Flow of magnetic repelling grains in a two-dimensional silo

Abstract

During a typical silo discharge, the material flow rate is determined by the contact forces between the grains. Here, we report an original study concerning the discharge of a twodimensional silo filled with repelling magnetic grains. This non-contact interaction leads to a different dynamics from the one observed with conventional granular materials. We found that, although the flow rate dependence on the aperture size follows roughly the power-law with an exponent 3/2 found in non-repulsive systems, the density and velocity profiles during the discharge are totally different. New phenomena must be taken into account. Despite the absence of contacts, clogging and intermittence were also observed for apertures smaller than a critical size determined by the effective radius of the repulsive grains.

Discharge of repulsive grains from a silo: experiments and simulations

“…c) Q = N tot /τ vs D (•) and solution of eq. 2 with parameters found in simulations (-) and those found in experiments [7] (--).…”

“…Finally, we computed the density of particles ρ x inside a rectangular box of 10d × D centred in the silo aperture as it was done with the experimental measurements in [7]. We found fluctuations around a mean value during the evolution of the discharge, see fig.…”

“…The different value obtained with repelling grains could be associated to the fact that the free-fall region does not really exist [8], since even in the aperture the outgoing magnets are interacting with the magnetic field of the neighbouring particles. Figure 3c , data fitting using eq.1 (-), and experimental fitting reported in [7] (--). c) Q = N tot /τ vs D (•) and solution of eq.…”

“…Because of its omnipresence in industry and agriculture, one of the most widely studied systems in granular matter is the discharge of grains from a silo [1][2][3][4][5][6][7][8][9][10]. In the pioneering work of Beverloo [2] describing the mass rate Q of grains of size d flowing through an orifice of diameter D under the influence of gravity g, it was found that Q = Cρ b √ g(D − κd) 5/2 , where ρ b is the apparent density of the material and C and κ are constants related to the particle nature and silo geometry.…”

“…A granular material is usually defined as a conglomerate of macroscopic particles characterized by a loose of energy due to elasticity and friction when particles collide or slide [6]. In a recent work [7], the author of this manuscript and colleagues presented experiments in a two dimensional cell filled with an assembly of magnets that do not interact through contact forces but through their repelling magnetic field. These contact-less particles are able to form stable piles with an average angle of repose, e-mail: fpacheco@ifuap.buap.mx to flow through an aperture when it is large enough, and to form arches and produce jamming as it happens with conventional grains.…”