Graduate Thesis Or Dissertation
 

Steady- and unsteady-state longitudinal water permeability of western hemlock

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  • A decreasing rate of flow was observed (after sufficient air and particulate matter were removed from the wood and water) under steady-state conditions for green western hemlock sapwood. The decrease is theorized to be due to viscoelastic behavior of pit membranes. An unsteady-state procedure for determining longitudinal liquid permeability of small wood specimens (about 3/4 inches) was developed. It predicts that a straight line relationship exists between the inverse square of pressure in a pressure cell and time over a limited pressure range when the liquid is allowed to flow through the specimen. Specific permeability can be calculated from the slope. The unsteady-state technique was much simpler to use than the steady-state method. Permeability coefficients determined by the unsteady-state method were generally higher than those arrived at by steady-state means. The reason for this difference is now known. Sapwood is more permeable than wetwood which is, in turn, more permeable than heartwood. This order is independent of the method of measurement. Saturated, green wetwood posseses a specific permeability of the same order of magnitude as green sapwood; but has a characteristic behavior under both steady- and unsteady-state conditions that differentiates it from sapwood. This was considered to be due to occlusion of pit membranes by extractives.
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