Infiltration through porous media - art. no. 021508

We study the kinetics of infiltration in which contaminant particles, which are suspended in a flowing carrier fluid, penetrate a porous medium. The p rogress of the "invader" particles is impeded by their trapping on active " defender" sites which are on the surfaces of the medium. As the defenders a re used up, the invader penetrates further and ultimately breaks through. W e study this process in the regime where the particles are much smaller tha n the pores so that the permeability change due to trapping is negligible. We develop a family of microscopic models of increasing realism to determin e the propagation velocity of the invasion front, as well as the shapes of the invader and defender profiles. The predictions of our model agree quali tatively with experimental results on breakthrough times and the time depen dence of the invader concentration at the output. Our results also provide practical guidelines for improving the design of deep bed filters in which infiltration is the primary separation mechanism.