Diffusion of a granular pulse in a rotating drum

TL;DR

This study investigates how small grains diffuse in a rotating drum, revealing normal diffusion behavior and that diffusion coefficients are unaffected by grain size, using simulations and theoretical analysis.

Contribution

It provides a theoretical framework for diffusion in confined granular systems and demonstrates normal diffusion with size-independent coefficients through simulations.

Findings

Diffusion in the rotating drum is normal, not sub- or superdiffusive.

Diffusion coefficients are independent of grain size.

Theoretical analysis clarifies the effect of the confining end-plate.

Abstract

The diffusion of a pulse of small grains in an horizontal rotating drum is studied through discrete elements methods simulations. We present a theoretical analysis of the diffusion process in a one-dimensional confined space in order to elucidate the effect of the confining end-plate of the drum. We then show that the diffusion is neither subdiffusive nor superdiffusive but normal. This is demonstrated by rescaling the concentration profiles obtained at various stages and by studying the time evolution of the mean squared deviation. Finally we study the self-diffusion of both large and small grains and we show that it is normal and that the diffusion coefficient is independent of the grain size.