Research on Discharge Characteristics of AC Excited Metal Needle-Water Electrode at Atmospheric Pressure

This reserach based on the atmospheric pressure alternating current (AC) metal needle-water electrode discharge device. And the influences of needle-water distance and supply powers on the discharge characteristics of metal needle-water electrode have been studied. The experimental results showed that the discharge of modes a and b occurred when the supply powers were small, and the discharge modes of them were unstable. The differences were that the discharge mode a was more like corona discharge, and the water surface under the needle electrode would be sunken. The discharge mode b was similar to spark discharge, and the discharge channel in the discharge gap was tortuous. Mode c only existed in the negative half cycle of discharge, and had an axisymmetric structure. Continuing to increase the supply powers, mode c switched to discharge mode d, which not only had the disk structure of mode c, but also had some bright filamentous discharge. The spatial-temporal evolution process of mode d discharge had been studied. It was found from the ICCD discharge images that the discharge morphology in the positive half cycle extended from the metal needle electrode to the water surface, and diffused into many filaments around the water surface. These discharge filaments had multiple contact points with the water surface, and the contact points moved continuously on the water surface during the discharge process. The negative half-cycle discharge morphology was axisymmetric as a whole, showing different layered structural characteristics. This structure was consistent with the glow discharge form or the Trichel pulse discharge structure. The experimental results showed that when the metal needle electrode was a positive high voltage electrode, the breakdown voltage dropped from 2.3 kV to 2.0 kV with the increase of supply powers, and the discharge start time in the cycle was advanced from 16 μs to 9 μs, while the maintenance voltage and discharge termination time had little change. When the metal needle electrode was a negative high voltage electrode, the breakdown voltage dropped from 1.4 kV to 1.0 kV as the supply powers increased. the peak current (about 40.0 mA) and peak power (about 50.0 W) of discharge were roughly equal. However, the peak values of the three were all less than the corresponding peak values of the positive half cycle. And the discharge energy of the positive half cycle was always greater than that of the negative half cycle. The influences of discharge gaps on the discharge characteristics of mode d have been studied. The results showed that when the metal needle electrode was a positive high voltage electrode, as the discharge gap increased from 1.0 mm to 5.0 mm, the breakdown voltage increased from 1.2 kV to 3.2 kV, the current peak value increased from 56.4 mA to 392.1 mA, and the power peak value increased from 68.9 W to 992.2 W, but the discharge start time in the cycle delayed from 6 μs to 16 μs, while the maintenance voltage and discharge termination time had little change. With a 6.0 mm discharge gap, there was no plasma generated in the first half cycle. When the metal needle electrode was a negative high voltage electrode, as the discharge gaps increased, the breakdown voltage increased from 1.0 kV to 1.9 kV, and the peak current and the peak power were approximately equal. There was no positive or negative correlation between the amount of conductive charge and the size of the discharge gaps. The conductive charge in the positive half cycle was basically maintained at 1.2×10-6 C. The discharge energy in the positive half cycle was always greater than that in the negative half cycle. © 2024 China Machine Press. All rights reserved.