Dynamic pressurization: novel method for measuring fluid permeability

The permeability of an aerogel can be determined during the process of supercritical drying by measuring the dilatation of the body as the pressure in the autoclave is changed. When the pressure is reduced in the autoclave by venting the supercritical fluid, the higher pressure inside the aerogel causes it to expand; the strain relaxes as the fluid flows out of the gel. We present an analysis of the the kinetics of this volumetric strain and apply it to a silica aerogel. The linear strain of the gel was measured with an LVDT mounted inside the pressure vessel. The permeability was obtained over a range of pressure from about 8 MPa to ambient pressure, and was found to vary inversely with the pressure, as expected from the Klinkenberg model. The permeability obtained by extrapolation to infinite pressure agreed with the independently measured liquid permeability obtained by beam-bending.