Metered vent controls the pressure within a liquid hydrogen tank. Vent size is chosen to permit a gas flow which corresponds to the boil-off rate necessary to maintain the desired bulk temperature of the cryogen

Ford, W.

Voss, J.

English

NASA Technical Reports Server

June 1970	 Brief 70-10122 
NASA TECH BRIEF 
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. 
Control of Equilibrium Pressure-Temperature Conditions in Cryogenic Storage 
The problem: 
The bulk temperature of any cryogenic liquid in 
storage is directly related to the pressure at which 
it is allowed to boil. For very cold cryogens, such as 
liquid hydrogen, a small increase in the containment 
pressure results in a significant increase in the bulk 
temperature with a corresponding decrease in fluid 
density, thus lowering the total mass of cryogen which 
can be stored in the container. 
F1 11 Air Trap Stack 
Air	 Orifice 
Trap1—i.,' 
L
iNormally Open Slow 
Vent Valve 
Selector Valve 
_, 
Regular Vent 
Valve	
(For Burst Diaphram) 
Cryogen Tank 
The solution: 
A metered vent has been developed to control the 
pressure within a liquid hydrogen tank. The size of 
the vent is chosen to permit a gas flow which corre-
sponds to the boil-off rate necessary to maintain the 
desired bulk temperature of the liquid hydrogen. 
How it's done: 
A slow-vent system is added to the normal venting 
provisions of the cryogenic storage tank, a large 
spring-loaded valve and a burst diaphragm. The slow-
vent is a normally open valve in series with a metering
orifice, placed in parallel with the normal vent valve. 
The metering orifice is sized for choked flow at the 
gas evolution rate that corresponds to the heat leakage 
into the liquid hydrogen from the environment. With 
well-insulated containers and ducting, the rate can be 
very low, while with uninsulated feed tanks, a much 
higher rate is experienced. The slow-vent valve main-
tains a positive pressure of a few inches of water in the 
tank. For any particular application, precise adjust-
ment of this pressure, and consequently the bulk 
temperature of the liquid hydrogen, can be obtained 
experimentally by varying the size of the orifice. 
This technique is equally applicable to other cryo-
gens, and can be expected to reduce substantially the 
conventional loss rates in equipment currently con-
trolled by spring-loaded vent valves. It provides a 
ready means for maintaining bulk temperatures at 
closely controlled levels, as well as minimizing storage 
losses. Also, the technique provides an economical 
means of restoring bulk temperature to the required 
level after transfer or transportation. 
Note: 
No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B70-10122 
Patent status: 
No patent action is contemplated by NASA. 
Source: W. Ford and J. Voss of 
North American Rockwell Corporation 
under contract to 
Marshall Space Flight Center 
-	 (MFS-18115) 
Category 03 
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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Control of equilibrium pressure-temperature conditions in cryogenic storage

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