Deposition of till droplets on a steel plate: simulations and experiments

Impact and solidification of tin droplets on a flat stainless steel plate was studied using both experiments and numerical simulation. In the experiments, tin droplets (2.1 mm diameter) were formed and dropped onto a stainless steel surface whose temperature was varied from 25 to 240 degrees C. Impact of droplets was photographed, and evolution of droplet spread diameter and liquid-solid contact angle measured from photographs. Substrate temperature variation under an impinging droplet was measured. A complete numerical solution of the Navier-Stokes and energy equations, based on a modified SOLA-VOF method, was used to model droplet deformation and solidification and heat transfer in the substrate. Measured values of liquid-solid contact angle were used as a boundary condition for the numerical model. The heat transfer coefficient at the droplet-substrate interface was estimated by matching numerical predictions of the variation of substrate temperature with measurements. Comparison of computer generated images of impacting droplets with photographs showed that the numerical model correctly modelled droplet shape during impact as it simultaneously deformed and solidified. A simple analytical model was developed to predict the maximum spread diameter of a droplet freezing during impact. (C) 1998 Elsevier Science Ltd. All rights reserved.