Investigation of particle size impact on dense particulate flows in a vertical pipe

Abstract

In this work, a semi-resolved computational fluid dynamics-discrete element method is employed to study the effects of fluid–particle and particle–particle/wall interactions on particle mixing and segregation behaviors and particle dynamics with different particle sizes in a vertical pipe. There are two species of particles with the same density in the vertical pipe: d1 = 10 (species 1) and d2 = 2–7 mm (species 2), and species 2 contains both fine and coarse particles. The Stokes number Stp is introduced to characterize the effects of different particle sizes on particle dynamics. First, the particle mixing and segregation behaviors with different size ratios are qualitatively analyzed. By comparing with smaller size ratios, obvious granular plugs and stronger contact force networks occur at larger size ratios. Second, after the segregation of species 1 and 2, the differences in dynamic characteristics between fine and coarse particles are explored. The normalized autocorrelation length scale, which is the ratio of propagation length of particle velocity fluctuations and particle diameter, is significantly different from fine to coarse particles. One notable feature is that two different flow regimes are found through the radial distribution function. Furthermore, the hydrodynamic stress and collision stress are defined to study the mechanism for the differences between fine and coarse particles. The results imply that the reason for the differences is that the collision effects go beyond the hydrodynamic effects with the increase in the Stokes number.