Study of heat transfer in wood before the onset of pyrolysis at the cone calorimeter scale

This work is dedicated to the heat transfer in wood subjected to a heat flux equal to 4 kW m −2 . This heat flux was chosen so that the temperature of the wood did not exceed 200 °C, thus avoiding pyrolysis. In addition, the wood was oven-dried to avoid water evaporation. Under these conditions, only heat transfer takes place. The goal was to focus on heat transfer and to model it very finely. Experimentally, wood samples were exposed to the heat flux from the cone heater of a cone calorimeter. Twelve thin-wire thermocouples were embedded in the wood samples to provide access to the in-depth temperature, and the heat flux distribution was imaged using a thermal camera. Eight different wood species were investigated in this work. Numerically, a 3-dimensional heat transfer model was developed. The experimental non-uniform heat flux distribution was used for the radiative heat flux conditions, the thermal conductivity was considered anisotropic and variable with temperature, and convection was described by convective exchange coefficients. This heat transfer model was used as a direct model for an inverse method aimed at determining unknowns, namely the convective exchange coefficient and the variation with temperature of the thermal conductivity perpendicular to the wood fibers, which was described by a second order polynomial. The numerical results are in good agreement with the experimental data, realistic convective heat transfer coefficients have been obtained, and thermal conductivities estimated by the inverse method are very close to those determined by the parallel hot wire method. This demonstrates the reliability of the model, boundary conditions, and thermal properties used.