Thermal storage investigation of a two-layered latent-sensible packed bed with PCM and rock spheres

Abstract

To improve the thermal performance of concentrated solar power (CSP) plants, this study establishes a novel two-layered latent-sensible packed bed to extend the application scope. The major innovation lies in the combination of nitrate-encapsulated phase change material (PCM) capsules and rock spheres in a two-layered configuration, which enhances operational efficiency and minimizes heat transfer temperature differences. A transient concentric-dispersion model is used for numerical simulations to study temperature evolution, thermocline temperature configurations, liquid fraction, sensible and latent energy storage, exergy rate, and exergy efficiency. Four configurations were evaluated: two-layered packed beds with PCM and rock spheres (Cases A and B) and single-layered packed beds with either PCM or rock spheres (Cases C and D). The analysis focuses on the dynamic behavior of thermal energy exchange within the PCM and rock sphere layers, highlighting the advantages and limitations of each configuration. The results show that the two-layered configurations have lower thermocline degradation and higher thermal efficiency. Specifically, the heat storage capacity increased by 15.18 MJ in the two-layered configurations. The exergy input time extended to 350 min in Case A and 342 min in Case B, compared to 260 min in Case C. Results indicate that this hybrid approach significantly reduces thermocline degradation and enhances the overall energy storage capacity and efficiency. The proposed two-layered latent-sensible TES showed higher exergy efficiency and energy storage density than both single-layered LHTES and SHTES, demonstrating improved thermal storage performance.