Influence of He and Ar Flow Rates and NaCl Concentration on the Size Distribution of Bubbles Generated by Power Ultrasound

A technique based on pulsed ultrasound and sonoluminescence emission was used to measure the size and size distribution of bubbles generated by 355 kHz power ultrasound under continuous Ar or He flow in aqueous NaCl solutions. It was observed that the bubble size strongly decreased with increasing NaCl concentration and that this decrease was much stronger than in solutions presaturated with Ar or He. This size decrease is attributed to the combination of the salting-out effect of the salt and the introduction of bubble nuclei by the continuous gas flow. Besides, the comparison of Ar and He bubbles underlines the effect of the gas diffusion coefficient on the bubble size reached.