Modeling of short-time penetration into complex porous structures

The short-time uptake of a fluid by porous media is important both in coating and printing operations. A new method to predict the short-time absorption into a real pore geometry, taking into account fluid properties, surface forces, and the complex pore geometry, is presented. The porous space is characterized by techniques described in the companion paper (Toivakka and Nyfors, 2000). The flows in the pores that connect to the surface are characterized by a series of hydraulic radii. The viscous resistance in these pore geometries, inertial forces at short times, and the actual contact angles at the advancing front are included. The model calcs. the rate of fluid uptake as a function of time. The model predictions are given for cubic, hexagonal, and random packing of spheres. The results are compared to exptl. values obtained with model coating layers of spherical plastic pigments. The comparison between the exptl. results and the predicted uptake rates into pores generated by random packing of spheres is good.