Heat transfer mechanisms and models for a gypsum board exposed to fire

Gypsum is a popular building material with excellent behaviour for fire protection. The main heat barrier in gypsum boards is due to dehydration at elevated temperatures, which is an endothermic reaction. This effect can approximately be captured by heat conduction models with an apparent heat capacity. However, these models are not capable of reproducing some of the details observed in experiments, in particular the temperature plateau at the unexposed face at around 100 °C. In this paper, the effects of vapour transport and condensation are included to improve the simulations. It is shown that, contrary to other findings in the literature, vapour transport without condensation has virtually no influence on the heat transfer. However, when including condensation, a mechanism similar to a heat pipe is able to reproduce the observed temperature plateau. To explain some contradictory results encountered in the literature, a large effort is devoted to rigorous mathematical formulations and to realistic material parameters. It is shown that some effects attributed to vapour transport in the literature are in fact due to inconsistent mathematical formulations.