An improved procedure for calculating the pore size distribution of filter cloths in capillary flow porometry

Pore size distribution is one of the most important structural characteristics of filter cloths and can, in theory, be used to predict filtration performance. Capillary flow porometry is a common method to determine the pore diameter(s) and the pore size distribution of a porous material. Equipment applying this method has many advantages, but data processing and further calculations still require refining to be fit for purpose in calculations of flow capacity. The present study aims to develop a new procedure for processing volumetric flow rate data and corresponding pressure, which are measured by capillary flow porometry. The processed data are further used to calculate the pore size distribution of textile materials. Six industrial samples of polypropylene filter cloth were examined using scanning electron microscopy and capillary flow porometry. The raw data measured by the capillary flow porometer were processed using the developed method that considers changes in flow regimes as pressure increases. In addition, the nonideality of pores, originating from tortuosity, an irregular cross-sectional shape of the pore, and the number of pores, were considered in calculations by combining all these characteristics in one single parameter. This work shows that pores in a textile material are not ideal cylinders. The standard pore size distribution calculations should consider an imperfect pore structure and, therefore, be corrected.