Research on the thermodynamic performance of cascade phase change thermal storage system under unsteady conditions

Cascaded phase change thermal storage (CPCTS) technology has broad application prospects in thermal energy regulation and management as a flexible and efficient means of thermal energy storage. However, most practical thermal storage engineering applications are under complex, unsteady conditions. Therefore, the effect of different arrangements of thermal storage units of low and medium-temperature phase change materials (PCM) on the thermodynamic performance of the thermal storage system under unsteady conditions is addressed in this paper, which has been studied less at present. This study focuses on the CPCTS device applied in the solar drying system and analyzes the thermodynamic performance of the cascade configuration under unsteady typical days. The results show that the two-dimensional model of the CPCTS is highly accurate when applied to the study of storage and exothermic processes. Under stable conditions, the effects of inlet temperature, flow rate, and melting point on the 3E (energy, exergy, and entransy) performance of single-stage phase change thermal storage (PCTS) systems were analyzed. It is found that the matching of the phase change material's melting point and the inlet temperature is the core factor determining the heat storage performance. Furthermore, the thermodynamic characteristics of four cascaded configurations are compared under unsteady typical day conditions. Research shows that the CPCTS system has significant performance advantages under complex weather conditions. CPCTS provides up to 39.50% higher thermal storage capacity than a single-stage system, more stable energy quality (exergy efficiency) than a single-stage system under unsteady typical daily operating conditions, and up to 33.82% higher heat transfer capacity (entransy efficiency). The results verify the potential of CPCTS systems in improving heat source adaptability and comprehensive thermodynamic performance. The research results provide a theoretical basis for multi-scale modeling and engineering optimization of CPCTS systems.