A Numerical Simulation and Experimental Comparison of Atmospheric Thermal Plasma Spray Coatings Between Internal and External Powder Injection Processes

This study presents two 3-D atmospheric plasma spray models, namely, internal and external powder injections, by using the computational fluid dynamics technique to study the status of the melting of a particle and its in-flight velocity during a porous ceramic layer fabrication process. A bulk fluid model, which solves the time-dependent standard k-ε model, is used in combination with a Lagrangian to track the trajectories of alumina particles. The results of the fluid-analytical models are compared with experimental measurements, and it is seen that the spray angle increases as the flow rate of the carrier gas increases, which is more significant for an internal than for an external powder injector. Internal powder injection gives a particle a greater in-flight velocity and particle surface temperature because of the location of the powder injector. It is seen that the particle injection velocity and the particle penetration depth vary with the particle size and the flow rate of the carrier gas and that the dispersion for the internal type is more concentrated than that for the external type because of the momentum. The surrounding setup also plays an important role in the process of plasma spraying.