Numerical modelling of single-bubble acoustic cavitation in water at saturation temperature

Abstract

Acoustic cavitation plays a major role in the enhancement of many Ultrasound-assisted processes, such as distillation and extraction. This work aims to numerically investigate single-bubble acoustic cavitation in water at saturation temperature. To this end. a new model that describes single-bubble acoustic cavitation was developed. One novel feature of this model is that it resolves the spatial variation of chemical species and energy in the bubble and surrounding liquid with the consideration of shell effect, which allows better prediction of heat and mass transfer during cavitation. This is realized by adopting a unique semi-lagrangian Finite Volume Method with dynamic mesh. Besides, a novel approach, which makes use of interfacial jump conditions that enforce simultaneous energy and mass conservation, is implemented in the model to allow simultaneous coupling of energy and mass transfer across the bubble interface. Dissociation of liquid molecules (chemical reactions) is taken into account. The developed model was used to investigate single-bubble acoustic cavitation in water at room temperature and saturation temperature. The simulation results showed that, despite the much stronger bubble collapse (about twice as strong), the volume-averaged peak temperature reached during cavitation in water at saturation temperature is lower compared to that at room temperature (3877K vs 4600K) due to higher amount of vapor trapped in the bubble during the collapse. Nevertheless, the amount of reactive free radical produced per bubble during the collapse at saturation temperature is much higher (1 – 2 order higher in amount) due to higher vapor molecule concentration in bubble. However, the spatial extent of radical production could be lower due to the much higher bubble expansion. The model and findings could be helpful for the design and optimization of Ultrasound-assisted processes.