Insulating qualities of frost and mechanisms for using frost in specific applications in controlled experiments are discussed. With available supply of moist air, frost possesses inherent advantage of easy insulation of cryogenic lines and improvement of overall system efficiency

Bronson, J. C.

English

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AEC-NASA TECH BRIEF
•:: 
rES -IV 
October 1970
	 Brief 70-10593 
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 Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Requests for individual copies or questions relating to the Tech Brief program may be directed to the Technology Utilization 
Division, NASA, Code UT, Washington, D.C. 20546. 
Frost as an Insulator 
Frost is generally considered as an undesirable, 
inert, homogenous, crystalline structure that must 
be eliminated to enhance the heat transfer of cooling 
coils. However, when frost forms under other con-
ditions, such as on the outside of cryogenic lines, its 
qualities can be used advantageously since it possesses 
an insulating capacity which compares favorably with 
some common low efficiency insulation materials 
such as shredded wood bark, insulating brick, asbestos 
sheet, and leather. 
Basic insights on the insulating quality of frost, and 
mechanisms for using frost in specific applications, 
have been derived from recent tests and studies. 
Frost is an ice layer formed by condensed crystals of 
liquid air. If the liquid air is allowed to escape, the frost 
layer cracks, sloughs off, shifts position, and repairs 
itself with consequent changes in insulating value 
and thermal conductivity. However, by maintaining 
relative humidity above set values, and blowing the 
moist air past cryogenic lines at certain velocities, 
frost can be formed to set thicknesses and densities 
which can be sustained. Once this occurs, liquid air 
run-off is eliminated and the frost layer becomes a 
uniform insulator. 
The quality of insulation was determined by a test 
in which temperature differences across a 1/4-in, thick 
wall of stainless steel test line were recorded. Using 
liquid hydrogen, the average start-up temperature 
difference across the wall was 203°R. After the forma-
tion of a frost layer 0.8-in, thick (89% air relative
humidity at 127 fpm), the average steady state temper-
ature difference had dropped to 31R. For liquid 
nitrogen the start-up temperature was 154R. A frost 
layer 0.6-in, thick (77% air relative humidity at 94 fpm) 
dropped the steady state temperature difference to 
23°R. This technique could be applied in operations 
where it is difficult to wrap or attach standard insulat-
ing materials. Conditions can also exist where space 
constraints or lack of access impedes the placing of 
insulation, or where existing insulation has fallen 
off. With an available supply of moist air, frost posses-
ses the inherent advantage of easy insulation of cryo-
genic lines which otherwise might not be protected, 
improving overall system efficiency. 
Note: 
Inquiries concerning this innovation may be di-
rected to: 
Technology Utilization Officer 
AEC-NASA Space Nuclear Propulsion Office 
U.S. Atomic Energy Commission 
Washington, D.C. 20545 
Reference: B70-10593 
Patent status: 
No patent action is contemplated by AEC or NASA.
Source: John C. Bronson of
Los Alamos Scientific Laboratory 
under contract to
Space Nuclear Propulsion Office

(NUC-1 1039) 
Category 03 
This document was prepared under the sponsorship of the Atomic
	 liability resulting from the use of the information contained in this 
Energy Commission and/or the National Aeronautics and Space document, or warrants that the use of any information, apparatus, 
Administration. Neither the United States Government nor any per-
	 method, or process disclosed in this document may not infringe pri-
son acting on behalf of the United States Government assumes any vately owned rights.
	 -
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Frost as an insulator

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