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Title: Effects of air speed and liquid temperature on droplet size

item Hoffmann, Wesley
item Fritz, Bradley - Brad
item BAGLEY, WILLIAM - Wilbur-Ellis Company
item Lan, Yubin

Submitted to: Journal of ASTM International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2011
Publication Date: 4/1/2011
Citation: Hoffmann, W.C., Fritz, B.K., Bagley, W.E., Lan, Y. 2011. Effects of air speed and liquid temperature on droplet size. Journal of ASTM International. 8(4):JAI103461.

Interpretive Summary: In response to continued stewardship efforts to mitigate spray drift, an increasing number of drift-reducing technologies are being developed and marketed for use with agricultural chemicals in aerial application treatments. With this growing market, there is a need to scientifically quantify and rate the effectiveness of these products in order to inform end users. Studies were conducted by ARS scientists to determine the effects of airspeed and spray solution temperature on the spray droplet size generated by different spray nozzles in a wind tunnel. The results showed that measured spray droplet size was significantly affected by airspeed and to a much lesser extent by liquid temperature. The implementation of these testing protocols will result in an improved and more equitable science-based evaluation program for drift reducing technologies and help applicators make equipment selection choices.

Technical Abstract: Advancements in both application hardware (e.g. nozzles and spray assist devices) and spray modification products have led to a number of products that are specifically designed to maximize the spray deposition and minimize off-target. Testing protocols are being developed to objectively measure spray drift reduction from a wide range of drift reduction technologies (DRTs) including spray nozzles, sprayer modifications, spray delivery assistance, spray property modifiers (adjuvants), and/or landscape modifications. Using a DRT evaluation protocol, the objectives of this work were to study the effects of different air speeds (i.e. air carrying droplets through the laser beam) on droplet size from different spray nozzles and spray solutions and to further evaluate the effects of differences in liquid and air temperature on droplet size at the different air speeds tested. Measured spray droplet size was significantly affected by changes in airspeed with the DV0.5 increasing by ~30-100 µm and the percent of spray volume less than 200 µm decreasing by 50% or more as the tunnel airspeed was increased from 0.5 to 6.7 m/s (1 to 15 mph), depending on the spray solution, spray nozzle, and air speed. The data also showed a lesser influence of temperature differential between the spray solution and ambient air, with the differences seen most likely resulting from changes in spray solution physical properties with the changes in liquid temperature. Most importantly, this study demonstrated that a reference nozzle evaluated under the same conditions resulted in the reduction in driftable fines while the DRT remained constant across all conditions tested. The use of a reference nozzle or system is critical to the success of any testing program that will be conducted at multiple test locations and under different operational conditions.