An improved categorization of vapor bubble collapse: Explaining the coupled nature of hydrodynamic and thermal mechanisms

This work presents a numerical and theoretical analysis of the intermediate bubble collapse, where in contrast to the thermally-induced or inertia dominated collapse, both the effects of liquid-vapor interfacial heat transfer and the advection of the surrounding liquid play an important role. A key distinguishing characteristic of this type of collapse is that the interfacial temperature and bubble pressure are continuously changing throughout the collapse process. This behavior is caused by a non-negligible value for the interfacial vapor velocity, which is characterized by a magnitude of the same order as the bubble surface regression rate. This behavior is in contrast to the inertial or thermal collapse, where, in these regimes, the vapor velocity is essentially zero. Incorporating the rate of change of background system pressure, a regime map for bubble collapse is also presented where the parameter space is defined by B-sat and xi and extends the previous categorization of Florschuetz and Chao (1965) where only B-eff was used. Specifically, the present work quantitatively shows that the collapse behavior changes when the process is initiated by a gradual rate of pressurization in the surrounding liquid phase instead of the often used approximation of a step change. (C) 2019 Elsevier Ltd. All rights reserved.