Streamer discharge evolution over water under atmospheric conditions: a multiphysics modeling study with qualitative relevance to water treatment performance

Abstract

Cold atmospheric-pressure plasma streamers offer a promising route for water and wastewater treatment. However, the multiscale physics governing their propagation and reactivity remain insufficiently resolved. This work develops an atmospheric-pressure wire-to-plane streamer source coupled with a plasma–fluid continuum model in COMSOL Multiphysics. Simulation results represent electric-field evolution, streamer-head velocity, space-charge dynamics, and gas–liquid interfacial fluxes. The streamer exhibits ionization degrees of 10 ⁻⁵ –10 ⁻⁴ , peak electron densities of 10 ¹⁹ –10 ²¹  m ⁻³ , and electric-field intensities reaching 1.5 × 10 ⁷  V/m near the water surface. Streamer velocity increases from 1.0 to 1.7 mm/ns as voltage rises from 10 to 20 kV, while penetration into the liquid begins after 4 ns of propagation. Parametric analysis shows that higher voltage enhances axial elongation but increases radial broadening, larger electrode gaps reduce peak fields by 30–50 %, elevated pressure suppresses electron density by up to 40 %, and increasing water conductivity from 5 to 600 μS/cm shortens streamer length by more than 60 %. These quantitative trends identify operating windows that maximize oxidant delivery across the gas–liquid interface. The computational framework provides quantitative design rules for optimizing plasma-based water purification across diverse operational conditions. The novelty of this study lies in investigating how operating conditions govern streamer morphology and treatment efficacy. The resulting quantitative design rules provide a foundation for optimizing and scaling plasma-based water purification technologies.