Abstract
Knowledge of the variability of fluid permeability of wood in general and of western hemlock in particular is of significant importance to the primary and secondary wood products processing industry of coastal British Columbia. For the purpose of this study, ten hemlock trees were randomly selected and specimens were prepared from three tree heights from each tree, namely, 1, 4 and 7 m. The air permeability of sapwood and heartwood in the longitudinal direction was measured using a dynamic method. Tracheid lengths were also obtained with a fiber quality analyzer and densities were measured by water displacement. The effect of tree height, tracheid length and density on the specific permeability of gross wood was then evaluated. The data revealed that height within the range measured has no effect on longitudinal permeability on heartwood whereas in sapwood the longitudinal permeability increases above 4 m of tree height. It was also found that longitudinal permeability was not significantly influenced by the tracheid length and wood density.
Highlights
Western hemlock (Tsuga heterophylla) is an important coastal species in British Columbia (B.C.) because it is one of the commercially valuable and highly demanded species in world markets, in Asia (Perez-Garcia and Barr 2005)
In the light of this investigation related to the fluid permeability of western hemlock the following conclusions can be drawn
Longitudinal permeability of western hemlock ranged from 0.01-2.34μm3/μm
Summary
Western hemlock (Tsuga heterophylla) is an important coastal species in British Columbia (B.C.) because it is one of the commercially valuable and highly demanded species in world markets, in Asia (Perez-Garcia and Barr 2005). An important characteristic of hemlock is its good treatability with fluids, but in spite of such reputation, hemlock still varies quite widely in its receptivity to treatment (Cooper 1973, Kumar and Morrell 1989) The reasons for this variability remain unclear, while it has been suggested that treatability is a function of anatomical structure, forest site and elevation (Miller 1961). The presence of wet pockets and juvenile wood in the heartwood zone and differences in internal wood structure could be possible causes for the variations in permeability and treatability of hemlock. This variability exists, there is little information known on the relative differences in permeability within hemlock (Erickson and Crawford 1959, Erickson 1960). Since hemlock is one of the important B.C. coastal species that has been successfully dried in radio frequency vacuum dryers in large cross-sectional sizes where longitudinal permeability becomes the most important factor controlling the rate of water loss is a significant reason for a better understanding of its variability for fluid flow within its structure (Avramidis 1999)
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