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Title: Development of a system for determining collection efficiency of spray samplers

Author
item Fritz, Bradley - Brad
item Hoffmann, Wesley

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2007
Publication Date: 6/20/2008
Citation: Fritz, B.K., Hoffmann, W.C. 2008. Development of a system for determining collection efficiency of spray samplers. Applied Engineering in Agriculture. 24:285-293.

Interpretive Summary: Airborne movement of aerially applied agricultural sprays is generally quantified using a passive droplet collector. The efficiency with which this collector samples spray droplets is critical to interpreting the results, and is a function of spray droplet size and wind speed that moves the spray droplets. A low air speed, spray dispersion tunnel was constructed and evaluated for use in passive spray collector efficiency studies. The air speed and spray concentration profiles in the working section of the tunnel, as well as the proposed test protocol, were found to be sufficient for evaluating a sampler of unknown collection efficiency. The dispersion tunnel and testing protocols provide a method for determining collection efficiencies for a number of spray flux collectors used by researchers, thus allowing for more detailed and comparative analysis of field collected data.

Technical Abstract: A low speed spray dispersion tunnel was constructed and evaluated for use in passive spray collector efficiency studies. The dispersion tunnel utilizes an air-assisted nozzle to generate a spray cloud with a volume median diameter of about 20 um. The air velocities in the testing section of the dispersion tunnel are uniform over a range of 0.6-6.7 m/sec. Spray flux measurements in the tunnel showed that the spray flux was less uniform at lower air velocities (0.6 m/sec) than at higher air velocities (>2m/sec). A proposed methodology for testing collectors for collection efficiency was evaluated. This method used theoretical collection efficiencies of cylinders to determine actual spray flux measured by soda straws and monofilament line and then estimate the actual spray flux in the space between these two samplers. This testing showed that both the soda straw and monofilament collectors measured simlar actual spray fluxes in the center of the working section of the dispersion tunnel. The calculated actual spray fluxes, along with a known volume of spray, showed tunnel losses of 50% to 88%, with greater losses at lower airspeeds. The dispersion tunnel and testing protocols outlined in this manuscript will be used to conduct further collection efficiency studies for a number of spray flux collectors used by researchers.