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 E… Show more
“…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.…”
Section: Resultssupporting
confidence: 74%
“…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].…”
“…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.…”
Section: Resultssupporting
confidence: 74%
“…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].…”
“…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.…”
We demonstrate experimentally that clogging in a silo correlates with some features of the particle velocities in the outlet proximities. This finding, that links the formation of clogs with a kinematic property of the system, is obtained by looking at the effect that the position of the lateral walls of the silo has on the flow and clogging behavior. Surprisingly, the avalanche size depends nonmonotonically on the distance of the outlet from the lateral walls. Apart from evidencing the relevance of a parameter that has been traditionally overlooked in bottleneck flow, this nonmonotonicity supposes a benchmark with which to explore the correlation of clogging probability with different variables within the system. Among these, we find that the velocity of the particles above the outlet and their fluctuations seem to be behind the nonmonotonicity in the avalanche size versus wall distance curve.
“…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.…”
We experimentally analyze the effect that particle size has on the mass flow rate of a quasi two-dimensional silo discharged by gravity. In a previous work, Janda et al. [Phys. Rev. Lett. 108, 248001 (2012)] introduced a new expression for the mass flow rate based on a detailed experimental analysis of the flow for 1-mm diameter beads. Here, we aim to extend these results by using particles of larger sizes and a variable that was not explicitly included in the proposed expression. We show that the velocity and density profiles at the outlet are self-similar and scale with the outlet size with the same functionalities as in the case of 1-mm particles. Nevertheless, some discrepancies are evidenced in the values of the fitting parameters. In particular, we observe that larger particles lead to higher velocities and lower packing fractions at the orifice. Intriguingly, both magnitudes seem to compensate giving rise to very similar flow rates. In order to shed light on the origin of this behavior we have computed fields of a solid fraction, velocity, and a kinetic-stress like variable in the region above the orifice.
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