EFFECTS OF THERMOCAPILLARY CONVECTION ON MELTING WITHIN DROPLETS

Abstract

A computational study of the effects of thermocapillary convection on melting of spherical droplets as a result of an incident uniform heat flux under zero gravity conditions is presented. The computations are based on an iterative, finite-volume numerical procedure using primitive dependent variables, whereby the time-dependent continuity, momentum, and energy equations in the spherical coordinate system are solved. During the early periods of the melting process, conduction mode of heat transfer is dominant. As the thermocapillary convection strengthens due to the growth of the melt zone, faster melting on the side of the droplet is observed compared with the conduction-only case. Because of the slanted shape of the interface caused by the preferred melting on the surface, a new recirculating vortex is created that promotes melting within the droplet. For moderate Pr-number fluids, the molten zone increases rapidly along the surface and reaches the unheated side, thus producing a solid inner core. The effects of the Biot number and the change in the sign of the surface-tension temperature coefficient (partialdiff sigma/ partialdiff T) on the melting pattern are also investigated.