Measuring Droplet Size of Agricultural Spray Nozzles-Measurement Distance and Airspeed Effects

Abstract

With a number of new spray testing laboratories going into operation and each gearing up to measure spray atomization from agricultural spray nozzles using laser diffraction, establishing and following a set of scientific standard procedures is crucial to long-term data generation and standardization across the industry. It has long been recognized that while offering ease of use as compared to other methods, laser diffraction measurements do not account for measurement bias effects due to differential velocities between differing sized spray droplets, and in many cases significantly overestimate the fine droplet portion of the spray. Droplet sizes and velocities were measured for three agricultural flat fan nozzles (8002, 8008, and 6510) each at three spray pressures (138, 276, and 414 kPa) at four downstream distances (15.2, 30.5, 45.7, and 76.2 cm) across a range of concurrent air velocities (0.7-80.5 m/s). At air velocities below 6.7 m/s, large gradients in droplet velocities resulted in overestimation of both the 10% volume diameter (Dv0.1) by more than 10% and the percent volume of the spray less than 100 µm (V<100) was overestimated two-to threefold. The optimal measurement distance to reduce droplet measurement bias to less than 5% was found to be 30.5 cm with a concurrent air velocity of 6.7 m/s for measuring droplet size from ground nozzles. For aerial spray nozzles, the optimal distance was 45.7 cm. Use of these methods provides for more accurate droplet size data for use in efficacy testing and drift assessments, and significantly increases inter-lab reproducibility.

Spray particle drift mitigation using field corn (Zea mays L.) as a drift barrier

“…Water alone and a solution of water plus 0.6 ppm of 1,3,6,8‐pyrene tetra sulfonic acid tetra sodium salt (PTSA) fluorescent tracer (Spectra Colors Corporation, Kearny, NJ, USA) were also included in the treatment list. Solutions were prepared with a 93.5 L ha −1 carrier volume and applications were performed at a constant wind speed of 6.7 m s −1 . Temperature (20 °C) and relative air humidity (60–70%) were recorded during application measurements.…”

Measuring Spray Droplet Size from Agricultural Nozzles Using Laser Diffraction

“…The spatial bias is reduced when testing nozzles in a concurrent airstream of 13 m/sec and with the measurement location located an appropriate distance from the nozzle, as the combination of these two parameters results in homogeneous droplet velocities throughout the spray cloud 4 . Further, the spatial bias is small (5% or less) for aerial nozzle testing due to the high concurrent airspeeds evaluated 7,8 . To determine the optimal test method to reduce the spatial bias with our current low and high speed wind tunnel facilities, the series of reference nozzles used to determine agricultural spray size classifications 9 were evaluated for droplet size using both laser diffraction and imaging methods 10 .…”

Optimization of variables for maximizing efficacy and efficiency in aerial spray application to cotton using unmanned aerial systems

“…Spray application quality is commonly assessed by the droplet size spectrum, deposition density, percentage coverage and distribution uniformity across the swath [29,30] . In the present study, cotton defoliant sprays were assessed based on droplet coverage and CV [31,32] . CV was calculated to evaluate the distribution uniformity of droplets at each sampling point using the follow calculation formulae [33] :…”