Abstract

Plasma Spraying is a coating process designed to deposit accelerated molten or semi-molten coating materials on prepared substrates. Suspension Plasma Spraying (SPS) is one type of Plasma Spraying with enhanced characteristics. Numerical modeling of this process helps us to find optimum operating parameters such as suspension injection position and standoff distance for substrates. A three-dimensional model of a plasma spraying system with radial suspension injection is studied in this work. To model turbulent flow of plasma, Reynolds Stress Model (RSM) is utilized. In addition, Lagrangian approach is used to track particles and two-way coupling is used to consider the effect of suspension on the gas flow. It should be mentioned that when mass flow rate of suspension is very high, the plasma plume cannot melt all particles that fly near the centerline. It is found that with optimum suspension mass flow rate, in general, almost all particles flying near the centerline are melted and reach high temperature. Furthermore, the effect of angle of suspension injection is studied. One can find that angles toward the gun give more penetration of suspension in the plasma plume, resulting in better melting and higher speed of particles. Finally, particle temperature, velocity and size distributions are studied at different standoff distances with respect to the plasma gun exit. It is shown that optimum standoff distance for the studied particles and plasma plume properties is between 3 to 6 cm. Less than 3 cm standoff distance, particles have no time to reach the melting point and the base liquid would not evaporate completely; and with more than 6 cm standoff distance, particles’ velocity will be significantly reduced. It should be mentioned that trajectory and penetration of suspension completely depends on velocity of suspension on one hand, and on the other hand temperature and velocity of the plasma plume. It is clear that for each condition, mass flow rate and velocity of plasma, the related modeling should be done to find velocity and temperature of particles.