Discharge and alignment of elongated grains from silo with rotating bottom

Kiwing To^1*

¹Institute of Physics, Academia Sinica, Taipei, Taiwan

* Presenter:Kiwing To, email:ericto@gate.sinica.edu.tw

We study the flow of elongated grains (wooden pegs of 20 mm long with circular cross-section of diameter 6 mm and 8 mm) from a silo (190 mm diameter and 400 mm deep) with a circular orifice of and a rotating bottom. The rate of elongated granular materials falling out of a silo is known to follow the Beverloo Law which predicts the discharge rate to increase with the 2½ power of the diameter of the orifice. However, if the orifice diameter is comparable to the characteristic size, defined as the diameter of a sphere with the same volume of the grain, Beverloo Law fails due to clogging at the orifice. Although clogs at the orifice can be released by rotating the bottom of the silo, the dependence of discharge rate on orifice diameter can be better fitted to an exponential increasing function instead of the Beverloo Law. Surprisingly, the discharge rate decreases with increasing speed of rotation of the bottom. Furthermore, the wooden pegs at the bottom of the silo are observed to align to the motion of the bottom. A simple argument is proposed to explain our findings.

Keywords: granular flow, silo discharge, elongated grain, clogging