Numerical Study of the Effects of Twin-Fluid Atomization on the Suspension Plasma Spraying Process

Suspension plasma spraying (SPS) is an effective technique to enhance the quality of the thermal barrier, wear-resistant, corrosion-resistant, and superhydrophobic coatings. To create the suspension in the SPS technique, nano and sub-micron solid particles are added to a base liquid (typically water or ethanol). Subsequently, by using either a mechanical injection system with a plain orifice or a twin-fluid atomizer (e.g., air-blast or effervescent), the suspension is injected into the high-velocity high-temperature plasma flow. In the present work, we simulate the interactions between the air-blast suspension spray and the plasma crossflow by using a three-dimensional two-way coupled Eulerian-Lagrangian model. Here, the suspension consists of ethanol (85 wt.%) and nickel (15 wt.%). Furthermore, at the standoff distance of 40 mm, a flat substrate is placed. To model the turbulence and the droplet breakup, Reynolds Stress Model (RSM) and Kelvin-Helmholtz Rayleigh-Taylor breakup model are used, respectively. Tracking of the fine particles is continued after suspension's fragmentation and evaporation, until their deposition on the substrate. In addition, the effects of several parameters such as suspension mass flow rate, spray angle, and injector location on the in-flight behavior of droplets/particles as well as the particle velocity and temperature upon impact are investigated. It is shown that the injector location and the spray angle have a significant influence on the droplet/particle in-flight behavior. If the injector is far from the plasma or the spray angle is too wide, the particle temperature and velocity upon impact decrease considerably.