Technique involves extracting known volume of fluid and measuring system before and after extraction, volume of entrapped gas is then computed. Formula derived from ideal gas laws is basis of this method. Technique is applicable to thermodynamic cycles and hydraulic systems

Hunter, W. F.

Jolley, J. E.

English

NASA Technical Reports Server

May 1971	 Brief 71-10094 
NASA TECH BRIEF	
41 
Manned Spacecraft 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 aubscription 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. f. 20546. 
Determination of Gas Volume Trapped in a Closed Fluid System 
A formula derived from the ideal gas laws is the 
basis of a technique for rapidly measuring the 
quantity of entrapped gas in a sealed fluid system. 
Applicable to many thermodynamic-cycle and hy-
draulic systems, the technique entails extracting a 
small, known volume of fluid from the system and 
measuring the pressure drop that results. 
Starting with a lengthy set of assumptions, the 
ideal gas law is used to describe the state of an 
entrapped gas bubble before and after fluid ex-
traction. The following equation results: 
V = P 1 P 2 ( V 1 - V 2 ) /P5 (P 1 - P2), 
where	 Vs is the volume of entrapped gas at,stan-
dard pressure,	 - 
P 1 is the initial system pressure, 
2 is the system pressure after fluid extrac-
tfon,	 - 
P S is the standard pressure, and 
(V 1 - V2 ) is the volume of fluid extracted. 
Thus, by extracting a known volume of fluid and 
measuring the system pressure before and after ex-
traction, the volume of entrapped gas can be 
computed. 
The accuracy of the result depends strongly on 
the correctness of the initial assumptions. In order 
to obtain useable data for V 5 , correction factors 
must be applied to compensate for such error sources 
as: 1) departures of the gas from the ideal; 2) 
elasticity and thermal expansion of the system con-
tainer; 3) solubility of entrapped gas in the fluid,
and vapor pressure of fluid in the gas; 4) variation 
in hydraulic pressure within the system; 5) measure-
ment under nonequilibrium conditions; and 6) leak-
age of fluid from the system. 
Because these corrections are complex, it is not 
practical to apply this technique for a single 
measurement oh one system. Rather, it is intended 
for use where multiple measurements are required, 
either in repeated checks of one system or in 
single determinations on many identical systems. 
Under such circumstances, the measurements may be 
calibrated empirically, or approximate correction 
factors may be applied in advance, and the tech-
nique can then be used to give a go/no-go indica-
tion rather than an accurate measurement. 
Note: 
No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Manned Spacecraft Center, Code JM7 
Houston, Texas 77058 
Reference: B71-10094 
Patent status: 
No patent action is contemplated by NASA. 
Source: J. E. Jolley and W. F. Hunter, of

North American Rockwell Corp.

under contract to

Manned Spacecraft Center
(M SC- 15685) 
Category 06 
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 owned-rights.
https://ntrs.nasa.gov/search.jsp?R=19710000093 2020-03-17T02:22:14+00:00Z


Determination of gas volume trapped in a closed fluid system

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