Water Mist Fire Suppression Performance And Nozzle System Parameter Optimization

To prevent the ozonosphere from being destroyed by Halon fire extinguishmentagents, water mist fire suppression technology has been become a Halon substitute forthe following advantages: no pollution to environment, less water consuming,extinguishing fire quiekly and little damage to protected objects. Water mistdeveloped from water spray system and had the advantage of both gas and waterfire-fight.The paper focuses on the fire extinguishing performance of water mist systemand the main contents are as followed.Based on the existing test chamber, this experimental study had taken diesel oilas the object of study, and carried out as two aspects, unshielded oil tray fire andunshielded spray fire in confined space. The change trends of gas temperature andoxygen concentration are get by experiments of the interaction between water mistand the fire plume by two kinds of nozzles. The results show that extinguishment ofspray fire need less time than oil tray fire.It makes analysis of the numerical simulation of the interaction between thewater mist and two kinds of fire used computational fluid dynamics softwareFDS(FireDynamicsSimulator), oil tray fire and spray fire, in the test room. The testmodel is built according to the actual size for truly reflect the characteristics of thefire. Based on taking large eddy simulation as turbulence, the combustion reaction issimulated by mixture fraction combustion model. Room temperature and oxygenconcentration are get by the simulation of interaction between water mist and fireplume for analysising extinguish mechanism of water mist.The results show thatextinguish mechanism of water mist is not identical on account of two differentpatterns between oil tray fire and spray fire.Numerical simulation study was carried out on the internal and external flowfield of the water mist centrifugal nozzle with FLUENT software. The impact of theexport radius was discussed, and orthogonal experiment was done to analyze threemain structure parameters of nozzle. Optimized structure parameters were got fromthe nozzle exit speed which was obtained by numerical simulation experiment. The simulation results show that the velocity increases quickly in the contractive sectionof nozzle, and while the export radius is0.8mm, the speed at the export will be amaximum. In the three main geometric parameters of nozzle, nozzle cylindricalsection diameter has the largest influence in the nozzle exit velocity, and it gets thebest results when diameter is smaller. Nozzle imported number is also the main factoreffect the nozzle speed, and speed increases with the import and export number, buttoo much number of import will increase the processing difficulty.