D. L. Reichard

Simulation of Drift of Discrete Sizes of Water Droplets from Field Sprayers

The drift distances of water droplets from field sprayers were determined for several variables with a computational fluid dynamics computer program. The simulation variables for drift distances up to 200 m included: droplet size (10 to 2000 mm), wind velocity (0.5 to 10.0 m/s), initial droplet velocity (0 to 50 m/s), discharge height (0.25 to 4.0 m), temperature (10° to 30° C), relative humidity (10 to 100%), and 20% turbulence intensity. Except at low temperature and high relative humidity, all 50-mm-diameter and smaller droplets completely evaporated before depositing 0.5 m below the point of discharge for all simulated conditions. Drift distances increased with increasing wind velocity and discharge height, but decreased with increasing initial downward droplet velocity for 100-mm-diameter and larger water droplets. Changes in ambient temperature and relative humidity had much greater influence on drift distances of water droplets less than 100-mm-diameter than on 200-mm-diameter and larger droplets.

NOZZLE WEAR RATES AND TEST PROCEDURE

ABSTRACT The wear rates of fan spray tips were determined. Both nominal capacity and construction material greatly influenced wear rates of the tips. Equations were developed for relationships between usage times and changes in flow rates through the tips. The percentage increase in flow rates for all brass, nylon, and stainless steel tips varied approximately with square root of time of use. Test results indicated that hours of use before 10% increase in flow rate increased rapidly with increased capacities of brass, stainless steel, nylon, and plastic tips. For all capacities tested, stainless steel tips were used an average of 5.6 and 2.1 times longer than brass and nylon tips, respectively, before flow rates through the tips increased ten percent. To reduce large variations in nozzle wear test results, a standard method for measuring nozzle wear rates was developed.

DRIFTSIM, A Program to Estimate Drift Distances of Spray Droplets

A BASIC language computer program (DRIFTSIM) was developed to rapidly estimate the mean drift distances of discrete sizes of water droplets discharged from atomizers on field sprayers. This program interpolates values from a large database of drift distances originally calculated with a flow simulation program (FLUENT). The simulations of drift distances up to 200 m (656 ft) included temperatures (10° to 30° C; 50° to 86° F), discharge heights (0 to 2.0 m; 0 to 6.56 ft), initial downward droplet velocities (0 to 50 m/s; 0 to 164 ft/s), relative humidities (10 to 100%), wind velocities (0 to 10.0 m/s; 0 to 32.8 ft/s), droplet sizes (10 to 2000 mm), and 20% turbulence intensity. The program requires about 15.5 Mb of disk space. Variables can be either in metric or English units and input can be either individual droplet sizes or size classes with portion of volume in each class.

DROPLET SIZE DISTRIBUTIONS ACROSS THE FAN PATTERNS OF NEW AND WORN NOZZLES

Droplet size spectra characteristics across the fan-patterns of new and worn nozzles with different capacities and constructed of different materials were investigated. Initial flow rates of the nozzles were 0.8, 1.5, 2.3 and 3 L/min, and the materials were brass, nylon, plastic, stainless steel and hardened stainless steel. Droplet size distributions from new nozzles with the same flow capacity, but constructed of different materials, were approximately the same. The weighted volume median diameter (_D_ v.5) of the spray distribution from each nozzle was determined from the volume of liquid spray and droplet size distribution at 2 cm intervals across the swath (41 points). The _D_ v.5 of all new nozzles, regardless of material, increased linearly as capacities of the nozzles increased. The _D_ v.5 was generally greater for worn than similar new nozzles.

SPRAY DEPOSIT PATTERNS OF AN ELECTROSTATIC ATOMIZER

The deposit patterns of spray droplets, relying primarily on electrostatic and gravitational forces for transportation and subsequent deposition, were investigated. Deposit distributions of charged sprays were measured in a wind tunnel and on artificial plants. The results indicate electrostatic forces can be used to improve the deposit efficiency of spray droplets but an additional force is required to improve canopy penetration and reduce drift susceptibility of airborne charged droplets.

