RESUMEN
We report experimental observations of polygon-shaped patterns formed in a vertically vibrated bed of circular cross-section. A phase map is determined, showing that the polygon pattern is established for Γ = A(2πf)(2)/g is > or approximately equal to 10. The sensitivity of the polygon structure to bed parameters was tested by studying beds of different particle sizes and fill levels. It was hypothesized that the polygon pattern observed in cylindrical beds is the corresponding pattern to the formation of arches in square-shaped beds. The close relationship between these two patterns was demonstrated by two observations: i) the radii of the arches of a corresponding square bed and the inner radius of the cylindrical bed were found to be very similar and ii) the boundary lengths of the two patterns were in good agreement.
RESUMEN
Axial dispersion rates of particles within horizontal rotating cylinders have been calculated for a decade of cylinder diameters. Throughout the range studied the rate of axial dispersion was found to be independent of the cylinder diameter. This phenomenon has been investigated further by spatially resolving the local contribution to the axial dispersion coefficient. This analysis demonstrates that, although the highest rates of axial dispersion occur at the free surface of the bed, there is a significant contribution to axial dispersion throughout the flowing region of the bed. Finally, based on an analogy with a Galton board, a linear relationship is proposed between the local rate of axial dispersion within a horizontal rotating cylinder and the product of the local particle concentration and the local shear rate in a plane perpendicular to the cylinder axis.
RESUMEN
The discrete element method has been used to examine axial dispersion within rotating cylinders containing two sizes of particle. Two bed configurations are considered: initially segregated, which consists of a pulse (narrow axial band) of small particles within a bed of large particles, and initially mixed, in which the cylinder is loaded with a homogeneous mixture of the two particle sizes. The dispersion of the small particles within initially segregated beds is found to depend strongly on the initial length of the pulse of small particles. Initially mixed beds are found to undergo a transient period in which the small particles disperse rapidly. Following this transient, axial dispersion of both particles sizes is found to follow Fick's second law, in that the mean squared deviation of the axial position of the particles is proportional to time. Axial dispersion coefficients have been calculated for initially mixed beds that have reached steady state; the axial dispersion coefficients of both particle sizes decrease as the volume fraction of small particles is increased.