Directional Permeability Of Softwoods


  • Gilbert L. Comstock


It is well known that the permeability of wood varies markedly in the three structural directions, but a satisfactory explanation for the magnitude of variation has not been offered. Based on available gas permeability data, the ratio of longitudinal to tangential permeability varies from 520 to 81,600, and the longitudinal to radial ratio varies from 15 to 547,000. Two hypothetical models of wood structure were analyzed to determine their usefulness in explaining the difference between longitudinal and tangential permeability. The closest approximation to published data was found by assuming that wood cells have tapered ends that overlap on the radial surfaces and that contain pits only on these tapered ends. For a fiber length to width ratio of 100, the model predicts permeability ratios of 10,000 and 22,500 for fiber overlaps of one-half and one-fourth of a fiber length.


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