Effect of density change on melting of unfixed rectangular phase-change material under low-gravity environment

An enthalpy method is employed to solve transport processes associated with the effect of density change on melting of unfixed rectangular phase-change material (PCM) under low-gravity environments. This method permits the phase-change problems to be solved within fixed numerical grids, hence eliminating the need for coordinate transformation. The PCM, initially and at its melting temperature, is placed inside a rectangular enclosure. The lower surface of the enclosure 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 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, and the effect of density change at the solid-liquid interface is treated via source and sink terms at the interface and at the outflow boundaries. The governing equations are discretized by using a control-volume-based finite difference scheme. The results are presented in the form of a parametric study of the effects of the solid/liquid density ratio, Archimedes number, Stefan number, Prandtl number, and geometric parameters on the melt thickness, downward solid velocity, elevation of the top surface, and volume of Le solid PCM. In general, the effect of the solid/liquid density ratio is small on melting characteristics in a low-gravity environment.