Numerical Modeling of Thermal and Hydrodynamic Processes During the Bubble Compression Due to the Ambient Pressure Rise in a Liquid

Recent attention has been focused on the use of the cavitation in developing the new type of chemical reactor. The idea is based on the hypothesis that temperature increase in collapsing bubbles is significant and sufficient for successful high-temperature chemical reactions of a certain types. The direct experimental determination of temperature inside cavitation bubbles is an extremely difficult task. The theoretical estimates, that do not take into account heat- and mass transfer mechanisms in “bubble-ambience” system, lead to enormous magnitudes of temperatures, up to a few thousands degrees. In this study, we report on numerical simulations of the processes occurring during the compression of a single spherical vapor bubble in infinite incompressible medium. The reduction of initially equilibrated bubble is provoked by abrupt pressure rise in a liquid. The mathematical model used for calculations is aimed to take into account heat transfer and phase transitions on the bubble/liquid interface in full details. It is shown that the heat absorption by liquid and vapor condensation on the bubble interface can significantly, by one or two orders of magnitude, reduce the rate of the temperature and pressure increase in the bubble. In particular, the regime, named Rayleigh-regime, has been detected. The pressure rise inside the bubble is very slow in this regime due to intense condensation of the vapor. As the result, the dynamic of the bubble collapse is basically unresponsive to the pressure rise inside the bubble. Virtually all external work contributes to the increase of the kinetic energy of the liquid in this case and the system is warmed up by the heat released during the condensation. The obtained results show that idea of mandatory significant temperature rise in collapsing bubbles during cavitation might be only a hypothesis that requires additional investigations involving careful consideration of thermal aspects of the problem.