Abstract: The gas-solids flow behavior in a two-dimensional riser was numerically simulated by combining computational fluid dynamics (CFD)and discrete element method (DEM).In particular,gas turbulence was investigated by standard k-ε two-equation model,and van der Waals force and rolling friction between particles were also considered.In the present study,the flow behavior of particles and gas was analyzed,distribution of particle concentration,velocity,granular temperature and gas velocity were obtained,and the effect of operating conditions on solids flow was also studied.The results indicated that particles flow showed significant non-uniformity in the riser,clustering was observed near the wall.The typical core-annulus flow structure with a dense phase near the wall and a dilute phase in the center was formed.In the vertical direction,it was divided into a dilute region in the upper zone and a dense region near the bottom in the riser.The results showed a certain amount of some backmixing of both particle and gas phase.Furthermore,it was demonstrated that particle velocity increased and particle concentration decreased with increasing superficial gas velocity,and particles had more non-uniform distributions.Larger solids mass flux led to more non-uniform solids distributions and higher particle concentration,while particle velocity was insensitive to change of solids mass flux.Simulated results were in qualitative agreement with experimental observations.

Key words: riser, discrete element method, computational fluid dynamics, heterogeneity

摘要： 采用离散单元法模型对二维提升管内气固流动特性进行了数值模拟。利用标准k-ε模型模拟气相的湍流流动,考虑了颗粒间的van der Waals力和滚动摩擦的作用。通过对颗粒和气体流动行为的分析,得到了颗粒浓度、速度、温度及气体速度等的分布,研究了表观气速和颗粒循环速率对颗粒流动的影响。结果显示:颗粒在提升管内呈现边壁浓、中心稀的环核流动及上稀下浓的流动结构;气固两相都存在一定程度的返混现象;增加表观气速,使颗粒浓度降低、速度增大,颗粒分布更均匀;增加颗粒循环速率,使颗粒浓度增大,而颗粒速度对颗粒循环速率的变化不敏感,颗粒分布的不均匀性更强。模拟结果与文献中实验定性吻合。

关键词: 提升管, 离散单元法, 计算流体力学, 不均匀性