Non-Darcian air flow in wood - Part 3. Molecular slip flow

In this study, the detection and evaluation of non-Darcian air flow due to slip flow through four species were carried out. The results indicated that non-Darcian air flow due to slip flow existed in all the specimen groups s tudied. The true permeability of red oak heartwood, red alder heartwood, po nderosa pine sapwood and Douglas-fir sapwood was 20.91, 7.05, 0.51 and 0.06 8 mu m(3)/mu m, respectively. The average ratios of the superficial specifi c permeability at 50 kPa mean pressure to the true permeability were found to be: 1.047 for red oak heartwood; 1.204 for red alder heartwood; 1.292 fo r ponderosa pine sapwood; and, 1.53 for Douglas-fir sapwood. The slip flow constant b was highest (26.5 kPa) for Douglas-fir sapwood, followed by that for ponderosa pine sapwood (14.6 kPa) and red alder heartwood (10.2 kPa), and lowest (2.3 kPa) for red oak heartwood. The radius (r) and the number o f average effective openings (n) were found to be: 17.432 mu m and 0.066 x 10(6) per cm(2) for red oak heartwood; 3.955 mu m and 7.5 x 10(6) per cm(2) for red alder heartwood; 2.972 mu m and 3.3 x 10(6) per cm(2) for ponderos a pine sapwood; and, 1.552 mu m and 3.6 x 10(6) per cm(2) for Douglas-fir s apwood respectively.