Study On The Effect Of Nozzle Inlet Fillet On The Performance Of Internal-mixing Air Atomization

At high gas-liquid relative velocity,internally mixed air atomization relies on the strong shear force of the gas and liquid surface to atomize the liquid into small droplets.Its main advantages include high atomization quality,low requirements for liquid properties,large orifice flow cross-section,and blockages are not likely to occur.In recent years,internally-mixed air atomizing nozzles have been widely used due to their excellent atomizing effect,and have also attracted the attention of many researchers.However,due to the extremely complicated process of internal-mixed air atomization,its complete and systematic research is still not in-depth.The main factors affecting the atomization quality are liquid properties,nozzle geometry,and operating conditions.In order to improve the nozzle atomization effect by optimizing the nozzle structure parameters at low cost,the fillet of the nozzle inlet was selected as the research object.The full text uses CFD numerical simulation,experimental research,and theoretical model verification to analyze the impact of the inlet fillet change on the entire air atomization process.The research scope covers the complete process of air atomization from the internal flow of the orifice to the first fragmentation to the second fragmentation.Internal flow simulation research found that the fillet inlet radius has a significant effect on the flow state and outlet parameters in the hole.Increasing the fillet inlet radius can significantly reduce the inlet air pressure required to achieve the same ALR,and reduce the gas-liquid mass flow at the outlet.As the fillet increases,the gas-liquid velocity difference at the outlet increases continuously.Under the same operating conditions,when the fillet increases from 0 to 0.5,the turbulent kinetic energy of the two-phase flow inside the orifice increases significantly,the turbulent viscosity decreases,the gas density decreases slightly,the gas velocity at the outlet increases less,and the liquid velocity decreases.Obviously,the gas content does not change much.When the fillet continues to increase to 1,the increase in the turbulent kinetic energy of the two-phase flow inside the orifice is small,there is almost no change in the turbulent viscosity,the gas velocity at the outlet increases greatly,the liquidvelocity does not change much,and the gas content increases.The spray macro-characteristic test found that with the increase of the rounded corners,the liquid fragmentation did not change significantly under the small ALR,and the spray cone angle increased significantly;under the large ALR,the place where the liquid once cracked occurred more and more away from the center of the nozzle The closer it is,the smaller the effect of the fillet.Theoretical model research verifies that the physical parameters calculated by CFD are more in line with the test law.The model calculation shows that the outlet liquid film decreases continuously with the increase of the fillet;the primary fragmentation model has a certain error under the small ALR,and is more accurate under the large ALR.The test of spray micro-characteristics found that in the spray field near the nozzle,the change of the fillet has a great influence on the initial fragmentation SMD under different working conditions,and the SMD decreases with the increase of the fillet.In the fog field at an axial distance of 15 cm,as the fillet increases,the droplet distribution of the secondary atomization field is more uniform,the number of small droplets increases,and the atomization effect becomes better;under the same working conditions,the SMD varies The rounded corners increase and decrease,but the SMD after the second fragmentation only has a greater impact under a small ALR,and all tend to weaken as the ALR increases.