Slip and No-Slip Flow in Micro- and Nano-Porous Media

It is now more evident that the no-slip boundary condition loses its accuracy in the case of micro- or nano-scale fluid flows. We develop micro- or nano-porous media having close-packed structures. A time of flight photobleaching velocity measurement technique is employed to determine the permeability and porosity of the media. Throughout the applied pressure range (100-2000 psi), the Newtonian fluids irrespective of their wetting property exhibit very low Reynolds number (<0.003). This laminar flow pattern validates the applicability of Darcy’s law for our microporous system (106-176 nm of hydraulic radius). Our results show that a linear relationship exists between permeability and porosity. The pressure driven flow experiment for n-octane through silica porous bed confirms the existence of slip flow. The measured slip length values are 12-20 times higher, compared to the theoretically predicted result from a molecular dynamics study. However, in presence of an aqueous film on the silica porous bed, the effective permeability for n-octane is lower compared to the absolute permeability, even in its slip boundary condition. The measurement approach is a useful method to evaluate multi-phase flow in nano-porous media.