The role of the friction coefficients in the granular segregation in small systems.

With the discrete element method, studies of the influence of friction coefficients on the granular segregation in a 2000 particle system have been performed. Segregation phenomena reported previously such as convection cells [Phys. Rev. Lett. 70, 3728 (1993), Exp. Fluids 51:795–800 (2011)] and intermediate phase [Phys. Rev. E 85, 061302 (2012)] were discovered in our simulations. Higher friction coefficients (between particles as well as between particles and container walls) generally speed up and strengthen the segregation process. Three stages of the segregation process were discovered, i.e. the initial segregation, the subsequent sinking of the large particles, and the long-time height fluctuation of the large particles. Furthermore, by systematically analyzing the variations of the scaling parameters (phase parameter λ and Lacey index M Lacey) with respect to different friction coefficients, we found that the initial segregation is completed by both mechanisms of particle arching and convection. In addition, both the friction drag from the container walls and the gravity forces contribute to the subsequent sinking of the large particles. Moreover, the height fluctuation of the large particles is proved to have a relation with restitution coefficients. Unlabelled Image • A typical BNE segregation process can be divided into three stages. • Higher friction coefficients lead to a faster and more complete segregation. • Both arching and convection contribute to the initial BNE segregation. • Both friction drag and gravity contribute to the sinking of the large particles. [ABSTRACT FROM AUTHOR]