Consider an idealized porous material consisting of straight, cylindrical pores of diameter d.

Assume that all pores are parallel to the x, y, or z axes and that they intersect at points

described by a simple cubic lattice of dimension l >> d. The overall dimensions of the sample of

this material are of the order of L, where L >> l. The volume flow rate Q in a single pore

segment is described by Poiseuille’s law:

Where ΔP is the pressure drop per segment. Evaluate the permeability for this material.