LES study on mechanisms of fire extinction by water mist in natural ventilation compartment

To study the relative contribution of various suppression mechanisms of water mist, the interaction of water mist and pool fire in natural ventilation compartment is investigated by large eddy simulation (LES), mixture fraction combustion model and Euler-Lagrange method. Parametric studies are further performed to determine the effects of droplet diameter on water mist entrainment and fire suppression under natural ventilation condition. The simulating results indicate that there are two different regimes in the temporal variations of smoke layer temperature: those are sudden cooling regime and gradual cooling one. It is also found that the thermal cooling effect is the main fire suppression mechanism in intermittent flame, buoyant plume and hot ceiling smoke layer, while in persistent flame the dominant suppression mechanism is the co-work of thermal cooling and oxygen dilution. Parametric studies results indicate that smaller diameters droplets have a lower extinguishing effect on the compartment fire with good ventilation.