P. C. H. Miller

Effects of formulation on spray nozzle performance for applications from ground-based boom sprayers.

Abstract The performance of agricultural spray nozzles has components relating to the droplet size and velocity distributions within the spray, spray structure, entrained air characteristics and the spray volume distribution pattern. The interaction of these physical performance parameters has been shown to influence target retention, efficacy and the risk of drift. Results from a number of studies have also shown that the physical properties of the spray liquid have a substantial effect on spray formation such that changes in formulation type can give changes in spray characteristics that would be equivalent to doubling the flow rate through conventional hydraulic flat fan nozzles. The interactions between the physical properties of the spray liquid and the characteristics of the spray formed is a function of nozzle design. However, analysis of a large data set for a range of types of hydraulic pressure nozzle has shown that sprays formed from liquids based on emulsions generally have a coarser droplet size distribution compared with sprays formed from surfactant solutions. Although some correlation between dynamic surface tension and viscosity with spray droplet size has been established, the results from work reviewed in this paper suggest that other factors also influence the spray formation process. Air induction and twin-fluid nozzles mix air and liquid in the spray formulation process to produce droplets with air inclusions. These nozzle designs have been found to have a performance that is more sensitive to changes in spray liquid properties compared with hydraulic pressure nozzles and to exhibit trends that are different from those of conventional nozzle types.

EFFECTS OF SOME AGRICULTURAL TANK-MIX ADJUVANTS ON THE DEPOSITION EFFICIENCY OF AQUEOUS SPRAYS ON FOLIAGE

Abstract The effects of 10 commercially available tank-mix adjuvants on the retention and coverage of aqueous sprays on foliage were examined quantitatively under track sprayer conditions, following application at their maximum recommended rates. Substantial enhancement of fluorescein retention was observed only on water-repellent barley and peas, but the differences in performance between the additives were considerable. Addition of the water-soluble tallow amine and nonylphenol surfactants gave the largest increases in retention, whereas there was little improvement in efficiency compared with water alone after inclusion of either the latex- or pinolene-based products or ammonium sulphate. Retention enhancement was also achieved using the mineral oil, vegetable oil, methylated vegetable oil and phospholipid ECs and the organosilicone surfactant, but this was often much less than that obtained for the water-soluble surfactants; the best EC was the methylated vegetable oil which also had the highest emulsifier content. Although spray quality was altered significantly in the presence of many of the adjuvants, modifications to this parameter alone could not account for changes observed in deposition efficiency, because retention enhancement was recorded in sprays with volume median diameters both smaller and larger than water. There was a better correlation between retention efficiency and the dynamic surface tension of the corresponding spray liquids, with the exception of the organosilicone, which, as expected from its high surface activity, gave essentially complete spray coverage on leaves. Nevertheless, good coverage could still be achieved by adding the two water-soluble surfactants, as well as the methylated vegetable oil and phospholipid ECs. Coverage performance of the other adjuvants tested was poor in comparison, reflecting, in part, their inferior retention enhancing properties.

The effect of some adjuvants on sprays produced by agricultural flat fan nozzles

Abstract Six commercially-available agricultural spray adjuvants were mixed with water and sprayed through a medium quality flat fan nozzle to evaluate their effect on the spray formation process and droplet size distributions. Droplet size and velocity distributions were significantly changed. Ethokem, which reduced droplet sizes and LI-700, which increased them, were selected for more detailed study with medium and fine quality flat fan nozzles. The adjuvants significantly affected the variation of droplet size within the spray and the thickness of the spray fan. Photographs showed that the mechanism of spray formation was changed by the addition of LI-700 and that droplets containing Ethokem had air inclusions.

