Experiment On Atomization Characteristics Of Micro-Atomizing Nozzle And Numerical Simulation Research

As we all know,coal plays the predominant role in the energy mix for a long time,which is determined by current energy status in China.What’s more,with the development of mine mechanization,underground dust pollution become increasingly serious.Though Spray dustsettling technology is widely used in coal mines,the dust reduction effect of traditional spray equipment is less well,especially the dust removal efficiency of respirable dust.Therefore,the current situation needs to be solved urgently.In this research,the atomization characteristics and dust reduction effect of Micro-atomizing nozzles are systematically studied through the combination of theoretical analysis,experimental research and numerical simulation.This type of nozzle has improved and enhanced the dust reduction effect of respiratory dust.The main research contents and achievements are as follows:Through investigation and actual measurement,three kinds of Micro-atomizing nozzles such as FA,FF,NN,etc.were selected and the atomization characteristics experiments were carried out.The effective range,atomization angle,flow coefficient,droplet particle size and other parameters of the nozzle under the combination of 30 working conditions formed by 6kinds of water supply pressure such as 0.5,1.0,2.5,2.5,3.0 MPa and 5 kinds of outlet diameter such as 0.4,0.7,1.1,1.5,1.9 mm are obtained.After analyzing the experimental data,the following conclusions are drawn: under the same outlet diameter,the nozzle flow and effective range of the three kinds of nozzles increase with the rise of water supply pressure,with the decrease of the particle size of the droplets.With the increase of water pressure,the atomization angle of the FA and NN nozzles increases first and then decreases,and the atomization angle of the FF nozzle increases in the same process.Fixed water supply pressure,nozzle flow,droplet particle size and atomization angle all increase with the increase of outlet diameter,while the effective range decreases.In terms of macro atomization characteristic parameters,FA and NN nozzle data performed better.In terms of droplet particle size,the median diameter and the average diameter of the NN nozzle are lower when the outlet diameter is less than 1.1 mm,and the FA nozzle droplet particle size is lower when the nozzle diameter is greater than 1.1 mm.Combined with the comprehensive consideration of spray system economy and safety,the NN nozzle of 0.7 mm caliber is preferred for further research.The nozzle flow and atomization angle data in the atomization characteristic experiment are set to the initial parameters to perform numerical simulation of the NN nozzle.The results showed that the axial velocity of the droplets increased with the rise of the water supply pressure,and the average axial velocity in the 0.5-1.5 MPa water pressure section increased by 10.5%,and then it tended to be flattened out,with an average increase of only 3%.With the increase of the gap between the droplet and the nozzle outlet,the axial velocity of the droplet decreases rapidly,with a decrease of more than 50%,in the same process,the particle size of the droplet decreases first and then increases,and the decreasing range is 0.4 to 0.8 m from the nozzle.The numerical simulation results show that the average velocity of droplets is between15.26 and 25.93 m/s in the range of 0.4 to 0.6 m from the nozzle,and the proportion of droplets in the effective dust reduction rate range is the highest.At a water supply pressure of 3.0 MPa,the proportion of droplets in the optimal dust reduction particle size range is the highest,with an average of 87.07%.Therefore,the optimal dust reduction interval of the 0.7mm diameter NN nozzle is determined to be 0.4～0.6 m from the nozzle outlet,and the corresponding water supply pressure for the best dust reduction condition is 3.0 MPa.Through the dust reduction experiment,it is found that the dust concentration and distribution before and after the spray section are quite different,and the dust reduction effect is remarkable,especially for the graded dust reduction efficiency of respiratory dust is higher than the full dust efficiency.In general,the dust reduction efficiency of full dust and respiratory dust increases with the increase of water supply pressure.The water pressure increased from 0.5 MPa to 3.0 MPa,and the efficiency of full dust and respiratory dust increased by 43.14% and 27.36%,respectively;when the water pressure is 3.0 MPa,the full dust and respiratory dust reduction efficiencies both reach their peaks,which are 76.05% and78.66%,respectively.Therefore,the experimental results show that the optimal dust reduction conditions derived from the simulation data are scientific and reasonable.