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An X-ray density analyzer was used to determine the evolution of the moisture content (MC) profiles of a wood board during drying. Tests were performed on quartersawn boards of five wood species (oak, beech, Scotch pine, birch, alder) of two thicknesses (20 and 40 mm) dried at low temperature. The water vapor diffusion coefficient and liquid permeability of each wood species were determined by inverse analysis of the profiles using a computational model of coupled heat and mass transfer. These parameters were also measured by classical methods for validation purposes. The inverse method gives values close to the measured ones when using the evolution of the moisture profile, but also quite remarkably when using only the evolution of moisture at the core of the board. On the contrary, the method is less accurate when using only the average kinetics as experimental information. [ABSTRACT FROM AUTHOR]

The aim of this article is to characterize the wood-water relationship and certain moisture transfer properties of Central African species for which very little data exists in the literature, i.e. Iroko, Padouk, Bibolo (Dibetou), Moabi, Doussié, Bilinga and Grenadilla. Moisture sorption isotherms were measured using the Dynamic Vapor Sorption method at 35°C. The Hailwood-Horrobin model was used to describe the sorption isotherm and the model parameters are given for each species. A rough estimation of the fiber saturation point could be made and is between 18.5% for Doussié and 26.5% for Bibolo. The water vapour diffusion coefficient in the radial direction of the wood was determined by the cup method at 35°C. Its value ranges from 1.72E-11 for Grenadilla to 1.71E-10 m2/s for Bibolo. It has been shown that the model proposed by Siau (1984) allows a relatively reliable estimation of the value of this parameter from wood density. The gas permeability was also measured on the same samples and ranged from 3.3E-19 m2 for Moabi to 3.78E-16 m2 for Bibolo. From these parameters, the apparent tortuosity and equivalent pore diameter for the mass flow were estimated for each species. [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]

Non-Fickian diffusion in native and thermally modified wood was analyzed by the inverse method. A low quality of the identified diffusivity values was found for the diffusivity which was either constant or varying with water content. This was explained by the non-Fickian behavior. It was especially distinct for thermally modified wood for which an increased delay in obtaining the hygroscopic equilibrium was clearly shown. Such a delay was explained by time required for molecular reorganization to produce new sorption sites. This phenomenon was accounted to improve the physical model by modifying the convective boundary condition. A relaxation mechanism was used for this purpose with an adequate time constant. [ABSTRACT FROM AUTHOR]

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• 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]