NONISOTHERMAL DIFFUSION OF MOISTURE IN WOOD AND SORPTION STUDIES

A series of experiments on nonisothermal diffusion of moisture in wood were performed. The relative humidities and temperatures of the surfaces and the fluxes were closely monitored.;The results were analyzed by using two models, the first of which is based on a gradient of activated moisture content, and the second is based on a gradient of chemical potential which contains an additional term to account for the effect of the temperature gradient. Both models predicted the observed flux reversal and the chemical potential model generally gave a better fit to the data. Further analysis of the data showed that the partial vapor pressure or moisture gradients alone do not describe nonisothermal diffusion, but that the temperature gradient must be taken into consideration.;Diffusion coefficients and sorption isotherms were obtained experimentally from specimens matched to the nonisothermal. The activation energies and differential heats of sorption were calculated. The above were used in the evaluation of the nonisothermal diffusion models.;Reversal of the flux direction was observed in all series proving the existence of the thermal diffusion phenomenon in wood.