Spray Cloud Research Articles

On-target deposit and vertical distribution of aerially released herbicides

As a component of the Fallingsnow Ecosystem Project, glyphosate and triclopyr herbicides (Vision®, Release®) were each applied to four experimental spray plots at nominal rates of 1.5 and 1.9 kg a.e. ha−1 respectively. Empirical studies were undertaken on these plots with the objectives of; a) quantifying mean on-target deposit and variability b) assessing the vertical distribution of active ingredient deposits through the vegetative complex and c) comparing herbicide deposit estimates on excised natural foliage with those on proximal 2-dimensional (2D) and 3-dimensional (3D) collectors. Experimental conditions were representative of difficult aerial application scenarios since the spray plots were small (4.9 to 10.4 ha), with irregular boundaries of mature timber, and in some cases substantial topographical relief. Deposit analysis confirmed that, in some circumstances, locations well within target areas were missed completely owing to inappropriate track spacing or swath offset. Excluding these points from the data analysis, results demonstrated overall mean deposition (mean ± SE) of glyphosate and triclopyr on aspen foliage equating to 68.45 ± 6.13 and 50.28 ± 6.01% of the nominal application rates (1.5 and 1.9 kg ha−1), respectively. A high degree of variation in deposit both within and between plots demonstrate that variation in operational parameters (e.g. track spacing, offset, release height and aircraft speed) as influenced by local site factors (e.g. proximity of standing timber, topographical relief) can be important determinants in uniformity and accuracy of herbicide deposit. A consistent trend (P < 0.001) in the deposition profile through tiered vegetative canopies was observed, with greatest impingement of the spray in the upper target canopy as noted above, and average 25% and 12% in the shrub and ground-level tiers respectively. Results suggest that for sites characterized by complex canopies, differential vertical deposition may be an important factor constraining the potential use of lower herbicide application rates, particularly where shrub or groundcover species are important competitors. In contrast, given that only a small proportion of the spray cloud penetrates and impinges in the lower vegetative tiers, animals foraging or living therein may receive substantially reduced exposures, mitigating against any potential direct effects. In general, poor correlations (r = 0.22 to 0.78) in deposit estimates based on either two-dimensional or three-dimensional artificial collectors as compared to excised natural foliage were observed. Significant differences (P < 0.05) also were detected among deposit estimates with no consistent trend in relation to herbicide treatment, sampler type or sampling height. These comparisons suggest that none of the artificial collector types tested accurately or consistently estimated true foliar deposit. Key words: alternative conifer release treatments, Fallingsnow Ecosystem Project, glyphosate, herbicides, herbicide deposit, tending, triclopyr, vegetation management, vertical distribution

Special Features of the Combustion of a Propagating Flame in a Polydisperse Fuel Spray Cloud

Article Special Features of the Combustion of a Propagating Flame in a Polydisperse Fuel Spray Cloud was published on December 1, 1997 in the journal International Journal of Turbo & Jet-Engines (volume 14, issue 4).

Prediction of spray drift using insecticide tracers and two types of collector

Abstract Two insecticides, carbaryl and chlorpyrifos, were evaluated at low concentrations as tracers to predict the behaviour of spray clouds of malathion at field strength. Aerial sprays were produced from a Cessna Ag Husky equipped with a dual liquid dispersal system, spraying simultaneously. Spray drift was measured at 90 or 30 m downwind using 1.6 mm polyester cord and 0.6 mm monofilament line suspended from a helium‐filled blimp tethered 15.25 m above ground level. Recoveries of malathion averaged 87.3% and 85.2% of the amount predicted from the tracers on the monofilament and polyester, respectively. The coefficients of variation for 12 flights were 50.9% for the monofilament line, and 17.4% for the polyester cord.

Air blast and heat radiation from fuel-rich mixture detonations

Large scale experiments were carried out to study the effect fuel concentration on air blast parameters and heart radiation from gaseous detonations. Hemispheric plastic envelope (4 meters in radius) was used with propane-air mixtures containing from 4 to 7 vol. % of fuel. The expressions for overpressures and impulses were determined in Sachs variables. The effect of fuel concentration on blast parameters is shown to be insignificant for the same amount of oxygen in the mixture volume. Thus the blast wave parameters can be described as for stoichiometric mixtures using additional scaling for the explosion energy according to oxygen content (cloud volume). The results of large scale experiments with fuel spray clouds containing 0.16–100 tons of fuel with mean concentration from stoichiometric (C 0) up to 3C 0 are reconsidered. These results confirm the proposed scaling of air blast parameters for a wide range of fuel types, cloud volumes and fuel concentrations. Detonations of fuel rich gaseous mixtures result in a strong heat radiation. Heat radiation energy, time and size of the fireball formed are studied as a function of fuel concentration.

