The 'Brazil-nut effect' in bidisperse particle laden flow on an incline

TL;DR

This study models and experimentally verifies the Brazil-nut effect in bidisperse particle suspensions flowing down an incline, revealing how particle size and flow parameters influence particle segregation and front formation.

Contribution

The paper introduces a lubrication theory-based model for bidisperse suspensions on an incline, predicting particle segregation patterns and shock structures, validated by experiments.

Findings

Larger particles tend to rise to the top, consistent with the Brazil-nut effect.

The model predicts distinct shock structures and particle fronts depending on parameters.

Experimental results agree well with the theoretical predictions.

Abstract

We study bidisperse suspensions -- suspensions where there are two particle species of the same density but different sizes -- of a viscous fluid on an incline. We use a lubrication theory/thin film model to form a hyperbolic system of three conservation laws for the height and particle volume fractions. The model predicts, over a range of parameters, that the larger particles rise to the top of the layer, consistent with the well-known `Brazil-nut effect' for granular media. The model predicts well-separated fronts of the two species of particles, behind a clear fluid front, at lower inclination angles and volume fractions. This corresponds to a triple shock structure in the system of conservations. At higher inclination angles and volume fractions the particles congregate at a high concentration at the leading front corresponding to a singular shock in the model. We find excellent agreement between theory and experiments in terms of the overall dynamic structures as the parameters vary.