Discharge of elongated grains from silo with moving orifice

‪Kiwing To¹, Chung-Ping Tang^1*

¹Institute of Physics, Academia Sinica, Taipei, Taiwan

* Presenter:Chung-Ping Tang, email:cptang@gate.sinica.edu.tw

We study the discharge process of a binary mixture composed of spherical grains (beads) and elongated grains (pegs) from a silo with rotating bottom. The diameter of the orifice is no larger than ten times the effective grain diameter (d). The discharge process can be categorized into permanent clog, intermittent or continuous flow depending on the orifice diameter (D), the composition and the rotation speed. The discharge rate of pure beads follows Beverloo. However, the discharger rate of mixtures of pegs and beads does not observe Beverloo Law in the intermittent flow regime. In contrast to binary mixture of beads of different diameter for which the discharge rate (W) varies linearly with composition, we find that W increases non-linearly with the bead fraction (r, defined as the mass fraction of spherical grains) for our binary mixtures of pegs and beads. Furthermore, the discharge rate can be fitted to the empirical form: W ∝ p+(b-p)(1-exp(-αr)). When D < 5d, the discharge rate is enhanced by rotation for all possible r. When 6d > D > 5d , the discharge rate increases with increasing rotation speed for pure beads and decreases with increasing rotation speed for pure pegs. When D > 5d, rotation always reduces the discharge rate for r < 0.43.

Keywords: granular flow, elongated grains, silo discharge, binary mixture, phase transition