Transient Heating and Melting of Particles in Plasma Spray Coating Process

Abstract

In the plasma spray coating process, solid particles are injected into a plasma jet. The heat transfer from the plasma to the particles results in heating and melting of the particles. The molten particles impact on a surface forming a thin coat. In this paper, we investigate the heating and melting of a spherical particle injected into a thermal plasma. The transient temperature distribution in the particle interior is obtained simultaneously with the temperature and number density variations of the ions, electrons, and the neutrals as well as the electric potential variation in the plasma. Our analysis incorporates a model for the production and recombination of electrons and ions. The transport in the plasma is modeled by considering the main body of the plasma as charge neutral and a charge sheath in the vicinity of the particle surface. The heat flux to the particle is evaluated by taking into account all modes of heat transfer to the surface. The temporal variations of the particle temperature distribution are calculated. Results are compared with the available predictions made without taking into account the gas ionization to assess the importance of ionization and particle charging on the heat transport to the particle. For argon, for the particle materials considered in this study, the effect of gas ionization on the heat transport was found to be negligible for plasma temperatures below 6500 K.