Influence of the gravity on the discharge of a silo

Abstract

We performed a series of experiments to investigate the flow of an assembly of non-cohesive spherical grains in both high and low gravity conditions (i.e. above and under the Earth's gravity). In high gravity conditions, we studied the flow of glass beads out of a cylindrical silo and the flow of metallic beads out of a vertical Hele-Shaw rectangular silo. Both silos were loaded in one of the gondolas of the Large Diameter Centrifuge facility (located at ESTEC) in which an apparent gravity up to 20 times the Earth's gravity can be established. To simulate low gravity conditions, we submitted a horizontal monolayer of metallic beads to the centrifuge force of a small rotation device (located at University of Liege). The influences of both gravity and aperture size on the mass flow were analysed in these various conditions. For the three systems (cylindrical silo, the Hele-shaw silo and the monolayer of beads), we demonstrated that (i) the square root scaling of the gravity found by Beverloo is relevant and (ii) the critical aperture size below which the flow is jammed does not significantly increase with the apparent gravity. Moreover, we studied in more details the Hele-Shaw silo in high gravity because this configuration allowed to determine local properties of the flow at the level of the aperture. We measured the velocity profiles and the packing fraction profiles for the various aperture sizes and apparent high gravities. We demonstrate the existence of a slip length for the flow at the level of the aperture. This later fact seems to result from the geometrical configuration of the silo.

Dynamic transition in conveyor belt driven granular flow

“…This confirms that the flow in the high-velocity regime is analogous to a gravity driven discharge of a two-dimensional silo with an effective gravity given by μg. Studies with controlled gravity have proven that the flow rate is proportional to the square root of the effective gravity acceleration [9]. Notice that A eff = A − kd and the fit yields k ≈ 3 in accordance with Ref.…”

“…The phenomenon is similar to the one observed during the discharge of a vertical silo through an opening in the base. Despite the many studies carried out in silo discharge (see for example [5][6][7][8][9][10] and references therein), little has been discussed on the belt driven flow rate through a bottleneck [11][12][13][14].…”

Linking bottleneck clogging with flow kinematics in granular materials: The role of silo width

“…The placement of an obstacle above the orifice can prevent clogging if its position is appropriately selected [6]. Other variables that have been shown to affect clogging are orifice geometry [16,17], particle shape [18][19][20], particle polydispersity [21], and gravity [22][23][24]. Nevertheless, we are not aware of any work looking at the influence of the width of the silo, a variable that in most of the existing experiments and simulations remains uncontrolled.…”

Role of particle size in the kinematic properties of silo flow

“…This √ 2gR scaling of the central velocity has been both experimentally [18] and numerically [19] demonstrated in recent times. Traditionally, it was related to the concept of the free fall arch, which suggests the existence of a hypothetical hemispheric [1] or parabolic [20] region proportional to R, just over the outlet, where the flow properties undergo a transition.…”