球形和方形湿颗粒团的碰撞模拟研究

Simulations of impact attrition of cuboidal and spherical wet agglomerate of fine particles

本研究利用颗粒离散元方法,并结合接触力学理论,对微米级颗粒组成的湿颗粒聚合体碰撞破损的细观力学机理进行了模拟研究。模拟的颗粒聚合体分成球形和方形。将两种形状的颗粒聚合体碰撞结果做比较,颗粒之间的接触采用干、湿接触两种模型并存的方式来模拟湿颗粒团碰撞中的不可恢复变形过程。在碰撞速度保持不变的情况,考察了不同液体黏度对颗粒聚合体碰撞的影响;在液体黏度保持不变的情况,考察了不同碰撞速度对碰撞结果的影响。研究结果表明,湿颗粒团表现出了与干颗粒团完全不同的损伤模式,没有产生类似于弹性颗粒团的裂解损伤。湿颗粒团在碰撞中,它的内部液桥数量会在与平板碰撞接触的初期快速减少,然后慢慢累计,或会超过湿颗粒团在碰撞前的液桥数量。这一现象在此仿真研究中首次被发现。比如,液体黏度为50mPa·s的方形湿颗粒团以2.0m/s撞击平板时,其内部液桥数可由约9400降低至约8700后,逐渐增加至11300左右;由低黏度液体组成的湿颗粒团在碰撞后会发生反弹现象。而随着液体黏度的增加,恢复系数会趋近于0。

In this contribution, a simulation tool is developed based on the discrete element method(DEM) and contact mechanics, which is able to investigate the deformation and attritionof wet agglomerates during different impact conditions. In the research, two types of agglomerates of particles are formed, namely, cuboidal and spherical agglomerates. The models of liquid and solid bridge have been implemented in the DEM to perform a detailed simulation for a better understanding of the soft, non-elastic deformation behavior of cuboidal and spherical wet agglomerates. As a result, the dependency of the restitution coefficient on the viscosity of the binder, impact velocity and agglomerate shape are obtained. Our research demonstrates that, unlike dry particle agglomerates, the attrition patterns of wet agglomerates cannot be classified as ‘fracture’. Interestingly, it is observed for the first time that the number of liquid bridges inside a wet agglomerate, when impacted,experiences a significant drop before accumulating and exceeding the original number of liquid bridges. This phenomenon is discovered for the first time. For instance, when impacting a cuboidal agglomerate with liquid viscosity of 50 m Pa·s at a velocity of 2 m/s, the number of liquid bridges drops from 9400 to ca. 8700, then increase up to ca. 11300;This research reveals that some wet agglomerates with lower liquid viscosity can rebound, while the coefficient of restitution tends to zero when liquid viscosity is increased.