Can we predict fire extinction by water mist with FDS?
Résumé
Among the primary phenomena observed when studying fire suppression are fuel surface cooling, fire plume cooling and inerting effects. The last two result from water evaporation generating a significant vapor concentration, thus leading to an important heat sink as well as displacement and dilution of both oxygen and fuel vapor. Fire Dynamics Simulator (FDS.v6) is expected to be able to reproduce these effects. Extinguishment criterion focusing on plume cooling and inerting effects is based on a dedicated heat balance, whereas suppression model related to fuel surface cooling evaluates the burning rate decrease according to an exponential law taking into account local water mass reaching the fuel surface per unit area and an empirical constant which penalizes the prediction ability. Therefore, a new model derived from an Arrhenius equation has been implemented, which links the burning rate to the fuel surface temperature. Numerical simulations are conducted and compared with experimental data for all extinguishing mechanisms.