The effect of water movement on specific heat of gypsum plasterboard in heat transfer analysis under natural fire exposure

Abstract

This paper presents the results of a numerical study of heat and mass transfer in gypsum plasterboard under natural fire conditions in buildings. The main objective of this study is to evaluate the effect of mass (moisture) transfer in gypsum plasterboard on its specific heat value so that temperature calculations in gypsum plasterboard in fire can be performed using heat transfer analysis only. For design purpose, this is useful because it will avoid the complexity of having to deal with combined mass and heat transfer. In this study, the effect of moisture in gypsum plasterboard is to increase the specific heat of dry gypsum plasterboard over the temperature regions of water evaporation. Due to mass (moisture) transfer, this additional specific heat value will be higher than that of the latent heat of water evaporation. A numerical parametric study has been performed to evaluate how the characteristics (fire load, ventilation condition and construction materials) of natural fires in buildings affect this additional specific heat of gypsum plasterboard. It has been concluded that this additional specific heat value is affected by the heating rate of natural fires and permeability of gypsum plasterboard. The heat rate is a function of the ventilation condition and construction materials. The additional specific heat due to moisture transfer increases with increasing heating rate of natural fires, but decreasing permeability of gypsum plasterboard. At permeability values higher than 10 −7 m/s, the effect of moisture transfer on the specific heat of gypsum plasterboard is negligible.