Simulation of Microbubbles during the Initial Stages of Breakdown in Cyclohexane

Abstract

The formation of a vapor microbubble has previously been suggested to be the initial mechanism in the process of dielectric failure of dielectric liquids. The bubble is generated by a rapid, highly localized heating of a volume close to a highly stressed electrode, caused by electric currents in the liquid at high voltages. In this paper, a numerical model is presented to investigate the dynamics of a single microbubble in a point-plane geometry in cyclohexane. A condition for the formation of a vapor bubble is discussed. Thereafter, a Computational Fluid Dynamics (CFD) model of two-phase flow with phase transition is used to study the dynamics of the bubble from generation to collapse, under a highly divergent electrostatic field in a subcooled liquid. The amount of subcooling in the simulations is 5 K, and it is found that convergence gets significantly weaker as the amount of subcooling increases. The bubble expansion is also simulated considering the electrohydrodynamic (EHD) processes in the liquid and vapor phases. Finally, it is shown how the electrostatic forces on the dielectric will cause a bubble to detach from the electrode. Index Terms —Dielectric failure, streamer initiation, bubble dynamics, electrohydrodynamics, computational fluid dynamic