On the mechanics of thermal collapse of a vapor bubble translating in an isothermal subcooled liquid

Abstract

In this work, we numerically simulate bubble radius and velocity in a thermal collapse of a vapor bubble translating in an isothermal subcooled liquid based on solving the equations of energy and motion simultaneously. The mechanics of the collapse in the thermal regime plays a significant role in the thermal convection from the vapor-liquid interface of a translating bubble. In our mathematical model, the equation of motion considers the added mass force due to phase change and shape change, while the equation of energy includes thermal conduction and convection. The simulations include both spherical and non-spherical bubbles, the effect of initial bubble diameter and degree of subcooling. The simulations have been performed in three modes of heat transfer (conduction, convection and combined conduction-convection) to observe their effect on the bubble dynamics. The numerical results have been compared with the two classes of thermal collapse experiments (Type A and B) and CFD analysis reported in literature. They agree well with the experiments and CFD-analysis. We have seen a remarkable effect of the initial shape of the bubble in terms of aspect ratio on the time scale and modes of the heat transfer and the collapse time. An interesting concern is that the mechanism of the collapse and the modes of heat transfer depends on how the collapse is initiated in the experiments. Type A and B thermal collapses are mainly classified based on the bubble motion and the modes of thermal transport from the interface.