Numerical Study of Kiln Drying Process of Lumber- The Effect ofOptimum Side Gap on Uniformity of Final Products

The main objective of this work is to obtain accurate predictions through numerical simulation models towards an optimum drying process of lumber with special focus on 105×105 mm western hemlock planks. The practical objective is to study the effect of previously suggested side gap between adjacent boards at different air velocities (Re numbers). A Fortran program is developed to solve the twodimensionalcoupled heat and mass transfer equations inside the wood during the drying process. The model considers the changes in air temperature and humidity due to heat and mass transfer to and from the upstream wood surfaces. The iterative SOR (Successive Over Relaxation) method is modified to increase accuracy and stability. Predictions for drying curves and temperature are in good agreement withexperiments. The effect of side gap on the drying process is also examined. Comparison between plots of statistical parameters for different side gaps is carried out for judgment about the uniformity of the products. Results indicate that without using the extra gap size there exists a considerable difference between the maximum and minimum final average moisture content of the boards in each row.

Keywords:

Convective kiln drying , western hemlock , numerical simulations , water vapor , bound water , free water , diffusion , capillarity , side gap , product uniformity