Multiphysics Modeling and Simulation of Electrical Breakdown in Liquid Medium
Published on May 1, 2017 in ICOPS (International Conference on Plasma Science)
· DOI :10.1109/plasma.2017.8496367
During the last two decades non-thermal plasma discharges in and in contact with liquids have received significant attention in view of their wide range of application – extending from chemical analysis, medical, water treatment, fuel processing etc . Despite the tremendous interest and advances attained in the experimental studies, modeling efforts providing a comprehensive understanding of the underlying physicochemical processes is limited. In the current work a mathematical model is developed to simulate electrical breakdown and the associated plasma formation in liquid medium. A density based compressible flow solver is coupled with electrical potential, energy and species solvers. A compact kinetics is considered which includes, electrons, positive and negative ions and associated ionization, recombination, and attachment reactions. Both electron impact ionization and field assisted emission (i.e. Zener tunneling) are taken into account. Ponderomotive  and electrostatic forces are considered to contribute to the body force term of the momentum conservation equation. The variation of density of the liquid medium is modeled via the Tait equation of state. Simulation is conducted for water for a pin-to-plate electrode arrangement driven by a pulsing power source having a nano-second rise time. Predictions from the model indicates that during the pre-breakdown stage the ponderomotive force cavitates the homogenous liquid by creating a pressure field that is significantly lower than the critical negative pressure of water. The cavitation sites are typically found to occur near the vicinity of the powered electrode and have a size of tens of microns. These cavitation sites act as nucleation sites during the pre-breakdown stage. Parametric studies are performed to identify the role of the different kinetics especially the field assisted ionization and the direct electron impact ionization.