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Title: The movement of fluids in conifer wood
Author: Bolton, A. J.
ISNI:       0000 0001 3469 2154
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1976
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After a brief introduction, a model describing axial flow of liquids through conifer sapwood is described. This model allows the variation of the volumetric flow rate through the tracheid lumen/bordered pit system with the magnitude of the applied pressure differential to be calculated, given a variety of values for physical constants, and tracheid lumen and bordered pit dimensions. The model takes into consideration the viscous resistance to flow (and the kinetic energy correction to such viscous resistance to flow) generated by the tracheid lumen, the pit apertures, the pit margo pores, and the annuli between the edge of the membrane torus and the pit border. The model also takes into account the established fact that the bordered pit membrane displaces in the direction of the descending pressure gradient, towards one of the pit apertures. The computer programme written to execute this somewhat involved analysis includes facilities for testing whether the assumption that flow is occurring in the laminar regime is correct, and for assessing the effect of error in any one of the assumed values of physical or dimensional quantities. Using data for first formed earlywood and centre of latewood tracheids of Scots pine as an example, the following general conclusions are reached: 1. That at-low applied pressure differentials the conductivity of earlywood tracheids is more than an order of magnitude greater than that of latewood tracheids. At high applied pressure differentials the earlywood membranes will deflect completely (aspirate), thus preventing flow, while latewood tracheids continue to conduct. At even higher pressure differentials, even these latewood membranes should, in theory, aspirate; 2. That with the exception of flow through latewood at high pressure differentials, the assumption that flow through such tracheids is laminar appears to be justified; 3. That kinetic energy corrections to viscous flow theory should only be significant with flow through latewood; 4. That more than two structural components in wood should contribute significantly to total resistance to flow. Subsequently presented experimental evidence, based on the study of gas flow through ponded and unponded wood, and through permeability specimens dried successively from different liquids, confirms this last prediction. These studies also provide evidence that the elasticity of the bordered pit membrane varies systematically across the growth ring, as predicted by the model. The presence of more than two structural components contributing to total resistance to flow through wood introduces theoretical shortcomings into previously used methods for the calculation of the radius and number of conducting pores in conifer wood, and for the estimation of the true liquid permeability of wood from gas flow data. A new computer based analysis designed to overcome these difficulties is presented. This is tested with only partial success in the prediction of the liquid permeability of Western Hemlock. There is good reason to believe that this lack of success was not due to a failure of the method (although ways of improving the method are identified) but due to an unexplained failure to measure the true liquid permeability of the specimens under test. Further rather more speculative biological and technological implications of the model are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available