Experimental Study On Propagation Characteristics Of The Primary Mode Of Pulsed Positive Streamer Discharge In Water

Streamer discharges in water have many potential applications in the degradation of organic compound,food processing,bio-medicine due to various kinds of chemical active species,such as hydroxyl,hydrogen atoms,hydrogen peroxide molecules,can be produced directly in the water by streamer discharge in water.Two distinct modes have been identified as the streamers develop in the water,termed as primary mode and second mode.So far,the primary streamer in water has not been fully studied.A few studies on the primary streamers have been reported in the literatures.The effect of applied voltage and water conductivity on the propagation characteristics of the primary mode,such as time lag and flare angle,have not yet been studied.In this paper,the primary streamer in water has been studied by shadow graph imaging technique utilizing a high speed frame camera system.The time lag and flare angle of primary streamer,and their dependence on applied voltage and water conductivity were investigated.The results are as follows:(1)At the same water conductivity,the time lag of primary streamer decreases with increasing the applied voltage and finally stabilized at about 320 ns.At lower applied voltage(15 to 17 kV),the time lag of primary streamer decreases with increasing the water conductivity.As the applied voltage increased beyond 18 kV,the water conductivity has no significant influence on the time lag of primary streamer.(2)The propagation speed of the primary streamer is about 4-6 km/s at the early stage and decreases to about 1.5 km/s within 20 ns.The water conductivity has no significant influence on the propagation speed of the primary streamer.(3)The flare angle of the fan-shaped structure of the primary streamer ranges from 150° to 210° depending on the water conductivity and the applied voltage.At the same water conductivity,the flare angle of the fan-shaped structure shows an increase tendency with increasing the applied voltage.At lower voltage(15 to 17 kV),the water conductivity has no significant influence on the angle of the fan-structure.As the applied voltage increased beyond 18 kV,the angle of the fan-structure decreases with increasing the water conductivity.