Abstract: Considering the multi-scale structure of the dense phase in the form of clusters and the dilute phase in the form of dispersed particles in the circulating fluidized bed, the relationship between accelerations and local structure parameters in the dense phase and dilute phase was established and the stability condition of the minimum energy dissipation by multi-scale drag force was proposed. Based on the bivariate extreme value theory, a cluster structure dependent (CSD) drag coefficient model was developed. Gas-solids flow behavior and cluster characteristics in risers were simulated using a two-fluid model. The concentrations of particles obtained by the CSD model showed better agreement with experimental results. Cluster diameter increased, reached a maximum and fell down to single particle diameter with increasing solids concentrations. In the simulation, the influence of accelerations of gas and particles could not be ignored because it appeared to be on the same order of magnitude as acceleration of gravity.

Key words: circulating fluidized bed, numerical simulation, mesoscale, bivariate extreme value theory, drag coefficient

摘要： 考虑到循环流化床中分散颗粒和颗粒聚团同时存在的多尺度结构，确定了密相和稀相加速度与计算网格局部参数之间的关系，建立了多尺度曳力消耗能量最小的稳定性条件，基于双变量极值理论，构建了考虑颗粒团聚效应的多尺度气固相间曳力模型。结合双流体模型，对循环流化床内气固流动特性以及颗粒聚团特性进行了模拟研究。通过与实验值比较，考虑颗粒聚团影响的计算模型可以更好地贴近实验结果，颗粒聚团直径随颗粒浓度增大呈现先增大后减小的分布趋势，气体和颗粒的加速度在模拟中与重力加速度同处一个数量级，求解过程中不能被忽略。

关键词: 循环流化床, 数值模拟, 介尺度, 双变量极值理论, 曳力系数