非均匀颗粒流动垂向分选实验研究

Experimental Studies on Vertical Segregation of Non-homogeneous Particles in Granular Flow

利用两个半径不同的同心圆筒组成环形流道,在流道上表面安装摩擦板带动颗粒流动,进行非均匀颗粒流动垂向分选实验.该实验方法使颗粒可在环形流道中循环流动,流动速度可调,流动时间不受限制,克服了以往实验中由于流道较短颗粒垂向分选不充分的弊病.实验证实了Savage提出的"空隙填充机制",小颗粒优先填充于颗粒流动过程中形成的空隙中,逐渐向下层迁移,形成垂向分选.实验结果还表明,快慢速流动两种不同条件下,颗粒垂向分选机制存在本质区别.在颗粒流动速度较小的情况下,颗粒间作用以摩擦为主,颗粒垂向分选的程度取决于颗粒流动过程中随机产生空隙的大小和数量,即主要受"空隙填充机制"控制;随着颗粒流速的加快,颗粒间的碰撞作用加强,碰撞应力逐渐起控制作用,小颗粒空隙填充几率相对减少,部分小颗粒甚至由于碰撞应力作用由下层重新回到上层,导致分选程度下降.

A series of experimental researches on vertical segregation of granular flow with nonhomogeneous particles had been carried out in an annular channel composed of two concentric cylinders with different diameters. Compared with the previous experiments, the particles could continuously flow in the circular channel, and the flow velocity and time could be adjusted so that the vertical segregation could be fully developed. Our experimental results verified ＂voidfilling mechanism＂ suggested by Savage for the vertical segregation, the small was prior to filling the void and moved down in granular flow. The results also showed that the segregation mechanisms were different on the two conditions of slow and rapid flow. In slow granular flow, the friction among particles was dominated and the vertical segregation status depended on the void number and size during the flow. However, in the rapid granular flow, the collision action took the place of friction, and the void-filling probability of small particle reduced. In this condition, Some small particles even came back upper layer because of the collision stress, and the vertical segregation become unconspicuous.