Effect of Surface Tension on the Cavitation Threshold of Water

Abstract

The threshold for transient cavitation in degassed water has been measured in a stationary wave system as a function of surface tension. A surfactant was used to vary the surface tension of water from approximately 70 to 30 dyn/cm2. The cavitation threshold was found to vary inversely with the surface tension in disagreement with the theoretical predictions of Apfel [J. Acoust. Soc. Amer. 48, 1179–1186 (1970)]. Glass capillary tubes were used to construct macroscopic models of microscopic crevices thought to nucleate cavitation. The crevices were coated with polystyrene in order to obtain a nonwettable surface. Measurements made of the receding contact angle of an air-water interface moving in the model crevice showed a critical dependence of the contact angle upon surface tension. Motion pictures will be shown of the receding contact angle as a function of surface tension and how this receding interface may nucleate cavitation. If an empirical relationship is made between the contact angle and the surface tension, and this empirical dependence used in Apfel's theory, then good agreement is obtained between theory and experiment. [Work supported by the Office of Naval Research and the Naval Academy Research Council.]