Predicting Fire Suppression Efficiency Using Polydisperse Water Sprays

Abstract

Thermoplastic fire suppression by water sprays is numerically investigated using an Eulerian-Eulerian two-phase approach. The polydisperse spray model is based on the moments of the droplet size distribution function. Turbulent combustion is approached using the Arrhenius/Eddy-Break-up model coupled with the RNG k − ϵ turbulence model. A multiphase radiative transfer equation including the contributions of soot, combustion products and water droplets is used to describe radiation. Pyrolyzate mass flow rate is predicted from a thermal degradation model for poly-methyl-methacrylate. The influence that the main parameters of the water spray system, located directly above the fire source, have on the fire suppression efficiency is examined. Over the wide range of spray conditions tested, it is found that, first, polydisperse sprays are generally more efficient than monodisperse sprays, and, second, for a polydisperse spray, there exists an optimal reference Sauter mean radius, which corresponds to the shortest time for fire extinguishment. Results indicate that the time for fire suppression using polydisperse sprays decreases as the water flow rate increases, but with an asymptotic behavior. Finally, the model is used to determine the minimal water flow rate required for extinction.