Study On Inhibition Mechanism Of Methane And Air Explosion By Ultrafine Water Mist

The frequent occurrence of gas explosion threatens the safety of industrial production seriously.Therefore,domestic and foreign scholars carried out amounts of research work on gas explosion suppression.Ultrafine water mist,as an effective explosion suppressant,is widely concerned in recent years.Significant progress has been made in both experiment and numerical simulation.However,the interaction mechanism between ultrafine water mist and gas explosion process has not formed a unified conclusion.For instance,some research results show that ultrafine water mist has an inhibition effect on gas explosion,while other research results show that it has an enhancement effect on gas explosion.In this paper,suppression of methane explosion by ultrafine water mist is regarded as the research object.And the suppression mechanism of ultrafine water mist on gas explosion is discussed by the combination of experiment and numerical simulation.The main work and conclusions are as follows:(1)A visualized experimental apparatus was designed and established to research the methane explosion suppression process by ultrafine water mist.And it consisted of a closed combustion chamber,a gas distribution system,an ignition system,a water mist generation system,and a test and control system.A phase doppler particle analyzer was adopted to measure the mist characteristics,a high-speed camera was used to record the dynamic evolution process of flame,and a high-frequency transducer was used to collect the explosion pressure response.Automatic control of ignition and spray was realized by programming language.(2)Experimental study on methane and air explosion suppression by ultrafine water mist was conducted under pressure atomization and ultrasonic atomization conditions.The diameter and velocity of water mist produced by pressure atomization were large,which resulted in the flame deformation and the increasing flame surface area.Therefore,the flame propagation velocity and the pressure rising rate were greatly improved.However,the diameter and velocity of water mist produced by ultrasonic atomization were small,which resulted that the vaporization rate of water mist was faster and the disturbance effect on flame front was weak.The main function was cooling and absorbing heat.Therefore,the flame propagation velocity and the pressure rising rate decreased significantly.And the explosion could be completely suppressed under certain conditions.(3)The effects of ultrafine water mist generated by two kinds of atomization method on the flame structure were studied.Under the pressure atomization condition,the flame structure changed obviously,and the tulip flame was not formed.Meanwhile,with increasing mist concentration,the appearance moment of "tulip" flame was delayed successively under ultrasonic atomization condition.The flame appeared "cellular structure" as the mist concentration reached a certain value.And the flame structure experienced four stages,"cellular formation"→"cellular development"→"cellular reduction"→"cellular disappear".(4)Base on the ultrasonic atomization method,the effects of additive concentration and species on flame propagation velocity and explosion intensity were studied by adding alkali metal additives in water mist.The results show that the addition of alkali metal additive can enhance the suppression effect of ultrafine water mist.The effect of additive on explosion reaction was related to the activity and concentration of addition radicals.The suppression order of different additives for methane explosion was:K2CO3>KCl>KHCO3>Na2CO3>NaCl.With increasing concentration of additives,the effect of explosion suppression was enhanced.(5)The three-dimensional numerical model of methane explosion suppression by ultrafine water mist was established.It consisted of the coupling of physical processes of mist vaporization,the turbulent flow of explosion flow field,the gas combustion and the heat and mass transfer.The interaction mechanism between ultrafine water mist and explosion flow field was studied,and the heat transfer of gas-liquid two phases,gas concentration dilution and flame front turbulence intensity under different water mist characteristic parameters were analyzed.The effect of ultrafine water mist on explosion process was obtained,the fundamental reason of the enhancement and suppression on the explosion by ultrafine water mist was discussed,and the discriminate condition of the enhancement and suppression on gas explosion by ultrafine water mist was proposed.