title: Outflow and clogging of shape-anisotropic grains in hoppers with small apertures.
abstract: Outflow of granular material through a small orifice is a fundamental process in many industrial fields, for example in silo discharge, and in everyday's life. Most experimental studies of the dynamics have been performed so far with monodisperse disks in two-dimensional (2D) hoppers or spherical grains in 3D. We investigate this process for shape-anisotropic grains in 3D hoppers and discuss the role of size and shape parameters on avalanche statistics, clogging states, and mean flow velocities. It is shown that an increasing aspect ratio of the grains leads to lower flow rates and higher clogging probabilities compared to spherical grains. On the other hand, the number of grains forming the clog is larger for elongated grains of comparable volumes, and the long axis of these blocking grains is preferentially aligned towards the center of the orifice. We find a qualitative transition in the hopper discharge behavior for aspect ratios larger than ≈6. At still higher aspect ratios >8-12, the outflowing material leaves long vertical holes in the hopper that penetrate the complete granular bed. This changes the discharge characteristics qualitatively.
authors.affiliation: Institute of Experimental Physics, Otto von Guericke University, 39106 Magdeburg, Germany. ralf.stannarius@ovgu.de and Faculty of Engineering and Technology, Future University, End of 90 St., New Cairo, Egypt.
authors.forename: A
authors.initials: A
authors.lastname: Ashour
authors.affiliation: Institute of Experimental Physics, Otto von Guericke University, 39106 Magdeburg, Germany. ralf.stannarius@ovgu.de.
authors.forename: S
authors.initials: S
authors.lastname: Wegner
authors.affiliation: Institute of Experimental Physics, Otto von Guericke University, 39106 Magdeburg, Germany. ralf.stannarius@ovgu.de.
authors.forename: T
authors.initials: T
authors.lastname: Trittel
authors.affiliation: Institute for Solid State Physics and Optics, Wigner Research Center for Physics, Hungarian Academy of Sciences, P. O. Box 49, H-1525 Budapest, Hungary.
authors.forename: T
authors.initials: T
authors.lastname: Börzsönyi
authors.affiliation: Institute of Experimental Physics, Otto von Guericke University, 39106 Magdeburg, Germany. ralf.stannarius@ovgu.de.
authors.forename: R
authors.identifier: http://orcid.org/0000-0002-6836-3663
authors.initials: R
authors.lastname: Stannarius