Summary
A number of workers have noted a marked decrease of wood permeability with increasing specimen length, and to date a model proposed by Bramhall has been used to explain the phenomenon. This describes the effect of random blockages on the permeability of an anisotropic porous medium. However, the model does not allow for the fact that transverse flow may allow longitudinal flow paths to circumvent blockages to some extent, so some deviation from it can be expected. The issue is an important one if laboratory experiments are to be used as a basis for the prediction of the behaviour of wood during impregnation or drying on a commercial scale. A modified model which allows for transverse flow is therefore developed. New experimental evidence which cannot be explained by the Bramhall model, but which can be explained by the new model, is presented.
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This paper was written while the author was Heritage Visiting Scientist at the Forest Products Laboratory, U.S. Department of Agriculture, and Visiting Professor at the Department of Forestry, University of Wisconsin, both at Madison, Wisconsin, USA. This support is gratefully acknowledged. The author would also like to thank Messrs. J. Ambler, M. C. Breese and S. H. Turner, who carried out some of the experimental work, and staff at the Commonwealth Forestry Institute, Oxford, who provided the Juniperus procera material tested
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Bolton, A.J. A reexamination of some deviations from Darcy's Law in coniferous wood. Wood Sci.Technol. 22, 311–322 (1988). https://doi.org/10.1007/BF00353321
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DOI: https://doi.org/10.1007/BF00353321