Superstructure spray and ice accretion on a large U.S. Coast Guard cutter

Superstructure spray flux and ice accretion were measured on a 115-m Coast Guard cutter in the North Pacific Ocean and the Bering Sea during February and March 1990. This was the first such measurement cruise on a large ship; all previous measurements were on trawlers and patrol boats. Spray event duration averaged 2.73 s, somewhat longer than events measured on a 35-m Soviet trawler. The drop number concentration of most spray clouds was high, ranging from 2.0 × 10 5 to 3.0 × 10 5 drops m −3. Spray cloud drop sizes ranged from 14 to 7700 μm, with a geometric median of 234 μm. Spray cloud liquid water contents had a very large range with a mean of 64.1 g · m −3. Ice accretion rates were low, but sufficient for observing greater ice thicknesses on decks than on bulkheads. The ice accretion process was also found to be extremely dynamic, alternately accreting and ablating several times before reaching maximum thickness. No simple relationships were found between time-series of ice thickness during two icing events and controlling environmental parameters.

Study of the droplet spray characteristics of a subsonic wind tunnel

A finite difference, two-dimensional potential flow solver, and a three-dimensio nal particle trajectory code have been written to compute water droplet trajectories in a subsonic incompressible flow wind tunnel. This method was used to study the spray cloud in the test section of a two-dimensional wind tunnel resulting from the injection of a distribution of water droplets in the settling chamber ahead of the inlet. The results of this computational study showed that the trajectories of the larger water droplets were affected by the droplet inertia and gravity more dramatically than that for the smaller particles. The calculated liquid water content across the test section indicated a high concentration near the tunnel centerline. The largest droplets were present at the test section only in the center one-third of the wind tunnel, whereas the smaller droplets spanned almost the entire test section width. This resulted in a computed droplet size distribution skewed toward the larger droplets in comparison with the initial Langmuir-D distribution. The distribution of particle sizes and concentrations required at the droplet injection point in the settling chamber for a Langmuir-D distribution of uniform liquid water content in the center third of the test section was computed.

The Transformation of Spatially Determined Drop Sizes to their Temporal Equivalents for Agricultural Sprays

A statement of formulation effects on atomization by agricultural nozzles is already a requirement for the registration of a new chemical or formulation in the USA and parts of Europe. The laser-based instruments used for obtaining such data can be divided into two types: those that analyse the sample signal either spatially or temporally. It is known that for agricultural nozzles operating from ground rigs without air assistance, spatial measurements of the spray cloud overestimate the small drop component. Consequently, spatially determined data can be used to separate different atomization methods and formulations on a qualitative, but not a quantitative, basis. Data acquired from temporal analyses of the drop spectra produced by agricultural nozzles using an Aerometrics PDPA 100-1D particle analyser are presented. The results show that for a given nozzle, there is a "coefficient" for each of the common spray descriptors (e.g. arithmetic mean, volume median diameter, etc.) whereby the spatially derived descriptor can be converted to its temporal equivalent, for a wide range of atomization pressures and formulations. Such "coefficients" would render spatially determined data more applicable to solving the problems involved in applying agrochemicals. However, these "coefficients" would have to be obtained in a manner applicable to spatial sampling methodology.

Pesticide application in relation to integrated pest management

Pesticides provide an important component of integrated pest management, but the timing, accuracy of dosage, and method of applying the pesticides need careful consideration to permit harmonisation with other control tactics. Concern about pesticide spray drift has led to categorising the spray quality of nozzles, which is defined by comparing the droplet spectra of selected reference nozzles measured with a laser light diffraction analyser. However, there is a conflict between a need for small droplets for increased biological efficacy and large droplets to reduce downwind drift. Registration authorities tend to favour a coarser spray with large droplets, and an untreated barrier area that can be left around a treated crop to protect sensitive crops downwind that can provide a refuge for natural enemies. In some circumstances, drift can be reduced with small droplets by electrostatically charging a spray. The charged spray needs to be released close to the crop to avoid the upward dispersion of droplets within a spray cloud due to mutual repulsion exacerbated by convective air movement. Increased deposition of charged sprays on the crop foliage is associated with less soil contamination which allows greater survival of ground-dwelling predators. This feature needs to be exploited by growing relatively narrow strips of a range of crops so that if one crop needs a pesticide treatment, natural enemies can be conserved in adjacent untreated crops. By careful selection of insecticides and dosage rates, these predators should be able to recolonise the treated area and thus integrate chemical with biological control. Application of more selective mycopesticides may require special formulations as well as particular droplet spectra. Pesticides can also be applied mixed with attractants such as pheromones, as a ’lure and kill’ technique.

