Time-resolved imaging of streamer formation inside gaseous bubbles in liquids

Abstract

Bulk liquid conditions can impact how plasma discharges behave in bubbles and affect the future implementation of plasma technologies for water treatment. A 2D plasma-in-liquid apparatus was used to investigate the effects of liquid conductivity on the propagation of nanosecond pulsed streamers in bubbles. ANSYS Maxwell was used to model the resulting static electric field. Electric field enhancement was found at the contact point between the bubble surface and the plexiglass, and can direct propagation of observed discharges. Nanosecond exposure time intensified charge-coupled device imaging was used to photograph the temporal development of the streamers in the bubble. At high liquid conductivity, surface hugging streamers stalled out axial streamers. However, at lower conductivity, increase in charge relaxation time and presence of charge carriers became important. Deposited charges on the interface led to development of opposing electric field and terminated streamer development. Presence of organic contaminants can increase conductivity of surface water. To maximize energy efficiency of future plasma-based water treatment reactor, it is important to take liquid conductivity into consideration. Shorter pulse width and rise time can potentially minimize development of surface hugging streamers, which is a major source of charge dissipation and thermal effects.