Propagation of Ultrasonic Waves in Vapours near the Critical Point

Abstract

An experimental study is made of the velocity and absorption of ultrasonic waves in carbon dioxide and ethylene at frequencies between ½ and 2 Mc/s and at pressures up to 100 atmospheres in a variable-path acoustic interferometer At pressures above 10 atmospheres the results are independent of frequency (in this range) in the gaseous phase. The velocity and absorption coefficient reach a minimum near the condensation point, but especially at the critical point itself have high and indeterminate values when the change of phase takes place The ultrasonic viscosities calculated from these measurements are of the order of 1000 timesthose derived from transpiration or low-frequency oscillation experiments.