Closed-loop rebreather system which includes pilot provides oxygen for use in aircraft by safe, reliable method of low weight and size and reduces expense of ground equipment. Water electrolysis generated oxygen is fed into rebreather loop which allows nitrogen elimination and water and carbon dioxide removal

Babinsky, A. D.

Kiraly, R. J.

Wynveen, R. A.

English

NASA Technical Reports Server

May 1972	 B72-10195 
NASA TECH BRIEF 
Ames Research Center	 -4r 
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. 
Aircrew Oxygen System 
The problem: 
To provide breathing oxygen for use in aircraft by 
a safe, reliable system of low weight and size which 
also reduces the expense of ground support equip-
ment, such as is required for LOX equipment. 
I	 Pilot	 I
IDeh
	
I Demand
Regulator
-
Water
Vent
 
HaO 
rt_Check 
Valve 
I	 I	 Blotrer 
I	 I	 I 
I______ I 
H2+C.	
CO2 Co 
	 H2
______________ centrator 
The solution: 
A closed-loop rebreather system which includes the 
pilot. Oxygen generated by water electrolysis is fed 
into the rebreather loop which provides for nitrogen 
elimination, water removal, and the removal of car-
bon dioxide.
How it's done: 
The arrangement of the system is shown in the 
figure. A blower is used to circulate breathing oxygen 
through the carbon dioxide concentrator which re-
moves the carbon dioxide from the circulating flow 
and transfers it to the hydrogen stream on the oppo-
site side of the concentrator cell. Parametric testing 
of single-cell carbon dioxide concentrators has dem-
onstrated good performance independent of oxygen 
flow rate. 
There is a possibility that the blower, check valve, 
and recirculating loop may not be necessary in the 
system since it does not appear that the convective 
transfer of carbon dioxide from the oxygen stream to 
the electrode is of significant resistance compared to 
the overall resistance of transfer of carbon dioxide 
from the oxygen to the hydrogen gas streams in the 
concentrator. In this event, the system would be 
simpler, with exhalation flow going directly through 
the concentrator and back to the pilot. 
The pilot's expiration enters the counter-lung which 
accommodates the pilot's tidal volume during breath-
ing to maintain the loop at constant pressure during 
the breathing cycle. Inhalation oxygen is drawn from 
the circulating loop through a heat exchanger used 
as a dehumidifier; this is required because the flow 
in the circulating loop will be about 49°C and nearly 
saturated with water vapor. A separator downstream 
of the dehumidifier removes the condensed water and 
directs it to a vent. 
Oxygen from the electrolysis cell enters the demand 
regulator to make up the oxygen consumed by the 
pilot, the carbon dioxide Concentrator, and system 
venting. Next, the oxygen is heated to a comfortable 
level for breathing by the pilot; during inhalation, 
Counter 
Lung
(continued overleaf) 
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the counter-lung is collapsed allowing this gas to 
enter the circulating loop. Check valves in the mask 
maintain the inspiration and expiration flows in the 
proper direction. The check valve in the recirculating 
loop prevents "short circuiting" in the breathing loop. 
The system also provides for breathing loop pres 
sure in excess of cabin pressure, as required at cabin 
altitudes above 38,000 feet (11.6 kin). The pressure 
breathing control will maintain the, breathing loop 
pressure constant at 3 psia (20.7 kN/m 2) at altitudes 
between 38,000 and 43,000 feet (11.6 and 13.1 km). 
Above 43,000 feet, loop pressure will remain at 18 
inches (4.48 kN/m 2) of water above ambient pressure. 
At cabin altitudes above 43,000 feet, pressure suits 
are required, and pressure breathing is accomplished 
by using air to pressurize the outside of the breathing 
bag in the counter-lung. The latter pressure is regu-
lated by an aneroid device similar to those employed 
in currently available pressure -breathing -demand 
oxygen regulators. 
It is necessary to remove the nitrogen from the 
breathing loop. Nitrogen is released by the human 
body because of the partial pressure gradients which
occur during the breathing of pure oxygen. The 
breathing loop system accomplishes this by venting a 
small portion of the pilot's exhaled gases. 
Notes: 
1. Details of the subsystem components are found in 
a series of Tech Briefs entitled, "Carbon Dioxide 
Concentrator," "Water Electrolysis Module," and 
"Counter Lung." 
2. Additional information may be obtained from: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP 72-10195 
Patent status: 
No patent action is contemplated by NASA. 
Source: Andrew D. Babinsky, Raymond J
.
 Kiraly,
and Richard A. Wynveen of

TRW, Inc.

under contract to

Ames Research Center 
(ARC-10247) 
B72-10195	 Category 05


Aircrew oxygen system

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