Numerical analysis and optimization of the charging process on a shell-and-tube latent heat thermal energy storage unit for a solar power plant with direct steam generation

A two-dimensional model of the charging process on a heat storage unit in a shell-and-tube type latent heat subsystem of a solar power plant with direct steam generation was constructed in this study. The effects of the outer diameter to inner diameter ratio, aspect ratio, phase change material (PCM) thermal conductivity, and heat transfer fluid (HTF) mass flow rate were investigated. Results show that increasing the PCM thermal conductivity, HTF mass flow rate, and aspect ratio of the heat storage unit can shorten heat storage time, but the ratio of the outer diameter to the inner diameter of the heat storage unit has an optimal value of 6 in this problem. Using response surface methodology analysis, the influence of the aspect ratio, outer-to-inner-diameter ratio, PCM thermal conductivity, and HTF mass flow rate on the storage time of the phase change heat storage unit is in descending order. After a genetic algorithm optimization, the storage rate of the heat storage unit increased by 35%. The results of this study can guide the heat storage unit to achieve a better practical application performance.