Assessment of Spray Drift and Droplet Size in a Centrifugally Air-Assisted Sprayer Utilising Particle Image Velocimetry Methodology

Abstract

This study focuses on the design and evaluation of a newly developed centrifugally air assisted spinning disc sprayer. The sprayer incorporates external fins that draw air in and direct the droplets downward, thereby helping to minimise spray drift, improve the precision of spray deposition and reduce unintended losses. The present work is performed for two different sprayer disc diameters viz., 60 mm and 80 mm. The study additionally includes experimental investigations examining factors such as disc speed, wind speed, flow rate and disc shape. In addition, droplet sizes were measured and the effectiveness of the spray was assessed in both intended and unintended areas. The 60 mm disc-diameter sprayer outperformed the 80 mm disc-diameter sprayer in all the examined conditions. At 2000 rpm, the highest recorded droplet size was 161 µm and over a range of 0 to 2 m, droplet deposition varied between 2.02 µL/cm² and 0.195 µL/cm². The average size of droplets measured at 3000 rpm was 128 microns and the droplet deposition varies between 1.375 µL/cm2 and 0.165 µL/cm2. Owing to their small mass and inability to overcome resistance, a portion of the droplet particles migrate upwards at different rotational speeds. The droplet behaviour in a centrifugal assisted sprayer may be affected by out-of-plane vibrations or wobbling of the spray mechanism. This phenomenon was observed over the rotational-speed range of 1000 to 3000 rpm. In the opposite direction, the deposition rate ranges from 0 to 0.3 µL/cm2. Overall, the findings provide useful guidance for the development of a rotating-disc sprayer with reduced spray drift.