Final report : farmer driven electrostatic low volume sprayer

The sprayer combines the principles of Controlled Droplet Application (CDA) and electrostatic charging to improve spraying efficiency. CDA emphasizes applying the correct and uniform size of droplets to use minimum volume and dose to achieve effective control. Electrostatically charged spray drops get attracted to the plant target and hence deposition is increased. The sprayer consists of a spinning-disc with an induction-type electrostatic charging system, mounted into a PVC pipe handle. The induction charging method was used because it has a low power requirement, i.e., only 0.7 watt. The position, size, and material of the charging electrode were optimized to give the best droplet charging performance. A 3.1 mC/kg spray charge was attained at 5000 rpm disc speed and 25 mL/min liquid flow rate. Eight size D batteries fitted inside the sprayer"s carrying handle provide power for the 3 watt DC motor that spins the disc and a 3 kV power supply which charges the spray droplets. When the sprayer is used continuously, the batteries should last at least 6 hours. Disc speed can be controlled by the operator to produce the correct droplet size for a particular target. Droplet size (vmd) ranges from 109 to 183 um depending on the disc speed and flow rate. Droplet size is reduced by 1 to 10% due to electrostatic charging. The ELVS"s field spraying capacity is higher than that of the conventional knapsack-type hydraulic nozzle sprayer (HNS), i.e., 0.12 - 0.16 ha/hr vs. 0.08 ha/hr. The reasons are: less water hauling time (20 li/ha is required for the ELVS while about 200 li/ha for the HNS), less frequent refilling of liquid tank, and less resting time. The ELVS also gives chemical deposits of 3.9 times higher for rice and 1.5 times higher for soybean plants than those given by the HNS. This could mean a reduction of at least 50% of the recommend chemical application rate. Electrostatic charging also reduced spray drift by 16%. Hence, hazards due to the operator"s exposure to toxic chemicals are reduced. Although the initial cost of the ELVS is twice higher than the HNS, the overall spraying cost is lower because of its lower requirements for labor and chemicals. (Author abstract)