Ultrasonic Propagation in High-Temperature Gases

Abstract

An ultrasonic pulse method (1 to 3 MHz) has been used to measure both sound speed and absorption in monatomic and polyatomic gases in a temperature range of 300° to 20 000°K and at atmospheric pressure. In monatomic gases in a temperature range where no ionization occurs, the ultrasonic technique described may be used to determine shear viscosity and thermal conductivity. In nitrogen and oxygen, in the range of 5000° to 10 000°K, relaxation times due to the excitation of bound electrons have been determined. In argon at T>8000°K, the effects of ionization and radiation on sound propagation are investigated. The temperatures were calculated from theoretical temperature-sound-velocity relations. The main emphasis of this work is to determine experimentally the acoustic properties of gases at elevated temperatures and to then relate these properties in terms of various relaxation mechanisms—including, for example, excited electronic states, ionization, and radiation. For all the gases investigated, the usefulness of ultrasonics to obtain previously unknown quantities will be discussed.