Eulerian simulation of heterogeneous gas–solid flows in CFB risers: EMMS-based sub-grid scale model with a revised cluster description
Eulerian simulation of heterogeneous gas–solid flows in CFB risers: EMMS-based sub-grid scale model with a revised cluster description
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DOI：
10.1016/j.ces.2007.11.023
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发表时间：
2008-03
影响因子：
4.7
通讯作者：
Junwu Wang;W. Ge;Jinghai Li
中科院分区：
文献类型：
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作者：
Junwu Wang;W. Ge;Jinghai Li
循环流化床立管内气固两相流动的特点是固体颗粒聚集形成动态的多尺度结构，如何量化这种非均质性是一个关键但尚未解决的问题。近年来，将能量最小化多尺度（EMMS）模型与欧拉方法相结合，在模拟CFB立管流体力学方面取得了令人鼓舞的结果。然而，由于使用了簇直径相关，目前的模型仍然局限于Geldart A粒子的模拟。本文采用双随机泊松过程的随机几何方法分析了循环流化床立管内固体浓度的波动特征，为确定簇内固体浓度提供了一种方法。利用已有的实验数据对预测结果进行了验证，并对先前开发的气固同时向上流动的EMMS模型提出了修正的簇直径相关性。根据我们之前的研究，将改进后的EMMS模型作为相间阻力的亚网格尺度模型纳入气固流动的欧拉-欧拉描述中，模拟了CFB立管中Geldart a和Geldart B颗粒的流体动力学。结果表明，实验发现的s型轴向空隙分布和堵塞现象可以很好地预测。一维滑移速度沿隔水管顶部减小，随截面平均空隙的减小而增大。实验发现固体浓度的均方根对其在给定位置上的平均值的依赖性也得到了很好的预测。
Gas–solid two-phase flow in CFB risers is characterized by the clustering of solid particles producing dynamical multi-scale structures, and how to quantify such heterogeneity is a critical yet unsolved issue. Recently, incorporating the energy minimization multi-scale (EMMS) model with Eulerian approach has obtained encouraging results for simulating the hydrodynamics in CFB risers. However, owing to the cluster diameter correlation used, the present model is still limited to the simulation of Geldart A particles. In this study, a stochastic geometry approach named doubly stochastic Poisson processes is used to analyze the fluctuation characteristics of solid concentration in CFB risers, which provides a mean to define the solid concentration inside clusters. The predicted results are validated by experimental data available in literature, and a revised cluster diameter correlation is then proposed for EMMS model previously developed for cocurrent-up gas–solid flow. Following our previous studies, the EMMS model thus improved is incorporated into an Eulerian–Eulerian description of gas–solid flow as a sub-grid scale model for inter-phase drag force, with which the hydrodynamics of both Geldart A and Geldart B particles in CFB risers are simulated. It is shown that the experimentally found S-shaped axial voidage profiles and the choking phenomenon can be well predicted. The computed one-dimensional slip velocities decrease toward the top of the risers and increase with decreasing cross-sectional averaged voidages. The experimentally found dependence of the root mean square of the solid concentration on its mean value at a given position is also well predicted.