锥形分布板射流流化床CFD模拟及参数分析

CFD SIMULATION OF THE JETTING FLUIDIZED BED AND ANALYSIS OF MODEL PARAMETERS

采用双流体模型结合颗粒动力学理论,对锥形分布板射流流化床内气固流动行为进行了三维的计算流体力学(CFD)模拟研究,系统分析了曳力模型、恢复系数和颗粒间摩擦力对射流流化床膨胀高度和气泡动力学行为的影响.结果表明,Syamlal-O’Brien和Gidaspow曳力模型低估了床内实际曳力,从而导致模拟膨胀高度低于实验值,而Modified Syamlal-O’Brien曳力模型能更好地预测床内实际曳力,计算结果与实验值吻合得较好;恢复系数对于射流流化床内气泡动力学行为有着重要影响,气泡的大小、上升速率和产生频率均随着恢复系数的增加而减小;颗粒间的摩擦力也是影响床层膨胀高度和床内气泡产生的重要因素.

A 3D CFD（computational fluid dynamics） simulation were conducted by the combining TFM（two fluid model） and KTGF（kinetic theory of granular flow） on the gas-solidflow behaviors in a jetting fluidized bed with conical distributor. The effects of the gas-solid drag force, the restitution coefficient of particle collision, the frictional stresses between particles on the bed expansion ratio and the bubble dynamics were evaluated by comparison with the experimental data. In the present research work, drag models of Gidaspow and Syamlal-O＇Brien underestimated the gas-solid drag force and predicted a smaller bed expansion in comparison to the corresponding experimental data. However, the modified Syamlal-O＇ Brien drag model based on the minimum fluidization conditions can improve the simulated results to accurately predict the bed expansion. The restitution coefficient of particle collision has a significant effect on the bubble dynamics in the fluidized bed. The larger restitution coefficient can decrease the energy dissipation leading to the smaller bubble size, the slower rise velocity and the less bubble frequency. The frictional stresses play an important role in the particle interaction in the region of high solid fraction. Without the effect of frictional stresses, the less particle interaction may reduce the momentum exchange between particles leading to the higher maximum solid packing, the smaller and less bubble, and the lower bed expansion.