Physical properties and chemical efficiency of an underwater dc discharge generated in He, Ar, N₂and air bubbles

Abstract

A dc excited discharge generated in bubbles (He, Ar, Air, N(2)) in liquid phase is investigated in this work. Voltage/current characteristics and emission spectra of the discharge are recorded in the current range 10-30 mA. Electron density in the discharge is measured from Stark broadening of the H(beta) line and is of the order of 2-6 x 10(20) m(-3), depending on the feed gas. Estimation of electron temperature is carried out based on the balance of charged particles. Gas temperature is estimated by the slope of the Boltzmann plot and by the simulation of the OH band with different T(rot)(1), T(rot)(2) and T(vib). Rotation temperature in the He discharge is 1200 K at I = 10 mA and linearly increases with current up to 1600 K. In the plasma of molecular gases the temperature is higher and almost constant at different currents. Chemical efficiency of the plasma is measured by the production of H(2)O(2) and by the destruction of Direct Blue 106 dye. The highest energy consumption of H(2)O(2) generation is achieved in the air discharge and it decreases up to 50% in the He plasma. Maximal efficiency of dye destruction is observed in the N(2) plasma characterized by an energy consumption of dye decomposition of 0.86 g kWh(-1).