Mixing within fracture intersections during colloidal suspension flow

Abstract

[1] The effects of mixing within pore or fracture intersections on dispersion in porous media are investigated through the development and use of different simulation techniques that play particular attention to the flow field and mass transport details inside the intersection region. The flow field in an orthogonal intersection is computed using a lattice Boltzmann technique. Particle trajectories are computed taking into account both convection and molecular diffusion and allow the calculation of the transverse and longitudinal dispersion coefficients over a wide range of Peclet number values. The mixing ratio in the intersection is also calculated and is used in two distinct ways to yield the transverse dispersion coefficient. It is found that a random walk method that is introduced here reproduces the dispersion coefficient with excellent accuracy in the low and moderate Peclet number range, thanks to the fact that it accounts for upstream motion of solute particles and for different travel times within each fracture. Both slip and no-slip conditions at the solid walls are used, and a direct comparison shows that the former, which is known to develop in the presence of a wetting film or a porous wall, for instance, reduces the longitudinal dispersion considerably but affects the transverse dispersion only slightly.