Ca(OH)_(2)脱水过程数值研究及强化

Numerical Study and Enhancement of Ca(OH)_(2)/CaO Dehydration Process

建立了Ca(OH)_(2)/CaO反应器脱水过程的多孔介质流动换热模型,对Ca(OH)_(2)/CaO热化学储能系统的脱水过程进行了三维数值模拟研究,分析了储能系统在脱水过程中温度、反应物浓度的动态变化,并针对该反应系统设计了一系列强化传热传质措施,通过增加多种类型翅片、添加多孔通道及金属板、改变反应器高径比、采用圆台型反应器来强化传热及传质,分析了各种工况下储能系统的温度、压力变化情况。结果表明:添加翅片有利于强化反应器的传热性能,提高脱水过程速率;添加多孔通道一方面可以强化传热,另一方面多孔结构可以作为水蒸气的扩散通道,减小水蒸气扩散阻力,强化传质;在孔隙率不变的前提下,增大反应器高径比会强化反应器的传热性能,但是会增加水蒸气扩散阻力。改变反应器高径比会对反应器传热及传质性能产生影响;采用圆台型反应器时,其脱水反应的快慢取决于反应器最大截面处的反应速率大小。相比于传质,传热对圆台反应器的脱水过程起主要影响;对于研究尺寸下的反应器,强化传热对反应系统性能的提升作用优于强化传质。研究结果可为热化学储能反应器的结构优化与性能提升提供一定的参考价值。

A flow and heat transfer model in porous medium for the Ca(OH)_(2)/CaO dehydration process is established.Three-dimensional numerical simulation is conducted to analyze the dynamic changes of temperature and reactant concentration during the dehydration process of the Ca(OH)_(2)/CaO thermochemical energy storage system.A series of measures are designed to enhance heat and mass transfer,such as adding various types of fins,porous channels and metal plates,changing the reactor height-to-diameter ratio and using a roundtable reactor.The temperature and pressure changes of the energy storage system under various operating conditions are analyzed.The results demonstrate that adding fins can enhance the heat transfer performance of the reactor and improve the dehydration rate.Adding porous channels not only can enhance heat transfer but also serve as a diffusion channel for water vapor,reducing the diffusion resistance of water vapor and enhancing mass transfer.Under the premise of constant porosity,increasing the height to diameter ratio of the reactor will enhance the heat transfer performance of the reactor,but it will increase the resistance of water vapor diffusion.When using a roundtable reactor,the speed of the dehydration reaction depends on the reaction rate at the maximum cross-section of the reactor.Heat transfer plays a major role in the dehydration process of the roundtable reactor compared to mass transfer.For reactors of research size,enhancing heat transfer has a greater effect on improving the performance of the reaction system than enhancing mass transfer.The result is helpful for the structural optimization and performance improvement of thermochemical energy storage reactors.