Macroscopic Modelling of an Agglomerated and Sintered Particle in Air Plasma Spraying

Low thermal conductivity of the powder material and high plasma temperatures generally lead to inhomogeneous heating of the particles in plasma spraying. Existing modelling techniques can determine the heat transfer within idealized spherical particles with homogenous morphology. In many practical cases, however, the particles exhibit an agglomerated morphology and consist of multiple smaller particles which are packed together. The reduced contact area between the individual smaller particles results in a drastic reduction of the effective thermal conductivity of the agglomerate. On the other hand, it enhances the heat transfer from the plasma gas due to the increased particle surface and allowing the hot plasma to penetrate inside the agglomerate. Moreover, the momentum transfer from the plasma to the agglomerate differs from that of a homogenous spherical particle which can significantly affect the heating dynamics of the agglomerate. All of the mentioned phenomena have been taken into account in a novel particle modelling approach, which is introduced in this study. The presented model is coupled with the particle laden free jet model and determined significant differences in kinematics and heating dynamics of an agglomerate compared to an idealized spherical particle with homogenous morphology.