pipe can be fabricated as a laminate of polypropylene, metal, and adhesive layers. This enlarged cross section of a typical preferred laminate is not to scale.

A preferred design calls for five major layers (see figure) laminated to a total thickness of 0.12 in. (3 mm). The middle layer is a coarse metal (e.g., copper) or polypropylene screen that acts as a separator to maintain the heat-pipe vapor space by separating two other major layers, which are copper felt wicks. The remaining two major layers, which are sealed together around their edges, are outer walls that constitute the heat-pipe envelope around the wicks and separator. Each outer wall comprises a strengthening sublayer of polypropylene, two sublayers of metal foil, and sublayers adhesive between the polypropylene and metal layers.

The wick layers can be pressed into the polypropylene wall layers (optionally with partial melting of the polypropylene layers) to increase the thermal conductance between the walls and wicks. The two outer walls are joined at their edges by placing their polypropylene layers in contact and then heating them and pressing them together.

The two metal foils in each outer wall serve as barriers against leakage. Because foils occasionally contain random pinholes, one foil layer per wall would not afford sufficient protection against leaks. However, when an outer wall contains two foil layers, it would be necessary for two pinholes to be aligned with each other (a highly improbable occurrence) to make a pinhole leak. Hence, the use of two foil layers per outer wall reduces the probability of pinhole leaks to a small value.

This work was done by John H. Rosenfeld, Nelson J. Gernert, David B. Sarraf, Peter J. Wollen, Frank C. Surina, and John E. Fale of Thermacore, Inc., for Johnson Space Center.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Thermacore International, Inc.
780 Eden Rd.
Lancaster, PA 17601
(717) 569-6551
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Refer to MSC-23400.

ORIGINAL URL - /Briefs/Feb04/MSC23400.html


NASA Tech Briefs Magazine

This article first appeared in the February, 2004 issue of NASA Tech Briefs Magazine.

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