Experimental study of factors influencing the risk of drift from field sprayers Part 2: Spray application technique.

Recently, spray drift and its effects have become an important aspect of risk assessment in the registration process of pesticides in Belgium. In this regulation, drift reducing spray application techniques can be used to reduce buffer zones. The purpose of this research is to measure and compare the amount of drift sediment for different spray application techniques under field conditions. A drift prediction equation for the reference spraying was used to compare other spraying techniques with the reference spraying, under different weather conditions. Drift measurements were performed for several combinations of nozzle type (flat fan, low-drift, air injection) and size (ISO 02, 03, 04 and 06), spray pressure (2, 3 and 4 bar), driving speed (4, 6, 8 and 10 km.h-1) and spray boom height (0.3, 0.5 and 0.75 m). Nozzle type as well as spray pressure, driving speed and spray boom height, have an important effect on the amount of spray drift. Larger nozzle sizes, lower spray pressures and driving speeds and lower spray boom heights generally reduce spray drift. Concerning nozzle types, air injection nozzles have the highest drift reduction potential followed by the low-drift nozzles and the standard flat fan nozzles

Experimental study of factors influencing the risk of drift from field sprayers, Part 1: Meteorological conditions

Spray drift can be defined as the quantity of plant protection product that is carried out of the sprayed (treated) area by the action of air currents during the application process. This continues to be a major problem in applying agricultural pesticides. The purpose of this research is to measure and compare the amount of drift for different climatological conditions under field conditions. Sedimenting spray drift was determined by sampling in a defined downwind area at different positions in a flat meadow using horizontal drift collectors for a reference spraying. Meteorological conditions were monitored during each experiment. A drift prediction equation for the reference spraying was set up to predict the expected magnitude of sedimenting at various drift distances and atmospheric conditions. The measurements proved the important effect of weather conditions (temperature, relative humidity and wind speed) on the amount of spray drift. A lower wind speed or a higher relative humidity decreases the amount of spray drift. Taking into account the correlation between temperature and relative humidity, a lower temperature will also result in lower drift values due to the cumulative effect of relative humidity. This equation can be used to quantify the effect of meteorological conditions, to compare measurements using other spraying techniques under different weather conditions to the reference spraying and to perform spray drift risk assessments

Pore-scale numerical investigation of pressure drop behaviour across open-cell metal foams

The development and validation of a grid-based pore-scale numerical modelling methodology applied to five different commercial metal foam samples is described. The 3-D digital representation of the foam geometry was obtained by the use of X-ray microcomputer tomography scans, and macroscopic properties such as porosity, specific surface and pore size distribution are directly calculated from tomographic data. Pressure drop measurements were performed on all the samples under a wide range of flow velocities, with focus on the turbulent flow regime. Airflow pore-scale simulations were carried out solving the continuity and Navier–Stokes equations using a commercial finite volume code. The feasibility of using Reynolds-averaged Navier–Stokes models to account for the turbulence within the pore space was evaluated. Macroscopic transport quantities are calculated from the pore-scale simulations by averaging. Permeability and Forchheimer coefficient values are obtained from the pressure gradient data for both experiments and simulations and used for validation. Results have shown that viscous losses are practically negligible under the conditions investigated and pressure losses are dominated by inertial effects. Simulations performed on samples with varying thickness in the flow direction showed the pressure gradient to be affected by the sample thickness. However, as the thickness increased, the pressure gradient tended towards an asymptotic value

Comparison between indirect and direct spray drift assessment methods

The drift characteristics of 10 different spray nozzles were tested using three contrasting drift risk assessment means namely; phase Doppler particle analyser (PDPA) laser measurements, wind tunnel measurements (both indirect drift risk assessments) and field drift experiments (direct drift risk assessments). The effect of nozzle size (ISO 02, 03 04 and 06) and nozzle type (standard flat-fan, pre-orifice flat-fan, air-induction) on droplet characteristics, drift potential and field drift were studied. A comparison was made between the results from the indirect and direct measurements to evaluate their potential for predicting the losses occurring from pesticide drift from held crop sprayers. In total, 90 PDPA laser measurements, 46 wind tunnel experiments and 61 field drift experiments were carried out with 10 different spray nozzles at a pressure of 300 kPa. The reference spray application for the field measurements was defined as a Hardi ISO F 110 03 standard flat-fan nozzle at a pressure of 300 kPa with a nozzle or boom height of 0.50 m and a driving speed of 8 km h(-1); conditions that were used for each of the comparative assessments of the different nozzle-pressure combinations. Results showed that with the indirect risk assessments (wind tunnel and PDPA laser measurement), driftability experiments can be made with different spraying systems under directly comparable and repeatable conditions and that both methods are suitable for relative assessments of drift risk. Measuring the proportion of the total volume of droplets smaller than 75 mu m diameter was best suited to represent the drift reduction potential in the field with different nozzle-pressure combinations. This was followed by the wind tunnel approach numerically integrating the measured fallout deposit curve. Both wind tunnel approaches for measuring airborne spray gave inferior results. Based on these indirect drift measurements and a statistical drift prediction equation for the reference spraying, it was possible to come to a realistic estimate of field drift data at a driving speed of 8 km h(-1) and a boom height of 0.50 m. (C) 2009 IAgrE. Published by Elsevier Ltd. All rights reserved