Modelling and experimental analysis of vacuum plasma spraying. Part II: prediction of temperatures and velocities of plasma gases and Ti particles ina plasma jet

A numerical model has been developed to calculate the spatial distributions of plasma gas temperature, enthalpy, velocity and fractions of dissociated and ionized species in a vacuum plasma spraying (VPS) plasma jet under a r ange of plasma current, Ar flow rate, H-2 flow rate and chamber pressure, a nd the trajectories, temperatures and velocities of Ti particles under typi cal processing conditions. The model uses FLUENT V4.2 commercial software, incorporating approximations to describe dissociation, ionization and recom bination reactions in the plasma jet. The calculations show that the spatia l distributions of plasma gas temperature, enthalpy, velocity, and degrees of dissociation and ionization in the plasma jet are mainly controlled by t he initial boundary values at the plasma gun exit, which are functions of t he VPS processing conditions. The model predicts that the plasma jet length increases with increasing plasma current and decreasing Ar flow rate and c hamber pressure, and shows a maximum with varying H-2 flow rate, agreeing w ell with measurements. Particle trajectory is largely determined by the ini tial particle position at the plasma gun exit. Particle temperature and vel ocity increase rapidly in the first 100 mm of the plasma jet and then becom e nearly constant at axial distances >150 mm. Particle temperature and velo city in the plasma jet decrease with increasing particle size and initial r adial position at the plasma gun exit.