Heat transfer and heat storage characteristics of calcium hydroxide/oxide based on shell-tube thermochemical energy storage device

Understanding the mechanisms and characteristics of heat and mass transfer is crucial for optimizing the design and operating parameters of Ca(OH)₂/CaO fixed bed reactors, thereby improving energy conversion efficiency and storage performance. In this study, a comprehensive physicochemical model of shell-tube thermochemical energy storage (TCES) indirect reactor is developed, considering chemical reaction, heat and mass transfer, and turbulent fluid flow. The influences of different parameters such as inlet temperature and flow rate of the heat transfer fluid (HTF) and the porosity of the reaction bed are studied to assess their impact on reaction time, heat transfer power, heat transfer efficiency, and TES efficiency in the reactor. The result indicates that the inlet temperature of the HTF and the porosity of the reaction bed significantly impact the TCES efficiency and heat transfer efficiency of the reactor. Increasing the temperature of the HTF can enhance the reaction kinetics, a higher inlet temperature corresponds to a larger peak molar flow rate of the steam outlet. When the reactor porosity decreases from 0.80 to 0.70 and 0.70 to 0.60, the reaction time increases to 69.70% and 98.66%, respectively. However, increasing the flow velocity of the HTF does not have a significant effect on shortening the reaction time. It is observed that the TES efficiency of the shell-tube indirect reactor is relatively low, as a significant portion of the input heat is lost through the HTF and steam flowing out. Compared with the heat exchange energy, the heat taken away by steam is about 60%. These research findings are essential for improving the design and achieving more efficient, stable, and sustainable TCES systems.