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United States Department of Agriculture

Agricultural Research Service


Location: Application Technology Research Unit

2013 Annual Report

1a.Objectives (from AD-416):
Determine the effect of wind speeds on the evaporation rates of pheromone from standard releasers. Develop a computer simulation program, based on two-phase flow dynamic models, to determine spray off-target losses from air-assisted sprayers used in crop productions from trees.

1b.Approach (from AD-416):
Evaporation rates of pheromone droplets will be tested in a wind tunnel specifically designed for this investigation. Wind speed is the main variable. Fifteen load cell units installed in the wind tunnel will be used to measure evaporation rates of pheromone droplets. The study of pheromone evaporation rates, totaling 165 treatments, will include 11 constant air speeds ranging from 0 to 10 m/s, five pheromone releaser surface areas, and pheromones of three molecular weights. Ambient air temperature will be maintained at 25°C for all tests.

Computer simulation programs will be developed for the prediction of spray droplet deposition discharged from air-assisted sprayers under different microclimatic conditions. The programs will use the mathematical models and algorithms based on simulation results from a computational fluid dynamics program (FLUENT). Two-phase flow models with stochastic process under turbulent conditions will be developed and used in the computer simulation. Evaporation of droplet dispersal will be included in the models. A CAD program (Pro/ENGINEER) will be used to establish geometries of nozzles, sprayers and trees. The join-mapping technique will be used to incorporate the geometrics of sprayers and field targets into FLUENT for simulation. Variables in the models include wind velocity, turbulence intensity, canopy structure, ambient temperature, relative humidity, spray droplet size distribution, space ratios between droplets and air, sprayer structure and travel speed. The accuracy of the computer simulation models for air-assisted sprayers will be verified under controlled conditions in a wind tunnel and in orchard and nursery fields.

3.Progress Report:

This is the final report for this project. Pheromone evaporation rates were evaluated with three different types of liquid pheromones (Monochamus Alternatus Hope (MAH), Dendroctonus Valens LeConte (DVL), Flies sex attractant (FSA)), five release areas (50.2, 132.7, 254.0, 346.2, 660.2 mm2) and 11 wind speeds (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 m/s). The MAH and DVL were emulsion while FSA was oil-based emulsion. Tests were conducted in a wind tunnel. When wind speed was 0, 5, and 10 m/s, the MAH evaporation rates were 74.9, 678.1, and 1017.8 mg/h, and the DVL evaporation rates were 1.8, 218.2, and 480.1 mg/h, respectively. The evaporation rate of MAH and DVL increased as the increase of wind speed and release area. When wind speed increased from 0 to 5 m/s and then to 10 m/s, the evaporation rate of MAH with 50.2 mm2 release area increased from 6.4 to 8.8 mg/h and then substantially increased to 16.3 mg/h. With the same three wind speeds, the MAH evaporation rates were 74.9, 678.1, and 1017.9 mg/h when the release area was 660.2 mm2. However, the FSA evaporation rate was negative under all test conditions, which indicated that the FSA absorbed more ambient water than the amount of pheromone released. Also, wind speed and release area had little effect on the FSA evaporation. These results demonstrated that the release area influenced the emulsion pheromone evaporation rate more than the wind speed. Therefore, the relationship between the release area and the distribution density of emulsion pheromone containers should be established to ensure pheromones to effectively cover entire target areas in forest and field applications. Evaporation of oil-based emulsion pheromone should be further investigated by avoiding the interference of moisture absorption.

Air velocity distributions discharged from axial fans commonly used in air-assisted sprayers were simulated with a computational fluid dynamics program. The simulation included two fan inlet designs and three outlet designs constructed with a computer-aided design program program. In the simulation, the outlet was divided into one, two and three ports. A cluster of droplets were also released into the air flows to investigate droplet dispersions and flight distances. The computer simulation demonstrated the discharged air speed varied with the fan inlet and outlet shapes. With a conical frame in the inlet, the outlet air speed increased from 19 to 26 m/s. Droplet cloud distributions varied with the fan outlet shape. The droplet distribution in the air from three ports had much less variation than that from a single port. Second atomization of droplets in high air streams was also observed with the computer simulation.

This project addresses critical elements for increasing pest control efficiency with less pesticide use envisioned in ARS parent project Objective 2.1 “Determine how water droplets amended with spray additives, relative humidity and the morphological surfaces of leaves affect the droplet evaporation time, spread factor and residual pattern on leaves”, and Objective 1 “Develop precision sprayers that can continuously match canopy characteristics to deliver agrichemicals and bio-products accurately to nursery and fruit crops”.

Last Modified: 4/23/2014
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