An ultrasonic technique for measuring the transient movements of a liquid-vapour interface

A pulsed ultrasonic technique is described which measures the transient movements of a liquid-vapour interface. The time for a reflected pulse to return from the vapour interface is converted to a pulse-height, providing a signal which may be displayed on the y trace of an oscilloscope, the x trace being real time. By use of a pulse repetition frequency of up to 20 kHz, the position of the vapour front with time may be displayed and recorded directly for boundary velocities of up to 100 m s −1 . The results obtained using this system in a typical application are compared with those derived from analysis of a fast cinephotographic record. The advantages of the ultrasonic system are its ready applicability to opaque media and the immediate availability of the information.