Measured and simulated particle flow field characteristics in high swirl, supersonic plasma spray

High power, supersonic plasma guns operating in the 100-200 kW range are a relatively new development in the thermal plasma spray coating process. These devices produce molten particles with three to four times the impact velocity of conventional plasma sprays. With this increased range of particle velocity it is important to understand the relationship between sprayed particle size, velocity, temperature, trajectory, and spray pattern Measurements of particle velocity, temperature, and size along with spray pattern characteristics have been obtained for a plasma spray system operating at 110 kW. The plasma and particle now fields were also simulated with a pseudo 3-D model. The model assumes that the gas flow is axi-symmetric while the particles are treated in a fully 3-D manner. The particle behavior is modeled by a stochastic discrete-particle model which includes turbulent dispersion. Because the flowfield has a high swirl number, it was found that the injection geometry plays a particularly important role in determining particle trajectory, heating, and acceleration. In spite of the complexity of the system, i.e., supersonic plasma velocity with a high swirl component, the simulation produced reasonably accurate mean velocities, temperatures, and particle trajectories although the agreement between the calculated and measured particle velocity, temperature, and size distributions indicate that not all aspects are adequately modeled.