Search

A three-dimensional computational model has been developed to describe the compressible, multi-component, turbulent, reacting plasma jet coupled with the orthogonal injection of carrier gas and particles. This model has been applied to plasma spray process that includes physical phenomena such as heating, melting, accelerating, and evaporation of in-flight particles. The entrained particles, NiCrAlY and ZrO2 , are discretely treated in a Lagrangian coordinate and stochastically generated by sampling from the probability distributions of the particle size and its velocity at the injection nozzle. In this study, special attention has been directed to the effects of carrier gas injection on the characteristics of plasma jet. The computational results show that the injection of carrier gas from the orthogonal injector above the plasma jet introduce the 3-D phenomena of plasma gas flow. The plasma jet is defected and the thermo-fluid flow near the injector is locally deformed.Copyright © 2003 by ASME

A comprehensive model describing the melting and oxidation of in-flight particles during plasma spray has been presented which includes the models for heat, momentum and mass transfer of carrier gas, and particle heating, acceleration and evaporation. The effect of evaporation-induced mass transfer on heat flux to the particle surface has been taken into consideration along with the effect of oxidation-induced evaporation due to the production of volatile oxides on the particle surface, and effects of variable plasma properties and non-continuum effects under plasma conditions. Computational results on molybdenum and zirconium particles in an argon-hydrogen DC plasma spray system have been obtained and discussed. The temperature and melting formation of particles with different sizes along their trajectories are depicted as well as other particle parameters such as velocity, evaporation rate and oxide content, which manifests that the behavior of particles are diverse due to particle size distribution in the spray coating operation. The effects of gun power on the heating, acceleration, melting, evaporation and oxidation of particles have also been discussed.