A double climatic chamber used to measure the diffusion coefficient of water in wood in unsteady-state conditions:: determination of the best fitting method by numerical simulation

The present work is devoted to the experimental determination of the bound water diffusion coefficient of wood in unsteady-state. A specific experimental device built for that purpose, together with an efficient analysis method, allowed the measurement to be reliable and accurate. The experimental device consists of two climatic chambers controlled at the same temperature, but operating at different relative humidity values. These chambers are connected through a tunnel and are equipped with paths for manual manipulation of the samples. This configuration allows the step in relative humidity to be obtained almost perfectly throughout the experiments. Moreover, the sample weighting occurs without any disturbances to the ambient conditions. The experiment has been simulated via a comprehensive numerical code. known as TransPore. for studying the heat and mass transfer in porous media. These simulations allow us to study in detail the effect of phenomena that are not possible to avoid during the experiment, such as the coupling between heat and mass transfer. the presence of lateral surfaces that exchange heat but no mass, and the resistance to mass transfer at the exchange face. These simulations have been used to test different classical methods for extracting the mass diffusion coefficient from the experimental curves. The best compromise is obtained with an analytical model developed for one space dimension and one variable that accounts for the resistance to mass transfer at the surface. Notice that only the mass diffusivity can be determined with this model: the corresponding mass transfer coefficient has no physical meaning. (C) 2001 Elsevier Science Ltd. All rights reserved.