Enhanced water activation in gas–liquid two-phase flow using air plasma droplets

Abstract

We report on our study of gas–liquid two-phase flow of air plasma and its associated dynamic behavior, droplet activity, and applications. The propagation of the air plasma jet within a Venturi configuration is significantly perturbed by the presence of water droplets due to the local modification of the electric field that results from polarization and charging of the droplets. This local modulation, in turn, decreases the discharge current pulses and the radiation intensity of optical emissions. With a change in inlet airflow dynamics from laminar to turbulent (5–10 L/min), the droplet diameter decreased exponentially under strong pressure from millimeter to several tens of micrometers, whereas the gas–droplet contact area increased substantially. The production of short-lived reactive aqueous species OH and O2− was enhanced at the gas–liquid interface of the biphasic plasma droplets, and the activities of different long-lived species (H2O2, NO3−, and O3) in the droplet were highly selective in droplet diameter and value of the Henry-law constants. This new plasma source architecture enables an in situ activation of water sprays by plasma jets at short time scales, providing a desirable and effective sterilization tool and wastewater treatment at a relatively low cost and ease of operation.