Nearly Complete Segregation of Submerged Grains in a Rotating Drum

TL;DR

This study demonstrates nearly complete segregation of submerged grains in a rotating drum, revealing how effective density ratio and flow dynamics influence segregation patterns, with validated simulations predicting these behaviors across parameters.

Contribution

The paper introduces experimental evidence and simulation validation for nearly complete grain segregation in submerged conditions, expanding understanding beyond dry granular systems.

Findings

Segregation patterns depend on effective density ratio D.

Increasing D transitions from mixed to fully segregated states.

Vortex dynamics vary with D and Reynolds number.

Abstract

Density-driven segregations, extensively studied in a simple rotating drum, are enriched with a wide range of underlying physics. Diverse symmetrical segregation patterns formed by mixing two types of dry mono-sized grains have been revealed due to variations in heavy and light grain densities, $\rho_h$ and $\rho_l$, and rotating speeds, $\omega$. We engender experimentally a nearly complete segregation, not occurring in dry conditions of the same $\rho_h$, $\rho_l$, and $\omega$, in submerged states. Further, based on the experiment-validated simulations, using coupled computational fluid dynamics and discrete element method, it is found the mixing index can be well predicted over a wide parameter space in the effective density ratio, $D=(\rho_h-\rho_f)/(\rho_l-\rho_f)$ with $\rho_f$ being the fluid density. Specifically, with increasing $D$ well-mixed states transit to fully-segregated states with a rising number of vortices and severer asymmetrical patterns. When the global Reynolds number $\mathrm{Re}_g$ is enlarged, the vortex area of heavy particles shrinks for lower $D$, while the area of light particles gradually saturates; meanwhile, for higher $D$ a new vortex with a continuously expanded area can be encountered in the light particle zone. These results improve our understanding of segregation transitions especially in submerged granular systems and shed new light on various science and engineering practices.