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June 1972


B72- 10368



AEC-NASA TECH BRIEF



AEC-NASA Tech Briefs announce new technology derived from the research and development program of the U.S.
AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial application. Tech Briefs are
available on a subscription basis from the National Technical Information Service, Springfield, Virginia 22151. Requests
for individual copies or questions relating to the Tech Brief program may be directed to the Technology Utilization
Office, NASA, Code KT, Washington, D.C. 20546.


Sonic Limitations and Startup Problems of Heat Pipes


A heat pipe is a thermal conductance device
capable of high heat transfer rates with essentially
isothermal operation. The operating characteristics of
a pipe with a given geometry may vary from excel-
lent to nonfunctional; axial temperature drops of several
hundred degrees have occurred in some cases.

The performance of a heat pipe depends on the
type of wick, working fluid, and the external conditions
imposed on it. The dynamics of the fluid flow are very
complicated. Under certain operational conditions the
vapor flow may be molecular or continuum, com-
pressible or incompressible; vapor velocities may be
sonic or supersonic; countercurrent flow of vapor and
liquid, with communication between flow paths, may
result. In designing heat pipes for high heat transfer
rates these factors must be taken into account.

A series of tests has been conducted to deter-
mine the effects of sonic vapor velocities on the opera-
tional and startup characteristics of heat pipes. It was
found that the introduction of small amounts of inert,
noncombustible gas aids startup in certain types of heat
pipes. Also, when the heat pipe is closely coupled to the
heat sink, the startup system must be designed to bring
the heat sink on-line slowly.

Notes:

1. The following documentation may be obtained from:
National Technical Information Service
Springfield, Virginia 22151
Single document price: $3.00
(or microfiche $0.95)


Reference: LA4518 (N7 1-1 8944), Sonic
Limitations and Startup Problems of Heat
Pipes

2. Technical questions may be directed to:

Mr. Glenn K. Ellis
Technology Utilization Officer
Office of Information Services
U.S. Atomic Energy Commission
Washington, D.C. 20545
Reference: TSP72-10368

Patent status:

Inquiries concerning rights for commerical use of
this information may be made to:

Mr. George H. Lee, Chief
Chicago Patent Group
U.S. Atomic Energy Commission
Chicago Operations Office
9800 South Cass Avenue
Argonne, Illinois 60439

Source: J.E. Deverall, J.E. Kemme and
L.W. Florschuetz
Los Alamos Scientific Laboratory
under contract to
Atomic Energy Commission
(AEC-10036)


Category 03


This document was prepared under the sponsorship of the Atomic
Energy Commission and/or the National Aeronautics and Space
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Government assumes any


liability resulting from the use of the information contained in this
document, or warrants that the use of any information, apparatus,
method, or process disclosed in this document may not infringe pri-
vately owned rights.



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