Blade pitch and air-outlet width effects on the airflow generated by an airblast sprayer with wireless remote-controlled axial fan

The airblast sprayers are equipped with a fan generating an air stream that helps the sprayed droplets to reach out and penetrate the tree canopy. Recently an automatic air regulation system has been developed and integrated in an airblast sprayer equipped with a conventional axial fan (900 mm diameter). This system, thanks to a wireless connection between a dedicated tablet and sprayers actuators, allows to remotely control the blade pitch and the air-outlet section, varying the characteristics of airflow generated by the fan. Therefore, the present work aims to characterize the different air streams derived from the combination of two fan outlet section widths (110 and 150 mm) and three blade pitches (20°, 25° and 30°). For each combination, the three components of air velocity (m s−1) were measured, taking as reference the plane following the theoretical trajectory of the main current leaving the fan. In this plane, velocities were measured at 1.0, 3.0, 5.0 and 10.0 m from the outlet section on both sides of the sprayer. At each distance, the velocities from 0.25 to 4.00 m in height were recorded. This same procedure was repeated in two planes parallel to the reference plane, 0.30 m behind and after respectively. Additionally, the velocities in the fan outlet section were also measured to obtain the airflow rate. In general, the outlet section and the blade pitch had a significant effect on the velocity components. An outlet section of 110 mm meant a smaller airflow rate and a higher initial velocity, while with 150 mm the airflow rate reduced and the initial velocity decreased. Velocities could be bigger by enhancing the blade pitch. The turbulence intensity was similar at 1.0 m distance in all cases.