Pushing of liquid drops by Marangoni force

Following initial observations in microgravity, on ground experiments pointed out that coalescence and wetting can be prevented by Marangoni forces at liquid-gas or liquid-liquid interfaces. Pushing of liquid droplets by a solid surface due to Marangoni forces can explain a number of relevant phenomena occurring during solidification, in particular the separation of immiscible alloys encountered in Material Science processings in microgravity. In this paper, numerical simulations have been performed to evaluate the Marangoni forces on a free droplet near a solid surface immersed in a transparent liquid matrix in the presence of different temperature gradients and,that explain a number of experiments made on ground in preparation of an experiment to be carried out in microgravity on a Sounding Rocket. Numerical results clarify questions of interest for solidification processes. In particular, they may provide some explanation for the minority phase separation during solidification due to the Marangoni repulsive forces that are experienced in the vicinity of the solidification front and that result in pushing of the liquid droplet towards the hot site of the sample. (C) 2002 Elsevier Science Ltd. All rights reserved.