Abstract

Suspension plasma spray is an emerging technology to produce functional nanostructured coatings at moderate cost. In general, in this technique, the liquid is injected radially into a high-velocity high-temperature plasma flow. After liquid breakup and evaporation, solid particles remain in the field and impact the substrate. Preliminary studies have shown that liquid jet atomization is the primary phenomenon that controls the coating quality. However, due to the complex thermophysical properties of plasma and its intricate flow physics, the breakup processes of liquid jets in plasma crossflows have not been investigated comprehensively yet. In general, the gaseous Reynolds number and the liquid-to-gas density ratio in this process are around 50 and 10,000, respectively, which are far outside the limits commonly observed in engines and wind tunnels. In this regard, detailed features of the breakup phenomena of the liquid jets injected in plasma and air crossflow are provided. Moreover, a case study has been established to analyze the effect of changing the surface tension of the liquid in the plasma spray process. The finite volume scheme is used to solve the incompressible variable-density Navier-Stokes equations. In addition, the volume of fluid (VOF) approach is utilized to track the gas-liquid interfaces. Finally, qualitative results such as instantaneous snapshots and shape of the liquid jet cross-sections, in company with quantitative data like including fracture point location, length of surface waves and size of the droplets have been presented.