A multi-scale Lattice Boltzmann model for simulating solute transport in 3D X-ray micro-tomography images of aggregated porous materials

A - Papers appearing in refereed journals

Zhang, X. X., Crawford, J. W., Flavel, R. J. and Young, I. M. 2016. A multi-scale Lattice Boltzmann model for simulating solute transport in 3D X-ray micro-tomography images of aggregated porous materials. Journal of Hydrology. 541 (Part B), pp. 1020-1029. https://doi.org/10.1016/j.jhydrol.2016.08.013

AuthorsZhang, X. X., Crawford, J. W., Flavel, R. J. and Young, I. M.
Abstract

The Lattice Boltzmann (LB) model and X-ray computed tomography (CT) have been increasingly used in combination over the past decade to simulate water flow and chemical transport at pore scale in porous materials. Because of its limitation in resolution and the hierarchical structure of most natural soils, the X-ray CT tomography can only identify pores that are greater than its resolution and treats other pores as solid. As a result, the so-called solid phase in X-ray images may in reality be a grey phase, containing substantial connected pores capable of conducing fluids and solute. Although modified LB models have been developed to simulate fluid flow in such media, models for solute transport are relatively limited. In this paper, we propose a LB model for simulating solute transport in binary soil images containing permeable solid phase. The model is based on the single-relaxation time approach and uses a modified partial bounce-back method to describe the resistance caused by the permeable solid phase to chemical transport. We derive the relationship between the diffusion coefficient and the parameter introduced in the partial bounce-back method, and test the model against analytical solution for movement of a pulse of tracer. We also validate it against classical finite volume method for solute diffusion in a simple 2D image, and then apply the model to a soil image acquired using X-ray tomography at resolution of 30 μm in attempts to analyse how the ability of the solid phase to diffuse solute at micron-scale affects the behaviour of the solute at macro-scale after a volumetric average. Based on the simulated results, we discuss briefly the danger in interpreting experimental results using the continuum model without fully understanding the pore-scale processes, as well as the potential of using pore-scale modelling and tomography to help improve the continuum models.

KeywordsX-ray images; Grey Lattice Boltzmann model; Solute transport; Pore-scale modelling; Multi-scale model; Soil
Year of Publication2016
JournalJournal of Hydrology
Journal citation541 (Part B), pp. 1020-1029
Digital Object Identifier (DOI)https://doi.org/10.1016/j.jhydrol.2016.08.013
Web address (URL)http://www.sciencedirect.com/science/article/pii/S0022169416305005
Open accessPublished as non-open access
Output statusPublished
Publication dates
Online09 Aug 2016
Publication process dates
Accepted08 Aug 2016
PublisherElsevier
Elsevier Science Bv
Copyright licensePublisher copyright
ISSN0022-1694

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