Studies of the properties of five metals with varying tube-wall thickness, with or without and internal coating of trifluorochloroethylene polymer, show that wall characteristics influence flow stability, affect heat transfer coefficients, and influence the transition point from dry- to wet-wall flow

Manson, L.

Miller, W. S.

English

NASA Technical Reports Server

May 1970	 Brief 70-10259 
.
NASA TECH BRIEF	 Al 
NASA Tech Briefs announce new technology derived from the U .S. space program. 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. 
Metal Cooldown, Flow Instability, and Heat Transfer

in Two-phase Hydrogen Flow 
.
An experimental investigation was conducted on 
the cooldown of coated and uncoated metal tubes, 
and of flow instability and heat transfer in two-phase 
hydrogen flow. The cooldown experiments were con-
ducted at relatively low pressures (50 to 100 psia); 
the instability investigation concentrated in the region 
of the critical pressure of hydrogen (188 psia). These 
studies were prompted by requirements for rapid 
chilling and startup of liquid hydrogen pumping 
systems. The results may be useful in the design of 
pumps and other low-temperature flow devices The 
work may be extended easily to cover other gases. 
The properties of five metals with varying tube-wall 
thickness, with or without an internal coating of 
trifluorochloroethylene polymer, were studied. Re-
sults showed that wall characteristics influence flow 
stability, markedly affect heat transfer coefficients in 
the dry-wall (film boiling) portion of the cooldown, 
and also influence somewhat the transition point 
from dry- to wet-wall flow. The insulating cotting 
stabilized the flow during cooldown, reduced vapor 
formation rate under rapid flow conditions, and 
accelerated cooldown rate during low-velocity flow. 
Equations have been derived for determining the 
optimum coating thickness. 
Theoretical steady-state heat-transfer functions 
proposed in the literature for two-phase hydrogen 
flow were compared with experimental heat-transfer 
data obtained in the dry-wall portion of the cooldown. 
Reasonable agreement was obtained at the initiation 
of cooldown (high wall temperatures). Agreement in 
the low wall-temperature region was not as good, 
possibly because of the effect of tube-wall parameters 
on flow near the wall, or as the result of a delay in 
recondensation of the vapor formed near the wall.
These two factors have not been included in steady-
state heat-transfer theory. 
The investigation of instability was performed using 
an electrically heated, tubular test section, through 
which two-phase hydrogen was passed. Flow stability 
regions and heat-transfer characteristics were deter-
mined simultaneously at pressures varying from near-
critical to critical. Unstable flow occurred even when 
the fluid remained subcooled through the entire test 
section. Under such conditions, the flow-rate required 
to suppress instability was relatively high, while with 
bulk boiling present, a much lower flowrate could be 
tolerated. Three modes of oscillation were identified 
in the unstable flow; all exhibited high damping 
characteristics. 
Notes: 
1. For information on a similar investigation of 
two-phase nitrogen flow, refer to Tech Brief B69-
10541, Cryogenic Fluid Flow Instabilities in Heat 
Exchangers. 
2. Requests for further information may be directed 
to:
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: TSP70- 10259 
Patent status: 
No patent action is contemplated by NASA. 
Source: L. Manson and W. S. Miller of 
North American Rockwell Corp. 
under contract to 
Marshall Space Flight Center 
(M FS- 18696) 
Category 04 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned.rights.
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Metal cooldown, flow instability, and heat transfer in two-phase hydrogen flow

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