Indirect determination of tangential and radial steam diffusitivity of beech.

In order to characterize the diffusion process of water in the hygroscopic range of wood, we propose to evaluate initially the diffusion coefficients of water vapour in the three orthotropic directions of wood. The diffusion coefficients of water vapour are deduced from the diffusion coefficients of an inert solute (helium) measured in a diffusion cell, type Wicke and Kall enbach, being in an unsteady state. The diffusion coefficients in the radia l and tangential directions measured at 30 degrees are independent of absol ute moisture content of wood. The values we find agree with ranges of varia tions given in the literature. The diffusion coefficient in the radial dire ction is roughly higher than the diffusion coefficient in the tangential di rection, probably due to the rays in the radial direction.