The influence of the dissolved ion concentration on the acoustic cavitation threshold of water

Abstract

The variation in the transient acoustic cavitation threshold of water was measured as a function of the dissolved ion concentration of various salts. The measurements were made with a resonant sphere system in which solid particle size, water temperature, and dissolved gas content could be controlled within a closed circulating system. The normal criterion used for a cavitation event was the detection, by a photomultiplier tube, of sonoluminescence produced by a collapsing cavity. Water with a specific conductance of about 1 μS cm−1 was assigned zero concentration for the first data point. Measurements were then made at successively higher concentrations, up to 10 mmoles 1−1. The salts were chosen to check and extend the measurements of a previous researcher [V. A. Akulichev, Sov. Phys. Acoust. 12, 144–149 (1966)], who first detected a dependence of the cavitation threshold on dissolved ion concentration. The results of our measurements show that the threshold increases with ion concentration, reaching saturation at concentrations of 2 mmoles 1−1 or less. This dependence is in the opposite direction to that observed by Akulichev. Our results will be analyzed with regard to the standard models of cavitation nucleation. [Work supported in part by the Office of Naval Research and the National Science Foundation.]