Plasma Flow Characteristics in a Spray-Type Dielectric Barrier Discharge Reactor

Abstract

A numerical simulation on the spray-type dielectric barrier discharge (DBD) is carried out for a mixture gas of nitrogen (N2) and sulfur hexafluoride (SF6) at atmospheric pressure to understand the electrical characteristics and the plasma flow dynamics that depend on design parameters and operating conditions. A 2-D axi-symmetric nonuniform grid is employed in the simulation code consisting of the following three numerical modules: 1) discharge module; 2) flow module; and 3) reaction calculation module. Through the coupling of these modules, the discharge and plasma flow characteristics are interactively calculated for discharge properties and behaviors of charged and neutral particles in the N2/SF6 plasma, including 26 species interacting among them by 59 reactions. As a result of numerical simulations, the effects of the spray hole and the gas flow on the plasma flow characteristics are discussed in the spray-type DBD reactor. The existence of a spray hole in the grounded barrier/electrode plate induces strong electric fields along the spray hole barrier wall, and these high fields trigger a localized discharge similar to the surface discharge. The localized discharge spreads out in the discharge region toward the powered electrode barrier and gives the discharge current a pulsed shape according to the group behavior of a high-density electron to eventually produce a high-density fluorine atom in both the spray hole and spray regions. When the spray hole radius decreases, the fluctuations of hole-induced electric field also decreases, accompanied by the reduced production of average densities of the electron and the fluorine atom. However, the reduced spray hole size enhances the advective velocity along the hole ax- - is, and therefore, the overall fluorine atom density over the substrate surface is increased. With increasing inlet gas flow velocity, the localized discharges occur more frequently because of electric potential formation by interacting among meta-stable species and ions to enhance the fluorine atom production. The fast advective velocity also enlarges the radial distributions of effluent rate and fluorine atom density in the spray region and on the substrate surface due to the transport of neutral particles.