Transient dynamics of bidisperse neutrally buoyant thin-film flow.

Particle-laden thin-film flows are widely seen in mining, water treatment, geology, and biology. A few continuum models, using diffusive flux and suspension balance approaches, have been proposed to study bidisperse suspensions with neutrally buoyant particles. We investigate the transient dynamics of these models by numerically solving the time-dependent PDEs and steady-state ODEs derived from their governing equations. We report on how the convergence time from transient to equilibrium varies based on several factors, such as initial particle concentrations of both species and their size ratio. For both models, we also compare their vertical concentration profiles over time for the extent of size-based segregation. Previous work has observed, for a thin-film flow in a planar channel, that larger particles accumulate near the centerline, while smaller particles enrich the walls. We show the distinctive segregation trends predicted by the two models in this case and compare them with existing experimental data. Finally, we briefly examine the relevance of the prior discussion to flows with negatively buoyant particles.