| In the process of spraying in the manual painting workshop,a large number of paint mist diffuses and escapes into the air,forming overspray mist,which seriously pollutes the environment in the manual painting workshop and endangers the health of spray workers.Therefore,how to improve the utilization rate of paint,energy saving and emission reduction,and improve the paint room environment are urgent scientific problems to be solved.Therefore,in this paper,through the quantitative analysis of the whole flow field of the spray gun,the emission and escape characteristics of paint mist in the spraying process were experimentally studied,and on this basis,an efficient,convenient and applicable spray spray control technology-----was proposed to optimize the nozzle structure of spray gun and introduce protective annular air film flow outside the spray gun jet.The purpose of this study is to provide accurate experimental measurement data of spray flow field,guide the design of spray nozzle and improve the environment in spray shop.The main contributions and innovations are summarized as follows:1、In this paper,a large-scale PIV experimental measurement system was used to visualize and quantitatively analyze the whole flow field of the spray gun.The experimental measurement results show that the velocity at the exit of the spray gun quickly reaches 24m/s,and then it exchanges strong momentum with the surrounding air and produces a large velocity attenuation.In the working area about 25cm-30 cm away from the nozzle,the velocity at the center line decays to about 10m/s.The radial velocity shows the characteristics of radial diffusion and mixing of ambient air into the mainstream.In the area near the nozzle and jet boundary,the jet velocity fluctuates with high intermittentness.The vortex structure is studied by the λci criterion,and a large-scale structure is formed at the nozzle exit.In the far field,the large-scale structure is gradually broken into small-scale structures.The proper orthogonal decomposition(POD)reveals that the escape of paint mist is mainly caused by the strong shear of the paint mist jet with the surrounding air,forming a vortex structure,causing the entrainment and radial diffusion of the spray gun jet.3、By optimizing the structure of the spray gun nozzle,an annular air flow with a velocity higher than that of the paint mist jet is introduced outside the spray gun jet.The annular air flow isolates the paint mist jet from the ambient air,and the annular high-speed air flow is sheared with the paint mist to form an inner vortex and suppress the escape of paint mist.The speed ratio of the spray gun paint mist jet and the annular air flow is different,and the control effect of the paint mist is different.Therefore,a two-dimensional particle image velocimetry(PIV)system is used to quantitatively analyze the influence of the annular airflow on the spray flow field at six velocity ratios.The results show that the annular airflow suppresses entrainment and transfers turbulent kinetic energy and momentum to the spray gun jet,which is an effective source control method.Under our experimental conditions,when the velocity ratio is 1.19,the control effect has a great advantage,and the spraying efficiency of the spray gun is increased by about 15%. |
PDF Full Text Request