Axial Particle Diffusion in Rotating Cylinders

TL;DR

This study models the axial interface dynamics of a binary particle mixture in a rotating cylinder as a one-dimensional diffusion process, analyzing how various parameters influence the diffusion constant and segregation effects.

Contribution

It introduces a combined microscopic and macroscopic analysis of particle diffusion in rotating cylinders, highlighting the impact of segregation and pressure differences on diffusion behavior.

Findings

Diffusion process accurately describes initial interface dynamics.

Radial segregation reduces interface drift velocity.

Microscopic diffusion coefficient aligns with macroscopic estimates at the cylinder's center.

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.