Pore-scale mixing and transverse dispersivity of randomly packed monodisperse spheres
U. M. Scheven
Accepted
We show that transverse dispersion in flow through randomly packed mono-disperse spheres (sphere diameter d) is a velocity dependent superposition of three separable random processes, diffusion with coefficient Dr, intrinsic mechanical dispersion with dispersivity lm=d/33 caused by advection on streamlines, and a newly idenitfied coupled mechanical dispersion with dispersivity lc=d/11, which arises by coupled advection and transverse diffusion at the pore scale. The velocity dependence of the transverse dispersivity is derived from first principles. Our analysis is insensitive to details of the pore geometry and is verified by PFG-NMR experiments which covered 4.5 orders of magnitude in reduced velocity.