TY - JOUR
T1 - Surface roughness effects in granular matter
T2 - Influence on angle of repose and the absence of segregation
AU - Pohlman, Nicholas A.
AU - Severson, Benjamin L.
AU - Ottino, Julio M.
AU - Lueptow, Richard M.
PY - 2006
Y1 - 2006
N2 - We investigate the effect of nanoscale variations in the surface roughness of individual particles on macroscale granular flow characteristics. Experiments were conducted in circular rotating tumblers with smooth and rough 2 and 3 mm steel particles. The smooth beads had a rms surface roughness of approximately 30 to 60 nm; rough beads had a surface roughness of approximately 240 to 350 nm. The dynamic angle of repose for rough particles increased by 10° to 25° over that of smooth particles over a wide range of rotation speeds. Even though surface roughness affects the angle of repose, we were unable to detect any segregation of bidisperse mixtures of rough and smooth particles in the radial direction in two-dimensional (2D) tumblers. Furthermore, no axial banding segregation occurred in 3D tumblers, both cylindrical and spherical. For mixtures of smooth and rough particles, the angle of repose increased monotonically with increasing concentration of rough particles. Particle dynamics simulations verified that the dependence of the angle of repose on the concentration of rough particles can be directly related to the coefficient of friction of the particles. Simulations over a broad range of friction parameters failed to induce segregation solely from differences in the angle of repose. These results indicate that nanoscale surface roughness can affect the flowability and angle of repose of granular matter without driving demixing of the bulk granular material.
AB - We investigate the effect of nanoscale variations in the surface roughness of individual particles on macroscale granular flow characteristics. Experiments were conducted in circular rotating tumblers with smooth and rough 2 and 3 mm steel particles. The smooth beads had a rms surface roughness of approximately 30 to 60 nm; rough beads had a surface roughness of approximately 240 to 350 nm. The dynamic angle of repose for rough particles increased by 10° to 25° over that of smooth particles over a wide range of rotation speeds. Even though surface roughness affects the angle of repose, we were unable to detect any segregation of bidisperse mixtures of rough and smooth particles in the radial direction in two-dimensional (2D) tumblers. Furthermore, no axial banding segregation occurred in 3D tumblers, both cylindrical and spherical. For mixtures of smooth and rough particles, the angle of repose increased monotonically with increasing concentration of rough particles. Particle dynamics simulations verified that the dependence of the angle of repose on the concentration of rough particles can be directly related to the coefficient of friction of the particles. Simulations over a broad range of friction parameters failed to induce segregation solely from differences in the angle of repose. These results indicate that nanoscale surface roughness can affect the flowability and angle of repose of granular matter without driving demixing of the bulk granular material.
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U2 - 10.1103/PhysRevE.73.031304
DO - 10.1103/PhysRevE.73.031304
M3 - Article
C2 - 16605514
AN - SCOPUS:33645023746
SN - 1539-3755
VL - 73
JO - Physical Review E - Statistical, Nonlinear, and Soft Matter Physics
JF - Physical Review E - Statistical, Nonlinear, and Soft Matter Physics
IS - 3
M1 - 031304
ER -