Mapping of acoustic streaming in sonochemical reactors

Abstract

Acoustic streaming is an important phenomenon observed in sonochemical reactors controlling the physical effects due to the cavitation. Not many efforts are observed, however, in exact quantification of the generated liquid circulation currents, experimentally or theoretically. The present work has been directed at quantifying the liquid circulation velocity using laser Doppler anemometry (LDA) and particle image velocimetry (PIV) techniques and establishing its dependency on the location in the reactor and the power dissipation levels. The measurements reported in the work are useful in understanding the flow distribution in the sonochemical reactor and can aid in strategic placement of the reactants in zones of maximum cavitational intensity as well as in strategic placement of process-intensifying parameters such as flow distributors and multiple transducers for eliminating zones with minimal cavitational activity. Theoretical analysis has also been carried out to compare the actual values of velocity measured using the two optical techniques. It has been observed that the liquid circulation currents are at a maximum near the transducer and secondary currents are generated at the reactor wall and the bottom. It has also been shown that the usefulness of ultrasonic horn-type reactors is restricted to a small size of reactors.