A comprehensive mathematical model of heat and moisture transfer for wood convective drying

Abstract

Abstract The focus of this study is the development of a specific drying model for the design and operation of drying systems for stacked lumber in drying chambers. Namely, a comprehensive three-dimensional (3D) mathematical model of heat and moisture transfer in stacked wood has been developed, where the wood was subjected to convective drying that accounts for the effect of the surrounding fluid flow. In developing the model, the characteristics of wood and fluid flow, i.e. velocity, pressure, temperature, relative humidity (RH) and moisture content (MC) are described by the conservation equations of mass, momentum and energy as well as thermodynamic relations. The model presented was solved numerically by means of the commercial software COMSOL Multiphysics. The simulation results were validated against experimental data under laboratory conditions. Air current circulation was found to be non-uniform during drying, which accounts for the different rates of temperature and MC in wood. At the initial stage of drying, this difference was relatively large but reduced gradually with the drying process. Meanwhile, the transient gathered phenomenon related to humidity around the stacked wood in the chamber was observed in response to air current circulation and evaporation rate of moisture. Finally, sources of error incurred in numerical calculations and actual detection were identified and discussed.