Fundamental characteristics of discharge plasma generated in a water cavitation field

In this study, the fundamental characteristics of discharge plasma, which is produced in water cavitation fields, was investigated experimentally. A high voltage was applied across the electrodes located in the cavitation field inside the treatment reactor. The maximum applied voltage corresponding to the discharge onset voltage was approximately 1 kV. The power consumption P of the reactor was measured as the conductivity of the treatment water was varied by changing the NaCl concentration up to 3.0% and as the frequency of the applied voltage was varied from 10 to 30 kHz. The power consumption P had a peak value during the changes in the conductivity of the treatment water. The emission intensity from ·OH and O in the plasma decreased as the conductivity increased. The emission from ·OH was detected at an NaCl concentration of 2.5%. The energy deposited to the plasma Ep and the conduction current in water Ew were estimated from the voltage and current waveforms. The Ep/Ew ratio, which is an important factor for efficient treatment, was approximately 3% at an NaCl concentration of 0.7% and a frequency of 10 kHz. This ratio increased to approximately 8% when the frequency was increased to 20 kHz. The experimental results indicated that increasing the frequency is an effective way of improving the treatment efficiency.