How surface tension of surfactant solutions influences the characteristics of sprays produced by hydraulic nozzles used for pesticide application

Abstract The sprays produced by hydraulic agricultural nozzles are influenced by the surface tension of the spray liquid, but models of spray formation relate only to pure liquids with constant surface tension. The way surfactant solutions affect spray formation is studied by investigating sprays of pure liquids compared with a range of surfactant solutions. Some surfactants caused changes in the appearance of the liquid sheet produced by the nozzles, which did not occur with pure liquids, and smaller spray drop sizes than pure liquids, suggesting that other surface properties may also be important.

Techniques for measurement of droplet size and velocity distributions in agricultural sprays

Abstract Two techniques for measuring the size and velocity of droplets in agricultural sprays produced by hydraulic flat fan nozzles have been evaluated for their ability to produce consistent results. These were a one-dimensional phase Doppler particle analyser (PDA) and a two-dimensional imaging probe of a Particle Measuring Systems (PMS) instrument, both measuring velocities in a single plane and operated in conjunction with a computer-controlled nozzle transporter to enable the whole spray to be sampled. The different operating principles of the instruments resulted in different droplet size and velocity distributions in relatively dense, polydispersed sprays. PDA gave consistently lower values for the volume median diameter and higher droplet velocities than PMS. PMS gave lower percentages of spray volume in droplets less than 100 μm in diameter, while the PDA indicated some large droplets that were not detected by PMS. The required sample size was smaller for PMS (3000 droplets) than for PDA (13,000 droplets). Both instruments are useful for measuring the characteristics of agricultural sprays, providing that their limitations are recognized. Appropriately configured, such systems enable droplet size and velocity distributions, entrained air velocities, droplet trajectories and the spatial structure of sprays to be determined.

A Review of Computer Models for Pesticide Deposition Prediction

This article reviews approaches to analytical pesticide deposition modeling for aerial, ground boom, and orchard airblast sprayer applications, and describes modeling approaches including the Lagrangian model commonly used for aerial spraying, which tracks the mean position and standard deviation of spray material released into the ambient environment. This review also describes the approaches used in mechanistic ground sprayer modeling, including near-nozzle effects and spray sheet obstruction of the ambient flow. The random-walk approach for ground spraying and the significant computational fluid dynamics (CFD) problem associated with modeling orchard airblast spraying are also described. These mechanistic approaches predict the spray deposition downwind from an application area for any set of initial conditions, and can recover results consistent with field datasets. Incorporation of spray deposition modeling into a Geographic Information System (GIS) platform is also discussed.

Wind tunnel velocity profiles generated by differentially-spaced flat plates

Abstract Production of linear shear with low turbulence level in a wind tunnel provides a convenient environment for testing the results of computational fluid dynamics simulations and equipment calibration. Boundary layer flow over a flat plate at zero incidence provides controlled deceleration of the approach flow according to plate length, with interacting boundary layers between adjoining flat plates merging to provide fully developed duct flow. In this way, an array of differentially-spaced flat plates can be used to modify a uniform wind tunnel velocity field to a specified velocity profile. A one-step iterative scheme is offered to determine plate spacings for simulation of weakly sheared flows, constrained by zero vertical pressure gradient in the downstream flow (representative of boundary layer conditions). The scheme is tested for realisation of uniform shear flow (maximum velocity variation ±10% of centreline velocity) by wind tunnel simulation, and produces reasonable results, at least comparable with previous studies.

Dynamics of Turbulent Air-Flow in Droplet Driven Sprays

This paper presents a study of the fundamental mechanics of droplet and gas motion in sprays. Only vertical sprays are considered and our theoretical analysis identifies two main flow zones, corresponding to where the droplet velocity is much greater than or of the same order as the induced air velocity . Analytical asymptotic results for the induced air velocity for small and large downstream distances confirmed a full numerical calculation and also agreed with experimental results. The second half of the paper deals with some of the most important aspects of spray jets in a cross flow. We find that the ratio of the cross-wind speed to the induced air jet speed U 0/V j is a crucial factor for specifying the dynamical behaviour. We present results for an axi-symmetric spray in uniform cross flow for both weak and strong cross-winds.