HR: 0830h
AN: H21D-0873    [PDF]
TI: Macroscopic Longitudinal Dispersion in Porous Media From Pore-scale Simulation
AU: * Bijeljic, B
EM: b.bijeljic@imperial.ac.uk
AF: Imperial College, Department of Earth Science and Engineering, South Kensington Campus, London, SW7 2AZ United Kingdom
AB: The behavior of longitudinal dispersion as a function of rate and the properties of the porous medium is important for the prediction of contaminant dispersal in aquifers, the performance of packed beds and nuclear waste containment. We describe a novel means of simulating dispersion within a network of pores which is completely physically based. The method uses the flow field calculated from an existing network simulator. We use particle tracking to move the contaminant through a semi-analytically defined flow field in each pore adding a random component to simulate molecular diffusion. We use physically consistent rules to transport particles across pore junctions. Periodic boundary conditions have been implemented, allowing us to simulate diffusion on the scale of centimeters with minimal extra computational effort. We benchmark the particle-tracking random-walk model by comparing the longitudinal dispersion with Taylor-Aris analytical solutions in single ducts. Previous workers have (e.g. Sorbie and Clifford, 1991, Damion et al, 2000, Bernabe and Bruderer, 2001) have only been able to provide qualitative insights into the effect of Peclet number and pore-scale heterogeneity on longitudinal dispersion with Peclet number. We use a range of homogeneous and heterogeneous networks, including topologically disordered lattices taken directly from glass bead-packs, sand-packs and consolidated Berea sandstone, to investigate the influence of pore-scale heterogeneity (connectivity, pore-size distribution) on macroscopic dispersion. We show that our technique can predict quantitatively experimental measurements of longitudinal dispersion over a wide range of Peclet numbers (0$<$Pe$<$105).
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2003 Fall Meeting