下行床气固两相流动计算流体力学模拟

基于颗粒相动力学理论 ,对层流机制表达的气固两相流体力学模型采用Reynolds平均的方法获得气固两相流的湍流模型描述 .其中 ,气相湍流行为以k -ε模型描述 ;颗粒相的碰撞行为以颗粒流的动力学模型表达 ;而湍流行为以kp 模型描述 .因此建立的k -ε -Θ -kp 模型综合考虑了气相和颗粒相的湍流运动以及颗粒的碰撞行为 .依据此模型建立了三维流体力学求解程序并对下行床气固两相流动行为进行了模型预测 .讨论了恢复系数的选取及壁效应假设 ,从机理上分析并考察了 3种模型的预测能力 .针对内径 1 40mm、高 7m的下行床冷态设备 ,在较宽的操作范围内 ,对比了详细的颗粒浓度和速度径向分布以及轴向参数分布 ,并对下行床的放大行为进行了预测 .

COMPUTATIONAL FLUID DYNAMIC MODELING OF HYDRODYNAMICS IN DOWNER REACTORS

On the basis of kinetic theory of particulate phase, a k-ε-Θ-k p model was derived by Reynolds averaging procedure on the laminar gas-solid CFD model.The gas phase was described by a standard k-ε turbulence model and the solid phase was described by the kinetic theory and k p turbulence model. This k-ε-Θ-k p model took into account the contribution of both particle collisions and particle turbulence to momentum and energy transportation. A three dimensional CFD code was developed to simulate the gas-solid flow in a downer reactor, which is 0.14 m in radius and 7 m in height. An important modification of restitution coefficient, e , was made to consider the wall effect on the two-phase flow. Three kinds of models were discussed and compared from the point of view of physical mechanism. The k-ε-Θ-k p model was used to predict the distributions of solids fraction, particle/gas velocity and pressure. The model predictions agreed well with the experimental data in the wide range of operating conditions. The characteristics of scaling-up of downers were also predicted and the results seemed encouraging.