A theoretical model is sought to explain recent experimental results which have shown the sudden onset of inertial cavitation after a significant period of ultrasound insonation. It is thought that there initially exists a population of bubbles with sub-optimal radii for inertial cavitation, which grow during the insonation period to become nuclei within the optimal size range to cavitate inertially. Rectified diffusion during bubble oscillation, and the changes in the bubble nucleation environment and their subsequent dynamics caused by ultrasonic heating, are amongst the mechanisms that could be responsible for nuclei growth. In this work, the effects of elevating the temperature of the medium surrounding a bubble, resulting in higher vapour pressures and decreased solubility of gas in the bulk medium, is investigated. A single bubble model is formulated by coupling a numerical solution of the mass diffusion PDE and the Rayleigh-Plesset Equation, taking into account temperature dependence of surface tension, vapour pressure, Henry’s constant and diffusion coefficient. It is shown that an increase in the temperature at HIFU-relevant heating rates is on its own not sufficient to increase the radii of sub-optimal bubbles into the optimal range for inertial cavitation to take place.
