Measurement of permeability I. Theory

According to Darcy's law, the rate of flow of liquid through a porous body is proportional to the pressure gradient in the pores. To measure the permeability, a pressure differential is applied across a layer of porous material and the rate of flow is measured. When the material is a gel, the analysis is complicated by deformation of the compliant sample under the applied pressure; in addition, there may be spontaneous contraction (syneresis) of the gel. In this paper, a viscoelastic analysis is presented that demonstrates the magnitudes of these effects. It is shown that the steady-state pressure distribution through the sample is nonlinear if the gel network is not purely elastic.