| Forest fires are one of the reasons for the huge loss of forest resources.Forest surface fires are the main cause of forest fires.In order to prevent forest fires,extinguishing forest surface fires is of great significance to protect forest resources and prevent forest fires.As the best substitute for chemical fire extinguishing agents such as halon fire extinguishing agents,water mist has the advantages of strong permeability,no pollution to the forest environment,purification of smoke and dust,and high fire extinguishing efficiency.It is gradually used in forest fire fighting.At present,water mist sprinklers have been used in forest firefighting,but there are few pertinent researches on water mist sprinklers for forest surface fires.Therefore,this paper designs a water mist sprinkler for forest surface fires.This paper completes the theoretical research on the water mist nozzle by analyzing the atomization principle of the water mist and the atomization form of the nozzle.According to the basic design concept of water mist nozzle,theoretical calculation is carried out,and an impact split-flow water mist nozzle for extinguishing forest surface fire is proposed and designed.Fluent software was used to simulate the impinging split-flow water mist nozzle,and the influence of the changes of key parameters affecting atomization,such as nozzle hole diameter,length and spray cone angle,on spray velocity and spray protection radius Rp were analyzed.The analysis results show that the velocity of fine water mist is significantly affected by the diameter of the nozzle hole and the length of the nozzle hole,and increases with the increase of the nozzle hole diameter and the decrease of the nozzle hole length;the spray protection radius is affected by the nozzle hole diameter and the spray cone angle of the nozzle hole.significant,and grows larger with both.The parameters were optimized by Design-expert,and the best parameters after rounding were selected to make the impinging split-flow water mist nozzle with the spray hole diameter of 2.1mm,the spray hole length of 4.4mm,and the spray hole spray angle of 55°.A simple spray experiment was carried out,and the measured spray protection radius was 57 cm,and the error with the Fluent simulation result was 0.8%,which proved that the optimization and simulation results were reasonable.Considering the safety of the fire test,in order to reduce the verification link and the number of tests,Pyrosim was used to carry out the numerical simulation of fire water mist fire extinguishing in the surface litter layer.The pine forest surface litter was selected for simulation analysis,the pine forest surface litter layer model was constructed in Pyrosim,and various test devices and water mist nozzles were set up.The influence of water mist droplet diameter,nozzle spray angle and spray speed on the fire extinguishing effect was explored.By analyzing the heat release rate curve and temperature curve changes,the optimal fire extinguishing parameters were obtained as droplet size 350μm,spray inclination angle 45°,The spray speed is 50m/s,the spray height is 1.2m,and the heat release rate curve is analyzed to obtain that the water mist fire extinguishing time is about 25 s.A preliminary fire-extinguishing experimental study was carried out using the designed impact split-flow water mist nozzle.A water mist fire-extinguishing system was established to carry out the test of water mist to extinguish the surface litter layer of pine forest,and the temperature curve changes of the experiment and simulation were verified when the water mist nozzle was at a height of 1.2m and the spray angle of the nozzle was 45°.The analysis results showed that the experimental and simulation fire extinguishing The time is about 25 s,and the maximum error is between 1 and 2s.The water mist fire extinguishing rules of the two reactions are the same,indicating that Pyrosim simulation can more accurately predict the fire development and fire extinguishing trend.Compared with the swirl nozzle and the ZSTWC type impact nozzle,the water saving is about 14% and the water saving is about 24%,which has obvious advantages in saving water.It is 6s and 4s faster than the swirling and ZSTWC type impact sprinklers respectively in extinguishing open fire,and the time to return to room temperature after extinguishing is 7s and 4s faster,which has certain advantages in extinguishing. |
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