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Wood permeability is a macroscopic property resulting from complex pathways at the cellular level. In this study, high-resolution X-ray CT scans were performed during longitudinal imbibition in Norway spruce to investigate the role of wood rays and tracheids network in liquid migration. A customized setup was designed to maintain the bottom face of a wooden cylinder in contact with water, without vibration, despite the sample rotation required during each scan. The results highlighted a contrasted role of latewood and earlywood in water migration. Liquid imbibition was fast in latewood, because the bordered pits are less prone to aspiration than in earlywood, due to their smaller diameter and larger cell wall thickness. In earlywood, the migration pattern was complex due to pit aspiration that isolate tracheids clusters. Indeed, the images revealed a significant contribution of wood rays in the migration pathways. Consequently, tracheids were not progressively filled in the longitudinal direction from one tracheid to the next, but they were filled laterally with water coming from wood rays at different heights of the cells. This explained entrapped air bubbles in the lumens and led to a 3D heterogeneous liquid distribution. [ABSTRACT FROM AUTHOR]

The study of moisture migration in Norway Spruce may reduce the discrepancy between measurements and simulations of transfers in buildings and thus be helpful for improving their performance and durability. For this purpose, X-ray imaging was used to study moisture migration in Norway spruce during imbibition at tissue level. Moisture content kinetics in earlywood and latewood, based on X-ray attenuation, was observed and measured through rigorous protocol. The imbibition process was studied in both longitudinal and radial directions. The results showed an easier migration of liquid in latewood than in earlywood in the longitudinal uptake. In the radial direction, the impact of compression wood as a barrier and the role of the anatomical structure in the liquid migration were highlighted by the direct visualization of filled tracheids. [ABSTRACT FROM AUTHOR]

The bark-water relation and the moisture transport in bark are essential for the living tree but also for the industrial utilization of bark. Thus the bark-water relation of beech (Fagus sylvatica ) and spruce (Picea abies ) have been studied in the present work. The sorption isotherms were determined at 35°C for both wood and bark and the water diffusivity was measured under steady state conditions (cup method) and under unsteady state conditions, i.e. via sorption test. The sorption isotherms were calculated based on the Hailwood-Horrobin (HH) model. It was observed that beech wood and bark have a similar hygroscopic behavior, whereas spruce bark is more hygroscopic than spruce wood in all the relative humidity (RH) ranges. The radial diffusivity was in the range 1.2 ⋅ 10-11-2.2 ⋅ 10-11 m² s-1 for spruce and beech bark, respectively, when the driving force of the diffusion is the gradient of bound water. [ABSTRACT FROM AUTHOR]

• Thermo-migration of water in wood investigated by in-situ micro-CT imaging. • An original setup was conceived to maintain the temperature gap during CT scanning. • The analysed scans show the dynamics of moisture migration from hot to cold sides. • Above the FSP point, liquid water appears close to the cold side as localized spots. • Simulations prove that the vapor density gradient is the relevant driving force. Wood used as a building material is exposed to non-isothermal and unsteady state conditions involving coupled heat and mass transfer within the porous media. These exchanges contribute to the regulation of relative humidity in a passive way and influence the energy performance of buildings. In order to characterize the importance of the hygrothermal behaviour of softwoods in this context, an experimental setup was developed to access to moisture fluxes and/or moisture content profiles in the presence of a known temperature difference imposed on both sides of the wood sample. This original setup was conceived to maintain the temperature gap during micro-tomography acquisition. Image processing allows the moisture content profiles to be obtained over time after changes of the thermal gradient. The simulation using a computational model of coupled heat and mass transfer confirmed that the gradient of vapor density is a relevant unique, "synthetic", driving force to account for moisture migration in non-isothermal conditions. [ABSTRACT FROM AUTHOR]