Multi-phase moisture transfer in the high-temperature drying of wood particles

Abstract

A transport model is presented of the drying of wooden particles exposed to convective/radiative heating in an inert environment. The mathematical formulation is based on the one-dimensional, unsteady conservation equations for enthalpy, mass and momentum for the solid, the liquid and the gas phase. Phenomena of moisture transport include water vapor convection and diffusion and capillary water convection in the pores of the particle, and bound water diffusion in the solid wood. Momentum transfer, for the liquid and the gas phase, is described according to the multiphase Darcy law. Local thermodynamic equilibrium is assumed, with a sorption isotherm that couples the moisture contents in the solid and the gas phases. The solution, obtained through implicit finite-difference approximations and the operator splitting technique, has been applied to investigate high-temperature wood drying on dependence of particle physical properties, heating conditions ( T r , h c ), initial moisture content (5–100% on dry basis) and particle size. Good agreement with experimental data is shown.