Influence of outlet size on atomization characteristics of internal mixing air atomization nozzles
[Objective]Pneumatic forces play a significant role in facilitating liquid fragmentation and atomization.At low injection pressures,air flow can enhance liquid atomization,thereby greatly improving the atomization effect.This study aims to optimize the spray effect by analyzing the impact of the outlet size of internally mixed air atomization nozzles on their atomization characteristics.Leveraging a custom-designed air atomization spray experimental platform,actual measurements were conducted on gas-liquid flow rates,atomization angles,droplet sizes,droplet velocities,and other characteristic parameters for air atomization nozzles with different outlet sizes.We then performed a comparative analysis of the experimental results.[Methods]This study utilized a gas flowmeter and a liquid flowmeter to measure the changes in gas-liquid flow rates under seven different outlet sizes(1.0,1.5,2.0,2.5,3.0,3.5,and 4.0 mm).A high-speed camera analyzed patterns of changes in atomization angles and effective atomization ranges.Additionally,a laser particle size analyzer and a particle image velocity instrument examined the distribution patterns of droplet sizes and droplet velocity characteristics within the jet field.[Results]Comparative analysis of the experimental results revealed that as the outlet size increased,the water flow rate of the nozzle gradually increased.When the outlet size continued to increase,the trend of water consumption growth gradually leveled off,exhibiting a logarithmic growth pattern.At constant water supply pressure,the water flow rate was inversely proportional to the air supply pressure.Conversely,at air supply pressure,the water flow rate was directly proportional to the water supply pressure.The gas flow rate increased linearly with the enlargement of the outlet size,with the change slope being inversely proportional to both the air supply pressure and the water supply pressure.Increasing the nozzle outlet size reduced the exit resistance of the air cap,causing the pressure in the mixing chamber to decrease.Consequently,the pressure difference between the mixing chamber and the water supply and air supply pipelines increased,resulting in higher water and gas flow rates of the nozzle increasing with the enlargement of the outlet size.As the latter increased,the gas-liquid ratio continuously decreased.The atomization angle rapidly decreased with the increase in the outlet size while the effective atomization range continuously increased.When the water supply pressure was set at 0.200 MPa,and the air supply pressure was set at 0.200,0.250,and 0.300 MPa,the Sauter mean diameter(SMD)increased by an average of 20.1％,23.3％,and 31.5％,respectively,for each 0.5 mm increase in nozzle opening size.However,when the outlet size reached 3.0 mm,further increases did not significantly increase the SMD but rather decreased it.Specifically,as the nozzle outlet size increased from 3.0 mm to 4.0 mm,the SMD decreased by an average of 7.1％,13.4％,and 16.6％,respectively,for each 0.5 mm increase in opening size.With both air and water supply pressures set at 0.200 MPa,the particle size distribution was close to a normal distribution when the nozzle outlet size was small,resulting in a relatively concentrated droplet diameter distribution.As the outlet size increased,the droplet diameter distribution gradually deviated from the normal distribution,shifting from a concentrated to a more divergent pattern.Observations of the droplet velocity cloud maps at different nozzle outlet sizes revealed that as the opening size increased from 1.0 mm to 2.5 mm,the maximum velocity also continuously increased.When the opening size reached 3.0 mm,the droplet velocity began to decrease with further increases in the outlet size.This trend was consistent with a decrease in the atomization region area and the atomization angle as the opening size increased.[Conclusion]For internal mixing atomization nozzles,increasing the outlet size reduced the exit resistance of the air cap,lowered the pressure within the mixing chamber,and gradually increased both the gas and water flow rates.With every 0.5 mm increase in opening size,the gas flow rate increased by an average of 6.9％,while the water flow rate increased by an average of 14.23％.The increase in water flow rate was greater than that of the gas flow rate,leading to a gradual decrease in the gas-liquid flow rate ratio of the nozzle.Consequently,the unit volume of liquid received less energy from the compressed air,leading to incomplete droplet fragmentation and an increased SMD.
air atomization sprayoutlet sizeflow characteristicsatomized particle sizedroplet velocity
万方数据
维普
