Gradient driven flow: Lattice gas, diffusion equation and measurement scales

Tracer diffusion and fluid transport are studied in a model for a geomarine system in which fluid constituents move from regions of high to low concen tration. An interacting lattice gas is used to model the system. Collective diffusion of fluid particles in lattice gas is consistent with the solutio n of the continuum diffusion equation for the concentration profile. Compar ison of these results validates the applicability and provides a calibratio n for arbitrary (time and length) units of the lattice gas. Unlike diffusiv e motion in an unsteady-state regime, both fluid and tracer exhibit a drift -like transport in a steady-state regime. The transverse components of flui d and tracer displacements differ significantly. While the average tracer m otion becomes nondiffusive in the long time regime, the collective motion e xhibits an onset of oscillation.