Droplet Drift Research Articles

Glyphosate Susceptibility of Different Life Stages of Three Fern Species

Abstract Glyphosate, a systemic herbicide, is used against weeds in agricultural fields as well as against invasive plants in pastures, forest plantations, and urban environments. Its frequent and widespread use can negatively impact the surrounding natural non-target vegetation following the accidental drift of spray droplets, leaching, or persistence as residues in the soil. Because ferns possess a life cycle with independent sporophytic and gametophytic generations, herbicides may cause a different impact on each life stage. The objective of the present study was to evaluate the effect of four concentrations of glyphosate (0.33, 0.65, 2.72, and 10.89 g active ingredient L-1) and water as control treatments on spores, gametophytes, and two sporophyte size classes of one native (Blechnum appendiculatum Willd.) and two introduced fern species in Mexico (Macrothelypteris torresiana (Gaudich.) Ching and Thelypteris dentata (Forssk.) E.P. St.John). Spore germination was evaluated 10 days after herbicide trea...

Perturbation theory for propagating magnetic droplet solitons

Droplet solitons are strongly nonlinear, inherently dynamic structures in the magnetization of ferromagnets, balancing dispersion (exchange energy) with focusing nonlinearity (strong perpendicular anisotropy). Large droplet solitons have the approximate form of a circular domain wall sustained by precession and, in contrast to single magnetic vortices, are predicted to propagate in an extended, homogeneous magnetic medium. In this work, multiscale perturbation theory is used to develop an analytical framework for investigating the impact of additional physical effects on the behaviour of a propagating droplet. After first developing soliton perturbation theory in the general context of Hamiltonian systems, a number of physical phenomena of current interest are investigated. These include droplet–droplet and droplet–boundary interactions, spatial magnetic field inhomogeneities, spin transfer torque induced forcing in a nanocontact device and damping. Their combined effects demonstrate the fundamental mechanisms for a previously observed droplet drift instability and under what conditions a slowly propagating droplet can be supported by the nanocontact, important considerations for applications. This framework emphasizes the particle-like dynamics of the droplet, providing analytically tractable and practical predictions for modern experimental configurations.

Electrically Enhanced Condensation II: Effects of the Electrospray

The effect of electrospray-produced microdroplets on the condensation of polar vapor is investigated theoretically and experimentally with a steam condenser. The phenomena considered include the equilibrium of electrically charged microdroplets with the vapor phase, and the electrohydrodynamic vapor flow induced by the drift of charged droplets. The experimental investigation of electrospray-supported condensation confirms a significant, 57%, improvement in condensation rate.

DEVELOPMENT OF FRACTAL ULTRA-HYDROPHOBIC COATING FILMS TO PREVENT WATER VAPOR DEWING AND TO DELAY FROSTING

Superhydrophobic films fabricated on copper and aluminum surfaces have potential applications to solve water condensation and frosting problems on chilled ceiling system. The rough surfaces of copper foils obtained by solution immersion method exhibit the existence of fractal structures. The hydrophobicity of copper surfaces is enhanced with fractal structures. The relationship between contact angles (CAs) and the fractal dimensions (FDs) for surface roughness of Cu samples with different etching time is investigated. Moisture condensation and frosting experiments on the two kinds of surfaces are conducted in natural environment under different chilling temperatures. During condensation, micro water condensate droplets drift down the surface like dust floating in the air. Several larger condensate droplets about 1–2 mm appear on the substrates after 3 h condensation. This continuous jumping motion of the condensate will be beneficial in delaying frosting. The results demonstrate that dense nanostructures on copper surfaces are superior to loose lattice-like microstructures on aluminum surfaces for preventing the formation of large droplets condensate and in delaying the icing. The large water droplets of 2–3 mm in diameter that would form on a common metal foil are sharply decreased to dozens of microns and small droplets are formed on a modified surface, which will then drift down like a fog.

