Improved PCM melting in a thermal energy storage system of double-pipe helical-coil tube

This study proposes the use of a double-pipe helical-coiled tube as an innovative well-performing phase change material (PCM) containment design for latent heat thermal energy storage (LHTES) systems. A 3D numerical model considering the convection effects during PCM melting is built and successfully validated via experiments. To assess the new LHTES design, the melting evolution of PCM in horizontal and vertical straight double-pipe LHTES systems with the same surface area is initially simulated and compared with the new same-size LHTES system. Thereafter, the thermal performance of the double-pipe helical-coil storage has been intensively investigated under various operational conditions. Results reveal that the thermal performance of the double-pipe helical-coil LHTES during the PCM melting phase is spurious compared with that of others. The required saving in the PCM melting time is approximately 25.7% and 60% for the horizontal and vertical straight double-pipe LHTES systems, respectively. Moreover, results show that the coil pitch has a remarkably impact on the total PCM melting time in the double-pipe helical-coiled tube, however the optimum coil pitch is 2 OD. The analysis also reveals that the initial temperature and Reynolds number (Re) of heat transfer fluid (HTF) are other factors that significantly affect the PCM melting process.