S. Edward Law

AGRICULTURAL ELECTROSTATIC SPRAY APPLICATION: A REVIEW OF SIGNIFICANT RESEARCH AND DEVELOPMENT DURING THE 20TH CENTURY

Abstract Electrostatic force fields are currently exploited for beneficially increasing the deposition efficiency of finely divided particulate matter used as inputs in the production and processing of food and fiber crops satisfying basic human needs. This paper chronicles the scientific and engineering contributions of numerous researchers throughout the 20th century whose work has established both the fundamental basis and the technical implementation of reliable dust- and spray-charging methods and reviews various systems developed for electrostatic deposition of agricultural particulates. The paper is dedicated to Professor Emeritus Henry D. Bowen of North Carolina State University in recognition of his many years of creative leadership in agricultural electrostatics.

Electrostatic Pesticide Spraying: Concepts and Practice

The system requirements and characteristics necessary for the design and development of electrostatic-spraying machines uniquely adapted to agricultural pesticide applications are presented. The fundamental approach utilizes an electrostatic-induction nozzle to atomize pneumatically the spray (e.g., 30-50 ¿m volume median diameter (VMD)) and to charge the conductive liquid (e.g., 10¿1¿104 ¿m) typically to a ¿10-mC/kg. charge-to-mass level. Aerodynamic trajection then disperses the charged pesticide droplets deep into the electrostatically shielded plant canopies where the electric field of the interspersed clouds space charge (e.g., ¿20 ¿C/m3) is mainly relied upon for deposition. While the transient charge- transfer capability of living plants has been experimentally verified as adequate for electrostatic, spraying, gaseous discharges between sharp leaf tips and incoming charged spray clouds have been shown to introduce a deposit-limiting condition which is dependent upon plant morphology. Mass-transfer studies of the agricultural electrostatic spraying system have documented increases in droplet deposition efficiency ranging from two- to seven-fold onto various model and biological targets as compar, d with similar, uncharged sprays and with, conventionally applied sprays. Field evaluations of full-scale prototype electrostatic pesticide-spraying machines have verified the insect-control efficacy of electrostatic applications of 1/2-rates of pesticide to be equal to conventional spray application requiring full rates.

Electrostatic Deposition of Pesticide Spray onto Foliar Targets of Varying Morphology

ABSTRACT SPRAY deposition onto broccoli, corn, cotton and cab-bage foliage was measured for three distinct methods of application. In an air-carrier stream, charged vs. un-charged droplets provided 1.8-, 2.0-, 2.5- and 7.0-fold deposition increases, respectively. Charged vs. conven-tional spraying provided 1.9-, 2.9- and 4.4-fold increases on broccoli, cabbage and corn plants. A deposit limited condition was verified for electrostatic spraying of foliar targets exhibiting leaf point.

Electrostatic Deposition of Pesticide Sprays onto Ionizing Targets: Charge- and Mass-Transfer Analysis

Electrostatic deposition of charged pesticide sprays onto biological targets may be undesirably limited under certain operational conditions by gaseous-discharge currents induced to flow between the incoming charged spray cloud and grounded points on the target (e.g. leaf tips). Spray deposition and charge transfer onto idealized target models as functions of target characteristics and intensity of spray-droplet charging are quantified experimentally to achieve a more fundamental understanding of this phenomenon. As compared to similar uncharged sprays, deposition onto smooth spherical, and planar targets was increased up to seven-fold and three-fold, respectively, at optimum spray-charge levels. Space-charge induced target ionization from a 20-mm point protrustion self-limited this electrostatic deposition to only a 3.5-fold increase for the spherical target but caused little reduction for the planar target. As compared with a hydraulic-atomizing nozzle, the charging nozzle increased deposition approximately eight-fold and 24-fold, respectively, onto the spherical and the planar targets. The ratios of charge-to-mass collected on all targets were unexpectedly found to exceed values calculated for the airborne charged-droplet cloud, indicating a possible contact-discharge during elastic collision of conductive droplets at the target.

