Heat transfer during simultaneous impact of two drops onto a hot solid substrate

A numerical method based on the Volume-of-Fluid approach has been used for simulating the simultaneous collision of two drops with a solid substrate. Heat transfer in the substrate and in the drop have been evaluated during the drop spreading and receding phases. The numerical model includes the liquid evaporation from the drop surface and especially in the neighborhood of the moving contact line. The evolution of the heat transfer rate at the liquid/substrate interface is also modelled theoretically by considering the development of the thermal boundary layers in the solid wall and in the spreading drop. The theoretical model does not take into account the effect of drop evaporation on the overall heat transport. It is shown that at high Prandtl numbers the heat flow is mainly determined by the instantaneous wetted area while for Prandtl numbers of order unity, the contribution of evaporation is significant. As a result, at high values of Prandtl number the agreement between the theoretical model and numerical prediction is significantly better than at the Prandtl number values of order unity.