Thermal energy storage enhancement of a forced circulation solar water heater’s vertical tank unit using phase change material

This work aims to investigate the thermodynamic effect of phase change material integration within vertical storage tanks that are connected to forced circulation solar water heaters, on their thermal energy storage capability. The phase change material is encapsulated in cylindrical and elliptical capsules, which are integrated at the bottom, middle and top sections of the tank. Hence, three parametric studies were carried out depending on the geometry of the encapsulation, besides to their integration position inside the tank, through computational fluid dynamic calculations. The numerical model was established under “OpenFOAM” and the enthalpy-porosity method for the phase change phenomena modeling was validated against the experimental data of the literature. For this purpose, the following thermal performance indicators were used: temperature, liquid fraction contours and the tank’s energy storage efficiency. It was found that the time required for a complete melting of the phase change material inside the cylindrical capsules is higher than that of the elliptical ones (beyond 17.50 s), for a fixed integrating location. Otherwise, 21, 23 and 17.50 s were necessary for the melting of the phase change material filling the vertical ellipse (top configuration), horizontal ellipse (bottom configuration) and cylindrical cavity (middle configuration) respectively. In addition, results showed that the shapes of phase change materials affect the thermal storage efficiency. For example, 25, 28 and more than 40 s were sufficient to reach 100% of the vertical tank’s storage efficiency for the following top configurations: vertical ellipse, horizontal ellipse and cylindrical cavity, respectively. Finally yet importantly, integrating the phase change materials at the middle section of the tank can be considered as the optimal configuration, because it allows a gain of 2 °C compared to the bottom and top zones.