Enhancing performance of latent heat thermal energy storage system through geometrical optimization of twisted heating dual-tubes

• Twisted dual tubes as a heating source for the PCM unit are investigated. • Five twisting angles are investigated: 0°, 360°, 720°, 1080°, and 1440°. • PCM unit with 1080° twisting angle showed optimal solidification and melting processes. • A 30.1% reduction in solidification time for 1080° twisted tubes compared to untwisted. • A 16.9% decrease in melting time was also achieved by 1080° twisted tubes. Improving the efficiency of thermal systems is one of the most important challenges facing researchers and engineers. Introducing simple geometric modifications to thermal systems can significantly enhance performance. This study numerically assesses the performance of a vertical latent heat thermal energy storage (LHTES) system employing twisted inner tubes in a double-tube arrangement. Five twist angles (0°, 360°, 720°, 1080°, and 1440° on a 25 cm tube length) were evaluated to investigate their impact on phase transitions, temperature patterns, and thermal energy storage efficacy, utilizing n-octadecane as the phase change material (PCM) and water as the heat transfer fluid. Validated numerical modeling is performed using the enthalpy-porosity method for transient assessments of melting and solidification. The findings indicated that the twist structure significantly enhanced convective heat transfer in the LHTES, accelerating the phase transition and thermal activity. The 1080° twist structure exhibited superior performance, achieving 30.1% reduction in solidification time, 16.9% reduction in melting time, and 8.5% reduction in energy discharge time compared with the baseline straight tube. The findings of this study provide design visions for developing compact, high-efficiency LHTES systems in renewable energy applications.