EMMS曳力模型及其颗粒团模型的构建和检验

Development and validation of cluster and EMMS drag model

准确描述颗粒团聚特性是发展完善基于多尺度最小能量原理(EMMS)的曳力模型的重要方向之一。提出描述颗粒团聚特性的数学模型,不仅符合物理判断,而且与实验结果吻合。采用颗粒团模型,改进EMMS曳力模型,与实验及直接数值模拟结果吻合较好。改进的曳力模型与欧拉-欧拉双流体方法耦合,实现了不同工况下A、B类颗粒流化床流动特性的数值模拟。成功预测了颗粒非均匀分布特性、局部滑移速度、局部非均匀度以及噎塞状态。

Reasonable description of cluster parameters is significant for the development of drag model for heterogeneous gas-solids flows. This study proposed the cluster model for solids concentration in clusters and the cluster size based on theoretical analysis. The profile of cluster parameters with solids concentration had a peak locating between local solids concentration of 0.1 and 0.15, indicating largest heterogeneity there. The cluster model was validated directly by experimental data. Energy minimum multiscale method （EMMS） was improved by introducing the cluster model. The improved drag model agreed well with the experiment-based empirical model. Drag correction factors of both models first decreased and then increased with increasing solids concentration, and tended to unity at extremely small solids concentration close to zero and solids concentration at minimum fluidization. The improved drag model was coupled with the two-fluid model for simulations of gas-solids flows in CFB risers containing Geldart A and B particles. Heterogeneous solids distributions, local slip velocity, local heterogeneity and choking state were predicted and agreed well with experimental results, indicating the reasonability of the cluster and drag models.