Utilizing vortex behaviour to minimize drift

Abstract The ULV spray emitted from a TBM flying in a cross wind was mapped by a scanning lidar system. The fate of the spray cloud for 2 min after release from the aircraft was followed as the material was transported downwind of the flight line. Vertical scans at 6 s intervals with 1 m‐3 resolution provided detailed insight into the entrainment of the spray into the wing‐tip vortices and ultimate release to drift or deposit. Relative concentration, dosage and deposit profiles are presented for this cross‐wind case. Vortex lifetimes were found to be significantly different for the up‐wind and downwind vortices. The majority of the near field deposit was associated with the up‐wind vortex while the drift was linked to the down‐wind vortex.

Polymer and invert emulsifying oil effects upon droplet size spectra of sprays

Abstract A series of wind tunnel atomization studies were carried out to investigate the effects of polymer and invert suspension oil “drift control adjuvants” upon the droplet size distribution spectra produced by nozzles typically used in aerial and ground based spraying of pesticides. A D8–46 disc and core was used as a typical aerial application nozzle, and an 8003 fan nozzle was used for the ground based sprayers simulation. The droplet size spectra were evaluated in a wind tunnel using a Malvern 2600 laser particle size analyzer immediately upon mixing and at 15 minutes after re‐circulation through a pumping system. The addition of the polymer‐based adjuvants significantly increased the droplet size spectra parameters of the spray cloud, but all the polymer products showed signs of breakdown of their molecular arrangements in the liquid medium, as a result of agitation. The invert suspension oil adjuvant did not change the droplet size spectra markedly, nor did it show signs of breakdown of the inte...

Dose transfer of Bacillus thuringiensis from cabbage to the diamondback moth: A graphical simulator

Abstract The application of agrichemicals is a highly inefficient process and one of the main causes of the environmental and health risks currently associated with pesticide usage. Efforts to mitigate this inefficiency have largely been unsuccessful, due principally to the poor understanding of the processes involved in the spray application of pesticides, from atomization to biological effect. A generalized model of the application system for pesticides from atomization to biological result is described in this overview. The model allows the investigation of the biological consequences of altering the application parameters for the bacterial insecticide Bacillus thuringiensis when used against the diamondback moth (Plutella xylostella L.) with cabbage as the substrate. Parameters input into the model include the in‐flight droplet size frequency distribution of the spray cloud, spatial distribution of the deposit, spread and subsequent environmental degradation of the deposit, and behavioral and toxicolo...

The Effect of Ambient Gas Temperature and Density on the Development and Wall Impingement of High-Injection-Pressure Diesel Fuel Sprays

An investigation of the effect of ambient gas temperature and density on diesel fuel spray penetration, spray angle, and wall impingement at an injection pressure of 75–134 MPa was conducted in a constant-volume bomb with a reconstructed Cummins PT fuel system by using a high-speed photographic technique. The results show that penetration does not increase monotonically with injection pressure, and ambient temperature has more effect on a high-pressure spray than on those with conventional pressures. With the high temperature, the penetration of a high injection pressure spray is reduced a bit, while the spray angle increases obviously. When the high-pressure spray impinges on a wall at ordinary temperature, the rebounding droplets can hardly be seen, but at higher wall temperature, a cloud of dense spray will be observed near the wall, and sometimes a vapor layer will be formed between the spray and the wall. Based on experimental results, an empirical formula considering the effects of both the ambient temperature and injection pressure is presented.

Spray droplet velocity and energy in intermittent flow from hydraulic nozzles

Intermittent operation of a hydraulic atomization nozzle has been investigated as a potential method for flow control without distortion of droplet size spectra. This study investigated the effects of intermittent flow on the droplet velocity and energy within spray clouds from flat-fan nozzles. Spray cloud specific energy and kinetic energy median diameter, an energy analogue to the volume median diameter were developed as indicators of agricultural spray cloud behaviour. Droplet velocity and energy were slightly reduced and kinetic energy median diameter increased as intermittency increased. A doubly asymptotic, exponential function accurately described the relationship between droplet velocity and size in intermittent sprays from stationary nozzles. Simple adaptation of a continuous spray model to intermittent spray clouds did not result in accurate prediction of spray droplet velocities.

