Utilizing phase change materials in thermal energy storage systems is commonly considered as an alternative solution for the effective use of energy. This study presents numerical simulations of the charging process for a multitube latent heat thermal energy storage system. A thermal energy storage model, consisting of five tubes of heat transfer fluids, was investigated using Rubitherm phase change material (RT35) as the. The locations of the tubes were optimized by applying the Taguchi method. The thermal behavior of the unit was evaluated by considering the liquid fraction graphs, streamlines, and isotherm contours. The numerical model was first verified compared with existed experimental data from the literature. The outcomes revealed that based on the Taguchi method, the first row of the heat transfer fluid tubes should be located at the lowest possible area while the other tubes should be spread consistently in the enclosure. The charging rate changed by 76% when varying the locations of the tubes in the enclosure to the optimum point. The development of streamlines and free-convection flow circulation was found to impact the system design significantly. The Taguchi method could efficiently assign the optimum design of the system with few simulations. Accordingly, this approach gives the impression of the future design of energy storage systems.

To overcome the weak conduction heat transfer of phase change materials (PCM), this investigation aimed to assess the behavior of a double-tube latent heat storage unit with circular fins through the charging process. The influence of free convection in the presence of fins of various arrangements and sizes was comprehensively studied. The geometrical characteristics of the fins, i.e., their size and number, were assessed to optimize their performance. Moreover, a sensitivity assessment was performed on the characteristics of the heat transfer fluid passing through the inner tube, i.e., the Reynolds number and temperature. Charging time diminished by 179% when nine 15 mm fins were added compared with the finless scenario, assuming the same phase change materials volume. Moreover, the system’s thermal recovery rate improved from 20.5 to 32.9 W when nine fins with the heigth of 15 mm were added. The use of more fins improved the thermal behavior of the phase change materials because of the higher total fin area. The melting time and heat storage rate changed by 76% and 71%, respectively, for the system with 19 fins compared with those with four fins. Moreover, the outcomes indicated that a higher heat storage rate can be achieved when the working medium’s faster flow and inlet temperature were used.