Numerical investigation of simultaneous heat and mass transfer mechanisms occurring in a gypsum board exposed to fire conditions

This paper investigates the simultaneous heat and mass transfer mechanisms occurring in a gypsum board exposed to fire conditions. An in-house developed code (HETRAN), simulating heat and mass transfer in porous building materials, has been used to predict the heat and mass transfer characteristics within gypsum boards. The code solves numerically a set of mass and energy equations appropriate for the heat and mass transfer in porous materials, assuming homogeneity, local thermodynamic equilibrium and mass transfer due to diffusion and pressure gradients. The predicted temperature evolution within the gypsum sample, with and without mass transfer, is compared to experimental data, demonstrating that vapor migration through the sample holds a significant role in the board behavior under elevated temperatures. The results demonstrate that vapor migrates towards both directions of the board (fire and ambient side), with diffusion mass transfer being the dominant mass transfer mechanism, whereas air moves towards the “fire side”. The dehydration front moves from the “fire side” to the ambient side, with a high velocity in the beginning, which reduces as the front moves through the gypsum sample to the ambient side.