Numerical study of singlet delta oxygen (O2(a1Δg)) generation and transport in the He/O2 atmospheric pressure plasma jet

Abstract

This paper investigates the spatial-temporal evolution and the transport of the singlet delta oxygen (O2(a1Δg)) of an atmospheric pressure plasma jet using a 2D fluid modeling. The plasma jet is produced in pure helium or helium with small oxygen admixtures (no bigger than 2%), by applying a constant DC voltage of +5 kV on the annular electrode. It is found that, at the 0.7% O2 admixture, a higher O2(a1Δg) density is obtained inside the tube before the jet impacts the substrate. After the jet propagates along the substrate surface, the peak O2(a1Δg) density is transferred from the tube to the gap. Varying the O2 admixtures percentage in the working gas changes the O2(a1Δg) spatial distribution. The O2(a1Δg) with two thinner edges is dominantly produced in the helium–air mixing layer for pure helium. The addition of O2 in the working gas leads to O2(a1Δg) production in the tube. Meanwhile, the thickness of the O2(a1Δg) edges increases in the helium–air mixing layer. But the radius of the O2(a1Δg) density channel continuously reduces with the O2 admixture. The O2(a1Δg) density and its surface flux first increase within the 0.7% O2 admixture and then decreases with the further augment of the O2 admixture. The influence of the gas flow velocity on the production and transport of O2(a1Δg) is also studied. Increasing the gas flow velocity changes the spatial distribution of the O2(a1Δg) density from the solid structure to the annular structure in the gap. At the same time, lower volume average density and instantaneous flux are obtained at larger gas flow velocity.