The influence of finite size particles on fluid velocity and transport though porous media

TL;DR

This study uses numerical simulations to show how finite-size particles influence fluid flow and transport in porous media, revealing that confinement effects significantly alter flow paths and velocity fields.

Contribution

It introduces a detailed numerical analysis of how particle confinement impacts fluid velocity and transport in porous structures, addressing a gap in existing models.

Findings

Particles cause re-routing of flow towards more permeable paths.

Confinement leads to ephemeral vortex formation at pore entrances.

Fluid velocity variance and mean are affected by particle size ratio.

Abstract

Understanding the coupling between flow, hydrodynamic transport and dispersion of colloids with finite-size in porous media is a long-standing challenge. This problem is relevant for a broad range of natural and engineered subsurface processes, including contaminant and colloidal transport, mixing of bio-chemical compounds, kinetics of reactions and groundwater bio-remediation, but also transport phenomena related to different systems like membranes, or blood flow. While classical models for colloidal transport rely on macro-dispersion theory and do not take into consideration the complex and heterogeneous structure of the porous host medium, recent studies take into consideration the detailed structure of the porous system and its impact on the fluid velocity. However, the impact of confinement condition, represented by the ratio of particles radius $a$ and pore throat size $\lambda$, has been overlooked. Here, we use numerical simulations of fluid particle dynamics in resolved porous media to demonstrate that particles confinement affects the fluid macroscopic velocity field u which in turn affects the particles transport itself. Our results show that even for small confinement conditions ($a/\lambda \sim 2$~\%), fluid and transported particles are dynamically re-routed towards more permeable paths. This leads to the emergence of ephemeral laminar vortexes at pore throat entrances and affects the variance and mean fluid velocity.