Simulation Study On Flow Characteristics Of Gas Fire Extinguishing Agent In Pipe Network Containing Branch

Fire is one of the important factors affecting the safety of aircraft.An automatic fire extinguishing system is usually required to improve safety in fire-prone zones of the aircraft.However,it has strict restrictions on the reliability of the fire extinguishing system,space as well as weight which requires extremely well-designed layout of the fire extinguishing pipe network.Among them,the flow characteristics and distribution rules of fire extinguishing agent in the pipe network containing branch are difficulties in restricting the design of fire extinguishing system.Currently,most of the researches in China are carried out through experiments supplemented by traditional engineering experience models,and they are difficult to adapt to the requirement of designing fire extinguishing systems with processes of unsteady multiphase flow similar to aircraft applications.To this end,this paper uses a combination of experimental and numerical calculations to simulate the discharge characteristics of CF₃Br fire extinguishing agent driven by nitrogen and the flow distribution law in the pipe network containing branch.Firstly,through the construction of the experimental platform,the flow and discharge characteristics of the CF₃Br fire extinguishing agent driven by nitrogen were studied in detail.The characteristics of the process of the fire extinguishing agent spraying from the bottle to the end nozzle were analyzed.The influence of the nozzle outlet area as well as the filling ratio on the pressure at the nozzle were studied in the single nozzle pipe network and the double nozzle pipe network respectively.Secondly,a one-dimensional simulation model of the flow characteristics of CF₃Br fire extinguishing agent pipe network was established by AMESim software.The Muller-Steinhagen model and the Shah model were used to calculate the frictional pressure drop of the pipeline and the heat exchange coefficient between the fire extinguishing agent and the pipe wall serving as the boundary input of the model.The simulation model was also compared and verified with the reference to the experimental data.The results show that the average pressure error between the simulation and experiment in the stable discharge stage is within 5%.Thirdly,the flow discharge characteristics of the single nozzle pipe network were simulated and calculated based on the above simulation model.The effects of pipe length,pipe diameter,friction coefficient,nozzle area and nozzle configuration on the pressure at the nozzle were studied.The research and the relationships among discharge pressures of several different configurations of nozzles were highlighted.Finally,based on the foundation of the above researches,the influence law of branch pipe length ratio,pipe diameter ratio and nozzle area ratio on the flow distribution characteristics in the branch was studied by using the established simulation model of branch pipe network.The influence laws of parameters such as the filling condition of the fire extinguishing bottle,the main and support pipe parameters as well as the friction coefficient on the flow distribution in the branch were analyzed under the condition that the nozzle area ratio is constant.The results show that the filling conditions and the main parameters have little effect on the flow distribution,but the friction coefficients and the branch pipe parameters have a great impact on the flow distribution.