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A multiscale study of structure and water transport in wood.

Adey-Johnson, Robin (2020) A multiscale study of structure and water transport in wood. Doctoral thesis, University of Surrey.

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This thesis set out to understand the water dynamics in softwood using a lattice Boltzmann model description of sorption, with microstructural information derived from X-ray Computed Tomography experiments and experimental validation of water dynamics using Nuclear Magnetic Resonance. This is the first substantive use of a new lattice Boltzmann model that includes multiphase liquid/vapour fluid dynamics in lumen with sub-resolution effective media to model cell wall sorption. This is also the first time these three technologies have been combined to study the sorption behaviour of softwood. A software package—ProTG—-was written to generate tesselating arrays of realistic two-dimensional tracheids, including pits, suitable for use as a bounceback mask in the lattice Boltzmann model. ProTG tracheids are created based on a statistical distribution of values for each of a number of anatomical parameters. To ensure these are realistic, Norway spruce (Picea abies) juvenile wood was imaged using X-ray micro computed tomography at a voxel size of 2.5 µm and seven anatomical parameters were measured for 1511 complete tracheids. Statistical distributions were fitted to measurements of: tracheid length; radial and tangential lumen diameter and cell wall thickness; cell overlap; and linear intra-tracheid pit density. The latter two distributions are novel, as they required a number of CT volumes to be acquired and stitched together. Lattice Boltzmann sorption simulations were carried out on an array of tracheids where both relative humidity and pit state (open, closed and dynamic) were varied. Significant differences were seen between drying behaviour with pits open and closed, while dynamic pits behaved similarly to closed pits. Cell wall desorption took place at 35% RH but not 65% RH: in the latter case the wet cell walls prevented tracheids with closed pits from drying. Finally, NMR drying and rewetting experiments were performed on dried cubes and green discs to provide qualitative validation of the lattice Boltzmann simulations. The initial drying of green discs was found to proceed significantly differently to subsequent drying cycles, and initial rewetting also differed from subsequent rewetting.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors : Adey-Johnson, Robin
Date : 29 May 2020
Funders : Engineering and Physical Sciences Research Council (EPSRC), Forest Research, Forestry Commission Scotland, Future Trees Trust, Trees4Future (EU FP7)
DOI : 10.15126/thesis.00854161
Contributors :
ContributionNameEmailORCID,,, Paul
Depositing User : Robin Adey-Johnson
Date Deposited : 09 Jul 2020 07:54
Last Modified : 09 Jul 2020 07:55

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