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The transverse flow rate of air through flat- or quarter-sawn boards of fifteen species including domestic and imported woods was measured. The test specimens were disk type and the thickness (d) was 5-20mm, though extreme thin specimens had been used in the past works. The pressure difference between the two faces of the specimen was in the range of 10-70cmHg. The permeability characteristics for each species and the effect of d on the permeability under both unsteady and steady states were discussed. The results obtained were as follows.(1) The transverse air flow through the specimen took place with a time lag for the start of reducing pressure. The flow rate increased gradually and, after a short or long increasing course, reached a constant value in the steady state. The time required to reach the steady state from the start and the flow rate at the state depended on wood species and d.(2) The transverse permeability value calculated on the basis of Darcy's law in the steady state (kg) was extremely different from one species to another. In coniferous trees, the range of kg at 5mm of d was (0.3-15.2)×10-5, and in broad leaved trees that of kg was (0.02-32.0)×10-5.(3) In the cases of six species among all species tested, kg showed nearly a constant value regardless of d. But in the cases of the other species, a linear relationship was found between d and logarithm of kg as expressed by kg=k0exp(b·d), and the sign of b was positive for seven species and negative for two species.(4) The longitudinal/transverse permeability ratio for the specimens of 20mm along the flow direction was within the range of (1.5-50.2)×103 in coniferous trees and changed over a wide range of 2.1×103-6.7×107 in broad leaved trees.

Transverse air permeability in fifteen wood species.