Non-Darcian Air Flow in Wood. Part 3. Molecular Slip Flow

Abstract

Summary 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 studied. The true permeability of red oak heartwood, red alder heartwood, ponderosa pine sapwood and Douglas-fir sapwood was 20.91, 7.05, 0.51 and 0.068μ3/μm, respectively. The average ratios of the superficial specific permeability at 50kPa mean pressure to the true permeability were found to be: 1.047 for red oak heartwood; 1.204 for red alder heartwood; 1.292 for ponderosa pine sapwood; and, 1.53 for Douglas-fir sapwood. The slip flow constant b was highest (26.5kPa) for Douglas-fir sapwood, followed by that for ponderosa pine sapwood (14.6 kPa) and red alder heartwood (10.2 kPa), and lowest (2.3kPa) for red oak heartwood. The radius (r) and the number of average effective openings (n) were found to be: 17.432μm and 0.066×106 per cm2 for red oak heartwood; 3.955 μm and 7.5 ×106 percm2 for red alder heartwood; 2.972μm and 3.3 ×106 percm2 for ponderosa pine sapwood; and, 1.552μm and 3.6 ×106 per cm2 for Douglas-fir sapwood respectively.