A Method to Estimate the Accuracy of Radial Flow-Based Permeability Measuring Devices

Radial flow experiment is often used to measure the permeability of fibrous porous media by the composites processing community. However, very little work has been done to calibrate the radial flow set-up with media of known permeability. This article presents a new method for calibrating the permeability measuring set-ups based on radial flows. A reference medium in the form of two concentric annular slits is created for the radial flow mold whose permeability is estimated analytically and numerically. It is observed that the experimentally measured permeability deviates from the theoretical and numerical permeabilities with an increase in the flow rate for an injection setup using a gear pump as well as a piston-cylinder pump. The deviation can be attributed to two possible reasons: one is the leakage between the calibration device and mold plate surfaces because of a slight mold deformation at higher flow rates, the other one is the increase in the gap clearance of the reference medium because of the higher gap pressures at higher flow rates. No such deviation is observed while measuring the permeability of a fiber mat at different flow rates. Hence, the proposed reference medium can calibrate a conventional radial flow-based permeability measuring setups at low flow rates; the accuracy thus obtained can be extended to higher flow rates as well if permeability of a fiber mat can be shown to remain constant with the flow rate.