Effect of static pressure on acoustic energy radiated by cavitation bubbles in viscous liquids under ultrasound

The effect of static pressure on acoustic emissions including shock-wave emissions from cavitation bubbles in viscous liquids under ultrasound has been studied by numerical simulations in order to investigate the effect of static pressure on dispersion of nano-particles in liquids by ultrasound. The results of the numerical simulations for bubbles of 5 mu m in equilibrium radius at 20 kHz have indicated that the optimal static pressure which maximizes the energy of acoustic waves radiated by a bubble per acoustic cycle increases as the acoustic pressure amplitude increases or the viscosity of the solution decreases. It qualitatively agrees with the experimental results by Sauter et al. [Ultrason. Sonochem. 15, 517 (2008)]. In liquids with relatively high viscosity (similar to 200 mPa s), a bubble collapses more violently than in pure water when the acoustic pressure amplitude is relatively large (similar to 20 bar). In a mixture of bubbles of different equilibrium radius (3 and 5 mu m), the acoustic energy radiated by a 5 mu m bubble is much larger than that by a 3 mu m bubble due to the interaction with bubbles of different equilibrium radius. The acoustic energy radiated by a 5 mu m bubble is substantially increased by the interaction with 3 mu m bubbles. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3626130]