Influence of spray characteristics on potential spray drift of field crop sprayers: A literature review

Spray drift is a practical consequence of agricultural spraying operations. Because of the agronomical and environmental impacts of this phenomenon, drift has been widely studied and extensive information is available. Here we present a literature review on the relationships between global physical descriptors of agricultural sprays, air conditions and resulting drift, generally studied in wind tunnels. Basic physical factors are droplet size, droplet velocity, and the physicochemical characteristics of the sprayed product. When possible, data available in the literature are collated to draw trends. Contradictory information sometimes appears especially regarding droplet velocity and drift control. The main physical factors consist generally of medians such as Volume Median Diameter (VMD or Dv50) that do not always represent the heterogeneity of a spray and especially the spatial distribution of particle size and velocity. Technological parameters such as nozzle height, spray angle, travel speed are then related to initial physical factors and their contribution to driftability of sprays.

Numerical modeling of the drift and deposition of droplets emitted by mechanical cooling towers on buildings and its experimental validation

A CFD numerical modeling for simulating the drift emitted by mechanical cooling towers located in built-up urban areas is presented. The averaged Navier–Stokes equations for the air motion are discretized through a finite volume method, with the k–ɛ model to simulate the turbulent flow. An appropriate set of boundary conditions is employed, in order to avoid the non-homogeneity problem in the Atmospheric Boundary Layer (ABL). A Eulerian–Lagrangian model is used to simulate the air–water droplet motion, taking into account the effects of evaporation. The results are validated with experimental data of the deposition of droplets emitted by a pilot cooling tower, obtained through a technique based on water sensitive papers. Local meteorological data are measured through a meteorological tower adjacent to the cooling tower. The present study shows the influence of variables such as the ambient dry bulb temperature, the ambient specific humidity and the droplet exit temperature from cooling tower on the water droplet deposition and on the size of the affected area for mechanical cooling towers. The numerical procedure has proved useful for obtaining the outlined objectives.

Environmental fate model for ultra-low-volume insecticide applications used for adult mosquito management

One of the more effective ways of managing high densities of adult mosquitoes that vector human and animal pathogens is ultra-low-volume (ULV) aerosol applications of insecticides. The U.S. Environmental Protection Agency uses models that are not validated for ULV insecticide applications and exposure assumptions to perform their human and ecological risk assessments. Currently, there is no validated model that can accurately predict deposition of insecticides applied using ULV technology for adult mosquito management. In addition, little is known about the deposition and drift of small droplets like those used under conditions encountered during ULV applications. The objective of this study was to perform field studies to measure environmental concentrations of insecticides and to develop a validated model to predict the deposition of ULV insecticides. The final regression model was selected by minimizing the Bayesian Information Criterion and its prediction performance was evaluated using k-fold cross validation. Density of the formulation and the density and CMD interaction coefficients were the largest in the model. The results showed that as density of the formulation decreases, deposition increases. The interaction of density and CMD showed that higher density formulations and larger droplets resulted in greater deposition. These results are supported by the aerosol physics literature. A k-fold cross validation demonstrated that the mean square error of the selected regression model is not biased, and the mean square error and mean square prediction error indicated good predictive ability.

Numerical Simulation of the Air-Assisted Boom Spraying and Droplets Transporting Process

The conflict between increasing the deposition on target and reducing off-target losses in conventional pesticide spraying is an issue. It has been confirmed that air-assisted spraying can effectively reduce the drift compared to the conventional spraying. The work presented here reports on the numerical simulation of an air-assisted boom spraying and droplets transporting process. The purpose of this study is to understand the gas and droplet two-phase flow fields and analyze the spraying distribution and droplets transporting under the different given operations of air assistance. The air-assisted spraying drift potential decreases with air-jet velocity. As the air-jet velocity is higher than 25m/s, the accretion of droplets on the upper surface of crop canopy focus on narrow areas. Air -assistance can reduce the drift of small droplets (50-200μm) effectively. In all cases, the angle between the air-jet and the nozzle is 0° or10°.

