Electrical discharge characteristics in water and shockwaves

Abstract

Summary form only given. An arc discharge in water can produce shockwave, ultraviolet radiation and radical species. In this paper, we have investigated shockwave intensity and discharge characteristics. We have developed high voltage pulse system in the experiment. An arc discharge was generated by applying a pulsed voltage of V=25 kV to the electrodes with spacing of 3 mm. Capacitance of C=10-50 nF was used. A tungsten tip was used as electrode. We also used a shockwave sensor and oscilloscope to investigate discharge characteristics. When the electrical energy is transferred from capacitor to discharge path in water, we observed three kinds of discharge characteristics according to voltage and capacitance. They are the natural discharge at low voltage and low capacitance, corona discharge at intermediate voltage and capacitance, and the arc discharge at high voltage and large capacitance. The arc discharge occurs after a certain delay time. We have solved the second order differential equations to find arc discharge energy and current. However, the discharge pattern during the delay time is the natural discharge. We also observed that the resistance and inductance change continuously during the discharge. We therefore conclude that the arc discharge is largely affected by the water capacitance between the electrodes. Shockwave is produced only when the arc discharge is generated. Shockwave intensity is mostly related to the discharge energy. It is also a function of discharge circuit, pulse duration, water conductivity, electrode size, gap distance and reactor configuration. However, the discharge energy is the most effective parameter of shockwave intensity. We have measured shockwave intensity for changing distance from shockwave source. More than 90% of energy stored in capacitor is transferred to the arc discharge, dissipating its energy through water. Shockwave velocity decreases very quickly as the wave propagates further away from the source.