Modeling of liquid detachment and fragmentation during the impact of plasma spray particles on a cold substrate

The flattening of a droplet impacting a solid surface plays a fundamental role in several industrial ap-plications. In plasma spray, the splats resulting from the impact, spreading, and solidification of molten particles are the building blocks of the spray coatings. Fragmented splats are formed on substrates held at room temperature and atmospheric pressure. Although the formation of a fragmented splat is attributed to the presence of adsorbates on the substrate surface, its dynamics have not been adequately addressed. In this study, a numerical model is developed to investigate the formation of fragmented splats during droplet flattening and solidification in plasma spraying conditions. Compressible Navier-Stokes equations are solved, and the volume of fluid (VOF) method is used to capture the liquid and gas interface. In ad-dition, the source term method is used to capture the solidification process during droplet flattening. In addition, a new boundary condition is defined to consider the effect of gas desorption on the substrate surface after droplet impact. The numerical results show that gas desorption from the surface produces a barrier layer between the droplet and the substrate. This high-pressure region detaches the edge of the spreading droplet from the surface and forms a liquid sheet. The liquid sheet rises above the substrate and spreads up to 2 times more than droplets impacting surfaces without gas desorption. The fragmentation of the liquid film follows the overspreading of the droplet. Moreover, the barrier gas layer reduces the heat transfer rate between the molten particle and the substrate. As a result, only a portion of the initial droplet remains at the location of the impact, which forms a small solidified splat.& nbsp;(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

The flattening process of a droplet impacting a solid surface is crucial in various industrial applications. In this study, a numerical model is developed to investigate the formation of fragmented splats during droplet flattening and solidification in plasma spraying conditions. The numerical results show that gas desorption from the surface produces a barrier layer, affecting the heat transfer and spreading of the droplet.