An alternative technique for determining the number density of acoustic cavitation bubbles in sonochemical reactors

[Display omitted] •A novel technique is developed for determining the active bubbles’ number in sonochemical reactor.•The technique is based on determining CCl4 conversions per bubble and in the whole solution.•An advanced cavitation model was applied for predicting the single bubble sono-conversion.•The number density of bubbles increased monotonically with ultrasound frequency increase.•High level of consistency between our findings and those found in the literature was obtained. The present paper introduces a novel semi-empirical technique for the determination of active bubbles’ number in sonicated solutions. This method links the chemistry of a single bubble to that taking place over the whole sonochemical reactor (solution). The probe compound is CCl4, where its eliminated amount within a single bubble (though pyrolysis) is determined via a cavitation model which takes into account the non-equilibrium condensation/evaporation of water vapor and heat exchange across the bubble wall, reactions heats and liquid compressibility and viscosity, all along the bubble oscillation under the temporal perturbation of the ultrasonic wave. The CCl4 degradation data in aqueous solution (available in literature) are used to determine the number density through dividing the degradation yield of CCl4 to that predicted by a single bubble model (at the same experimental condition of the aqueous data). The impact of ultrasonic frequency on the number density of bubbles is shown and compared with data from the literature, where a high level of consistency is found.