涡流空气分级机近导叶处团聚体解团机理研究

Research on the mechanism of disaggregation of particle aggregates near the guide vanes of turbo air classifier

超细颗粒往往会因为黏附力形成团聚,从而限制了通过气力分级制备粒径小且分布范围窄的超细粉体。研究团聚体解团机理可为提出解团措施提供理论依据。利用EDEM二次开发功能通过颗粒工厂生成团聚体,基于FLUENT-EDEM耦合进行涡流空气分级机环形区近导叶处区域团聚体运动及其解团过程的数值模拟,研究了不同入口风速下对团聚体解团的影响程度,并揭示了团聚体在环形区近导叶处区域的解团机理。结果表明,在导叶近壁面区域气力流场的剪切力无法使团聚体解团,流场中解团是由于团聚体与固壁面碰撞而引起的。在转笼转速为1200 r·min^(−1),入口风速为6、12、18、24 m·s^(−1)的情况下,单颗粒占比数随入口风速由71.7%增大到88.39%,而未解团的团聚体由24.8%减少到10.51%,部分解团后形成的团聚体的占比均不超过4%,表明单个团聚体在流场中解团程度较大,入口风速增大会提高环形区近导叶处粉体分级时的分散性,引入无量纲参数——相对碰撞次数验证了这一结果。

Ultrafine particles tend to agglomerate due to adhesion,which limits the preparation of ultrafine particles with small size and narrow distribution range through pneumatic classification.Studying the mechanism of agglomeration disaggregation can provide a theoretical basis for proposing measures to disaggregate.In this paper,application programming interface(API)of EDEM is used to generate the aggregates in the particle factory,and the numerical simulation of the movement of the aggregates and their disaggregation process near the guide vanes in the annular region of a turbo air classifier is carried out in FLUENT-EDEM coupling.The influence of different inlet air velocity on the aggregates is studied and the mechanism of disaggregation of aggregates near the guide vane in the annular zone is revealed.The results show that disaggregation of the aggregates near the guide vanes in the flow field is caused by the collisions between the aggregates and the wall of guide vanes,but not the shearing force of the flow field.When the rotating velocity of the rotor cage is 1200 r·min-1 and the inlet air velocity is 6,12,18,and 24 m·s-1,respectively,the proportion of single particles increases from 71.7%to 88.39%and the proportion of the aggregates decreases from 24.8%to 10.51%with the increase of inlet air velocity,the proportion of aggregates after partial disaggregation does not exceed 4%,indicating that the increase of inlet air velocity will improve the dispersion of powder near the guide vanes in the turbo air classifier.The introduction of dimensionless parameter—relative collision number verifies this conclusion.