Modelado y simulacion de la mitigacion de una flama con spray fino de agua

MODELLING AND SIMULATIONS OF FLAME MITIGATION BY FINE WATER SPRAY Lipjainen A.L., Snegirev A.Yu. Saint-Petersburg State Polytechnic University Email: alex.lipjainen@gmail.com ABSTRACT Rapidly growing technology of fire suppression by high-pressure fine water sprays exploits its capability to mitigate gaseous flame faster with smaller water flow rate, yet applying environmentally friendly andtoxically safe extinguishing agent. For the optimum use of water in fire suppression, two contradictory requirements should be met: efficient delivery of the dispersed water into the flame zone and rapid droplet evaporation. The most important goals of this work are development of mathematical model of a turbulent evaporating spray, incorporation of the model into the existing in-house Fire3Dsoftware, and investigation of the interaction of fine and coarse water sprays with buoyant turbulent diffusion flame. At current moment, major result is that mechanisms of spray-flame interaction are identified, and the drastic differences between the coarse and fine water sprays are demonstrated. For the two distinct cases of flame suppression we demonstrate that the effect of spray refinement dependson the sprayplume momentum ratio. 1. 2. INTRODUCTION ...................................................................................................................1 MODEL DESCRIPTION ........................................................................................................1 2.1. Gas phasemodeling.........................................................................................................1 2.2. Liquid phase modeling ....................................................................................................2 2.3. Modeling sprinkler spray.................................................................................................2 3. RESULTS AND DISCUSSION..............................................................................................33.1. The effect of spray dispersion on its dynamics and structure...............................................3 3.2. Why finer spray suppresses flame more rapidly?.................................................................3 3.3. Spray dispersion may not be advantageous..........................................................................5 4. CONCLUSIONS.....................................................................................................................7 REFERENCES ................................................................................................................................7 1. INTRODUCTION This work is a part of ongoing project of Microsoft Research Corp. and SPbSPU: MicroTEST-FireEx. This project aims to develop the appropriate mathematicalmodel, to incorporate the model into the existing in-house Fire3D software, and to investigate numerically the interaction of fine water spray and buoyant turbulent diffusion flame. As a result, the mechanisms of spray-flame interaction are identified, and the effect of spray characteristics on fire suppression efficiency is determined. In addition to our earlier study [1-2], two cases of flamesuppression are considered in this work to demonstrate that the effect of spray refinement depends on the spray-plume momentum ratio. 2. MODEL DESCRIPTION 2.1. Gas phase modeling The model for the gas phase is the Navier-Stokes equation system for the multicomponent reacting mixture. In this work, URANS simulations are performed by solving Favre-averaged component, momentum and enthalpy transportequations. Modified k-ε model is used to predict 1

mean turbulent fields. Modification of model, closing approaches and discretization of equations were described in [1-2]. 2.2. Liquid phase modeling A Lagrangian approach is applied to model evaporating spray. Given the gas flow characteristics, multiple discrete droplets are tracked along their trajectories, [1-2]. To make computations...