Heat transfer to a particle from a thermal plasma

摘要

A numerical analysis of heat transfer to a spherical particle from a plasma has been carried out. The study has direct applications in plasma-aided manufacturing processes. Both DC and RF induction plasma systems have been considered. Based on the typical operating conditions, two different limits in plasma heat transfer have been addressed. For both the limits, new numerical models have been developed to accurately determine the heat transfer from a plasma to a solid particle.;In the first part of this dissertation, heat transfer to a solid sphere moving in RF plasma has been investigated. For this case, the collisionless thin sheath limit $rm(lambdasb{m} ll lambdasb{D} ll rsb{p})$ is appropriate, where $lambdasb{rm m}$ is the mean free path, $lambdasb{rm D}$ is the Debye length, and r$sb{rm p}$ is the sphere radius. The flow Reynolds number based on the sphere diameter has been considered in the intermediate range (Re $sim$ 5-100). The continuity, the momentum conservation, and the energy conservation equations for the neutrals and those for the charged particles have been simultaneously solved with the Poisson's equation for the self-consistent electric field. A model for production and recombination of the charged particles has been incorporated in the formulation. A finite difference method has been used to solve the governing equations. The flow field, the temperature distributions, the charged particle number density variations have been obtained and the heat transport to the sphere surface has been determined. The effects of Reynolds number, the far field plasma temperature, and the sphere surface temperature on the electric sheath around the sphere and on the heat transport to the sphere, have been delineated.;In the second part of this dissertation, heat transfer to a spherical particle in a quiescent DC plasma has been analyzed. For this case, it has been shown that the Debye length is the smallest length scale in the problem, and the collisionless thin sheath limit $rm(lambdasb{D} ll lambdasb{m} ll rsb{p})$ is appropriate. The sheath around the sphere has been considered collisionless where the fluxes of ions and electrons have been calculated by the free fall relations. Continuum conservation equations have been solved in the quasi-neutral region to obtain the temperature distributions, the charged particle number density variations, and the electric potential distribution. The heat transport to the sphere has been determined for a range of far field temperature and sphere surface temperature. Results indicate that the Nusselt number increases with far field temperature due to increased recombination of charged particles at the sphere surface. At higher temperatures ($>$12000 K) the heat transport from charged particles becomes the most dominant mode of heat transfer and is significantly greater than conduction from the neutral gas.