Bipolar Spray Charging for Leaf-Tip Corona Reduction by Space-Charge Control

Previous studies in the development of electrostatic crop-spraying technology have confirmed a process limitation due to gaseous discharges induced to flow from earthed plants under action of intensely charged pesticide spray clouds. This paper reports the development and evaluation of a bipolar spray-charging strategy introduced in an effort to further increase the electrodeposition efficiency of charged airborne spray droplets by minimizing corona discharge at prominent leaf tips of such target plants. It was hypothesized that a properly constituted bipolar spray cloud would eliminate this detrimental corona neutralization of the approaching spray by reducing to below threshold the space-charge electric field imposed at the periphery of the target-plant canopy, while still maintaining an adequate local space-charge field within the electrically shielded plant canopy to enhance droplet deposition. Veriable-frequency bipolar square-wave functions ranging from 12 to 36 Hz were input to an induction-charging nozzle to produce spray clouds having the desired space-charge characteristics. Results of experimental charge-and mass-transfer analyses document that the bipolar strategy successfully eliminated induced target-corona but failed to provide any electrodeposition benefit within shielded target zones. As compared with uncharged sprays, however, unipolar-charging enhanced the droplet deposition within similar targets by factors of 1.3- and 1.5-fold for corona and noncorona target conditions, respectively.

Control of Pathogenic Microorganisms and Turbidity in Poultry-Processing Chiller Water Using UV-Enhanced Ozonation

Abstract UV-enhanced ozonation experiments on unscreened overflow chiller-water from a commercial poultry-processing plant successfully compared the oxidative and bactericidal effects of four treatments (viz., O2/O3, O2 /UV, ( O2/O3/UV, and O2 as the control). Optimal treatments provided greater than 99.9% control of pathogenic microorganisms. Results far exceeded the USDA-FSIS requirements of at least a 60% reduction of aerobic plate count (APC) bacteria including similar reductions in coliforms and E. coli, as well as the maintenance of light transmission at a value no less than 60% that of fresh water, consequently permitting 90% recirculation of the required 0.5 gal (1.9 L) overflow per carcass. Also an additional synergistic reduction (≥0.8 Log CFU/mL) in APC bacteria was documented for ozone acting in concert with UV photons as compared with the sum of the effects of O3 and UV acting in series. Economic analysis of operational and maintenance costs for this UV-enhanced ozonation system estimates annual savings of ∼

Transient Charge Transfer in Living Plants Undergoing Electrostatic Spraying

244000 in a 1/4-million bird per day plant achieving water savings of 426000 L/day (113000 gal/day).

Depositional Characteristics of Charged and Uncharged Droplets Applied by an Orchard Air Carrier Sprayer

ABSTRACT MATURE cotton plants undergoing stress were sub-jected to three different types of varying electric fields so that the charge-transfer characteristics through these plants could be measured as a function of drought-stress severity. No significant reduction in the transient charge-transfer ability of the plants was observed as plant moisture ranged from field saturation to a level of stress beyond biological recovery. The research eliminated drought stress as a pertinent factor in scheduling the application of electrostatically charged pest-cide sprays.

Induction Charging Characteristics of Conductivity Enhanced Vegetable-Oil Sprays

ABSTRACT MASS-TRANSFER of fluorescent tracer onto front-sides and backsides of targets deployed throughout a large-scale grid was determined for comparison between charged and uncharged spray from air-atomizing electrostatic nozzles and uncharged spray from conventional hydraulic nozzles. Depending on target location, electrostatically charged spray achieved deposition increases ranging from 1.5 to 2.4-fold over uncharged droplets from the same air-atomizing induction-charging nozzles. The highest electrodeposition benefit was achieved on target backsides. Deposition of charged droplets did not surpass that achieved with 370 jum VMD (volume median diameter) droplets from conventional hydraulic orchard spraying nozzles. Suggested improvements to the electrostatic system included lowering the per-nozzle liquid flowrate to 160 mL/min to facilitate a 4-fold increase in droplet charging.

Perturbations of Charged-Droplet Trajectories Caused by Induced Target Corona: LDA Analysis

ABSTRACT THIS work extends the electrostatic-induction droplet-charging principle into the domain of usually nonconductive vegetable-oil-based sprays for pesticide application. Included are: (a) the theoretical and experimental analysis of physical properties determining chargeability by induction; (b) charge-transfer enhancement by incorporation of additives; and (c) verification of chargeability in currently developed induction spray-charging nozzles.