Influence of interactions between bubbles on physico-chemical effects of acoustic cavitation

Ultrasound technology has been extensively used as one of the efficient and economic methodology to achieve the desired outcomes in many applications by harnessing the physico-chemical effects of acoustic cavitation. However, the cavitation-associated effects, primarily determined by the oscillatory dynamics of cavitation bubbles, are considerably complex and still remain poorly understood. The main objective of this study was to perform a numerical analysis of the acoustic cavitation (i.e., the cavitation dynamics, the resultant temperature, pressure and chemical yields within collapsing bubbles), particularly focusing on the influence of the interactions between bubbles. A comprehensive model was developed to simulate the acoustic cavitation dynamics via combining the influences of mass transfer, heat conduction and chemical reactions as well as the interaction effects between bubbles. The results demonstrated that only the large bubble exerts a greater impact on the small one in a two-bubble system. Specifically, within parameter ranges covered this study, there are noticeable decreases in the expansion ratio of the small bubble, the resultant temperature, pressure and molar yields of free radicals, hence weakening the cavitation intensity and cavitation- associated physico-chemical effects. Moreover, the influences of the interactions between bubbles were further assessed quantitatively under various parameters, such as the ultrasound amplitude P_A and frequency f, the distance between bubbles d₀, the initial radius of the large bubble R₂₀, as well as the liquid properties (e.g., surface tension σ and viscosity μ). It was found that the suppression effect can be amplified when subjected to ultrasound with an increased P_A and/or a decreased f, probably due to a stronger cavitation intensity under this condition. Additionally, the suppression effect is also enhanced with a decrease in d₀, σ and μ, but with R₂₀ increasing. This study can contribute to deepening knowledge about acoustic cavitation and the resultant physical and/or chemical effects, potentially further facilitating the ultrasound-assisted various applications involving acoustic cavitation.