Interaction between corner and bulk flows during drainage in granular porous media

TL;DR

This paper introduces a dynamic dual-network model to analyze the interaction between primary piston-like and secondary corner flows during drainage in granular porous media, revealing how flow mechanisms depend on capillary and Bond numbers.

Contribution

The study presents a novel dual-network model that captures both bulk and corner flow mechanisms during drainage in granular media, incorporating detailed analysis of capillary bridge shapes and hydraulic conductivity.

Findings

Flow mechanisms vary significantly with Capillary and Bond numbers.

The model quantifies the secondary flow contribution in connected corner pathways.

Wetting-phase connectivity influences flow dynamics during drainage.

Abstract

Drainage in porous media can be broken down into two main mechanisms: a primary piston-like displacement of the interfaces through the bulk of pore bodies and throats, and a secondary slow flow through corners and films in the wake of the invasion front. In granular porous media, this secondary drainage mechanism unfolds in connected pathways of pendular structures, such as capillary bridges and liquid rings, formed between liquid clusters. To represent both mechanisms, we proposed a dynamic dual-network model for drainage, considering that a gas displaces a wetting liquid from quasi-2D granular porous media. For this model, dedicated analyses of the capillary bridge shapes and hydraulic conductivity were conducted so that the secondary drainage mechanism could be properly quantified at finite speeds. With the model, an investigation of the wetting-phase connectivity and flow during drainage was carried out, covering a broad range of flow conditions. Results indicate that the span of liquid-connected structures in the unsaturated region, as well as their ability to contribute to flow, varies significantly with Capillary and Bond numbers.