Numerical Modeling of Fire Suppression Using Water Mist. 4. Suppression of Liquid Methanol Pool Fires

Abstract

Abstract : This report is the fourth in a series dealing with numerical modeling of fire suppression using water mist. While the first two reports examined the interaction of water mist with two-dimensional methane air diffusion flames, the third report presented a numerical model for studying methanol liquid pool fires, As shown in that report, numerical results exhibited a flame structure that compared well with experimental observations and thermocouple temperature measurements. In the present report we describe results for water-mist suppression of liquid methanol pool fires. The interaction of water-mist with pulsating pool fires is studied. Time dependent heat release rate profiles and temperature profiles identify the location where the water droplets evaporate and absorb energy. Numerical results are also presented for the effect of water mist on steady methanol pool fires stabilized by a strong co-flowing air jet. The relative contribution of the various suppression mechanisms such as oxygen dilution, radiation and thermal cooling on overall fire suppression is investigated. Parametric studies are performed to determine the effect of droplet injection density, velocity and droplet diameter on entrainment and overall suppression of pool fires. These results are reported in terms of reduction in peak temperature, effect on burning rate and changes in overall heat release rate. Numerical simulations indicate that small droplet diameters exhibit smaller characteristic time for decrease of relative velocity with respect to the gas phase, and therefore entrain most rapidly into the diffusion flame. Hence for the co-flow injection case, smaller diameter droplets produce maximum flame suppression for a fixed amount of injection spray density.