PCM MELTING IN A BOTTOM-HEATED ENCLOSURE

The melting process of a Phase Change Material (PCM) within a bottom-heated enclosure featuring vertical metallic fins is studied on a fundamental level, combining theoretical and numerical approaches. A scale analysis is performed in the absence of fins in order to identify the order of magnitude of the melt layer height and to predict the transition time from the conduction-driven melting to the convection-driven one. The influence of the presence of vertical fins on the evolution of the melting interface is studied by means of numerical simulations. The obtained results highlight the significance of the aspect ratio, which relates the enclosure's height to the fin spacing, on the melting phase. In particular, three different thermal behaviors are detected: Rayleigh–Bénard cells are observed during the melting in the cases with small aspect ratios, whereas conduction dominates in the cases with large aspect ratios. Interestingly, with intermediate spacing configurations, solid drops are generated when the horizontal flow channels originating from the fins come into contact. These solid drops are observed to descend and ultimately complete their melting on the heated bottom surface of the enclosure. The results shed light on the fundamental processes involved in the PCM melting and the dependence on the aspect ratio within the enclosure, helping identify the best configurations of heat exchangers filled with phase change materials.