快速流化床颗粒团絮特征的MP-PIC数值模拟

MP-PIC simulation of particle clusters in fast fluidized bed risers

为了研究快速流化床颗粒的团絮特征,建立了基于多相质点网格法的快速流化床气固多相流三维数理模型,气相场采用大涡湍流模型,通过求解牛顿运动方程得到颗粒相运动信息,气固间相互作用力采用Gidaspow曳力模型,固体间作用力通过计算颗粒应力梯度得到。基于该模型,对三维快速流化床上升管(H=3 m、d=0.1 m)气固流动开展了数值模拟,并与实验进行了校正,研究了在气速工况Ug=5.28 m?s-1下的颗粒(ρp=2650 kg?m-3、dp=250μm)团絮性质,实现了对上升管内颗粒团絮的基本类型(条形团絮、马鞍形团絮、U形团絮)的成功预测,并揭示了不同类型团絮在上升管内形成、发展、聚并直至破碎的演化规律。结果表明,上升管径向颗粒团絮的平均颗粒浓度分布呈现中间低两边高的环核结构,颗粒团絮速度的分布与其相反;随着轴向高度的增加,颗粒团絮的颗粒浓度逐渐降低而速度逐渐增加,但达到一定高度后变化减缓。

A three-dimensional Eulerian-Lagrangian model,based on MP-PIC method,was developed to simulate particle clusters in fast fluidized bed risers.In the model,gas phase was simulated by large eddy simulation(LES),real particles were displaced by numerical-particles and particles was described by Newton movement equations,drag between gas and particles was calculated by Gidaspow model,and normal stress of particles was calculated and interpolated into Eulerian grids to describe particle contraction.The model was used to simulate gas solid movement in a 3D fast fluidized bed riser with dimension of height H=3 m and diameter d=0.1 m and adjusted according to experimental data.Cluster characteristics of particles(ρp=2650 kg.m^-3 and dp=250μm)was studied at operational condition of Ug=5.28 m.s^-1 gas velocity.The results indicate that the MP-PIC simulation can recognize different shapes of clusters,such as stripe-shaped,saddle-shaped and U-shaped,as well as disclose cluster development including formation,expansion,coalescence and breakup.Mean particle concentration distribution of clusters in the riser cross section shows a core-annular structure with low middle and high edge concentrations,which is opposite to mean cluster velocity distribution.The mean particle concentration of clusters decrease while the mean cluster velocity increase with increase of riser height,but the change of both concentration and velocity slows down above certain riser height.