Relationship between a diffusion model and a transport model for softwood drying

Transfer equations in a transport model for wood drying are rearranged to give equations that have similar form to those of Luikov's drying model. In this way the transport coefficients in these equations are derived from the transport model and are functions of moisture content, temperature, wood properties (density, permeability, and bound water diffusivity), and properties of moisture (liquid density and viscosity, vapor density, and viscosity). The above-derived equations are used to examine the relationship between the transport model and the simple diffusion model. It is shown that the diffusion model can be regarded as a simplified form of the transport model when the effect of temperature gradient is neglected. The diffusion model is applicable to cases where the temperature gradient is flat or the coefficient for the temperature gradient is small compared to that for the moisture content gradient. In other cases, or where the wood temperature is of concern, the transport drying model should be employed.