Friction Induced Segregation of a Granular Binary Mixture in a Rotating Drum

Abstract

The segregation phenomena of a mixture of two types of particles with different frictional properties in a rotating drum are studied by simulations which mimic the granular flow by a surface flow and a bulk solid rotation. The surface flow is modeled by rules similar to sandpile models. Radial segregation is clearly observed but will occur only if the rotational transport rate is less than some critical value. Furthermore, linear growth in segregation is also observed in the early stage of demixing, similar to observations of real experiments. [S0031-9007 (97)04873-4] PACS numbers: 46.10. + z, 05.70.Jk, 64.75. + g Granular materials (see Refs. [1,2] for reviews) consist of macroscopic solid particles which are not especially interesting if considered individually. However, unusually collective behaviors such as heaping [3,4], fluidization [5,6], and segregation [7,8] are observed when these solid particles are subjected to excitations. Since these collective behaviors are produced by hydrodynamic, frictional, and geometric nonlinear interactions among the particles, the mechanisms underlying these collective behaviors are not well understood yet. Here we are interested in the problem of segregation of binary granular materials in a rotating drum or cylinder which have received a lot of attention recently [7-11]. Although many system parameters, such as sizes, shapes, friction, filling factors, etc., can affect the segregation mechanism, earlier studies of the segregation problems were mainly concerned with the geometric effects or size factors [12][13][14] because these effects can be readily simulated by methods of Monte Carlo or molecular dynamics. However, a friction driven segregation mechanism is proposed recently to explain the observations of the segregation of a mixture of grains of nearly the same size [9] but of different frictional properties in a rotating cylinder. Very little is known about the nature of the proposed friction driven segregation mechanism.In this Letter, we report the results of a new simulation model which is designed to study the friction driven segregation mechanism. Our simulation model is essentially an extended version of the well known sandpile model proposed by Bak, Tang, and Wiesenfeld (BTW) [15] that exhibits self-organized criticality (SOC), but with two types of grains. Rules similar to the sandpile model are constructed to incorporate the difference in the frictional properties of the two types of grains. Additional rules are also added to mimic the material transport in a rotating drum or cylinder. Therefore, our model can be qualitatively mapped to the rotating drum experiments. We find that radial segregation, similar to the size segregation, can be observed in our friction driven model. However, this radial segregation will occur only if the rotational transport rate v is less than some critical value. Furthermore, our results also show that the dynamics of friction driven seg-regation is similar to those driven by size effects as both segregations increase linearly w...

Role of friction in compaction and segregation of granular materials

“…Experiments are performed for mixtures of many particles of two different species (for a review see [12]) and with single intruder particles in systems of a single species [13]. Existing theoretical modeling of segregation due to rotation [6,14,15] and to pouring [10,16] is based on kinetic phenomena: segregation is explained as a result of different flow properties of the different species. Monte Carlo simulations of dynamic phenomena in vibrated systems give insight into segregation [17] as well as compaction dynamics of single species systems [18].…”

Compacity influence in reorganization of two dimensional granular packings: Numerical model

“…Powder Technology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / p ow t e c particular avalanches, segregation, flow [9][10][11][12][13][14] and rearrangements on the surface of three dimensional system due to inertial effects [15]. Sedimentation, soil erosion and debris flow in rivers has also been modeled by cellular automata [16,17].…”

Segregation and stability of a binary granular heap

“…Several previous studies [16,19,22], both numerical and experimental, have also found that size differences lead to radial segregation, with smaller shapes moving to the drum center. Interestingly, other work [14,18] shows that differences in stability angle can also cause radial segregation, with shapes of higher stability moving to the center. The size and shape characteristics can compete with each other.…”

“…In fact, heterogeneous mixtures commonly undergo segregation, a phenomenon of great interest for materials processing [6]. Segregation of binary mixtures also occurs in the laboratory, in vibrating bed [7,8] and rotating drum experiments [9][10][11][12][13][14][15][16][17][18][19][20][21][22], and upon pouring into a Hele-Shaw cell [23][24][25]. It can be caused by differences in particle size, shape, smoothness, or density.…”