Optimization of High Voltage Ripples for Alternate Propagations of Streamer Discharges and Water Droplets Produced by Electrospray

Abstract

For a new water treatment technique, there are many studies on streamer discharge propagation into a gas-water mixture produced by electrospray. Generally, it is difficult to produce both the streamer discharge and the rme water- electrospray from an injection needle as a coexistence state. In our previous report, we carried out alternate propagations of the discharges and water droplets produce by electrospray, by using superimposed repetitive pulses onto a DC Voltage. However, in order to decompose a solution containing a hardly decomposable suUstance at a practical level, it is necessary to further improve the stauility of electrostatic spray. From long ago, it is known that a water droplet pulsates greatly at a natural frequency with a small external force. We thought the pulsation of a water droplet would help to improve the stability of the electrostatic spray. We examined the equivalent radius and natural frequency of the water droplet on the electrospray needle. We find that a superposition of high voltage ripples of the order of102 Hz onto a positive dc voltage is effective for the stability of electro spraying of water. However, the high voltage ripples oftcn induce flashover. We used nanosecond pulse high voltage having a long tail. Nanosecond pulse high voltage can initiate discharge propagations with a high probability. We expected that low frequency component of“ a long tail” is effective for the pulsation of a water droplet and stauility of electrostatic spray improved. As a result, improvement of alternate propagations of the discharge propagation and the fine water-spray could be successfully achieved.