Study On Dispersion Characteristics Of Perfluorohexanone Under Low Pressure

In order to comply with the development trend of Halon airborne fire extinguishing system replacement,this paper coupled the numerical simulation method of VOF-DPM atomization model and vaporization model,and used the experimental verification platform of spray independent temperature change to study the dispersion performance of perfluorohexanone under low pressure and multiple temperatures,and developed the dispersion mechanism of perfluorohexanone under low pressure.The main research contents of this thesis are as follows:Firstly,a numerical model of perflourohexanone dispersion with multiple air pressure gradients and multiple temperature gradients synchronized is constructed.According to the stage characteristics of atomization and vaporization during the release process of perfluorohexanone,UDF technology was used to capture the formation time,velocity,particle size,location and other data of atomized droplets of perfluorohexanone,and the dispersion model of perfluorohexanone coupled with atomization and vaporization was constructed for the first time.Combined with the stable pressure injection experimental device,the spray cone Angle of perfluorohexanone and the mass flow rate at the nozzle outlet under normal environment were preliminatively verified.The margin of errors on two counts is within 5%,indicating that the model has a high calculation accuracy.Secondly,the atomization characteristics of perfluorohexanone under multi-pressure and multi-temperature gradient were studied based on the VOF-DPM atomization model.The phenomenological and atomized particle size characteristics of perfluorohexanone were analyzed under three kinds of ambient pressure(101 k Pa,75 k Pa and 49 k Pa)and five kinds of ambient temperature(-5℃,5 ℃,15 ℃,25 ℃ and 35 ℃).It was found that the primary breakup of perfluorohexanone was dominated by KH-RT instability.With the decrease of ambient pressure and air density,the interaction between droplet and air is weakened,and the secondary breakup effect of perfluorohexanone becomes worse.When the ambient air pressure decreased from 101 k Pa to 75 k Pa and 49 k Pa,the atomized particle size of perfluorohexanone droplets increased by 37.99% and 48.61% respectively.Thirdly,the vaporization characteristics of perfluorohexanone based on the Species Transport equation under wide pressure were studied.According to the vaporization characteristics under three ambient pressures(101 k Pa,75 k Pa and 49 k Pa),the diffusion and concentration characteristics of perfluorohexanone were analyzed.It was found that the vapor concentration of perfluorohexanone decreased with the decrease of ambient pressure.When the pressure dropped from 101 k Pa to 49 k Pa,the concentration of perfluorohexanone decreased by 15.38%.The reason is that the decrease of ambient air pressure weakens the atomization effect,and the number of droplets generated by secondary crushing decreases,which leads to the lower vapor concentration of perfluorohexanone.Finally,the reliability of the dispersion model which coupled atomization with vaporization of perfluorohexanone was verified.In this thesis,an experimental platform was established to verify the changes of particle size and velocity field of perfluorohexanone at different ambient temperatures(25 ℃,50 ℃,70 ℃ and 90 ℃),and compared with the numerical simulation results,it was found that the coupling degree was high.The high-speed region of the spray increased with the increase of ambient temperature,and the particle size reduction rate of perfluorohexanone droplets increased with the increase of axial distance,with a change rate between 20.81% and 28.61%.Therefore,perfluorohexanone has good dispersion performance in low pressure and multitemperature environment,which can be applied to multi-pressure and multi-temperature gradient environment.The research results of this thesis provide theoretical and technical support for the design of civil aircraft fire extinguishing system.