In recent decades, thermochemical heat storage has been considered as a promising candidate to make long-term storage and long-distance transportation of thermal energy possible. Especially, the thermochemical heat storage system Ca(OH)₂/CaO is thought as one of the most potential thermochemical processes for storing middle- and high-temperature thermal energy. In this study, we have investigated the heat and mass transfer characteristics of a three-dimensional fixed-bed reactor with a direct wall heat exchanger using a finite element software. The effect of the porosity, wall temperature, and reaction kinetics on the reactor performances was investigated in detail. Also, the entropy generation due to heat transfer, mass transfer, and chemical reaction during the dehydration/hydration process occurring in the porous reactant were studied. The results indicated that increasing the heat conductivity of the bed can enhance the reaction performances dramatically for both dehydration and hydration processes. A lower porosity, higher wall temperature, and higher reaction rate can have an obvious positive influence on the dehydration reaction. The reaction rate almost has no effect on the entropy productions of reaction and mass transfer during the energy storage process. The entropy generation due to heat transfer process and chemical reaction plays an important role during both dehydration and hydration processes. The results might provide the guidelines on designing or selecting the heat exchanger of a reactor for thermochemical energy storage.

中文翻译：

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热化学能储存系统Ca（OH）₂ / CaO固定床反应器的热力学分析

在最近的几十年中，热化学储热被认为是使热能的长期存储和长距离传输成为可能的有前途的候选者。特别是热化学蓄热系统Ca（OH）₂/ CaO被认为是存储中高温热能最有潜力的热化学过程之一。在这项研究中，我们使用有限元软件研究了带有直接壁式热交换器的三维固定床反应器的传热和传质特性。详细研究了孔隙率，壁温和反应动力学对反应器性能的影响。而且，研究了在多孔反应物中发生的脱水/水合过程中由于传热，传质和化学反应而产生的熵。结果表明，增加床的导热率可以显着提高脱水和水合过程的反应性能。孔隙率较低，壁温较高，较高的反应速率对脱水反应有明显的积极影响。在能量存储过程中，反应速率几乎不影响反应的熵产和传质。由于传热过程和化学反应而产生的熵在脱水和水合过程中都起着重要作用。结果可能为设计或选择用于热化学能量存储的反应堆的热交换器提供指导。