Capillary underwater discharges in repetitive pulse regime

Abstract

In this study a capillary underwater discharge, that is sustained with AC (50 Hz) voltages up to 7.5 kV, is investigated. In a capillary discharge scheme, the current is, at some point along its path between two submerged electrodes, flowing through a narrow elongated bore in a dielectric material. When the current density is sufficiently high, local boiling and subsequent vapour breakdown results in the formation of a plasma within this capillary. At the same time the capillary emits an intense jet of vapour bubbles. Time-dependent electrical current, voltage and light emission curves are recorded for discharges in solutions of NaCl in distilled water and reveal different discharge regimes, depending on the conductivity and the excitation voltage, ranging from repetitive microsecond discharge pulses to a quasi-continuous discharge with a glow-like voltage-current characteristic.PACS: 52.80.Wq

Surface Treatment of Cotton Yarn by Underwater Capillary Electrical Discharge

“…2. The mechanism of capillary discharge generation is similar to that of diaphragm discharges and recently it has been described in [15]. As it has been shown in [15], current flow through a narrow capillary results in overheating of the liquid and in formation of small steam-andgas bubble ( Fig.…”

Time-resolved optical and electrical characteristics of capillary underwater discharges

“…For AC (50 Hz) capillary discharges, two different discharge regimes occur (depending on conductivity and excitation voltage) ranging from repetitive microsecond discharge pulses at a frequency of 100 Hz to discharge pulses followed by a quasicontinuous discharge with a glow-like voltage-current characteristic (duration of optical emission up to 10 ms) [8]. Figure 2 shows typical voltage and current traces for low initial conductivity (100 µS cm −1 , 6.1 kV rms, 5 mA rms (left)) and high initial conductivity (1 000 µS cm −1 , 2.4 kV rms, 45 mA rms (right)).…”

“…One approach to generate plasma in an electrically conductive liquid is the capillary discharge scheme [8][9]. In a capillary discharge scheme, two submerged electrodes are separated by a thick dielectric with one or more bores.…”

Hydrogen peroxide production in capillary underwater discharges

“…It is assumed that the capillary plasma is initiated by the breakdown of a water vapor bubble inside the capillary, the bubble being nucleated due to ohmic heating of the liquid filling the capillary. For AC (50 Hz) capillary discharges, two different discharge regimes occur, depending on conductivity and excitation voltage, ranging from repetitive microsecond discharge pulses at a frequency of 100 Hz to discharge pulses followed by a quasi-continuous discharge with a glow-like voltage-current characteristic (duration of optical emission up to 10 ms) [8].…”

“…In a capillary underwater discharge, plasma is generated in an elongated bore (length-to-diameter ratio 1) in a dielectric plate separating two submerged electrodes [8][9]. In diaphragm discharges on the other hand, the length-to-diameter ratio of the pin-hole is typically about 0.1 ÷ 1 [10][11][12][13].…”