Numerical Simulation Of Trifluo-romethyl Bromide Flow Characteristics In Tube Based On CFD

Aircraft as a large complex system have high requirements for safety,reliability and economy.The fire extinguishing system as the last line of defense for fire protection is essential for the safety of the aircraft.However,the design of the fire suppression systems is still heavily dependent on physical experiments.The release of the fire extinguishing agent is a typical high-speed unsteady two-phase flow process.Wherefore the physical test is timeconsuming and difficult to explore the influence mechanism of various factors.This paper focuses on the unsteady flow characteristics of gas fire extinguishing agent in the tube.By establishing a three-dimensional numerical simulation model with phase transition,the flow release characteristics of trifluo-romethyl bromide driven by nitrogen in tube are simulated.Firstly,according to Henry’s law and Raoult’s law,the trifluo-romethyl bromide /nitrogen storage state calculation model was established,and the two-parameter Antoine equation was used to establish the calculation model of the storage pressure varied with ambient temperature.And the accuracy of the two computational models were verified by comparison with experimental and literature data.Secondly,based on the FLUENT,a three-dimensional simulation model for the flow characteristics of trifluo-romethyl bromide in the tube driven by nitrogen was constructed.The mixture model in multiphase flow calculation was used to describe the flow process of trifluo-romethyl bromide.In addition to considering the variation of the saturation temperature of trifluo-romethyl bromide with pressure,the phase transition process of trifluo-romethyl bromide was described based on the kinetic theory of gases.And the implantation of the phase transition model was achieved by programming the code.Then,the numerical simulation of the flow and release process of trifluo-romethyl bromide in tube was carried out.The variation of the parameters such as the pressure and temperature inside the bottle,the pressure of the pipeline and the phase transition rate during the release process,and the characteristics such as the velocity,temperature,flow rate and composition change of the outflowing trifluo-romethyl bromide were analyzed.The reliability of the computational model was verified from various aspects in combination with experimental and literature data.Finally,based on the above model,the effects of filling conditions,pipeline structure,pipeline roughness and local high temperature on the flow and release characteristics of trifluo-romethyl bromide in the tube were discussed.The results show that the filling conditions and pipeline structure have a great influence on the release characteristics of the fire extinguishing agent,while the pipeline roughness and local high temperature have little effect on the release of the fire extinguishing agent.