Research On High Pressure Fine Water Mist Fire Suppression System Key Problems And Its Performance

It is discovered that Halon fire-extinguishing chemical wreck the ozone layer by science determination and experiment. And its destroy will threaten human living space and body health. With the increasing requirement for environmental safety,it is inevitable trend that Halon will be banned completely. Water mist has big surface area,hence it can absorb rapidly quantity of heat and is converted into steam which drops the erature and oxygen concentration. By comparing to other fire suppressions,high-pressure water mist system has significant advantages of effective fire extinguishing and environment-friendly,and has been recognized as the most potential substitute of halon fire-fighting system. Therefore,research on basis theory and fire suppression test of the spray has great significance for the development and application of the high-pressure water mist fire extinguishing technology. The main contents of this dissertation are as followed.By summarization for the newest developing situation of domestic and overseas water mist fire extinguishing technology,the mechanisms and advantages of mist fire suppression are analysed. Key problems and basic countermeasure are defined.According to analysis of liquid atomizing characteristics and practical requirement of water mist fire suppression,centrifugal type pressure nozzle is determined as atomizing device of the water mist system. Based on the theoretical analyses of the inner flow field of the nozzle,the relations of its atomizing characteristics with the structural parameters and pressure are concluded. Numerical value simulation and analysis of flow field in nozzle accomplished by FLUENT sfotware. A new nozzle was developed, and has been counerred china invent pantent for its low using water quantity and high fire suppression efficiency.Combined spray head is made up of some independent nozzles,its performance depends on function and distrbution of the nozzles. By changing amount and distrbution of the nozzles,Combined spray head has more flexibility in design and use.Motional model of mist droplets is built on the basis of boundary storey theory,their flying velocity and distance can be calculated. By analyzing transfers law of heat and quality of the droplets in fire,vaporizing speed and time of the droplets are concluded,and then the most fixing height interval of spray heads can be established.Experiments on the structure parameters and working pressure of nozzles affecting the flow coefficient and atomizing characteristics are carried out by the use of turbine flowmeter and laser particle size analyzer. The results show that: the flow coefficient increases and mean diameter of the droplets decrease when the pressure raised,but he flow coefficient and uniformity degree index of mist droplets change hardly.Combined spray head will produce bigger size droplets than single nozzle. This illustrates that interferences between mist cones are in existence and lead to some small droplets disappearing. Hence combined spray head has better uniformity degree of mist droplets than single nozzle.A lot of fire suppression experiments were accomplished for the nozzle developed. It may be seen that fine water mist for the nozzle to produceare specially effective for extinguishing solid and liquid fire or restraining combustion speed. The influences of fire scale and nozzles position on fire extinguishing performance may be summed up in effect of spray intensity. It is necessary fire extinguishing factor that there is enough spray intensity in burning region. With raise of nozzle workong pressure,the spray intensity and momentum of droplets increase. The droplets can surmount the resistance of heat airflow and flame,and directly make cool core region of combusition, fire extinguishing efficiency notably rise. Therefore,high-pressure water mist fire suppression technology has notable superiority to those of low-pressure system. Lastly, some problems left and further researches in high-pressure water mist fire suppression system are also discussed in short.The results of the experiments show that: the nozzle has low using water quantity and high fire suppression efficiency and been counerred china invent pantent. The high pressure water mist fire suppression system adopting the nozzle has been legalized by china ship's classificaion society(CCS), and was applied in ships.