Effects of molten salt multi-thermophysical properties on performance of the latent heat thermal energy storage system and synergetic optimization investigation

Molten salt is a typical PCM in solar thermal utilization, the disadvantage of low thermal conductivity has been improved by various methods. However, only enhancing the thermal conductivity can't reach a satisfactory optimization goal. Aiming to improve the key thermal performance indexes of LHTES, multi-properties collab-orative equivalent optimization is preliminarily presented here, which partly breaks the fixed mode of purely enhancing thermal conductivity. A numerical simulation model of a typical shell-and-tube storage tank was established, and a L25(56) orthogonal simulation experiment was carried out. By evaluating the key thermal performance indexes and through range analysis, the influence laws and importance order of thermophysical properties are obtained. Moreover, the relationship between the key performance indexes and thermophysical properties is fitted, and a rough alternative optimization quantitative relationship is obtained. The results show that thermal conductivity and phase transition temperature have the greatest influence on almost all perfor-mance indexes at the early stage (1 h-1.5 h), and the specific heat capacity and latent heat gradually exceed them after 1.5 h. Compared with the stored exergy and stored heat energy during 4 h, the benefit from thermal conductivity enhancement during 2 h is nearly three and four times, respectively. Therefore, low thermal con-ductivity can be compensated by decreasing the phase change temperature in the case of fast energy storage process, while by increasing the specific heat capacity and latent heat in the case of slower one. After evaluating the feasibility and cost of adjusting each thermophysical property, the synergetic optimization scheme has more practical value.