Numerical analysis of non-isothermal remelting and solidification during molten droplet impact on a substrate

The non-isothermal phase change behavior of a droplet impingement on a solid substrate is studied which can be used to select the operating parameters in processes like microcasting and spray deposition. The governing equation for the flow field is solved using a finite difference scheme with a two-step projection method on a fixed computational grid. The Volume of Fluid (VOF) method is used to track the free surface and the Continuum Surface Force (CSF) method is used to model the surface tension. An enthalpy formulation of the energy equation with a porosity model is used to solve for the temperature. A comparison with published experimental findings is used to validate the numerical model and a good agreement is observed. The effects of convection terms in the energy equation are examined and the physics of spreading and solidification are studied. A parametric study relating the effects of substrate preheating and impact velocity on remelting, cooling rate and spreading has also been carried out. It is observed that the spreading time may not be negligible compared to the solidification time unlike what is assumed in some literature. The flow field during spreading and recoiling does have a significant impact on the cooling rates and microstructure properties. It is also concluded that higher remelting can be achieved by preheating the substrate and with slower droplet impact velocity.