Dynamic thermal and mechanical performances of the molten salt thermocline storage tank for charging process: A numerical simulation study

Single-tank molten salt thermocline storage enables cost-effective and high energy density heat storage compared to traditional dual-tank systems. The dynamic evolution mechanisms of thermocline and tank wall stress dominate the efficiency of energy storage systems and tank safety. Therefore, a three-dimensional transient thermal-mechanical coupling numerical model was developed to quantitatively analyze the thermal and mechanical properties under different charging parameters, which provides theoretical support for the safety design of the tank and the optimization of charging parameters. The dynamic correlation between the thermocline evolution and the tank wall stress was revealed, and the double peak characteristic of tank wall stress moving with the thermocline was found. The relationship between the temperature distribution and deformation of the tank wall was clarified, and the “viscosity effects” of molten salt in the charging process was also found. The results show that the thermocline thickness decreases with the increase of the inlet flow rate, decreases first and then increases with inlet temperature decrease, and the thermocline thickness reaches a minimum of 0.75 m when the inlet temperature is in the range of 415–465 °C. The top and bottom of the tank wall are high risk areas for stress yield, with a maximum stress of 175 MPa. The total deformation of the tank wall gradually increases from 10 mm at the bottom to 100 mm at the top, and the upper two-thirds of the tank wall exhibits the most significant deformation.