基于气泡和聚团的结构模型及其应用

Structural model based on bubbles and clusters and its applications

综合考虑鼓泡流化床内气泡及聚团对床内细颗粒流动的影响,建立基于气泡和聚团的结构曳力模型及结构参数模型,同时,借助计算流体软件预测细颗粒在鼓泡床中流动状态。首先,基于细颗粒在鼓泡流化床的流动状态,在介观尺度上将床内气固流动结构划分为3个子结构,即气泡相、相间相及乳化相(聚团相)。然后,综合考虑细颗粒鼓泡流化床中气泡和聚团对气固流动的影响,根据力平衡、质量守恒建立基于气泡和聚团的结构参数模型及结构曳力模型。通过对结构参数模型封闭求解,得到11个结构参数值(f_b,U_b,d_b,U_(gb),f_i,U_(gi),ε_i,f_e,U_(ge),ε_e,d_c)。对结构参数计算结果进行分析,结构参数模型能够很好反映床内流动情况及床内各结构参数之间的关系,并能有效地预测颗粒聚团直径。此外借用非均匀因子,耦合结构曳力模型及结构参数模型到欧拉双流体模型对气固在床内流动行为进行数值模拟。模拟结果表明,使用基于气泡和聚团的结构曳力模型能够较好地预测细颗粒在鼓泡流化床中的流动行为。在对模拟结果中颗粒径向浓度比较时,可以发现,相对比基于气泡模型的结构曳力模型,使用基于气泡和聚团的结构曳力模型的模拟结果与实验结果更一致。

Considering the effects of bubbles and clusters on the transport between gas and particles for the Geldart A particles in the bubbling fluidized beds, the structural parameters model and structural drag model were built. Meanwhile the behavior of fine particles in bubbling fluidized beds was predicted by incorporating the structural parameters model and structural drag model into the two-flow model. According the flow behavior of Geldart A particles in bubbling fluidized beds, the flow structure in beds could be divided into three homogeneous dispersed phases, bubble phase, interphase and emulsion phase （cluster phase）. Then, through the force balance and mass balance, the structural parameters model and drag model which are based on the bubbles and clusters are built to consider the effects of bubbles and clusters on the flow behavior synthetically. The structural parameters （fb, Ub, db, Ugh, f, Ugl, el, fo, Uge, ee, de） are obtained by solving seven independent equations made up of momentum conservation equation, mass conservation equation, and empirical correlations. The structural parameter model and structural drag correlation axe incorporated into the two-fluid model to simulate the hydrodynamicsof Geldart A particles in bubbling fluidized beds. Comparing the structural parameters in the result, it could be found that the structural parameters describe the flow structure correctly and reflect the relationship among the flow structural parameters. The simulation results show that the drag model based on the bubbles and clusters could predicted the flow behavior of fine particles well. In the comparison of the radial solid concentration, it could found that, compared to the drag model based on the bubbles, the radial solid concentration is more consistent with the experimental data when the drag model based on the bubbles and clusters is used.