Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2003
Publication Date: 4/20/2004
Citation: Fox, R.D., Derksen, R.C., Zhu, H., Downer, R.A., Brazee, R.D. 2004. Collection Efficiency of Airborne Spray with Nylon Screen. Applied Engineering in Agriculture. 20(2): 147-152. Interpretive Summary: Accurate measurement of airborne spray drift is critical for scientists conducting research on spray drift. Results from such studies are used by regulator agencies such as US Environmental Protection Agency, and ultimately by growers and commercial applicators who apply pest control agents to agricultural and nursery crops. In this study, we evaluated several screens for their efficiency in collecting airborne spray droplets, similar in size (30 to 44 ìm diameter) to those found several meters downwind from a sprayed orchard or field crop site. Several air velocities (2, 4, and 6 m/s) were used in a wind tunnel study to simulate possible wind conditions that a grower may encounter. We found that a nylon screen with a porosity of about 56% was best. Then we compared the collection efficiency of the best screen with string, plastic tape, and paper - other materials often used to collect airborne spray. The screen was more effective than plastic tape and paper, and nearly as effective as string in collecting airborne spray droplets. Further studies compared the total amount of spray collected on a wall of screens with the total spray produced at the nozzle. Collection efficiency of the screens was about 120 to 130% based on the frontal area of the screen fibers. Theory predicts that the collection efficiency of similar cylindrical collectors should be about 90 to 100% for conditions similar to those used in this study. Thus measured drift values obtained using these screens must be corrected to accurately determine spray drift amounts. Spray drift values are used in writing regulations and experimental values are critical to approved application procedures. Thus these results are very important to state and federal regulatory agencies, to pesticides manufacturers, and to researchers who determine the best methods for reducing drift to a minimum.
Technical Abstract: Nylon filter screens of several porosity and fiber size were evaluated for effectiveness in collecting spray droplets. Droplets with volume median diameters of 30 and 44 µm, transported by air speeds of 2, 4, and 6 m/s were used. Collection efficiency of the best screen was compared to string and plastic tapes of several widths. This screen appeared to be nearly as efficient as strings and much better than plastic tapes, based on collection efficiency per unit frontal area. Total spray collected on an array of screens was compared to the total spray emitted from the air atomizing nozzles. Results were compared with the classic results of May and Clifford (1967). The screen collection efficiency was about 120% for 30 ìm droplets and 140% for 44 ìm droplets, using calculation methods similar to those of May and Clifford. Air velocities were measured with no screens and behind single screens, for a wind tunnel speed of 4 m/s and a nozzle air pressure of 138 Kpa (20 psi). Air speed behind screens with a porosity of 39% was about 50% of air speed behind screens with 53% porosity.