Performance optimization of a solar drying system with cascaded phase change thermal storage based on dynamic drying model

Solar drying technology has garnered significant attention due to its low-carbon characteristics and economic benefits. However, traditional solar drying systems are limited by the intermittent and fluctuating nature of solar energy, which makes it challenging to ensure continuous operation. In this study, a solar drying system with cascade phase change thermal storage is innovatively proposed to realize the constant, efficient, and stable operation. System performance is investigated at multiple time scales, including typical daily and annual conditions, through a combination of numerical simulation and experimental validation. An equivalent time theory is introduced to establish a continuous dynamic drying model, enabling the analysis of storage/exothermic and drying characteristics under varying operating conditions. Furthermore, a dynamic operation strategy optimization method is developed to improve system performance. Results show that under typical daily conditions, the proposed system increases thermal storage capacity by up to 8.64% compared with a single-stage phase change thermal storage system, while the solar energy utilization rate reaches 49.31% on the winter solstice. After optimization, moisture evaporation increases by 8.61%, overall system efficiency improves by 13.05%, and inlet air temperature fluctuation is reduced by 35.7%. The peak system efficiency reaches 60.5% in July. This study provides significant scientific value for the design of solar drying system thermal integration and the optimization of operation strategy.