Pre-breakdown cavitation development in the dielectric fluid in the inhomogeneous, pulsed electric fields

TL;DR

This paper investigates the development of pre-breakdown cavitation nanopores in dielectric fluids under pulsed electric fields, identifying three regions with distinct cavitation behaviors and analyzing pore dynamics and shapes.

Contribution

It introduces a detailed analysis of cavitation nanopore development in inhomogeneous electric fields, highlighting three characteristic regions and their effects on breakdown conditions.

Findings

Three characteristic regions near the electrode with distinct cavitation behaviors.

Identification of conditions under which nanopores grow to cause breakdown.

Analysis of cavitation pore expansion and shape dynamics.

Abstract

We consider the development of pre-breakdown cavitation nanopores appearing in the dielectric fluid under the influence of the electrostrictive stresses in the inhomogeneous pulsed electric field. It is shown that three characteristic regions can be distinguished near the needle electrode. In the first region, where the electric field gradient is greatest, the cavitation nanopores, occurring during the voltage nanosecond pulse, may grow to the size at which an electron accelerated by the field inside the pores can acquire enough energy for excitation and ionization of the liquid on the opposite pore wall, i.e., the breakdown conditions are satisfied. In the second region, the negative pressure caused by the electrostriction is large enough for the cavitation initiation (which can be registered by optical methods), but, during the voltage pulse, the pores do not reach the size at which the potential difference across their borders becomes sufficient for ionization or excitation of water molecules. And, in the third, the development of cavitation is impossible, due to an insufficient level of the negative pressure: in this area, the spontaneously occurring micropores do not grow and collapse under the influence of surface tension forces. This paper discusses the expansion dynamics of the cavitation pores and their most probable shape.