Off‐target glyphosate deposits from aerial silvicultural applications under various meteorological conditions

AbstractAerial spray applications of the herbicide glyphosate were made over a forest canopy under various meteorological conditions. A ‘Thru Valve Boom’ dispersal system carried by a Cessna 188 fixed‐wing aircraft flying at 49 m s−1 was used to generate an aqueous spray cloud with a volume median diameter of 150 μm. Glyphosate deposits from multiple overlaid crosswind line sources released at 10 m above ground level were measured on ground sheets and artificial foliage at downwind distances between 50 and 400 m. Trials were conducted in stable, neutral and unstable atmospheric boundary layers with average wind speeds between 2·2 and 5·7 m s−1 and vertical intensities of turbulence between 0·07 and 0·16. Linear regression lines fitted to logarithmically transformed measurements and downwind distances (x) gave statistically significant correlation coefficients (P = 0·01), and were compared by ANOVA. Glyphosate deposits on ground sheets and artificial foliage were attenuated at rates inversely proportional to x to the power 1·7‐4·3. Regression line comparison showed that, in general, deposits on ground sheets decreased with increasing wind speed and intensity of turbulence, and some statistically significant differences were found in slopes and elevations of regression lines from different trials. However, deposits at the 50‐m station increased with wind speed due to the large‐drop cloud component. Regression line comparison for deposits on artificial foliage showed that, in general, they were highest in the intermediate wind speed‐neutral stability case and similar in the high wind speed‐unstable and low wind speed‐stable boundary layers, although deposits at the 50‐m station also increased with wind speed.

Drop Size Spectra and Deposit from Aerial Spraying With and Without a Polymeric Adjuvant

In a study reported in the literature, an aqueous solution of a polymer, Sta-Put, was shown to increase the drop sizes of the spray cloud when atomized using hydraulic nozzles in an airstream (speed, 192 km/h) under laboratory conditions. The objective of the present study was to examine if Sta-Put can influence the drop size spectra of the spray cloud under field conditions when applied through rotary atomizers using a fixed-wing aircraft flying at a speed of 160 km/h. Tank mixes were sprayed aerially with and without Sta-Put. Size spectra of drops were measured at the target site on Kromekote cards. Deposits were assessed on balsam fir-shaped aluminum branch tips, natural fir needles, and glass plates.

Assessing the performance against houseflies of indoor aerosol space sprays. Part I. Factors examined during tests with houseflies in free flight

AbstractThe development of a mathematical model which, by quantifying the interaction of a population of houseflies with an ageing spray cloud, is capable of predicting the knockdown and kill performance of insecticidal aerosol formulations shown against houseflies, Musca domestica L., will be presented in a series of four separate papers. In this first paper, measurements were made of insecticide collected by houseflies during free flight using a standard room‐spray technique. With pressure‐packed aerosol formulations where the solvent is the principal change, it was shown that both knockdown and mortality responses of the insects were directly related to dose collected. The process of droplet collection was most significantly influenced by their size and availability, dependent upon the time after spraying, the position of insect release and the activity of individual adult M. domestica. The knockdown or mortality response of the insect to given amounts of insecticide was largely unaffected by the remaining solvent, although, with mineral oil, some inhibition was noted at low mortality levels. The amount of insecticide accumulated by houseflies in their initial flight was of prime importance in determining the overall effect. Flies remaining not knocked down at the end of the exposure period were shown to be so because they had accumulated less toxicant and not necessarily because they were more tolerant of the insecticide. The establishment of a relationship between the number of flies in flight and time after release has provided a key function for incorporation into the model.

Water droplet impingement on airfoils and aircraft engine inlets foricing analysis

This paper includes the results of a significant research program for verification of computer trajectory codes used in aircraft icing analysis. Experimental water droplet impingement data have been obtained in the NASA Lewis Research Center Icing Research Tunnel for a wide range of aircraft geometries and test conditions. The body whose impingement characteristics are required is covered at strategic locations by thin strips of moisture absorbing (blotter) paper and then exposed to an airstream containing a dyed-water spray cloud. Water droplet impingement data are extracted from the dyed blotter strips by measuring the optical reflectance of the dye deposit on the strips with an automated reflectometer. Impingement characteristics for all test geometries have also been calculated using two recently developed trajectory computer codes. Good agreement is obtained with experimental data. The experimental and analytical data show that maximum impingement efficiency and impingement limits increase with mean volumetric diameter for all geometries tested. For all inlet geometries tested, as the inlet mass flow is reduced, the maximum impingement efficiency is reduced and the location of the maximum impingement shifts toward the inlet inner cowl.

