Vaporizing small portion of cryogenic liquid into pressurizing gas reduces amount of pressurizing gas required to expel cryogenic liquid from tank. Specific example of injecting helium gas, stored at same temperature of liquid hydrogen, through submerged porous plate directly into liquid hydrogen is described

Conrad, E. W.

Johnson, W. R.

English

NASA Technical Reports Server

July 1971	 Brief 71-10219 
NASA TECH BRIEF 
Lewis Research Center 
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 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. 
Submerged Gas Injector Expels Cryogenic Liquids from Tanks 
:1
The amount of pressurizing gas required to expel 
a cryogenic liquid from a tank can be reduced by 
vaporizing a small portion of the cryogenic liquid into 
the pressurizing gas. It is often desirable to accom-
plish this while using a cold pressurizing gas at the 
cryogenic liquid temperature and without heating the 
bulk liquid in the tank. 
The principle has been successfully demonstrated 
by injecting helium gas through a submerged porous 
flat plate directly into liquid hydrogen, rather than by 
admitting the helium into the vapor space (ullage) 
above the liquid. As the helium bubbles up through the 
liquid hydrogen, the hydrogen vaporizes and diffuses 
into the helium bubbles. The bubbles become satur-
ated with hydrogen gas and are carried into the ullage 
volume, where the partial pressures of the helium and 
hydrogen vapors add to the total expulsion pressure. 
Since the helium is injected at the temperature of the 
liquid hydrogen and no external heat is applied, all 
of the heat of vaporization comes from the bulk liquid. 
For a specific application, the helium is stored as a 
pressurization gas at the temperature of liquid hydro-
gen in order to minimize the volume and weight of the 
helium storage tanks. Heating the gas reduces the 
amount of helium required for pressurization, but adds 
the weight and complexity of heating equipment. Ex-
periments have shown that the weight of helium re-
quired for the submerged-injector method, using cold 
helium at liquid hydrogen temperature, is approxi-
mately the same as that required for a warm-gas sys-
tem at a tank pressure of 130.9 kN/m 2
 (19 psia). This 
weight is approximately one-fourth of that required 
to pressurize with cold helium admitted above the 
liquid.
Notes: 
1. Other means could also be used to vaporize 
cryogenic liquid into the pressurizing gas. For ex-
ample, the conventional diffusion nozzle used to 
admit pressurizing gas above the liquid could be 
replaced by a venturi nozzle with a dip tube extend-
ing from the low-pressure region in the nozzle 
throat into the bulk liquid. In the nozzle throat, the 
liquid drawn up through the dip tube would vapor-
ize and mix with the pressurizing gas. 
2. The principle of the submerged gas injector could 
also be adapted for subcooling the cryogenic liquid, 
since the heat of vaporization comes from the 
liquid. 
3. This innovation is in the conceptual stage only, 
and, as of the date of publication of this document, 
no model or prototype has been constructed. 
4. The following documentation may be obtained 
from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: 
NASA-TN-D-4102 (N67-33441), Helium Pres-
surant Requirements for Liquid Hydrogen 
Expulsion Using Submerged Gas Injection 
Technical questions may be directed to:

Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B71-10219
(continued overleaf) 
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.
https://ntrs.nasa.gov/search.jsp?R=19710000218 2020-03-17T02:19:03+00:00Z
Patent status: 
No patent action is contemplated by NASA. 
Source: W. R. Johnson and E. W. Conrad 
Lewis Research Center
(LEW-1123 1) 
Brief 71-10219	 Category 03,07


Submerged gas injector expels cryogenic liquids from tanks

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