CFD Simulation of Spraying with Air Jet

Droplet drift is always an accompaniment of pesticide spraying and can cause serious consequences. In this paper, we used a computational fluid dynamics software package (FLUENT) to analyze flow fields of spraying with air jet under different conditions in the tunnel model, and compared the effect of air jet on spray deposition and drift. Results of this study indicate that air jet can act directly on the spray droplets and affect their distribution and movement. Larger jet velocity has better performance on the drift reduction and droplet deposition. Droplets in the flow fields with larger jet velocity can get more kinetic energy and arrive at the root of crops easilier. When droplets are released straight down, larger velocity of droplets can be given and better performance can be achieved either in terms of drift reduction or droplet deposition.

CFD Simulation of Spraying with Air Jet

Droplet drift is always an accompaniment of pesticide spraying and can cause serious consequences. In this paper, we used a computational fluid dynamics software package (FLUENT) to analyze flow fields of spraying with air jet under different conditions in the tunnel model, and compared the effect of air jet on spray deposition and drift. Results of this study indicate that air jet can act directly on the spray droplets and affect their distribution and movement. Larger jet velocity has better performance on the drift reduction and droplet deposition. Droplets in the flow fields with larger jet velocity can get more kinetic energy and arrive at the root of crops easilier. When droplets are released straight down, larger velocity of droplets can be given and better performance can be achieved either in terms of drift reduction or droplet deposition.

Deposition of Aerially Released Bt over a 2 km Sampling Grid

A data set was collected to determine the downwind distance at which currently used near-field mechanistic pesticide deposition models (as formulated in AGDISP 8.26) should hand off to long-range pesticide drift models. This article presents the collected data as well as some comparison to existing, near-field deposition models. A 2 km 2 km grid of deposition samplers was deployed in the basin and range country of central Utah. Twenty aerial Bt spraying trials were undertaken. The trials showed very little deposition at 2 km downwind, but measurable material was detected in some of the tests at that distance. Mass balance was attempted but ranged from below 0.1 to over 2 due to high uncertainty in both the method and the collection efficiency of the samplers. Nevertheless, mass balance showed a strong trend with atmospheric stability in these trials, and results indicate that much material lofted out of the sampling domain during trials undertaken in unstable atmospheric conditions. This study confirms the inability of the Lagrangian model as formulated in AGDISP to adequately model fine droplet drift at distances beyond approximately 250 m depending on ambient conditions. A second article will describe the evaluation and configuration of a long-range pesticide drift model interfaced with AGDISP.

Combustion of thermite systems in thin layers with an open surface

SHS combustion of thermite compositions in the form of thin layers without formation of a continuous layer of cast products is studied. It is shown that combustion of thin layers of high-temperature compositions can be accompanied by almost complete dispersion of liquid-phase combustion products. The height of filling material and the caloric content of the mixture are effective parameters to control the size of the dispersed particles of cast synthesis products. It is established that the macrostructure of synthesis products is formed in the vicinity of the combustion wave through coalescence and capillary drift of metal droplets.

EVAPORATION AND WIND DRIFT LOSSES DURING SPRINKLER IRRIGATION INFLUENCED BY DROPLET SIZE DISTRIBUTION

ABSTRACTIrrigated agriculture is often criticized for its poor resource‐use efficiency in the case of sprinkler systems in comparison with localized irrigation. Water losses due to evaporation of droplets during flight and wind drift of droplets out of the target area are often generalized regardless of the context in which they were measured, and may reveal the evaporation capacity of the measurement facility rather than that of the irrigation system itself. Using an approach combining in situ measurement (rainfall, electric conductivity) and simulations, losses were estimated according to droplet size distribution. Droplets less than 1 mm in diameter displayed the highest losses. Losses due to evaporation represented 30‐50% of total loss; the remaining 50–70% were due to wind causing small droplets to drift outside the target zone. With a Rain Bird 46 sprinkler, total losses for the different periods of the day should not represent more than 20% at any time, or less than 4% for a 24‐h irrigation period in the climate conditions that prevail in summer in the south of France. Copyright © 2011 John Wiley & Sons, Ltd.

