Design of droplet size measuring system of air-assisted spraying and experiment on its influencing factors

In order to easily test droplet size in different spraying conditions, a droplet size measuring system of air-assisted spraying was designed. The system can accurately regulate nozzle position, spraying angle, spraying pressure and wind speed. The adjustment ranges of nozzle xyz three-dimensional position are 0-0.9, 0-0.8 and 0-0.7 m with adjustment accuracy of 0.04 mm, while the adjustment range of spraying angle is 0-360° with adjustment accuracy of 0.005°. The spraying pressure adjustment range is 0.2-0.5 MPa, and the relative error is not more than 1.5%. The wind speed adjustment range is 0-15 m/s, and the relative error is not more than 4.17%. The test results of influence of wind speed on droplet size show that the commonly used three statistics items D32、D43 and DV0.5 increase as wind speed rising, and the average rates of change of the three statistics are 2.62, 3.59 and 6.83 μm·s/m. When the wind speed increases from 3 to 15 m/s, the three statistics increase by 46%, 26% and 71% respectively. The test results of influence of spraying pressure on droplet size show that D32、D43 and DV0.5 increase as spraying pressure rising, and the average rates of change of the three statistics are -90.33, -232.3 and -300.2 μm/MPa respectively. When the pressure changes from 0.2 to 0.5 MPa, the three statistics decrease by 31%, 36% and 56%. It can be concluded that wind speed and spraying pressure affect droplets size much, and the influence should be considered when the two factors are controlled in spraying system.