Thermodynamic analysis of molten salt-based single-tank thermal energy storage system with heat transfer enhanced by gas injection

In this study, the feasibility of gas injection for enhancing heat transfer in a molten salt thermal storage system was experimentally investigated. The convective heat transfer coefficient induced by the gas injection was quantitatively measured. A predictive model was developed to estimate the heat transfer coefficient with respect to the gas injection rate. A comparative analysis between gas-injection and non-injection cases was also performed from a thermodynamic perspective to verify the feasibility of the method. The heat transfer coefficient was within the range of 359–1283 W/m2-K, depending on the gas injection rate. The developed model estimated the measured values within an average absolute error of 2%. From the comparative analysis, the gas injection method improved thermal efficiency from 86.3% to 95.1%. The energy loss induced by the gas injection was within the range of 0.2%–1.1% of the total stored energy. The gas injection also shortened the energy discharge time by 32%–41% owing to the heat transfer enhancement. The proposed method also improved the system performance by enhancing the exergy transfer rate from the salt to the water. These results indicate that a gas injection method is a potential candidate for improving molten salt thermal storage systems.