Law of spatial airflow velocity distribution for wide-swath air-blast sprayer

Abstract: Spraying droplet adhesion and deposition were affected by the external flow field distribution of the air-blast sprayer. The swath of an air-blast sprayer can be expanded through expanding the duct and elongating rectangular outlet. In this paper, a wide-swath air-blast sprayer was applied as the experimental platform and its external airflow velocity field was tested. The duct of the wide-swath air-blast sprayer used in the experiment was made up of a cylindrical segment, a contractive segment, and an expanding segment. An axial fan was installed inside the cylindrical segment, and there were a semi-elliptical fluid director and distributors in the contractive segment. One end of the expanding segment was connected with contractive segment and the other was a rectangle outlet. The long side of the rectangle outlet was vertical to the ground and the axis of the duct was parallel to the ground simultaneously when testing was conducted. The airflow speed field of the wide-swath air-blast sprayer was tested indoors. The airflow speed sampling points were located with a sampling frame made up of lattices (11×11cm), and the airflow speed field and spray swath were tested in cross-sections 1m, 1.5m, 2m, and 2.5m away from the outlet. The average of ten testing wind speeds at each sample point was taken as the final speed of that point. The free turbulent jet theory was applied for data analysis. The distribution and variation mechanism of the wide-swath air-blast sprayer airflow velocity were obtained. The experimental results indicated that the relationship between the axial longitudinal time-averaged wind speed and the air blast distance of the wide-swath air-blast sprayer took on an attenuated power function with the fan power supply in different frequencies. The axial longitudinal time-averaged wind speed was in line with the attenuated power function regular pattern to which the axial longitudinal speed of the three-dimensional free turbulent jet was submitted. The relationship between swath and air blast distance of the wide-swath air-blast sprayer presented a linear direction. According to the experimental data, the jet boundary curves were regressed. The top boundary curve and the bottom boundary curve of the jet along the outlet's long axis was not the same, as there was a vortex structure between the jet and the ground. The "virtual source," a point at which the top boundary and the bottom boundary intersected was not on the horizontal axis of the duct. The angle between the top boundary and the horizontal axis of the duct was 20.5°, while the angle between bottom boundary and the horizontal axis was 28.8°. Meanwhile, it was found that the two boundaries of the jet along the outlet's short axis were in keeping with the same regular pattern. The "virtual source," a point at which two boundaries intersected was on the horizontal axis of the duct, and the angles between the two boundaries and the horizontal axis of the duct were approximately 4.18° and 4.23° respectively. At cross-sections 0.5m, 1m, 1.5m, 2m, and 2.5m distances away from the duct outlet, the distributions along the outlet's short axis direction of the axial wind speed were similar. However, the distributions were not similar along the long axis direction. After a three-dimensional surface of airflow velocity field was reconstructed, two peaks of wind speed appeared along the long axis direction inside the boundary layer.