Discharge flow of a granular media from a silo: effect of the packing fraction and of the hopper angle

International audienceSilos are widely used in the industry. While empirical predictions of the flow rate, based on scaling laws, have existed for more than a century (Hagen 1852, translated in [1]-Beverloo et al. [2]), recent advances have be made on the understanding of the control parameters of the flow. In particular, using continuous modeling together with a mu(I) granular rheology seem to be successful in predicting the flow rate for large numbers of beads at the aperture (Staron et al.[3], [4]). Moreover Janda et al.[5] have shown that the packing fraction at the outlet plays an important role when the number of beads at the apeture decreases. Based on these considerations, we have studied experimentally the discharge flow of a granular media from a rectangular silo. We have varied two main parameters: the angle of the hopper, and the bulk packing fraction of the granular material by using bidisperse mixtures. We propose a simple physical model to describe the effect of these parameters, considering a continuous granular media with a dilatancy law at the outlet. This model predicts well the dependance of the flow rate on the hopper angle as well as the dependance of the flow rate on the fine mass fraction of a bidisperse mixture

Profils de vitesse des écoulements granulaires

Nous présentons une étude expérimentale et numérique de l'écoulement sur plan incliné de milieux granulaires monodisperse et bidisperse ségrégé. Après présentation des profils de vitesse théoriques attendus, et ceux observés expérimentalement et numériquement, que l'augmentation de la vitesse d'écoulement par la présence de grandes particules à la surface a lieu sur les écoulements de faibles épaisseurs. Dès que l'écoulement est plus épais, on retrouve numériquement la superposition des deux profils monodisperses, contrairement au cas expérimental

Modèle stochastique de compaction d'une poudre cohésive

Nous proposons un modèle stochastique unidimensionnel pour représenter la compaction d'une poudre cohésive. Ce modèle est basé sur l'existence de blocs de grains séparés par des voûtes macroscopiques créées par la cohésion entre les grains. Les résultats de ce modèle sont en bon accord avec des observations et mesures expérimentales effectuées sur une poudre issue de l'industrie nucléaire.We present a stochastic model for the compaction of a cohesive powder. This model is based on clusters of grains. The numerical results of this model are in qualitative good agreement with experimental results issued from an experimental setup of a horizontal vibration of a container filled with a cohesive powder

Ecoulements granulaires bidisperses sur plans inclinés rugueux

Pour comprendre la grande mobilité des écoulements naturels, nous nous sommes intéressés à l'étude des écoulements granulaires monodisperses et bidisperses. L'étude des écoulements granulaires monodisperses a montré l'existence d'un diamètre de billes pour lequel la friction est maximum. Ce diamètre dépend des caractéristiques du plan rugueux (diamètre des rugosités et espacement entre les rugosités), et peut être déterminé à l'aide d'un modèle de stabilité sans paramètre ajustable. L'étude des écoulements bidisperses a mis en évidence, du fait de la répartition inhomogène des billes lors de l'écoulement, de nombreuses interactions, répartis suivant deux effets : les effets de lignes qui ont une influence sur la morphologie du dépôt (formation ou non de doigt) et les effets d interface (interactions des petites billes avec le plan rugueux et interaction des petites billes avec les grosses billes) qui ont une influence sur l épaisseur du dépôt et sur la rhéologie de ces écoulements.AIX-MARSEILLE1-Inst.Médit.tech (130552107) / SudocSudocFranceF

Discharge flow of a granular media from a silo: effect of the packing fraction and of the hopper angle

Silos are widely used in the industry. While empirical predictions of the flow rate, based on scaling laws, have existed for more than a century (Hagen 1852, translated in [1] - Beverloo et al. [2]), recent advances have be made on the understanding of the control parameters of the flow. In particular, using continuous modeling together with a mu(I) granular rheology seem to be successful in predicting the flow rate for large numbers of beads at the aperture (Staron et al.[3], [4]). Moreover Janda et al.[5] have shown that the packing fraction at the outlet plays an important role when the number of beads at the apeture decreases. Based on these considerations, we have studied experimentally the discharge flow of a granular media from a rectangular silo. We have varied two main parameters: the angle of the hopper, and the bulk packing fraction of the granular material by using bidisperse mixtures. We propose a simple physical model to describe the effect of these parameters, considering a continuous granular media with a dilatancy law at the outlet. This model predicts well the dependance of the flow rate on the hopper angle as well as the dependance of the flow rate on the fine mass fraction of a bidisperse mixture

The effect of cohesion on the discharge of a granular material through the orifice of a silo

We present the results of both experimental and numerical investigations of the silo discharge for a cohesive granular material. In our study, thanks to a cohesion-controlled granular material (CCGM) we propose to investigate the effect of the cohesive length lc, on the discharge of a silo for two different configurations, one axisymmetrical, and one quasi-2D rectangular silo. In both configurations, an adjustable bottom is used to control the size of the orifice. As observed for cohesionless granular material by previous studies, the mass flow rate and the density through an orifice are mostly controlled by the diameter of the orifice D. The experimental results of the quasi-2D silo are compared with continuum numerical simulations

Discharge flow of a granular media from a silo: effect of the packing fraction and of the hopper angle

Silos are widely used in the industry. While empirical predictions of the flow rate, based on scaling laws, have existed for more than a century (Hagen 1852, translated in [1] - Beverloo et al. [2]), recent advances have be made on the understanding of the control parameters of the flow. In particular, using continuous modeling together with a mu(I) granular rheology seem to be successful in predicting the flow rate for large numbers of beads at the aperture (Staron et al.[3], [4]). Moreover Janda et al.[5] have shown that the packing fraction at the outlet plays an important role when the number of beads at the apeture decreases. Based on these considerations, we have studied experimentally the discharge flow of a granular media from a rectangular silo. We have varied two main parameters: the angle of the hopper, and the bulk packing fraction of the granular material by using bidisperse mixtures. We propose a simple physical model to describe the effect of these parameters, considering a continuous granular media with a dilatancy law at the outlet. This model predicts well the dependance of the flow rate on the hopper angle as well as the dependance of the flow rate on the fine mass fraction of a bidisperse mixture

The effect of cohesion on the discharge of a granular material through the orifice of a silo

We present the results of both experimental and numerical investigations of the silo discharge for a cohesive granular material. In our study, thanks to a cohesion-controlled granular material (CCGM) we propose to investigate the effect of the cohesive length lc, on the discharge of a silo for two different configurations, one axisymmetrical, and one quasi-2D rectangular silo. In both configurations, an adjustable bottom is used to control the size of the orifice. As observed for cohesionless granular material by previous studies, the mass flow rate and the density through an orifice are mostly controlled by the diameter of the orifice D. The experimental results of the quasi-2D silo are compared with continuum numerical simulations

Angular particle sliding down a transversally vibrated smooth plane

International audienceWe present a theoretical, numerical, and experimental study about the sliding motion of an angular particle down a vibrated smooth plane. The model is based on a Coulomb's friction law with a unique friction coefficient. The model is solved numerically and is tested with controlled experiments. Different motion regimes are identified and the particle behavior is governed by two dimensionless parameters. The comparison between experimental and numerical results gives an indirect access to the dynamic friction coefficient