NUMERICAL-SOLUTION FOR MELTING OF UNFIXED RECTANGULAR PHASE-CHANGE MATERIAL UNDER LOW-GRAVITY ENVIRONMENT

An enthalpy method is employed to solve transport processes associated with melting of an unfixed rectangular phase change material (PCM) in a low-gravitational environment. This method permits the phase-change problems to be solved within fixed numerical grids, hence eliminating the need for coordinate transformation. The PCM, initially at its melting temperature, is placed inside a rectangular enclosure. The lower surface of the container is then exposed to a uniform temperature higher than the PCM melting temperature. The difference in densities of solid and liquid causes a force imbalance on the solid in the gravitational and low-gravity environments. In the case where the density of the solid phase exceeds that of the liquid, the solid continually moves downward as melting progresses and hence generates a flow field within the liquid. The problem is formulated as a one-domain problem with the possibility of melting from all the PCM surfaces, and no approximation is made about the liquid film thickness under the melt. The governing equations are discretized by using a control-volume-based finite difference scheme with a new iterative method to correct for the downward solid-phase velocity. This will also speed up the convergence of the numerical procedure. The results are presented in the form of a parametric study of the effects of Archimedes number, Stefan number, Prandtl number, and the geometric parameters on the melt thickness, the downward solid velocity, the elevation of the top surface, and the volume of the solid PCM. They show that in a low-gravitational environment, the melting rate is very slow.