A random-walk model for dispersion of heavy particles in turbulent air flow

Walklate, P. J.

doi:10.1007/bf00121873

Cited by 66 publications

(39 citation statements)

References 22 publications

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“…Droplet transport (Walklate 1987;Ghosh and Hunt 1998) and spray drift potential (Holterman et al 1997;Mokeba et al 1997;Baetens et al 2007; Butler Ellis and Miller 2010) were described intensively and many solutions were proposed to reduce their adverse effects. However, mechanisms governing spray retention, which is the amount of sprayed product actually retained by plant leaves, are still misunderstood despite the growing interest of researchers.…”

Section: Introductionmentioning

confidence: 99%

The effect of surface orientation on spray retention

2014

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Research in precision spraying investigates the means to reduce the amount of herbicide applied by directing droplets more accurately towards the weeds. The trend in the development of spot spraying equipment is an increase of the spatial resolution and new actuators that are able to target very small areas. However, there is a lack of methods for assigning rates of herbicides relating target to optimal droplet features. A wide range of droplet impact angles occurs during the spray application process because of droplet trajectories and the variability of leaf orientation. In this study, laboratory experiments were conducted to highlight the effect of surface orientation on droplet impact outcomes (adhesion, rebound or splashing) on two very difficult-to-wet surfaces: an artificial surface with a regular roughness pattern and an excised black-grass leaf with an anisotropic roughness pattern. Measurements were performed for different surface orientations with a high-speed camera coupled with backlighting LED. Droplets of two formulations (distilled water and distilled water + a surfactant) were produced with a moving flat-fan hydraulic nozzle to obtain a wide range of droplet sizes and velocities, which were measured by image analysis. Increasing surface angle reduces surface area available for droplet capture. Droplet impact behaviors are then modified since surface tilt induces a tangential velocity component at impact and, consequently, a reduction of the normal component. Impact modifications have also been observed due to the anisotropic roughness pattern of a black-grass leaf.The integration of droplet-surface interaction information offers a significant way to further improve the precision spraying efficiency by considering the optimal droplet size, speed and ejection angle depending on the target surface and architecture.2

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Section: Introductionmentioning

confidence: 99%

The effect of surface orientation on spray retention

2014

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“…Csanady, 1964), models tracing a number of particles describing the interaction with turbulence in different ways (e.g. Gosman and Ioannides, 1981;Shuen et al, 1983;Walklate, 1987;Ichard and Melheim, 2010), and analytical reasoning revealing increased knowledge and reasonable parameterizations (e.g. Csanady, 1963).…”

Section: Parameterizationsmentioning

confidence: 99%

Dispersion and fall out of heavier particles

Astrup

2016

Radioprotection

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-Nuclear accidents have so far been expected to release gasses and aerosols, but other CBRN events and also nuclear accidents with release of core particles can be expected to also release larger particles to the atmosphere. If not so large and heavy, that they fall to the ground immediately they may like gasses and aerosols be transported more or less far by the wind. The present paper focuses on the growth of plumes of such particles larger and heavier than aerosols and transported by the wind. Implementation in existing decision support puff dispersion programs requires a parameterization of this growth, and two reasonable describing parameterizations have been found, one in the literature, one proposed here, and both are compared to experimental work found in the literature. The parameterization from the literature has been implemented in the dispersion program RIMPUFF, which has subsequently shown that the effect on fall out to a large extent overrules the effect on the dispersion of such particles.

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“…Deposition is optimized when the probability of a droplet to collide with the target is maximal considering the whole droplet size and velocity distributions. Physical transport of 10 droplets (Wang et al, 1995;Walklate, 1987) and spray drift potential (Holterman et al, 1997;Lebeau et al, 2011;Teske et al, 2002) have been investigated and modeled intensively based on spray characteristics (droplet size and velocity distributions) and environmental conditions (release height, meteorological conditions, etc.) to improve deposition.…”

Section: Introductionmentioning

confidence: 99%

Measurements of reference ISO nozzles by high-speed imaging

Cock

Massinon

Nuyttens³

et al. 2016

Crop Protection

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Agricultural spray characteristics determine the efficiency of a pesticide application because size and velocity affect droplet trajectory and impact behavior.At present, the relevance of different characterization techniques remains controversial since discrepancies may be significant between measurements performed in different laboratories.A digital image acquisition technique and analysis algorithm is proposed for droplet size and velocimetry measurements as an alternative to well-established techniques such as the Phase Doppler Particle Analyzer (PDPA) or laser diffraction spectrometry (LDS). The algorithm requires double exposed shadow images acquired in a back-lighted arrangement with a Particle Image Velocimetry (PIV) camera and a pulsed light emitting diode (LED). Spatial illumination heterogeneities are corrected by subtracting from each image a mean background acquired on several images without any particle. The algorithm accuracy is ensured by the rejection of out-of-focus particles using a focus parameter depending on gradient intensity at the particle edges. Thresholds for focus particle selection were determined by studying the evolution of the focus parameter and the error on particle size measurements from images containing droplets with * Corresponding author

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A random-walk model for dispersion of heavy particles in turbulent air flow

Cited by 66 publications

References 22 publications

The effect of surface orientation on spray retention

The effect of surface orientation on spray retention

Dispersion and fall out of heavier particles

Measurements of reference ISO nozzles by high-speed imaging

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