A numerical study of water-mist suppression of large scale compartment fires

Abstract

The focus of this paper is on simulating water mist suppression of fires in large enclosures. A two-continuum formulation is used in which the gas phase and the water-mist are both described by equations of the Eulerian form. The water-mist model is coupled with previously developed codes based on the multi- block Chimera technique for simulating fires. Computations are performed to understand the various physical processes that occur during the interaction of water-mist and fires in large enclosures. Droplet sectional density contours and velocity vectors are used to track the movement of water-mist and to identify the regions of the fire compartment where the droplets evaporate and absorb energy. Parametric studies are performed to optimize various water-mist injection characteristics for maximum suppression. The effects of droplet diameter, mist injection velocity, injection density, nozzle locations and injection orientation on mist entrainment and flame suppression are quantified. Numerical results indicate that for similar injection parameters such as mist injection density, injection velocity and droplet diameter, the time for suppression was smallest for the top injection configuration. Water-mist injection through the side walls, the front and rear walls and through the floor were found to be less efficient than the top injection configuration. These results are compared with our earlier predictions on water-mist suppression of small scale methanol pool fires and other experimental studies.