Thermal conductivity of wood—models for different stages of combustion

The effective thermal conductivity is one of the most important parameters for modelling of thermo-chemical conversion of wood. It changes both with temperature and with conversion of the wood. There have been suggestions on modelling of this problem, together with measurements, in earlier works, especially for wet and dry wood, but for char the knowledge is poor. Here, two principle models of effective thermal conductivity on the basis of the pore structure in wood are validated by a comparison with direct numerical simulation of the fibre structure. The validation leads to a more general model, both for conductivity in the perpendicular and parallel directions relative to the fibres in the wood. In addition, the model expresses the effective thermal conductivity of char, since the wood material maintains its fibre structure during conversion. The effective thermal conductivity is estimated from given values of temperature, density and moisture content of the wood. It can also be applied to pellets and chipboards.