The discharge characteristics of the microsecond pulsed underwater streamer discharge in a multi-needle electrode configuration

Abstract

The underwater streamer discharge has received extensive attention in the field of environmental protection, because it can generate free radicals and reactive oxygen species directly in water. The multi-needle electrode is a basic electrode configuration for achieving large-volume underwater streamer discharge. Understanding the discharge characteristics of the multi-needle electrode configuration is important for the design of the large-volume discharge reactors. In this paper, a multi-needle electrode that can assemble 21 needles was employed. The number of anode needles generated a streamer discharge during a single pulsed discharge and the differences in morphological characteristics of the inside and edge of the electrode array were investigated by using an ultra-high-speed camera system. The electric field distribution of the multi-needle electrode was simulated by using COMSOL software, and the effect of the electric field distribution on the discharge of multi-needle electrode was studied. The discharge energy efficiency of the multi-needle electrode configuration was evaluated. It was found that 21 needle electrodes were not discharged simultaneously during a discharge pulse. The number of discharged anode needles gradually increases and then reaches a maximum value (≤ 21). The maximum number of discharged anode needles during a single discharge pulse increases with increasing voltage and needle spacing. During the same one discharge pulse, the filament generated from the needles at the edge of the electrode array develops longer and deviates more largely from the needle axis than that generated from the needles inside the electrode array. Such characteristics are primarily owing to the disturbance of the electric field among the electrode array. The electric field generated by each anode needle are disturbed each other, making the intensity of the electric field and the deviation of the electric fluxline from the needle axis at the edge of the needle-array significantly greater than that of the inner ones. As the needle spacing decreases, the disturbance of the electric field among the electrode array gets stronger, consequently, the differences in morphology of the discharge at the edge and inner needles become more significant, and the energy efficiency of the discharge drops remarkably.