Study of the Influence of Oxygen on the Hydrodynamic Behavior of Helium Atmospheric Pressure Plasma Jet by Shadowgraphy System

Abstract

This work investigates the effect of oxygen (O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) as gas admixture on hydrodynamic characteristics of a coaxial double-ring electrode helium plasma jet by a “Z-type” shadowgraphy system. The shadowgraphy images and visual optical photographs show that the addition of O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> will slow down the transition of gas flow from the laminar region to the turbulent region regardless of the plasma is ignited or not. The hydrodynamic behaviors of the plasma jet at the impact region for epoxy resin (EP) and aluminum substrates are also researched. The addition of oxygen reduces the vortex on the surface of both EP and aluminum surface. As a result, with the increase of O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , the decrease of gas temperature caused by reduction of electrons and the reduction of the density difference between the mixed gas and the ambient air weaken the gas velocity and results in a weaker collision between the gas and the substrate, which is the main factor for less vortex on the substrate surface.