Role of physical factors on pesticide performance in forestry: An overview

Abstract Most modern pesticides are expensive. Application of excessive dosage rates is likely to cause undesirable biological side‐effects and is economically wasteful. Non‐uniform distribution of the spray cloud, or application at the wrong time, may result in failure to control the pest. It is the responsibility of the field operator to acquire sufficient knowledge and skill to ensure proper use of the control agents, to increase efficiency of their usage and to reduce unwanted side‐effects. To achieve this goal, he must take into consideration the various physical factors that govern field performance of pesticides. A simple relationship exists between the spray volume and emission rate used, and droplet size produced. The use of extremely low spray volumes (i.e., those less than 2.0 litre per ha) for forest insect control in Canada, as opposed to higher volumes used in agriculture, necessitates the release of fine droplets (ranging from 20 to 70 μm in diameter) to obtain adequate coverage of the target area. These droplets take a long time to sediment downwards, evaporate in‐flight, become smaller in size and/or form powdery residues, thus contributing to off‐target drift and impaired droplet adhesion to target surfaces. Physical factors such as rain washing, degradation by sunlight and erosion by wind also influence the longevity of pesticide deposits on foliage which is crucial during the critical period of pest control. Factors affecting the mode of entry into insects are related to the type of ingredients used in formulation. If a pesticide acts via crawling contact, formulations which would provide surface deposits would be more beneficial than emulsions or oil‐based mixes which tend to undergo penetration into foliar cuticle. Physical factors that affect field performance of a pesticide tank mix are related to phase separation and ‘breakdown of emulsions’ in the application equipment; ‘agglomeration and caking’ of wettable powder dispersions at the bottom of the tank; impaired flow behaviour of highly viscous formulations; and coarse atomization of high‐viscosity tank mixes leading to poor target cover.

Spray deposit patterns and persistence of diflubenzuron in some terrestrial components of a forest ecosystem after application at three volume rates under field and laboratory conditions

AbstractSpray deposit patterns and persistence of diflubenzuron [1‐(4‐chlorophenyl)‐ 3‐(2,6‐difluorobenzoyl)urea] in white pine (Pinus strobus L.) and sugar maple (Acer saccharum Marsh.) canopies, forest litter and soil were studied after aerial application of a 250 g kg−1 wettable powder formulation, ‘Dimilin® WP‐25’, at 70 g active ingredient (a.i.) ha−1, using three volume rates (10, 5 and 2.5 liters ha−1) over three blocks in a mixed forest near Kaladar, Ontario, Canada, during 1986. Spray droplets were sampled at ground level using ‘Kromekote®’ cards, and diflubenzuron deposits were collected on glass plates. Droplets were the largest (with a volume median diameter of 250 μm) at the 10 liters ha−1 rate, resulting in the highest number of droplets per cm2 on the Kromekote cards and deposits of diflubenzuron on glass plates. Deposits on foliage, litter and soil were also correspondingly the highest. At the 5.0 and 2.5 liters ha−1 rates, volume median diameter values were smaller (195 and 150 μm, respectively) and deposits on the substrates were markedly lower. In the spray block that received 10 liters ha−1, diflubenzuron persisted in foliage as long as 120 days after treatment, but it lasted for only about a week in forest litter and soil samples. At 5 and 2.5 liters ha−1, diflubenzuron failed to persist in foliage as long, and residues in litter and soil, which were barely above the quantification limit, persisted only for a few days.Laboratory studies, conducted under constant meteorological conditions using different droplet‐size spectra, showed that deposit levels were not affected when the volume median diameter of the spray cloud decreased from 253 μm to 145 μm, but were markedly reduced as this progressively decreased from 92 to 37μm. The dissimilarities between the field and laboratory findings were attributed to meteorological and other factors influencing droplet deposition on tree canopy in aerial applications of pesticides over forests.

DIELECTRIC BOUNDARY EFFECTS ON ELECTROSTATIC CROP SPRAYING

ABSTRACT An experimental study determined the passive effects of planar boundaries beneath idealized spray targets on the electrodeposition of spray onto the targets. The presence of grounded and dielectric boundaries positioned one diameter beneath 76-mm diameter spheres was found to significantly reduce spray deposition on the spheres. Reduction of mass transfer as compared to unbounded targets averaged 15.2 and 22.9% for the dielectric and grounded boundaries, respectively. Charge transfer and duration of the spraying event were similarly affected by presence of the boundaries. The dielectric film was observed to accumulate a surface charge during the spraying event and maintain the charge after the spray cloud had departed.