A novel device to measure gaseous permeability over a wide range of pressures: characterisation of slip flow for Norway spruce, European beech, and wood-based materials

摘要

A novel device was conceived and built to measure the apparent gaseous permeability of porous media over a large range of permeability values (10(-10)-10(-18) m(2)) and mean pressures (from 1 bar down to ca. 40 mbar). An extensive series of experimental data are presented and analysed for various porous media: (1) Norway spruce (Picea abies) and European beech (Fagus silvatica) in the three anatomical directions, and, for comparison, (2) three simpler porous media, i.e. an autoclaved aerated concrete (AAC, light concrete) and two wood-based panels. For all porous media, the intrinsic permeability, the gas slippage factor, and the effective pore size were determined from the variations of the apparent permeability as a function of mean pressure. These results are in good agreement with those of previous studies for spruce and bring new insights for beech and wood-based materials, in general. For all products, the effective pore sizes identified with the new instrument are closely linked to the medium morphology. In particular, it was found that in spite of the huge anisotropic ratios between wood's longitudinal and tangential directions, the identified pore size is similar and corresponds to anatomical features: openings in margo for spruce and scalariform perforation plates for beech. Besides, the pore size identified for beech in the radial direction suggests that radial permeability is most probably controlled by the openings in ray cells (either pits or intercellular voids).