Diffusive stability for a sonoluminescing gas bubble

The mass diffusion between the gas inside a bubble and the gas dissolved in liquid was considered for the stability of a sonoluminescing gas bubble. Barodiffusion, which is the mass flow due to the pressure difference between the gas pressure inside the bubble and ambient pressure, was also taken into account in addition to the mass diffusion due to concentration defects. Calculated results revealed that a steady-state balance of the mass flow between the bubble and the air dissolved in water could be maintained at partial pressures of about 0.03similar to0.14 atm, depending on the equilibrium bubble radius and driving sound amplitude. The calculated results provided an explanation of the observed results for an air bubble, which had not been properly understood before., The possibility of a diffusive stability being achieved at a lower partial pressure, as low as 3 mmHg, which is for a sonoluminescing argon bubble with extreme stability, was also discussed. The mass ejection mechanism in this case turned out to be barodiffusion. The expansion ratio of the maximum radius to the equilibrium radius was found to be a crucial parameter in determining the diffusive equilibrium condition.