Discrete element simulation of dry adhesive granular flow in a vertical pipe

Abstract

The transportation and storage of granular materials with adhesive properties often involves particulate flow through narrow pipes, which is accompanied by still poorly understood dynamic behavior. Due to the difficulty in achieving a quantitative understanding of such flows based solely on experiments, here we perform particle-based numerical simulations of vertical pipe flows of adhesive granular materials using the discrete element method (DEM). Our simulations unveil different regimes of vertical pipe flow depending on the pipe-to-particle diameter ratio and the interparticle adhesive strength. Surprisingly, we find that the particle mass flow rate through the pipe increases substantially with this adhesive strength. This rather counterintuitive result is caused by an enhanced tendency of the particles to form stable agglomerates around the pipe symmetry axis, thus leading to reduced interaction of the particles with the frictional pipe walls. By contrast, incorporation of particle-wall adhesive interactions leads to exactly the opposite behavior, with such interactions dictating the granular dynamics in the pipe and leading to lower mass flow rate values compared to cohesionless flows. Furthermore, we show that the different flow regimes are associated with distinct spatiotemporal patterns of the granular solid fraction along the pipe axis (density waves). Therefore, our results provide theoretical references for future experimental research and application of adhesive granular flows through narrow pipes.