A Study On The Gas Density Of The Discharge Filament Of A Microsecond Pulsed Streamer Discharge In Water

Underwater streamer discharge can directly generate high electric field,shock wave,ultraviolet light and a variety of free radicals and molecular chemical active species in water.It has been proved a promising technique in environmental and biomedical fields,such as harmless treatment of organic pollutants in water,disinfection and sterilization of water and algae removal.The gas density of the filament of a pulsed streamer discharge in water is an important parameter for understanding the physical and chemical processes of streamer discharge in water.It is a challenge to measure the gas density of the filament of a streamer discharge in water for its highly transient characteristic.So far,there is still no mature method to measure the gas density of the filament of a streamer discharge in water.By assuming that the radial density of streamer filament is uniform,our laboratory has developed a shadow image method for measuring the gas density of the filament of a streamer discharge in water.Based on this method,we have measured the gas density of the filament of a streamer discharge in water and investigated its spatiotemporal evolution characteristics.The dependence of the gas density of the filament on the voltage and water conductivity was investigated.The main results are as following:(1)The radius of a discharge filament is in the range of 100-500 ?m.The radius decreases with increasing the distance from the tip of the anode.Both the voltage and water conductivity have significant influence on the radius of the discharge filament.The radius of the discharge filament increases with increasing the voltage and the water conductivity.(2)Depending on the voltages and water conductivity,the length of the discharge filament at 4 ?s from the start of the pulse is of 4-8.5mm and shrinks with time.The length of the discharge filament increase with increasing the applied voltage.At the same voltage,the discharge filament has the longest length at 100 ?S/cm water conductivity.The length of the discharge filament drops as the water conductivity gets lower or higher than 100 ?S/cm water conductivity.(3)The gas density of the filament ranges within 200-900 kg/m3.It increases with increasing the distance from the tip of the anode.The gas density at each position in the discharge filament oscillates with a period of about 10 ?s.The gas density of the discharge filament decreases with increasing the voltage and the water conductivity.(4)The gas mass of a discharge filament is of 0.00014-0.00045 g(0.14-0.45 mg).it increases with increasing the voltage and the water conductivity.(5)The deposited energy of a single discharge pulse has significant influence on the gas density,the radius and the gas mass of a discharge filament.The higher the deposited energy,the greater the radius,the smaller the gas density,and the greater the gas mass of the discharge filament.