Multiscale modelling of dual-porosity porous media; a computational pore-scale study for flow and solute transport.

This study aims to understand and quantify the solute exchange term by applying a dual-porosity pore-scale network model to relatively large domains, and analysing the pore- scale results in terms of the classical dual-porosity (mobile-immobile) transport formulation.

We examined the effects of key parameters (notably aggregate porosity and aggregate permeability) on the main dual-porosity model parameters, i.e., the mobile water fraction ( φm ) and the mass transfer coefficient ( α). Results were obtained for a wide range of aggregate porosities (between 0.082 and 0.700). The effect of aggregate permeability was explored by varying pore throat sizes within the aggregates. Solute breakthrough curves (BTCs) obtained with the pore-scale network model at several locations along the domain were analysed using analytical solutions of the dual-porosity model to obtain estimates of φm and α. An increase in aggregate porosity was found to decrease φm and increase α, leading to considerable tailing in the BTCs. Changes in the aggregate pore throat size affected the relative flow velocity between the intra- and inter-aggregate domains. Higher flow velocities within the aggregates caused a change in the transport regime from diffusion dominated to more advection dominated. This change in- creased the exchange rate of solutes between the mobile and immobile domains, with a related increase in the value of the mass transfer coefficient and less tailing in the BTCs.

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For more information about Thin Porous Media research and Multiscale Porous Media Lab in the Hydrogeology Research Group of Utrecht Univerisity, please find them here:
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