非热平衡多孔介质内反应与传热传质耦合过程

Coupled processes of chemical reaction, heat and mass transfer in non-thermal equilibrium porous medium

采用局部热不平衡假设,对发生强吸热化学反应的多孔介质体系建立了反应与传热、传质耦合问题的数学模型,采用Ergun Forchheimer Brinkman方程描述多孔介质中的流体流动.运用交替方向隐式(ADI)方法对模型离散求解,并采用文献中的实验数据对模型进行验证.计算了不同条件下颗粒物料层内气体和固体骨架的温度场、产物气体浓度场以及固体转化率分布,以得到多孔介质体系内固有化学反应时的传热、传质规律.结果表明,不能忽略固体骨架与流体间的温度差.入口渗流速度、入口气体温度以及固体颗粒尺寸是影响系统反应特性的重要参数.研究结果对具有强吸热反应的固定床反应器的设计和运行具有一定的参考作用.

A mathematical model describing the coupled processes of endothermic chemical reaction, heat transfer and mass transfer in porous media was established by using the assumption of local thermal nonequilibrium, which was required when the local thermal equilibrium between the fluid and solid phases broke down. The Ergun-Forchheimer-Brinkman model was used to represent the fluid flow within the porous media. An alternate dimension implicit method was adopted to solve this model numerically and the mathematical model was validated by comparing the numerical results with the experimental data in literature. The gas temperature fields, porous matrix temperature fields, the concentration fields of product gas as well as the distribution of the fractional conversion of solid reactant were obtained by changing various parameters. The results show that, the temperature difference between gas and porous matrix can not be neglected. The velocity in porous media at entrance, gas temperature at entrance and particle size were the important parameters which influenced significantly the reactive characteristics of the porous system. The results are useful in the conceptual design and operation of fixed reactor involving intense endothermic reactions.