Abstract
Evaluation of the number of cavitation bubbles in an ultrasonic standing wave field is studied experimentally with light scattering through the measurements of the scattered light intensity from the bubbles with periodic variation synchronous to the period of sound at various contents of the dissolved oxygen (DO). It is shown that at moderate amplitude of sound pressure the averaged level of a waveform of scattered light from the bubbles at an antinode of sound pressure increases as a content of DO in a distilled water becomes larger, and then it decreases after the maximum appears. At higher amplitude of sound pressure, the maximum of the averaged level shifts towards the lower side of DO content. It is also shown that there is a cavitation threshold of DO content and at higher amplitude of sound pressure the threshold appears at lower DO content. The measured results correspond to the number of bubbles at the antinode, while the DO content does to the whole amount of cavitation bubbles in a vessel. The present method enables an evaluation of relative variation in the number of cavitation bubbles at antinode of sound pressure, which is important for accomplishment of high efficiency in sonochemical reaction.
