Optical and Electrical Diagnostics of the Effects of Conductivity on Liquid Phase Electrical Discharge

The influence of solution conductivity on liquid phase pulsed electrical discharge was investigated by optical emission spectroscopy in a reactor with point-to-plane electrode geometry. The emission intensities of hydroxyl (OH) radical, hydrogen (H) radical, and oxygen (O) radical were measured using an emission intensity calibration method which used argon gas as a chemical actinometer. Control experiments showed that the addition of argon (Ar) bubbles did not disturb the electrical discharge. It was also found that the Ar emission peak at 750 nm is linearly related to the peaks of the other major species of interest (OH, H, and O) and that the slopes of these lines depend upon the solution conductivities. Therefore, the calibration method allows comparison of the radical generation rates in solutions of different conductivity. Hydrogen (H₂), oxygen (O₂), and hydrogen peroxide (H₂O₂) were measured using gas chromatography and spectrophotometric methods. The results showed that OH radicals and H₂O₂ decreased with increasing solution conductivity consistently with previous results. The intensities of O and H radicals and the generation rates of H₂ and O₂ were found to have extrema values at a conductivity of 150 μS/cm, and these results in combination with the electrical diagnostics (current waveform and overall power input) and images of the discharge channels imply changes in discharge properties at this conductivity due partly to power input changes from the spark gap. This work clearly demonstrates the close coupling of radical and molecular species formation in liquid phase electrical discharge.