Ultrasonic measurement of condensate film thickness

The current work describes a modified time-of-flight ultrasound signal processing technique applied to the study of a distal liquid layer with a free surface. The technique simulates multiple reflections analytically and determines the film thickness by comparison to the measured pulse echo signal. The technique is applied with 20 MHz transducers to an n-pentane film condensing on a copper plate. The technique proved capable of measuring liquid thickness from approximately 8 pm, 1/6 the acoustic wavelength in pentane, to greater than 5 mm. Near the lower thickness limit, echoes from the liquid/vapor interface overlap each other and the significantly larger echoes from the metal/liquid interface. (C) 2008 Acoustical Society of America