Acoustic cavitation field prediction at low and high frequency ultrasounds

Sonochemistry, or chemistry under ultrasound, has increased in interest in the past few years. Electricite de France is involved in scaling up this new technology to industrial plants. The propagation of a power ultrasound wave (from 20 to 800 kHz) through a liquid initiates a little-known phenomenon called acoustic cavitation. Inceptions and germs grow into bubbles which collapse, possibly giving rise to extreme conditions of temperature and pressure (assessed to be up to 10 000 K and 500 atm). These conditions initiate and greatly enhance chemical reactions. Thus, it is important to know where bubbles are and how intense cavitation is, depending on geometric and acoustic factors. Then, mathematical modelling may help to predict acoustic cavitation fields. Two computations, the first one based on linear acoustic equations and the second one based on fluid dynamics equations, are presented. Calculated pressure fields are obtained in the case of a cylindrical sonoreactor at 28 and 500 kHz. The comparison with experimental observations and measurements shows good agreement with both theory and calculations.