Axial particle diffusion in rotating cylinders

Abstract

We study the interface dynamics of a binary particle mixture in a rotating cylinder numerically. By considering only the particle motion in axial direction, it is shown that the initial dynamics can be well described by a one-dimensional diffusion process. This allows us to calculate a macroscopic diffusion constant and we study its dependence on the inter-particle friction coefficient, the rotation speed of the cylinder and the density ratio of the two components. It is found that radial segregation reduces the drift velocity of the interface. We then perform a microscopic calculation of the diffusion coefficient and investigate its dependence on the position along the cylinder axis and the density ratio of the two particle components. The latter dependence can be explained by looking at the different hydrostatic pressures of the two particle components at the interface. We find that the microscopically calculated diffusion coefficient agrees well with the value from the macroscopic definition when taken in the middle of the cylinder.

Resolving a paradox of anomalous scalings in the diffusion of granular materials

“…8, the estimates in Table 1 and the numerical evidence for collapse under Eq. 3 with DðCÞ ¼ 1 þ ðC − 1∕2Þ because T Ã is valid for constant D only, and neither the experimental (35,36) nor the simulated (34,37) data is sufficiently well esolved to specify the form of DðCÞ used here.…”

In situ, near real-time acquisition of particle motion in rotating pan coating equipment using imaging techniques

“…Reported values of D lie in the range 1 × 10 −4 -10.4 × 10 −4 cm 2 /s for drum speeds in the range 10-65 rpm. Dury and Ristow (1999) conducted a numerical study of the interface dynamics of a binary particle mixture in a rotating cylinder. They concluded that the dependence of D with rotation speed ( ) is linear only for low speeds (Hogg et al, 1966) and that a quadratic function gives a better fit when a broader range of rotation speeds is considered.…”

Tangential velocity profiles of granular material within horizontal rotating cylinders modelled using the DEM

“…Rotary cylinders or kilns are widely used in industry for processes such as mixing, drying, coating and performing chemical reactions. Granular motion within these cylinders is also an area of significant research interest due to the rich array of phenomena exhibited [1][2][3]. Depending on the system conditions, several different flow regimes have been identified within rotating cylinders including: sliding, surging, avalanching, rolling, cascading, cataracting and centrifuging [4,5].…”