For environmental control system functions sensitive to atmospheric composition, components are test-operated in helium-oxygen and nitrogen-oxygen mixtures, pure oxygen, and air. Transient heat- and mass-transfer tests are conducted for carbon dioxide adsorption on molecular sieve and for water vapor adsorption on silica gel

Blakely, R. L.

Nelson, W. G.

English

NASA Technical Reports Server

June 1970
	
Brief 70-10094 
NASA TECH BRIEF H 
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. 
Atmospheric Composition Affects Heat-and Mass-Transfer Processes 
Major parts of Environmental Control Systems 
(ECS), such as ventilation, humidification, tempera-
ture control, and purification subsystems, are affected 
by atmospheric composition. Such key components as 
heat exchangers, condensers, and adsorption beds 
rely on heat- and mass-transfer processes for opera-
tion; the atmospheric gas is normally used to reject 
the ECS heat load; and, in some cases, a portion of the 
gas is processed to remove carbon dioxide and other 
undesired constituents. Since heat- and mass-transfer 
rates, together with pressure drops, depend upon the 
physical properties of the process gas, the performance 
and size of the ECS are affected by atmospheric com-
position. 
For those ECS functions most sensitive to atmos-
pheric composition, typical components have been 
test-operated in various atmospheres: helium-oxygen 
(He-02 ) and nitrogen-oxygen (N 2 -0 2) mixtures at 5, 
7, and 10 psia; pure oxygen at 5 psia; and air at 14.7 
psia. The partial pressure of oxygen in the mixed-gas - 
atmospheres was fixed at 3.5 psia. Transient heat-
and mass-transfer tests were conducted for carbon 
dioxide adsorption on molecular sieve and for water 
vapor adsorption on silica gel; steady-state heat-
transfer tests were run on a typical heat exchanger. 
Pressure drop data were obtained both for the adsorp-
tion beds and for the heatxchanger. 
Sample adsorption-bed designs were generated by 
a computer program which used the experimental 
heat- and mass-transfer data. All of the molecular 
sieve designs were adiabatic, because the bed tempera-
ture did not increase significantly on adsorption of 
carbon dioxide. However, both adiabatic and iso-
thermal designs were used for the silica-gel beds, 
because the high heat of adsorption and large amount
of water adsorbed produced significant changes in the 
adiabatic bed temperatures design, thereby requiring 
large beds. The isothermal silica-gel beds, designed 
for minimum size, were between 1/3 and 1/6 the size 
of the adiabatic designs. An actual silica-gel bed 
design probably would be externally cooled during 
adsorption. Therefore, the size of the bed would lie 
between limits determined for the adiabatic and iso-
thermal designs. 
For the sample adsorption-bed designs, weight 
savings of up to 5% were generally obtained by using 
N 2 -0 2 gas mixtures at higher pressure levels. In the 
case of the heat exchanger, some saving in total weight 
was obtained by using He-0 2 gas mixtures at higher 
pressure levels. The heat exchanger itself weighed 
less for N 2 -0 2 gas mixtures, but this was offset by 
higher pressure drop, which necessitated the use of a 
higher-power, heavier fan motor. 
Notes: 
1. Information derived from this program may be 
applied in the design of environmental control 
systems used in aircraft, commercial buildings, 
subways, and industrial facilities. 
2. The following documentation may be obtained 
from:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: 
NASA-CR-891 (N67-37320) Engineer-
ing Criteria for Spacecraft Cabin Atmos-
phere Selection
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately ownedrights.
https://ntrs.nasa.gov/search.jsp?R=19700000090 2020-03-17T00:22:48+00:00Z
Patent status: 
No patent action is contemplated by NASA. 
Source: R. L. Blakely and W. G. Nelson of 
McDonnell Douglas Corporation 
under contract to 
NASA Headquarters 
(HQN- 10271) 
Brief 70-10094	 Category 04


Atmospheric composition affects heat- and mass-transfer processes

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