電圧脈動効果による静電噴霧用単一針電極からのストリーマコロナと微小液滴群の交互拡散

抄録

This paper presents an experimental study on water treatment by electrospray and plasma discharge from a syringe needle. Our aim is to improve the activity of the plasma-chemical reactions in the fog produced by the electrospray. In this study, we propose a pulsed power technique to allow alternating expansions streamer corona discharges and fine water droplets with an alternating frequency of the order of 10² Hz. Under a dc voltage without any ripples, it is difficult to achieve the alternating expansions of the streamer corona and the water droplets. For the successful control of the alternating expansions, an impulse voltage consisting of δ-function-like front and long exponential tail are repeatedly superimposed onto the dc voltage. The discharge light signals detected by a photomultiplier indicate that the streamer propagation is caused by the δ-function component of the superimposed impulse. High-speed photographic observations of the water droplets show that the streamer discharge is followed by the water spray expansions produced by the long tail component of the superimposed impulse. The long tail component has a very important role to deform a large water droplet on the needle tip from the hemispherical shape into the Taylor-cone shape. We confirm that the alternating expansions of the discharge and the water droplets are not allowed when the superimposed impulse dose not contain the long tail. The frequency component of the long tail is roughly equal to the natural vibration frequency of the hemispherical droplet on the needle tip. We confirm that the stability of the water spray propagation strongly depends on the frequency components of the superimposed impulse.