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Knowledge of the speed of sound in fluids is valuable in many ways.
Accurate speed-of-sound data verify PVT measurements, and, thus,
improve the accuracy of equations of state, and provide information on
the ratio of heat capacities through the following relationship:
where W is the velocity of sound, Cp and Cv are heat capacities, rho is fluid density, and P is pressure. Speed-of-sound data tie together the caloric property of heat capacity to the PVT surface thereby providing an essential consistency check in the development of accurate equations of state. In practical applications, speed-of-sound data are necessary to determine flow rate through a sonic-nozzle flowmeter and to verify the operation of ultrasonic flowmeters.
The spherical acoustic resonator measures the speed of sound in gas. The average internal radius of the sphere is determined by making measurements on a gas whose speed of sound is well known. In this case, argon was used. The measurement parameters are as follows:
The expanded uncertainty (95% confidence interval) for speed-of-sound measurements is ±0.05%. The properties of argon gas, as well as a detailed description of the theory of operation of the spherical resonator, can be found in:
Moldover, M.R.; Mehl, J.B.; Greenspan, M.J. Acoust. Soc. Am. 79: 2; 1986.
The speed-of-sound in liquids will be measured by the pulse-echo interference method. Twin crystals, one emitter and one receiver, are placed at the ends of a cylinder whose length has been measured. By determining the pulse repetition frequency at which maximum constructive interference occurs, the speed-of-sound can be calculated. The measurement parameters are:
The expanded uncertainty (95% confidence interval) for
speed-of-sound measurements is ±0.05%.
Contact: |
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Dr. Richard A.
Perkins |
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