Microscopic Motion of Particles Flowing through a Porous Medium

TL;DR

This study uses simulations to analyze microscopic particle motion in porous media, revealing how particles navigate junctions, the role of interactions in delays, and conditions for destabilizing trapped particles.

Contribution

It provides new insights into particle dynamics at the pore scale, including flux distributions, waiting times, and hydrodynamic interactions in porous structures.

Findings

Particle flux into pore exits matches fractional channel areas.

Waiting times are governed by two-particle interactions.

Hydrodynamic interactions can relaunch trapped particles.

Abstract

We use Stokesian Dynamics simulations to study the microscopic motion of particles suspended in fluids passing through porous media. We construct model porous media with fixed spherical particles, and allow mobile ones to move through this fixed bed under the action of an ambient velocity field. We first consider the pore scale motion of individual suspended particles at pore junctions. The relative particle flux into different possible directions exiting from a single pore, for two and three dimensional model porous media is found to approximately equal the corresponding fractional channel width or area. Next we consider the waiting time distribution for particles which are delayed in a junction, due to a stagnation point caused by a flow bifurcation. The waiting times are found to be controlled by two-particle interactions, and the distributions take the same form in model porous media as in two-particle systems. A simple theoretical estimate of the waiting time is consistent with the simulations. We also find that perturbing such a slow-moving particle by another nearby one leads to rather complicated behavior. We study the stability of geometrically trapped particles. For simple model traps, we find that particles passing nearby can ``relaunch'' the trapped particle through its hydrodynamic interaction, although the conditions for relaunching depend sensitively on the details of the trap and its surroundings.