| Fire is one of the main disasters that cause the loss of valuable forest resources.Compared with other fires,forest fires have the characteristics of strong early concealment,rapid spread and difficulty in fighting.In recent years,forest fires in China have still occurred from time to time,bringing great losses to ecology,society and people.Therefore,how to deal with early forest fires efficiently and environmentally is one of the key tasks of forest fire prevention.At present,portable pneumatic fire extinguisher,as a common forest fire extinguishing equipment in China,occupies an important position in forest fire fighting.However,at present,most portable pneumatic fire extinguishers have problems such as unstable fire extinguishing efficiency and easy reburning of fire field after fire extinguishing,and cannot effectively extinguish trunk fire of coarse branches and surface smoldering fire.Therefore,how to effectively improve the fire extinguishing performance of such pneumatic fire extinguishers is of great significance for fighting early forest fires and preventing fire spread.In view of the above problems,this thesis designs and builds a pneumatic fire extinguishing experimental device based on the portable portable pneumatic fire extinguisher 6MF-30.Through the combination of theoretical analysis,numerical simulation and laboratory experiments,the synergistic operation method of adding fire extinguishing agent(water)to this type of pneumatic fire extinguisher is studied,and its fire extinguishing performance is optimized.The airflow-water synergistic fire extinguishing experiment was carried out by the experimental device to explore the effect and law of airflow-water synergistic fire extinguishing.The main conclusions are as follows:(1)The aerodynamic performance parameters of the designed and built pneumatic fire extinguishing experimental device were measured,and the attenuation of jet velocity at different rotational speeds was studied by combining CFD numerical simulation.It was found that the higher the rotational speed of the impeller was,the faster the jet attenuation rate was.At a distance of about 3 m from the center of the impeller,the jet velocity values at three different speeds(2000 r/min,4000 r / min,6000r/min)are close.The increase of outlet airflow speed only increases the fire extinguishing distance within a certain range(2.5 m away from the impeller center),but it cannot fundamentally solve the problems of jet end combustion and fire reburning.(2)After exploring the airflow-water synergistic mode and analyzing the selfpriming water inlet mode of the cylinder,it is found that the water injection success rate is low and the stability is poor.Therefore,the collaborative scheme of water injection at the outlet of the cylinder provided by the pump is determined.It is found that when the impeller rotating speed is 4000 r / min,the longest distance of the jet can reach more than 6 m,and the width of the coating cover to the ground can reach about 0.6 m.In addition,the synergistic scheme of water mist nozzle was studied,and the feasibility of water mist nozzle injection collaboration was analyzed.It is found that the water consumption per unit time is less after the optimization of water spray nozzle,and the average water consumption per minute of three different numbers of nozzles is about2.2 L,which is 63 % less than that of water injection pipe.(3)The effectiveness of airflow-water synergistic fire extinguishing was studied based on fire extinguishing experiment,and the difference of fire extinguishing effect before and after optimization was compared and analyzed: The airflow-water synergistic fire extinguishing method can significantly shorten the fire extinguishing time,reduce the average fire extinguishing time by about 150 s,and greatly improve the fire extinguishing efficiency.The water mist penetration of airflow-water synergistic fire extinguishing is strong,which accelerates the cooling rate of the wooden stack center and is suitable for the suppression of smoldering fire.In addition,the water mist nozzle synergistic fire extinguishing reduces the water consumption per unit time(the average water injection per unit time is 4.2 L less than that of water pipe injection per minute),and the average fire extinguishing time is about 38 s(23 s more than that of water pipe injection).The fire extinguishing effect is good,and it has high application value in the fire extinguishing scenario of water shortage.The synergistic fire extinguishing of airflow and water increases the fire extinguishing range while improving the fire extinguishing efficiency,which can assist the pneumatic fire extinguisher at non-rated speed to effectively extinguish the fire,reduce the risk of combustion and reburning,and is of great significance to improve the fire extinguishing performance of portable pneumatic fire extinguishers.The research results provide a reference for the optimization and development of airflow-water fire extinguishers,and lay a theoretical foundation for the analysis and research of airflowwater synergistic fire extinguishing.This thesis contains 60 figures,17 tables and 99 references. |
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