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对于循环流化床内气固两相流动,三维全循环计算流体力学(Computational Fluid Dynamics,CFD)模拟是最直观可靠的模拟方式。然而,受计算资源和模型的限制,目前的模拟工作大多对构体进行简化,如仅考虑提升管段,或采用二维长方形代替三维构体,或对实际装置几何尺寸进行成比例缩小等等。对几何结构的简化,忽略了出入口、周向结构或返料装置等因素对流动行为的影响,因而计算结果不能准确反映真实流场。采用基于结构的多流体模型(the Structure-dependent multi-Fluid Model,SFM)耦合能量最小多尺度模型(the Energy-Minimization Multi-Scale model,EMMS)修正曳力,完全依据实验参数建立构体和设定边界条件,对中试规模循环流化床进行三维全循环动态模拟。计算结果表明,三维全循环模拟不仅能定性预测快速流态化中典型的上稀下浓和边壁浓中心稀的非均匀分布,定量对比颗粒循环通量、浓度和速度信息与实验值也吻合较好。由于三维全循环模拟不存在几何结构简化,能直接表征真实工况和流场,特别适合于结构复杂的大尺寸工业装置模拟。
For gas-solid two-phase flow in CFB, Computational Fluid Dynamics (CFD) simulation is the most intuitive and reliable simulation method. However, due to the limitations of computational resources and models, the current simulation work mostly simplifies the structure, such as only considering the riser section, replacing two-dimensional rectangle with three-dimensional structure, or scaling the actual device geometry. The simplification of the geometric structure, ignoring the entrance, the circumferential structure or return device and other factors on the flow behavior, so the results can not accurately reflect the real flow field. The structure-dependent multi-fluid model (SFM) coupled energy-minimization multi-scale model (EMMS) was used to modify the drag force, and the structures and structures were completely established based on the experimental parameters Boundary conditions, the pilot scale circulating fluidized bed three-dimensional full-cycle dynamic simulation. The calculation results show that the three-dimensional full-cycle simulation can not only qualitatively predict the typical non-uniform distribution of the upper dilute concentration and the concentrated central dilute in the fast fluidization, but also quantitatively compare the particle flux, concentration and velocity with the experimental data better. Because there is no geometrical structure simplification in three-dimensional full-cycle simulation, it can directly characterize the real working conditions and flow field, and is especially suitable for the simulation of large-scale industrial devices with complex structure.