Melting process of a phase change material using single and double elliptic charger applied in thermal storage for building application: A numerical study on effect of position and aspect ratio

Nowadays phase change materials are considered as very useful and innovative working medium that can be used in different engineering systems for various purposes, including the thermal stabilization regime in building elements, cooling of electronic systems, development of thermal energy storage devices and other fields. The present research deals with numerical analysis of phase change material melting behavior in a closed adiabatic cavity under an influence of one or two elliptical local heaters that can be considered as local charges for the working material. Using the finite element technique, the governing partial differential equations formulated using primitive variables and enthalpy-porosity formulation have been solved numerically. The computational results have been validated utilizing published experimental and numerical data. Influence of the local heaters position and its shape on evolution of melting process has been studied. It has been revealed that in the case of vertically oblong one elliptical heater the melting rate is the maximum, while for the case of circular charger one can find a minimum melting rate. It has been ascertained that more intensive melting occurs when the charger is placed near the bottom wall (S_v = 0.2) and for this case the non-dimensional charging time for MF = 1 is about 2. While for other cases less intensive meting can be found. Moreover, in the case of elongated chargers for vertical axis (Ar = 0.1) and for horizontal axis (Ar = 10) the melting occurs intensively, namely the non-dimensional charging time for MF = 1 is about 1.5, while the maximum values (at about 24) of the average Nusselt number during the melting process are for Ar = 0.5 and Ar = 1.0. The highest values of the average Nusselt number (at about 12) are related to the minimum melting time (at about 1.1) that can be found for cases 6 and 9 when two chargers are placed in central part or along the bottom line.