Thermal energy storage and retrieval characteristics of a molten-salt latent heat thermal energy storage system

In the present study, a shell-and-tube latent heat thermal energy storage (LHTES) system is built using the eutectic molten salt as the phase change material (PCM) to make an efficient use of solar energy at medium-temperature of around 200.0 °C. The nickel foam is embedded in pure PCM (molten salt) to form composite PCM to improve the performance of the LHTES system through enhancing the effective thermal conductivity of the PCM. The performances of the systems using pure molten salt and composite PCM are investigated both experimentally and numerically. The oil is used as the heat transfer fluid (HTF) and the influence of mass flow rate of the HTF on the thermal energy storage and retrieval is investigated in the experiments. The charging and discharging time durations, mean power and energy efficiency are estimated to evaluate the performance of the LHTES system. Meanwhile, a three-dimensional (3D) numerical model is developed based on the enthalpy-porosity model and two-temperature energy equations to investigate the thermal energy storage and retrieval of the LHTES system, and the detailed heat transfer characteristics during the melting/solidification of the PCM are understood. The results indicate that encapsulating molten salt with nickel foam to enhance the effective thermal conductivity of the PCM can improve the performance of the LHTES system. The information provided in the present study will be helpful for the LHTES system design, construction and application using molten salt for solar energy storage.