Electromechanical densitometer continuously measures the densities of either single-phase or two-phase flowing cryogenic fluids. Measurement is made on actual flow. The instrument operates on the principle that the mass of any vibrating system is a primary factor in determining the dynamic characteristics of the system

Jacobs, R. B.

Macinko, J.

Miller, C. E.

English

NASA Technical Reports Server

April 1967	 Brief 67-10080 
NASA TECH BRIEF	
_1a 
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. 
Instrument Continuously Measures Density of Flowing Fluids 
Scotch I—ISynchronous Motor 
Yoke	 r-1 and Clutch 
Diaphragm Seal 
Dynamometer 
Ball Bearing 
Spline (Guide) 
Vacuum Space	
LTJ_ 
Insulation 
Pressure 
flh1flh1fl
	 Housing	 Bellows
 (
Transfer Line 
Coupling 
The problem: 
To design an instrument that will continuously 
measure the densities of either single- or two-phase 
flowing cryogenic fluids. In addition the measure-
ment must be made on actual flow, and not on a 
sample whose accuracy is doubtful. It is desirable to 
know the mass flow rates of cryogenic fuels and 
oxidizers to rocket engines during tests. The changes 
in density which can occur during transfer of the 
fluids make volume flow measurement unsatisfactory. 
Frequently mass flow rate is determined by obtaining 
a product of density and volume flow rates. The 
major difficulty with this method has been the lack of 
a satisfactory technique for measuring the density of a 
flowing fluid.
The solution: 
An improved electromechanical densitometer based 
upon the principle that the mass of any vibrating 
system is a primary factor in determining the dynamic 
characteristics of the system. Thus if the fluid flow-
ing through a system measurably affects the vibrating 
mass of the system, a means of measuring fluid density 
is provided. 
How it's done: 
The densitometer uses a movable section of the 
flow passage vibrated transversely at a constant 
amplitude and frequency as the sensing element. As 
the fluid passes through this tubular section, sup-
ported at each end by a bellows, a driving mechanism 
imparts an oscillating (sinusoidal) motion to both the 
0	 (continued overleal) 
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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movable flow passage and the fluid passing through it. 
A dynamometer (force gage) linked between the tubu-
lar member and the driver continuously measures the 
acceleration reaction (product of mass and accelera-
tion) of the fluid in the passage. Since the transverse 
motion of the movable section of the flow passage 
is dependent not only upon the force supplied from 
the mechanical oscillator but also upon the mass of 
the system (tube plus fluid), the mass of the system or 
tube motion basically becomes a function of the dens-
ity of the fluid. Thus by measuring the force with the 
dynamometer the density of the fluid can be deter-
mined. Since the force generates an electrical signal 
(the output of the dynamometer) in phase with the 
motion and proportional to resultant maximum 
force, this signal after rectification by appropriate 
circuitry provides a resulting signal that is propor-
tional to the maximum force. Consequently, the elec-
trical signal is a measure of the fluid density in the 
passage. 
Notes: 
1. Additional advantages of this instrument are its 
simplicity, reliability, and good frequency response. 
2. Mass flow rate is frequently determined by obtain-
ing ihe product of density and volume flow rates. 
This densitometer provides a very satisfactory 
technique for measuring the fluid density necessary 
for this mass flow measurement.
3. Performance results have indicated that this dens-
itometer is well suited for service in liquid oxygen 
and nitrogen single- and two-phase flow systems, 
and with only minor changes for use with liquid 
hydrogen. 
4. Additional details are contained in: The Review of 
Scientific Instruments, vol. 34, no. 1, p 24-27, 
January 1963. 
5. Inquiries concerning this invention may be di-
rected to:
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B67-10080 
Patent status: 
This invention has been patented by NASA (U.S. 
Patent No. 3,298,221), and royalty-free license rights 
will be granted for its commercial development.
Inquiries about obtaining a license should be ad-

dressed to NASA, Code GP, Washington, D.C. 20546.
Source: C. E. Miller, R. B. Jacobs,

and J. Macinko
of the National Bureau of Standards 
under contract to

Lewis Research Center 
(Lewis-309) 
Brief 67-10080	 .	 Category 01


Instrument continuously measures density of flowing fluids

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