An apparatus, operating on the principle of wet and dry bulb thermometry, permits intermittent or continuous measurement of the concentration of droplets dispersed in a gas stream over a wide range of gas pressure

Booth, F. W.

English

NASA Technical Reports Server

December 1964
	 Brief 64-10237 
NASA TECH BRIEF
	
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-..	 -- ----
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint 
industry with the technical content of an innovation derived from the space program. 
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Apparatus Measures Concentration of Suspended Droplets in

Gas Streams 
Gas Flow 
I 
Wet-Bulb Cell 
Wet-Bulb Thermocouple 
Orifice
Wick 
Liquid Reservoir 
Dry-Bulb Thermocouple
Screen 
Dry-Bulb Cell
Heater Leads  
Resistance Heater 
Heating	 Celli
 . > 
Flow Control Valve 
Gas Flow =wW Gas Inlet 
The problem: Determining the concentration (mass concentration of droplets dispersed in a gas stream
	
per unit volume) of droplets of water or other liquids
	 over a wide range of gas pressure. 
	
condensed from vapor or mechanically entrained in
	 How it's done: The apparatus contains an expan-
	
gas streams subjected to various pressures. In wind- 	 sion chamber which is divided into three connecting 
	
tunnel experiments and in many process industries, for 	 cells: a heating cell, a dry-bulb cell, and a wet-bulb 
	
example, it is important to know the concentration of
	 cell. A screen partitions the heating cell from the dry-
	
water droplets in air saturated with water vapor at
	 bulb cell, and an orifice separates the latter from the 
	
points upstream and downstream of moisture entrain-
	 wet-bulb cell at the top of the chamber. Flow of gas 
ment separators. 	 into the tube at the bottom of the apparatus is regu-
	
The solution: An apparatus, operating on the prin-	 lated by a flow-control valve. The heating cell contains 
	
ciple of wet- and dry-bulb thermometry, which per-
	 an electrical resistance heater in the walls of a hollow 
	
mits intermittent or continuous measurement of the 	 tube which provides an unrestricted passage for the 
(continued overleaf) 
	
This document was prepared under the sponsorship of the National 	 this document, or that the use of any information, apparatus, method, 
	
Aeronautics and Space Administration. Neither the United States Govern, 	 or process disclosed in this document may not infringe privately-owned 
	
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes	 rights; or B. Assumes any liabilities with respect to the use of, or for 
	
any warranty or representation, express or implied, with respect to the	 damages resulting from the use of, any information, apparatus, method, 
	
accuracy, completeness, or usefulness of the information contained in	 or process disclosed in this document. 
https://ntrs.nasa.gov/search.jsp?R=19640000066 2020-03-11T17:04:18+00:00Z
gas. A thermocouple extending into the dry-bulb cell 
measures the dry-bulb temperature of the gas, and a 
thermocouple covered with a wick saturated with the 
liquid in the gas stream measures the wet-bulb temper-
ature of the gas flowing through the wet-bulb cell. 
In making a measurement with the apparatus, a 
sample of the saturated, wet gas at a given pressure and 
temperature is introduced into the heating cell where 
it is isothermally expanded. As a result of this expan-
sion, the droplets originally present in the gas are con-
verted into vapor and the gas becomes unsaturated. 
The gas stream then passes through the screen (which 
mixes the gas and vapor to ensure a homogeneous 
unsaturated condition) into the middle cell where the 
dry-bulb temperature is measured. The wet-bulb tem-
perature of the gas is measured as it passes across the 
thermocouple in the wet-bulb cell. The orifice between 
the dry- and wet-bulb cells, which is replaceable to 
provide desired flow rates, causes the gas to flow 
across the wick on the thermocouple at the proper 
velocity for accurate measurement of the wet-bulb 
temperature. 
From the wet- and dry-bulb temperature measure-
ments, the percentage of unsaturation of the gas leav-
ing the top of the apparatus (or relative humidity in 
the case of water vapor) is easily calculated or read 
from standard reference tables. The calculated data 
may then be used to derive the concentration (mass 
per unit volume) of vapor in the exhaust gas from pub-
lished tables or by means of a simple formula. This 
value is then multiplied by the expansion ratio of the
gas flow on both sides of the flow control valve to ob-
tain the concentration of the total liquid content 
(vapor plus droplet concentration) in the original gas 
stream. Since the original gas stream was saturated 
with respect to its vapor content (at the inlet tempera-
ture) the concentration of vapor in the original stream 
is readily calculated or determined from tables and 
subtracted from the total concentration to obtain the 
concentration of droplets originally present in the 
stream. 
Notes: 
1. Liquid-filled thermometers can be used instead of 
thermocouples for temperature measurement in the 
apparatus. 
2. If only approximate measurements are required, 
the heater cell may be omitted. 
3. Further technical information concerning this in-
invention is described in U.S. Patents 2,926,521 
and 2,939,311. Inquiries may also be directed to: 
Technology Utilization Officer 
Langley Research Center 
Langley Station 
Hampton, Virginia, 23365 
Reference: B64-10237 
Patent status; NASA encourages the immediate 
commercial use of this invention. It is owned by NASA 
and inquiries about obtaining royalty-free rights for its 
commercial use may be made to NASA Headquarters, 
Washington, D.C., 20546.
Source: Franklin W. Booth 
(Langley-3 1) 
Brief 64-10237	 Category No. 01


Apparatus measures concentration of suspended droplets in gas streams

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