ROLE OF ZONES OF LOW HYDRODYNAMIC DRAG IN COLLOID DEPOSITION AND RE-ENTRAINMENT IN POROUS MEDIA

Filtration theory predicts that colloid deposition rate coefficients increase with increasing fluid velocity. This predication holds true in the absence of an energy barrier between the colloid and collector. However, when the colloid and collector are like charged, as occurs predominantly in environment; then an energy barrier to deposition exists. Experiments in porous media performed in the presence of an energy barrier demonstrate that the deposition rate coefficients decrease with increasing fluid velocity. This indicates that hydrodynamic drag mitigates colloid deposition in porous media, and may do so either by direct removal of colloids associated with either the primary or secondary energy minima; or indirectly, by the combined influences of hydrodynamic and electrostatic forces. Colloid deposition in porous media is thought to involve both primary and secondary energy minima. To examine the effect of hydrodynamic drag on colloid association with primary energy minima, impinging jet systems were examined. This presentation contrasts colloid deposition and re-entrainment behavior in porous media and impinging jet systems, in order to elucidate the mechanisms by which hydrodynamic drag mitigates colloid deposition in porous media.