Modelling of airflow through a stack in a timber-drying kiln

A two-dimensional pore-scale model is used to predict air flow through a wood drying stack for which both the interstitial and the average flow can be considered as two-dimensional.Timber-drying kilns consist of two parts, a centre region and staggered end sections, each with different flow characteristics. In the centre region the flow resembles flow through a duct and empirical models from literature were used for the evaluation of the pressure loss across the timber stack. The staggered ends, resulting from the stacking method, were analyzed by considering them as porous media. A unified modelling theory for the prediction of the pressure drop of crossflow in a prismatic structure was proposed. The model was derived by volumetrically averaging the equations of motion over an arbitrary two-phase system of stationary solids and a traversing fluid. Closure was obtained by using a formerly introduced rectangular representation of the pore space morphology. The model was applied to a typical stack in timber-drying kilns situated in the southern and eastern parts of South Africa. A scale model was built and accurately tested in a wind tunnel. The predicted results compared favourably to the test results.