Spray drift as influenced by meteorological and technical factors

The objective of this study was to investigate spray drift from a conventional field sprayer as influenced by meteorological and technical factors, and to provide spray operators with data on which to base sound judgements when applying pesticides. The study was conducted in grazing fields and cereal crops. Interpreting the results from 15 field trials under varying meteorological conditions using different boom heights and driving speeds indicates that, during normal spraying conditions, the most decisive factors influencing the total spray drift (TSD) will be boom height and wind speed, followed by air temperature, driving speed and vapour pressure deficit. One important finding was that TSD (within the encompassed range of meteorological conditions and a boom height of 0.4 m) could be expressed as a simple function of the fraction of droplets ≤ 100 µm. In cereal crops: TSD = 0.36 + 0.11× [fr. (d ≤ 100 µm)] and in grazing fields, TSD = 1.02 + 0.10× [fr. (d ≤ 100 µm)]. In most cases a fraction of the airborne drift passed over the 6 m sampling mast located 5 m downwind of the spray swath. Under specified conditions, the present results indicate a simple relation between the total spray drift and volume fractions of droplets ≤ 100 µm. Given the nozzle type, it was concluded that the most decisive factors determining TSD are wind speed and boom height. Evaluating the relative importance of the meteorological and technical factors contributes to increasing knowledge in this field of research.

A constitutive equation for droplet distribution in unidirectional flows of dilute emulsions for low capillary numbers

The concentration distribution of droplets in the unidirectional flow of an emulsion for small capillary numbers (Ca) can be written as a balance between the drift flux arising from droplet deformation and the flux due to shear induced migration. The droplet drift flux is modeled using the O(Ca) theoretical results of Chan and Leal [J. Fluid Mech. 92, 131 (1979)], while the flux due to shear-induced migration is modeled using the suspension balance approach of Nott and Brady [J. Fluid Mech. 275, 157 (1994)], whereby particle migration is ascribed to normal stress gradients in the flowing dilute emulsion. In the limit of vanishingly small capillary numbers, the leading order contribution of the normal stresses in dilute emulsions arises from droplet-droplet interaction and thus scales as ϕ2τ, where ϕ is the droplet volume fraction and τ is the local shear stress. In our model, the normal stress calculations of Zinchenko [Prikl. Mat. Mekh. 47, 56 (1984)] are connected to our gradient diffusivity data computed from droplet trajectories [M. Loewenberg and E. J. Hinch, J. Fluid Mech. 338, 299 (1997)] via a reduced droplet mobility to derive the droplet flux due to shear-induced migration. As an example, the model is applied to the tube Poiseuille flow of a dilute emulsion at small Ca. It is demonstrated that the unsteady concentration distribution of droplets resulting from arbitrary time-dependent average velocity obeys a self-similar solution, provided the thickness of the droplet-depleted region near the walls is always nonzero.

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.

Spray Droplet Size, Drift Potential, and Risks to Nontarget Organisms from Aerially Applied Glyphosate for Coca Control in Colombia

