Effect of electrical conductivity of water on plasma-driven gas flow by needle-water discharge at atmospheric pressure

In this study, we investigated the process of gas flow formation, which is driven by atmospheric-pressure plasma. The plasma discharge was produced by a high voltage of 5–7.5 kV_0p and was generated between a needle electrode and water surface. Gas flow formation caused by the discharge was observed using the Schlieren visualization technique. Mie-scattered light was detected after the introduction of micrometer-sized particles, which were illuminated by a laser light source. It was determined that the generated gas flow velocity had a strong dependence on the magnitude of the water conductivity. The gas flow velocities for water conductivity values of 0.8 μS/cm and 5 μS/cm were approximately 28 m/s and 8 m/s, respectively. The time evolution of the electric field between the needle electrode and water surface caused different flow formations, and the evolution was affected by the process of charge accumulations in the water and its glass cell container. This charging effect determined the strength of the electric field. The formation of the gas flow required a high electric field, and the process occurred in approximately 10 μs As the pulse width of the applied voltage decreased, the velocity of the resulting gas flow also reduced. It was therefore concluded that the gas flow formation was dependent on the strength and time duration of the present electric field.