Segregation by friction

Abstract

PACS. 45.70.Mg -Granular flow: mixing, segregation and stratification. PACS. 46.55.+d -Tribology and mechanical contacts. PACS. 83.10.Rs -Computer simulation of molecular and particle dynamics.Abstract. -Granular materials are known to separate by size under a variety of circumstances. Experiments presented here and elucidated by modeling and MD simulation document a new segregation mechanism, namely segregation by friction. The experiments are carried out by placing steel spheres on a horizontal plane enclosed by rectangular sidewalls, and subjecting them to horizontal shaking. Half the spheres are highly smooth; the remainder are identical to the first half, except that their surfaces have been roughened by chemical etching, giving them higher coefficients of friction. Segregation due to this difference in friction occurs, particularly when the grains have a relatively long mean free path. In the presence of an appropriately chosen small "hill" in the middle of the container, the grains can be made to completely segregate by friction type.

Competition of Brazil nut effect, buoyancy, and inelasticity induced segregation in a granular mixture

“…One of these cases is Ref. [14], where a mixture of spheres that only differ in friction coefficients (static, dynamic and rolling) is horizontally vibrated. They find complete mixing -that is, no segregation-for a flat plate while segregation is only observed when the plate was slightly inclined.…”

The timescales of granular segregation in horizontally shaken monolayers

“…In this class of system, the differential drive between each of the particle species, which can be interpreted as different frictional interactions of two types of grains with the surface of the oscillatory tray, is the principal driving mechanism for segregation. However, the segregation by friction on its own is not sufficient to always explain the behaviour of particles on the oscillating plate as shown experimentally by Kondic et al [30].…”

Hydrodynamics of binary mixtures of granular gases with stochastic coefficient of restitution

“…In the polydisperse case (which corresponds to the typical situation encountered in nature and industry), granular gases exhibit a host of specific effects, the most prominent being undoubtedly their tendency to spontaneously segregate under external forcing (Ottino & Khakhar 2000;Shinbrot & Muzzio 2000;Rapaport 2001;Farkas et al 2002;Kudrolli 2004) as a result of small differences in the properties of their constituents: differences in mass, shape, frictional (Kondic et al 2003;Ulrich, Schröeter & Swinney 2007) or inelastic (Serero et al 2006;Brito et al 2008) properties may yield segregation. In the case of dilute granular gases, one of the prominent segregation mechanisms is the Soret effect (Hsiau & Hunt 1996;Schröter et al 2006) or its single-particle manifestation, thermophoresis, which drives large or massive particles to move down temperature gradients (Goldhirsch & Ronis 1983a,b).…”