Traveling Granular Segregation Patterns in a Long Drum Mixer

Abstract

Mixtures of granular media often exhibit size segregation along the axis of a partially-filled, horizontal, rotating cylinder. Previous experiments have observed axial bands of segregation that grow from concentration fluctuations and merge in a manner analogous to spinodal decomposition. We have observed that a new dynamical state precedes this effect in certain mixtures: bi-directional traveling waves. By preparing initial conditions, we found that the wave speed decreased with wavelength. Such waves appear to be inconsistent with simple PDE models which are first order in time.Comment: 11 page

Shape dynamics of interfacial front in rotating cylinders

“…In industrial applications, rotating cylinders are primarily used for mixing different components [2]. But it is well known that particles of different sizes or density show radial segregation on small time scales and axial segregation on large time scales which compete against the mixing process [2][3][4][5][6][7][8][9].…”

“…no radial core was found. Recently, experimental evidences were given for two new mechanisms of axial segregation, namely traveling waves [8] and avalanche mediated transport [14] which were only observed when nonspherical particles were used.…”

Granular Segregation as a Critical Phenomenon

“…Segregation is not only of fundamental interest but it is also of practical importance with applications in areas ranging from industry[2] to geology [3]. In recent years, there has been an upsurge of interest in small scale laboratory studies where vibration [4,5], avalanching in partially filled horizontal rotating drums [6,7] and stratification in vertically poured mixtures [8] have all provided interesting examples of pattern formation.Our focus is on quasi-2-dimensional horizontally driven layers of binary mixtures of particles [9,10] as this gives the practical advantage that any collective behavior is readily visualized and gravity is effectively eliminated. Moreover, the material is in contact with the drive throughout the motion.…”

Segregation and stability of a binary granular heap

“…Confining the grains to a single layer allows us to track visually the exact configuration of the grains during the rotation. It also eliminates the axial segregation into bands that has been observed in three-dimensional experiments and models of binary mixtures [10,13,17,19,20,22]. We can then focus purely on radial segregation, which also occurs in three-dimensional rotating drums [12,15] in a wider range of conditions than axial segregation.…”

“…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.…”