A wind tunnel atomization study was conducted to measure the emission droplet size spectra for water and Glyphos (a glyphosate formulation sold in Colombia) + Cosmo-flux sprays for aerial application to control coca and poppy crops in Colombia. The droplet size spectra were measured in a wind tunnel for an Accu-Flo nozzle (with 16 size 0.085 [2.16 mm] orifices), under appropriate simulated aircraft speeds (up to 333 km/h), using a laser diffraction instrument covering a dynamic size range for droplets of 0.5 to 3,500 μm. The spray drift potential of the glyphosate was modeled using the AGDISP spray application and drift model, using input parameters representative of those occurring in Colombia for typical aerial application operations. The droplet size spectra for tank mixes containing glyphosate and Cosmo-Flux were considerably finer than water and became finer with higher aircraft speeds. The tank mix with 44% glyphosate had a D v0.5 of 128 μm, while the value at the 4.9% glyphosate rate was 140 μm. These are classified as very fine to fine sprays. Despite being relatively fine, modeling showed that the droplets would not evaporate as rapidly as most similarly sized agricultural sprays because the nonvolatile proportion of the tank mix (active and inert adjuvant ingredients) was large. Thus, longer range drift is small and most drift that does occur will deposit relatively close to the application area. Drift will only occur downwind and, with winds of velocity less than the modeled maximum of 9 km/h, the drift distance would be substantially reduced. Spray drift potential might be additionally reduced through various practices such as the selection of nozzles, tank mix adjuvants, aircraft speeds, and spray pressures that would produce coarser sprays. Species sensitivity distributions to glyphosate were constructed for plants and amphibians. Based on modeled drift and 5th centile concentrations, appropriate no-spray buffer zones (distance from the end of the spray boom as recorded electronically ±5%) for protection of sensitive plants were 50–120 m for coca spray scenarios and considerably lower for poppy spray scenarios. The equivalent buffer zone for amphibia was 5 m. The low toxicity of glyphosate to humans suggests that these aerial applications are not a concern for human health.

Deposition of Aerially Applied Spray to a Stream within a Vegetative Barrier

Drift of aerially applied forest herbicides can result in chemical deposition to streams. Riparian vegetation is expected to attenuate drift, but there is little corresponding data. A field study was conducted in the Coast Range west of Corvallis, Oregon, to evaluate the effectiveness of forested riparian buffers. The buffers studied are typical of those used for small and medium fish-bearing streams in western Oregon as mandated by the Oregon Forest Practices Act. A helicopter sprayed two tracers over four transects. Twenty trials were conducted, resulting in over 1400 tracer samples. Results confirm that these vegetative barriers are effective at reducing deposition into streams. Reduction of deposition on artificial foliage samplers placed immediately above the stream surface ranged from 37% to 99% and averaged 92%. Reductions were less clear in stable atmospheric conditions due to low wind speed and highly variable wind directions. Low wind speed conditions are not generally high-drift scenarios, but there is evidence that drift of suspended droplets beyond the barrier, comprising a small fraction of the total mass, increases in stable conditions.

Investigation of liquid droplets drift affected by side airflow

Investigation of liquid droplets drift affected by side airflow

SWAT developments and recommendations for modelling agricultural pesticide mitigation measures in river basins

Pesticides are useful for agriculture because of their ability to protect crops against pests. At the same time, excessive loading of pesticides in water bodies can produce toxic conditions that harm sensitive aquatic species, and render the water unfit for human consumption. Therefore, measures need to be designed, evaluated and undertaken in order to reduce pesticide pollution. In this study we focus on the Nil catchment, a small basin situated in the centre of Belgium. The necessary database and a watershed model (Soil and Water Assessment Tool—SWAT) were available to simulate different agricultural management scenarios. In order to make the model accurately predict pesticide loading to the river and instream transport, it was necessary to make several modifications to the source code. Special attention was given to implement an estimator for point losses (e.g. cleaning of spray equipment) and droplet drift, and improve the representation of physical processes in filter strips. The closing of mass balances is also described. Once the model was modified and calibrated, it could be used to simulate the pesticide mitigation strategies and evaluate their effectiveness. The simulation results revealed that strip-cropping seems to be more efficient than the sowing of cover crops, contour farming, the construction of filter strips, a 40% reduction of point losses and finally conservation agriculture. Several recommendations are given for further improvement of SWAT for management use.