Intensification of cavitational activity using gases in different types of sonochemical reactors

Abstract

Different gaseous additives can be used to intensify the cavitational activity in the sonochemical reactors as the presence of gases introduces heterogeneity in the liquid continuum. The extent of intensification is dependent on different parameters including the type of reactor especially in terms of the geometry and arrangement of transducers. The present work deals with understanding the effect of type of sonochemical reactor on the intensification of cavitational activity achieved using different gaseous additives. The different reactors used in the study include conventional ultrasonic horn reactor and a new design of large scale reactor operating at similar frequencies. Model reactions of Weissler reaction and salicylic acid degradation, which are both dictated by the production of hydroxyl radicals, have been used for quantification of cavitational activity. The different gaseous additives used in the work include air, oxygen, nitrogen and carbon dioxide. Effect of flow rate on the cavitational activity in both the sonochemical reactors has also been examined for the specific case of air as additive. Theoretical modeling studies have also been performed using COMSOL to predict the pressure field distributions and explain the effect of type of sonochemical reactor on the degree of intensification described as the percentage increase obtained due to the presence of additive. Overall it can be said that presence of gases enhances the cavitational activity and the effect is dependent on the type of reactor. The work presents new design related information in terms of effect of the type of reactors on the degree of intensification using gaseous additives, which would be especially important for all gas–liquid applications of sonochemical reactors.