Granular flow from silos with rotating orifice

Abstract

For granular materials falling through a circular exit at the bottom of a silo, no continuous flow can be sustained when the diameter D of the exit is less than 5 times the characteristic size of the grains. If the bottom of the silo rotates horizontally with respect to the wall of the silo, finite flow rate can be sustained even at small D. We investigate the effect of bottom rotation to the flow rate of a cylindrical silo filled with mono-disperse plastic beads of d = 6 mm diameter. We find that the flow rate W follows Beverloo Law down to D = 1.2d and that W increases with the rotation rate ω in the small exit regime. If the exit is at an off-center distance R from the axis of the silo, W increases with rate of area swept by the exit. On the other hand, when the exit diameter is large, W decreases with rotation speed at small ω but increases with ω at large ω. Such non-monotonic behavior of W on rotation speed may be explained as a gradual change from funnel flow to mass flow due to the shear at the bottom of the silo. arXiv:1902.00393v1 [cond-mat.soft]

Particle flow rate in silos under rotational shear

“…In this work, we numerically analyzed the granular flow in a silo with a rotating bottom. This system had been explored experimentally very recently [1], and motivated the numerical and theoretical analysis presented here. The paper is organized as follows: in Sec.…”

“…1 illustrates the simulated system, which resembles the experimental setup described in Ref. [1]. The system consists of a cylindrical container of height h = 40 cm and radius R c = 9.5 cm, with a circular aperture at the bottom wall and particles with d = 5.8 mm.…”

“…Very recently, To et al explored the discharge of a cylindrical silo with a rotating bottom [1]. Interest-ingly, they found continuous flow for orifice sizes, notably smaller than D * .…”

Granular internal dynamics in a silo discharged with a conveyor belt

“…The inclusion of a reduced aperture in the expression using a term proportional to the particle size d p alludes to the idea of vena contracta, according to which grains do not cross the orifice in the region close to the edges. Although this phenomenon does not actually take place (Van Zuilichem, Van Egmond & De Swart 1974), (1.1) results an effective approximation to predict the flow rate in silos. Concerning the D 5/2 scaling (which would be D 3/2 in a two-dimensional silo), it was inferred from a dimensional analysis (Hagen 1852;Tighe & Sperl 2007) and justified by the velocity of the grains at the silo orifice with v ∝ √ gD, where g is the acceleration due to gravity, a hypothesis that was confirmed years later (Dorbolo et al 2013;Arévalo et al 2014).…”

“…Recently, there has been a growing interest in studying some variations from the canonical system in this field: a static silo with an orifice in the centre of a flat bottom. Some examples are the use of forced silos (Madrid, Darias & Pugnaloni 2018), submerged silos (Koivisto et al 2017), lateral apertures (Zhou et al 2017), corrugated walls (Wójcik et al 2017), hoppers (Darias et al 2020), eccentric rotating orifices (To et al 2019) or silos discharged with a conveyor belt that extracts the grains through an orifice at its bottom (figure 1). The latter has been proven a good strategy to control the grain velocity in the discharge of granular silos.…”