On the accuracy of capillary flow porometry for fibrous filter media

The largest error source by far was the volatility of fluorinated compounds commonly used as wetting liquids. While the vapor pressures of such compounds may be relatively low, their use in combination with a flow of air through the porous matrix can have an enormous effect on the evaporation rate during a scan. Neglecting this effect (which obviously depends on the scan rate) may ultimately result in an error of almost arbitrary magnitude in the pore size distribution. Silicone oil on the other hand has a negligible volatility and provides reliable results for a wide range of operating conditions. The liquid viscosity in the tested range of 5-100 mm2/s played a comparatively insignificant role. These and other factors of uncertainty are discussed on the basis of experimental data.