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Assessment of different coarse graining strategies to simulate polydisperse gas-solids flow
Chemical Engineering Science ( IF 4.7 ) Pub Date : 2018-04-01 , DOI: 10.1016/j.ces.2018.01.003
Liqiang Lu , Yupeng Xu , Tingwen Li , Sofiane Benyahia

Abstract Continuum methods require the additional development of solids stress closures for polydisperse powders based on complex kinetic theories that are non-trivial to develop, code, and numerically converge for the wide range of fluidization regimes from very dilute to dense/frictional flow limit. On the other hand, it is straightforward to model the flow of polydisperse granular materials by treating particles as discrete rigid bodies that are tracked following simple physical laws of motion. The coarsening of these discrete methods by lumping several particles in a parcel alleviates the significant computational cost associated with these discrete methods while introducing some inaccuracies in the numerical results. In this research, we explore two different coarse graining methods that can be applied to polydisperse powders, namely the same statistic weight method (SSW) and the same size parcel method (SSP), and assess their accuracy by comparison with the finest simulation results obtained with a discrete element method (DEM). For Geldart group B powders fluidized at a relative low superficial velocity, the numerical results indicate that the SSW is more accurate than the SSP method. For type A powders fluidized at relatively high velocity, these two methods predict similar results. Interestingly, up to four times increase in the speed of simulation of the SSP method was obtained because the original polydisperse powder is scaled to a mono-disperse system in terms of particle-particle collision. These results suggest that the SSP method is more favorable for the simulation of fluidized beds due to its accuracy and efficiency while the SSW method may be used for granular flow and dense fluidized bed systems where capturing the size segregation of particles due to collision is important.

中文翻译:

模拟多分散气固流动的不同粗粒化策略的评估

摘要 连续介质方法需要基于复杂动力学理论对多分散粉末的固体应力闭合进行额外的开发,这些理论对于从非常稀到稠密/摩擦流动限制的广泛流化状态进行开发、编码和数值收敛是非常重要的。另一方面,通过将颗粒视为遵循简单物理运动规律跟踪的离散刚体,可以直接对多分散颗粒材料的流动进行建模。通过将几个粒子集中在一个包裹中来粗化这些离散方法,减轻了与这些离散方法相关的显着计算成本,同时在数值结果中引入了一些不准确性。在这项研究中,我们探索了两种可应用于多分散粉末的不同粗粒化方法,即相同统计权重法 (SSW) 和相同尺寸包裹法 (SSP),并通过与离散元法 (DEM) 获得的最精细模拟结果进行比较来评估其准确性。对于以相对较低的表观速度流化的 Geldart B 组粉末,数值结果表明 SSW 比 SSP 方法更准确。对于以较高速度流化的 A 型粉末,这两种方法预测的结果相似。有趣的是,SSP 方法的模拟速度提高了四倍,因为原始多分散粉末在粒子-粒子碰撞方面被缩放为单分散系统。
更新日期:2018-04-01
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