Influence of the Distributed Phase of Gas Bubbles on a Pulsed Electrical Discharge in Water
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IED PHYSICS
Influence of the Distributed Phase of Gas Bubbles on a Pulsed Electrical Discharge in Water V. A. Panova, *, L. M. Vasilyaka, S. P. Vetchinina, V. Ya. Pecherkina, and A. S. Savelieva aJoint
Institute for High Temperatures, Russian Academy of Sciences, Moscow, 125412 Russia *e-mail: [email protected] Received September 14, 2017
Abstract—The development of a pulsed electrical discharge in water with vapor–air microbubbles, the volume distribution of which in water is close to uniform, has been studied experimentally. The presence of volumetric microbubbles with an average diameter of ~50 μm and a bulk gas content of no more than 1% does not change the thermal mechanism of the development of the discharge in water with a conductivity of ~300 μS/cm at overvoltages of 1–1.5, the minimum breakdown voltage being ~9 kV. Under these conditions, the determining role is played by the surface bubbles, which change the observed mechanism of the discharge development. The discharge is initiated in the surface bubbles simultaneously on both electrodes. The growth of the cathode channel at a velocity of ~60 m/s leads to the closure of the 1-cm-long gap during a time of ~160 μs. DOI: 10.1134/S1063780X1809009X
INTRODUCTION In the world literature, the importance of studying the development of electrical discharges in liquids (in particular, in water) has been noted many times in connection with the development of promising plasma methods for the purification of aqueous solutions or the preparation of aqueous media [1, 2]. The simulation of the discharge development in bubbles [3–6] (or in small groups of them [7]) placed in a liquid shows that the breakdown of such bubbles is mainly determined by the field strength, the size of the bubbles (more precisely, by the pR value, where p is the pressure inside the bubble and R is the bubble radius [5]), and the dielectric constant of the liquid. The effect of the bubble size is explained by the presence of a critical length for the avalanche–streamer transition, while the dielectric constant of the liquid determines the distribution of the electric field inside the bubble, which, in turn, specifies the type of streamer trajectory (diametrical or along the surface) during the breakdown of the bubble [4]. As a whole, the experimental results on the breakdown of individual bubbles [8, 9] do not contradict these conclusions. The methods developed for the numerical simulation of the development of a discharge in liquid in the presence of bubbles rely on the kinetic calculation of the concentrations inside each bubble and are not suitable for the simulation of the development of a discharge within a reasonable time in the microbubble environment (liquid volume) in which bubbles are distributed in with a certain number density. Note that, in
this case, it is rather difficult to take into account all collective effects. Nevertheless, the development of breakdown in a single bubble does not yet guarantee the closure of the discharge gap. Therefore, to solve the breakdown probl
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