Fluidic oscillator measures the humidity of the hydrogen stream leaving a hydrogen-oxygen fuel cell. The instrument provides continuous readings with a certain speed of response

Prokopius, P. R.

English

NASA Technical Reports Server

March 1967	 Brief 67-10063 
NASA TECH. BRIEF	
-a 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
•	 Fluidic Oscillator Used as Humidity Sensor 
Delay Line (Oscillator Temperature) 
Input Stream	 I Reference I	 j 
unction Data Analyzer  
jCDWint) The rmowuple	 Amplifier I )Transistorized Discriminator Analog Computer) Fluidic Osdilator
'staI _________________
Transducer	 Amplifier
Direct-Cur	 m rent 
Voltage Freauency 	 Mass Ratio 
Attad,ment Wall Outlet Stream	 I	 Electronic Analog Recerder 
I Counter 
Power For Calibration Check 
Stream
SCHEMATIC OF FLUIDIC OSCILLATOR 
A test program was undertaken to investigate 
the dynamics of hydrogen—oxygen fuel cell systems. 
In the type of system presently being studied, the 
water produced in the cells is removed in vapor form 
by a recirculating stream of hydrogen. Part of the test 
program consists of introducing controlled disturb-
ances into the humid hydrogen stream that enters the 
fuel cell and studying the effects of these disturbances. 
To study the effects on the fuel cell water removal 
processes, it is necessary to know, on a continuous 
basis, the humidity (steam-to-hydrogen mass ratio) of 
the hydrogen stream leaving the fuel cell. The instru-
ment to be used for measuring the recirculating stream 
humidity, in addition to being a continuous reading 
device, has to have a certain speed of response. Since 
a measurement technique or a humidity transducer 
with the required speed of response could not be 
found, an instrument based on a fluid oscillator 
concept was designed and developed. 
Complete details of this effort are contained in a 
technical memorandum, "Use of a Fluidic Oscillator 
as a Humidity Sensor for a Hydrogen—Steam Mix-
ture," by Paul R. Prokopius, Lewis Research Center, 
No. E-3413, May 1966. 
A test program was conducted on the instru-
ment to define its steady state and transient perform-
COMPLETE HUMIDITY SENSOR 
ance. The test program also resulted in a determina-
tion of the failure modes and accuracy limitations of 
the instrument. An analog computer program that 
serves as a data analyzer and converts the humidity 
sensor from an indirect to a direct reading instru-
ment was also developed. The program converts the 
normal instrument output of frequency of oscillation 
at a given temperature and pressure directly to a 
steam-to-hydrogen mass ratio reading. 
The calibration accuracy was approximately ±2 
percent in mass ratio, over the mass ratio calibration 
range of 0.8 to 2.1. Analysis of frequency response 
data indicated that the response of the sensor was 
flat at least to the 3 cps limit of the test apparatus. 
Note: 
Copies of the technical memorandum are available 
from: Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B67-10063 
Patent status: 
No patent action is contemplated by NASA. 
Source: P. R. Prokopius 
(Lewis-340) 
Category 05 
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. 
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Fluidic oscillator used as humidity sensor

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