Theoretical and numerical analysis of a PCM melting in a rectangular cavity

The melting of a Phase Change Material (PCM) placed in a bottom-heated cavity with and without metallic fins is studied on a theoretical and numerical level. A scale analysis is performed to evaluate the order of magnitude of the melt layer height and the transition from the conduction-driven to the convection-driven melting, while numerical simulations are employed to study the effect on the PCM melting of different fin numbers. The obtained outcomes highlight three different thermal behaviours: Rayleigh–Bénard cells, in the cases with no or few fins (large spacing scenario); pure conductive melting, in the cases with many fins (small spacing scenario); solid drops, originating when the horizontal melt layers from the fins top meet, in the cases with an intermediate number of fins (intermediate spacing scenario). The results evidence the fundamental processes involved in the PCM melting, in order to identify the optimal configurations of thermal energy storages filled with PCMs.