| Since it was found that the traditional halon fire extinguishing agent has a damage on the ozone layer and it cannot be repaired,water mist fire extinguishing technology has been paid more and more attention.Water mist fire suppression technology not only is widely used in civil buildings,public buildings and marine applications,but also plays an important role in the field of energy and industry.All along,people have worked on improving the performance of water mist fire suppression.However,the problems such as too low spraying speed,too small flow rate and too large nozzle size have not been solved yet.This paper focuses on the above problems,optimizing the structure of pressure type water mist nozzle,and the optimized water mist nozzles are applied to the fire incident caused by indoor gas leak,then the effectiveness of fire extinguishing is investigated.Specific research contents are as follows:First of all,pressure swirl water mist nozzle is simulated numerically by the FLUENT numerical simulation software the research object.The water mist particle size distribution of the nozzle is analyzed,and whether the particle size conforms to normal distribution is tested,so as to complete judging the accuracy of structure.Then the computational grid independence test is carried out,and the influence of nozzle geometry parameters on the spray effect of water mist is discussed.The effects of export quantity,inlet diameter ratio and outlet diameter ratio on spray velocity and spray pressure are emphatically investigated.It is found by simulation that the above three parameters have influence on spray effect,and the influence of inlet diameter ratio on spray effect is significant.Secondly,the numerical simulation of the external flow field of the optimized pressure swirl water mist nozzle is conducted.Open the discrete phase tracking model,then complete selecting and setting the turbulence model,boundary condition,initial condition and solution methods.Capturing the change of spray shape over time,the particle size distribution,and the velocity change of water mist droplets at different sections and pressures are compared and analyzed.The simulation show that increasing spray pressure,not only help to expand the scope of protection,but also can improve the ability of droplet flame to penetrate flames.In vertical distance Y=-30 mm from nozzle outlet,broken water mist droplet has basically reached equilibrium state.When the injection pressure reaches 0.5MPa,the drops are almost completely broken.Finally,a gas-liquid two phase numerical model between the water mist and fire caused by the indoor gas leakage is established.Use the finite rate combustion model and the interaction model between eddy dissipation turbulence and chemistry to complete the simulation of the flame stable combustion,then open the water mist DPM discrete phase model;to analyze and record the interaction process between water mist and fire process.Observe the flame pattern and the dynamic changes of flame,the variation of the flow field temperature and the concentration of the resultant before and after the action of water mist,are compared and analyzed.The influence of particle size,flow rate and velocity of water mist on fire suppression effect is discussed.The simulation results show that the optimized water mist nozzle can effectively suppress the fire caused by the leakage of indoor natural gas.It is very important to set the particle size,flow rate and velocity of the water mist properly. |
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