Comparative analysis on gas–solid drag models in MFIX-DEM simulations of bubbling fluidized bed

In this study,the open-source software MFIX-DEM simulations of a bubbling fluidized bed(BFB)are applied to assess nine drag models according to experimental and direct numerical simulation(DNS)results.The influence of superficial gas velocity on gas–solid flow is also examined.The results show that according to the distribution of time-averaged particle axial velocity in y direction,except for Wen–Yu and Tenneti–Garg–Subramaniam(TGS),other drag models are consistent with the experimental and DNS results.For the TGS drag model,the layer-by-layer movement of particles is observed,which indicates the particle velocity is not correctly predicted.The time domain and frequency domain analysis results of pressure drop of each drag model are similar.It is recommended to use the drag model derived from DNS or fine grid computational fluid dynamics–discrete element method(CFD-DEM)data first for CFD-DEM simulations.For the investigated BFB,the superficial gas velocity less than 0.9 m·s^(-1) should be adopted to obtain normal hydrodynamics.

基于MFIX开源程序下的气固两相流动特性的数值模拟

基于MFIX开源程序建立了三维喷动床内气固两相流动模型,利用MFIX-离散单元法(DEM)模型对源程序进行不同曳力模型的数值模拟计算,得到颗粒在三维喷动床内的流动特性,同时结合实验对喷动床内0.2~2.0 s内的颗粒流动特性进行了分析。结果表明:数值模拟与实验结果相似度较高,Gidaspow模型床高与实验结果较接近,但该模型床高波动范围较大,而Syamlal-O’Brien模型相对较为接近实验结果;2种曳力模型下model B比model A的死区范围小,采用model B流动性更强;随着时间的推移,床高会出现一个极值点,在此点前后床高波动较大, model B的床高极值点比model A的高,且Syamlal-O’Brien模型比Gidaspow模型出现床高极值的时间点往后推移。

液固流化床内双组分颗粒流动数值模拟

采用MFIX-DEM方法对液固流化床内双组分不同密度的颗粒流动进行数值模拟,用BVK曳力模型计算相间作用力,研究表明:在固相颗粒与流体的密度差带动下,轻颗粒向上运动,重颗粒向下运动,最终两种颗粒实现分离;在颗粒的运动过程中,颗粒的压力梯度力在总力中占主导地位,是颗粒随机运动的主要因素;碰撞力在颗粒的混合过程中起主导作用,轴向曳力在颗粒的分离过程中起主导作用;颗粒拟温度受颗粒的体积分数制约,双组分颗粒中重颗粒的颗粒拟温度相对较大。