An inverse moisture diffusion algorithm for the determination of diffusioncoefficient

The finite difference approximation is applied to estimate the moisture-dep endent diffusion coefficient by utilizing test data of isothermal moisture desorption in northern red oak (Quercus rubra). The test data contain moist ure distributions at discrete locations across the thickness of specimens, which coincides with the radial direction of northern red oak, and at speci fied times. Also, the rate of moisture variation at each specified time and location must be known or correctly estimated. The functional form of the diffusion coefficient as well as the boundary conditions at the surfaces ar e not known a priori. The resulting system of finite difference equations d efines an inverse problem, whose solution may be sensitive to small changes of input data. Results indicate that the diffusion coefficient increases w ith increasing moisture content below the fiber saturation point, which def ines the upper limit applied by the diffusion theory.