Pesticide Tracers for Measuring Orchard Spray Drift

Airborne spray and ground level deposits of permethrin were measured downwind from semi-dwarf apple trees sprayed with an orchard air sprayer. Collectors were located from ground level to an elevation of 10 m (32.8 ft) and out to 240 m (787 ft) downwind from the sprayed tree row. A mixture of permethrin and water was sprayed at 468 L/ha (50 gal/acre) during nine passes on days 1, 2, and 3. The wind was light and variable on day 1 but wind speed was about 4 to 6 m/s (6.4 to 9.7 mile/h) on days 2 and 3. Ground level deposits decreased as downwind distance increased. On day 1, no permethrin was detected beyond 60 m (197 ft) from the tree row. At 30 m (98 ft) from the tree row, deposits on Line 1 (sprayed without trees) was about the same as deposits on Lines 2 and 3 (sprayed through trees). Airborne spray permethrin deposits were affected by wind speed; at all sample sites, deposits on strings at elevations from 1.5 to 4.5 m (4.9 to 14.8 ft) were less when wind speed was less. At the 60 m (197 ft) location, deposits tended to be more uniform over elevation than at locations closer to the sprayed trees. In general, deposits on string decreased with increased elevation.

Air Jet Velocities From a Cross-flow Fan Sprayer

Transverse profiles of air velocity were measured along the jet centerlines at 0.05 to 6 m (0.16 to 20 ft) from the outlet of a two-unit, cross-flow fan orchard sprayer. Velocity profiles were obtained for fan speeds of 1080 and 1476 rpm and with the upper fan both vertical and inclined downward 20° from vertical. Observed maximum velocities along the lower jet centerline agreed with those predicted by a plane jet model. Outlet air velocity at 1476 rpm was about 1.6 times the velocity at 1080 rpm. For an inclined upper fan, air velocities at the lower elevation increased 10% at 3 m (9.8 ft) from the outlet. When the upper fan was inclined 20°, the interaction of the two jets appeared to form a persistent flow field in which velocities alternately increased and decreased over the range from 0.15 to 1 m (0.49 to 3.3 ft) from the outlet. The inclined upper jet apparently deflected the top of the lower jet toward the ground, which may tend to keep spray-droplets near the ground and thereby reduce drift loss from spray operations.

Deposition and Effectiveness of Charged Sprays for Pest Control

ABSTRACT EXPERIMENTS were conducted to determine the effects of various parameters on the deposition and distribution of charged spray on artificial targets and bean plants in the laboratory. The overall ratio of charged to uncharged spray deposit on a two-leaf artificial target was 2.27:1. For a multi-level artificial target, charged sprays provided better distribution of deposits than uncharged sprays and generally provided greater total deposits at air atomizing pressures of 138 kPa and below. Sprays from the electrostatic nozzle controlled insects in cabbage and broccoli plots as well as sprays from a hollow cone pattern nozzle. With a systemic herbicide and calm wind, charged sprays controlled grass as well as sprays from fan pattern nozzles.

A Video Analysis System for Measuring Droplet Motion

A motion analysis system for measuring position, velocity, and acceleration of spray drops was developed. The system operates at synchronous rates from 15 to 180 fields/s, but by use of a high-speed strobe as a shutter, multiple images per field (picture) permit droplet tractories to be captured. Pictures of droplets from 500 to 3000 µm in diameter, moving at velocities from 50 to 500 cm/s (1.6 to 16 ft/s)can be stored. The system captures successive images of a spray drop in motion in one field; then drop position is measured as a function of time, and velocity and acceleration of spray drops can be calculated. Examples of captured fields and calculations are given.

Computerized Weighing System for Analyses of Nozzle Spray Distribution

ABSTRACT AN automated computerized weighing system, developed to analyze spray distributions across spray patterns for various nozzle operating conditions provides a means of rapidly evaluating the effects of several variables on spray distributions. Complete measurement and evaluation of a spray pattern, including graphic representation of distribution and coefficient of variation versus nozzle spacing requires approximately 10 min. The distribution patterns and coefficient of variation results obtained with the electronic weighing method were consistent, the repeatability was good and the results generally were comparable to patternator results.