Modelling pyrolysis of charring materials: determining flame heat flux using bench-scale experiments of medium density fibreboard (MDF)

Medium density fibreboard is a homogenous wood product which is a suitable candidate for validating the pyrolysis model of charring materials. For comparison between model and experiment, this article presents the burning behaviour of MDF under cone calorimeter with different experimental conditions. The total incident heat flux, as a significant boundary condition for pyrolysis modelling, is specifically studied both experimentally and theoretically. The experimental conditions were found to have no significant impact on the ignition phase however the sample thickness would lead to different burning behaviours. The total incident heat flux led by cone and flame at sample surface was experimentally measured and the experimental results were evaluated using non-flaming experiments with inert gas. An analytical model based on classical ignition theory is developed to address the mechanism of mass loss caused by incident heat flux, involving the effects of char layer and back boundary. The model shows that the mass loss rate correlates linearly with the total incident heat flux for a specific char layer thickness and back boundary condition. The model was validated for the non-flaming and flaming experiments to further justify the reliability of heat flux measurements. An empirical equation describing the flame heat flux is proposed.