Modelling of transport processes in a developing char

A mathematical model, simulation results and laboratory experiments are reported to describe the degradation of fire retardant polymeric materials. The model describes the heat and mass balances of a polymer layer with finite thickness. The degradation is initiated by a constant heat flux at the top of the layer. It is assumed that the polymer degrades to a fixed mass of char and volatile gas in an instantaneous step, at the moment when the temperature reaches a critical value. The most important heat transport mechanism is conduction, which dominates the temperature profile. The mass transport of gas is described by Darcy's law, with a simplifying condition that the overall solid volume is constant during degradation. The transport processes have been modelled in one spatial dimension. Calculations and experiments have been carried out to establish the effects of critical parameters such as layer thickness, heat flux and material properties.