Thermal analysis of a triplex-tube heat exchanger system incorporating multiple phase change materials

This study investigates the thermal storage performance of a heat exchanger system consisting of three concentric tubes, where the inner and outer tubes carry a heat transfer fluid (HTF), and the middle tube is filled with three types of phase change materials (PCMs) arranged in both radial and circumferential cascades. Due to their ability to absorb and release heat during phase transitions, PCMs make latent heat storage one of the most effective methods for charging and discharging thermal energy. In this study, three commercially available PCMs with distinct melting points are utilized: RT55 (PCM-1), RT60 (PCM-2), and RT65 (PCM-3). A two-dimensional numerical model using the finite volume method is developed to analyze the thermal behavior and storage performance of the triplex-tube heat storage system. The numerical model is validated by comparison with previously published numerical and experimental results from the literature. The influence of arranging cascaded PCMs in radial and circumferential directions is examined to identify the optimal configuration that improves both melting behavior and storage performance.