Experimental and modeling study on thermal performance of hydrated salt latent heat thermal energy storage system

Phase change material (PCM) holds tremendous promise in the fields of renewable energy utilization and waste heat recovery. In this context, a series of experiments of low-temperature hydrated salt latent heat thermal energy storage (LHTES) system have been conducted to investigate its thermal performance and charging-discharging behavior. Sodium acetate trihydrate mixed with nucleating agent and thickening agent was applied as the PCM and filled into the experimental tube. The temperature evolution of PCM was observed and thermal properties were measured. Numerical model was established to monitor the phase transition process and predict the temperature distribution of PCM filled tube, to make a comparison with the experimental results. It revealed that heat conduction played predominate role in heat transfer when the PCM temperature was below the fusion value, whereas the natural convection was the controlling mode when liquid PCM appeared during the phase transition process. The tube diameter and flow rate were studied to present their effects on the performance of heat storage/release. Compared to smooth tubes, the stainless steel fins and aluminum fins with various thickness added to inside of the tube to enhance the heat transfer. It was found that the heat transfer between thermal fluid and PCM relied greatly in the geometry of the storage tube and fins attribution. The optimized fins geometry can effectively reduce the charging time and discharging time by 27% and 24%, respectively. Our conclusions drawn from this research can provide a theoretical basis for the application of the low-temperature hydrated salt LHTES system.