Continuum plasma flow past a sphere

Abstract

Flow of a collision-dominated weakly ionized gas over a solid sphere is investigated in the limit λm≪λD≪rp, where λm is the mean free path, λD is the Debye length, and rp is the sphere radius. Such flow is encountered in plasma heating of metallic/ceramic powders in rf plasma-aided manufacturing processes. The flow Reynolds number (Re) based on sphere diameter is in the intermediate range (Re∼5–100). The continuity, the momentum conservation, and the energy conservation equations for the neutrals and those for the charged particles are simultaneously solved with the Poisson’s equation for the self-consistent electric field. A model for production and recombination of the charged particles is incorporated in the formulation. The surface of the sphere is considered as a sink for the charged particles and is at the floating potential. A finite difference method is employed to solve the governing equations. The flow field, the temperature distributions, the charged particle number density variations are obtained and the heat transport to the sphere surface is determined for a range of flow Reynolds number. The effects of Reynolds number, the far field temperature, and the surface temperature on the electric sheath around the sphere surface and on the heat transport to the sphere, are delineated.