EVALUATION OF DIFFUSION-COEFFICIENT AND SURFACE EMISSION COEFFICIENT BY AN OPTIMIZATION TECHNIQUE

The rate at which wood dries can be expressed by two factors: (1) the diffusion coefficient, as an indication of internal resistance to moisture removal, and (2) the surface emission coefficient, as an indication of external resistance to moisture removal. An optimization technique was applied to calculate these two coefficients. Unlike existing methods where these coefficients are evaluated at only one point, usually at one-half of the evaporable water remaining in wood, this optimization technique used the entire drying data. The technique searches for the optimum pair of coefficients based on the least squares principle. The performance of this method was demonstrated by reanalyzing published data using a digital computer. The results indicate that a more accurate prediction of the drying process can be achieved by the optimization method than by existing methods. The dependence of the diffusion coefficient on moisture content and sample thickness is discussed.