Simulation of Microbubbles during the Initial Stages of Breakdown in Cyclohexane

University essay from KTH/Fysik

Author: Henrik Frid; [2013]

Keywords: ;

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 dynamics

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