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A computational study aiming to simulate an oxygen single acoustic bubble oscillation under a dual-frequency sonication was presented in this paper. The non-linear response of the bubble to the superposition of two fields of ultrasonic waves was investigated through dynamics parameters, collapse ratios and average velocities. The main goal of this analyze is to link the properties of the wave resulting from the dual-frequency excitation to the dynamics behavior of the bubble. The obtained results prove that, in contrast with the mono-frequency, coupling a wave to lower frequencies enhances the collapse duration and raises the compression ratio in the case of 35 kHz, while associating any of the studied waves to a higher frequency elevates the number of bubble oscillations during a time interval as compared to mono-frequency. The total sonochemical production has been investigated in accordance with the dynamics results, as well as the proportions of the three predominant free radicals, that show a dependency on the value of the basic frequency.

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The present paper consists of a numerical study attempting to characterize the bubble population within a sonochemical reactor through modeling and simulating the number density of bubbles and the void fraction. In a first step, both previous parameters were estimated under 1.52 bar and various acoustic frequencies ranging from 20 to 1000 kHz in function of normalized time. The results showed that the average number density of bubbles, varying within the interval 2.8104−1.4 × 1012 bubbles dm−3, follows a clear monotonous evolving trend as the frequency increases, while the average void fraction, comprised between 9.05 × 10−5 and 1.95 × 10−4, demonstrates no dependency of acoustic conditions. In a second step, an energy analysis was performed at microscopic and macroscopic scales, which led the authors to figure out that the evolution of the number density of bubbles in function of acoustic frequency is mainly governed by the energy required to maintain oscillating the single cavitation bubble.

The mechanical disturbance created by an ultrasonic wave travelling through a liquid medium induces the formation of cavitation that oscillates due to rarefaction and compression of the wave. The duration and the magnitude of the pressure applied by the ultrasonic wave at each instant would generate a specific impact on the variation of the bubble radius, the temperature, the pressure and the mass inside it. In this paper, a numerical study is conducted to simulate four waveforms (sinusoidal, square, triangular and sawtooth) travelling an aqueous media saturated with oxygen with an amplitude of 1.5 and 2 atm and a frequency of 200, 300 and 500 kHz. The purpose is to highlight the mass evolution within acoustic cavitation bubble during one cycle due to physical transformations and sonochemical effect. The obtained results demonstrated that square signal enhances temperature and pressure growth inside the bubble, as well as mass transfer by evaporation and condensation. This leads to an improvement of produced quantities of free radicals but also to a selectivity of O as a major product in the detriment of HO and OH. These trends are less and less observed when passing to sinusoidal, triangular and square signal.