Melting of a phase change material within a spherical enclosure is considered. The phase change material is initially at its saturation temperature. Suddenly the enclosure temperature is increased to a fixed value. The density of the solid is assumed to exceed the density of the liquid, the implication being that the solid continually drops toward the bottom of the shell as melting progresses. This motion of the solid generates a flow field within the liquid. A mathematical model is developed and confirmed by experimental evidence. The interface positions and the temperature profiles for various Stefan and Fourier numbers are determined, and the energy storage characteristics are studied. It is found that the convective effects can be neglected only at small Stefan numbers.

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