Electro-hydrodynamic and plasma phenomena in corona — Liquid interaction

We observed motion of liquids (water and oils with different conductivities) under the influence of corona discharges while using wire-to-plane geometry (high voltage wire above a rectangular vessel with a metal bottom-plate and transparent plastic walls). It was possible to see the internal motion within the transparent liquid volume by suspending small (3 μm) silica particles in the liquid and illuminating a cross-section of the liquid volume with a green laser beam sheet. Intense motion was also very clearly revealed on the liquid surface. In that case liquid transparency was not required. In addition to the intense motion observed within the volume and on the surface of the organic liquids, deionized water moved upward on the clear plastic walls of the vessel and sprayed outwards into the air atmosphere under the corona influence. It was remarkable that rather small variations of liquid composition sometimes completely changed the form of electro-hydrodynamic motion: from the electro-convective cells elongated in a transverse direction, to the polygonal Bénard-like cells [1]; vortices similar to those caused by a fluid sink, and soliton-like standing jets were also observed. In most cases, significant corona current increase resulted in formation of turbulent motion, analogous to chaotic liquid boiling, although some liquids demonstrated rather high stability of regular motion. Deformation of a liquid surface under the influence of surface charge was probably the major cause of formation of vortices; surface charge also caused formation of electrical discharges in the volume of oil, probably between the surface and the bottom metal plate electrode.