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what is electrostatic spraying for agricultural applications? For the protection of crops pesticides are used, which are toxic chemicals designed to control pests, diseases or weeds. But they have their own fair share of disadvantages. They can contaminate air, water sources, animal’s, birds, aquatic life when they seep from fields, so due to this the applications of pesticides must be done with caution and accuracy. The most important factor that could affect the success of application would be choosing the right equipment. With the help of sensor and image analyzing technologies probability of success can be increased. Also, with the help of Electrostatic spraying the drift potential can also be reduced.
Electrostatic sparing has been used in many other applications such as painting, ink printing, etc. Research tells us that electrostatic spraying is much more efficient than normal spraying, there is less water consumption. It has its own difficulties.
In this report we will see how we can use electrostatic spraying with modern technologies to increase the accuracy and efficiency of it application.
The application of the pesticide in a proper way is very important for the biological efficacy. There are many factors that affect the implementation. They include weather conditions, spray pressure, nozzle conditions, speed, boom height, etc.
So, the safety and effectiveness are both related to the equipment used. Pesticides are used along with water in varying amounts and it is named according to the amount of water used, like high volume, low volume, etc.
High volume spraying has an application rate of >400 Lha^-1, the size of the droplets varies from 300 to 500 um, in such application the efficiency is low, while chemical waste and environmental pollution are both high.
During low volume application the rate is 50 to 400 Lha^-1 and droplets sizes are from 125 to 250 um. In this type chemical waste and spray drift is predominant while the efficiency is moderate. In ultra-low volume spraying the rate is <5 Lha-1 and droplet size is 5 to 50 um. It is more efficient and with less chemical waste.
Electrostatic painting process is based on that the opposite charges attract each other. Which results in a more uniform coat of paint, less waste and reduced material cost. Electrostatic spray technology was first invented in the early 1930s for the aim to improve spray deposition on the canopy. Harold Ransburg created the first electrostatic application system in 1940s. The auto mobile manufactures took it and added their own improvements to it until later after the 1980s it was used by the agricultural community.
The methods in which the electrostatic spraying can be carried out are of 3 types. They include induction charging, ionized field charging and direct charging. In induction a high voltage electrode is placed close to where the liquid in being emitted from the nozzle, and is +ve charged, while a conductive water-based pesticide is at the earth potential which is –ve charged due to the attraction of electrons.
In case of ionized field charging, also a high voltage is applied to pinpoint and create an electric field around it that suffices the air molecules. Positively charged conductor repels the positive ions. The process of direct charging includes a semi conductive spray liquid, which has an electrical resistivity of 104–106-ohm m, is exposed to a high voltage, as the liquid comes out of a narrow slit mutual repulsion between the parts of the liquid overcomes the surface tension and ligaments reformed. The ligaments break into droplets because of the axisymmetric instability.
The coulomb’s law states that “if the two charges have the same sign, the electrostatic force between them is repulsive, if they have opposite signs, the force between them is attractive.” so when the droplets leave the nozzle they are negatively charged and then they are attracted to the positively charged leave surface.
Blewett found that the use of a reduced volume charged spray system significantly increased the deposition and the decay time of captain dislodge able foliar residue as compared to that of the conventional spray. Patel et al designed the an air assisted electrostatic nozzle based on induction charging. The nozzle was light weight, very efficient, reduced pesticide use and human health hazards, and was ecofriendly.
The conventional sprays include an equal number of protons and electrons while the electrostatic system receives the negative and positive charge from the electrodes surrounding the nozzle. As the charged droplets reach the target they induce an opposite charge on the leaf, activating the electrostatic process in which the charged droplets are attracted to both the upper and lower parts of the Leafs.
In this study two types of sprayers were tested, petrol engine-driven mobile sprayer and PTO driven mounted type orchard-row crops sprayer.
Petrol engine-driven mobile sprayer.
This consists of petrol engine, air compressor, spray tank and spray unit. Air gets mixed with spray liquid in the spray gun and atomization as well charging of liquid occurs in the spray gun. Foe safety low voltage is used, a 9V battery is in the handle of the spray gun. Electrostatic charged imparted in not strong enough to harm people.
The flow rated can be controlled by the flow disks. Which was 150 to 240 ml per min. The pressure was about 4bar when the throttle was released.
PTO driven mounted type orchard-row crops sprayer
This type of sprayer has, sprayer tank super charger, pump, hand wash tank, boom and filters. The charging unit is to be attached to the tractor’s battery via conducting wire. Sprayer has a super charger instead of a blower. The flow rate on both sides can be controlled and it is 225 ml per min. Nozzle can be adjusted for different wide ranges. The problem with it is that it gets heated the nozzle temperature was 30C while the average of supercharger was 105C, due to which a special cooling system was used.
The efficiency of spraying depends largely on even and targeted liquid distribution. Uneven coverage causes waste, contamination and costs money. This type of sprays produces extremely fine or very fine droplets. Conventional sprays are not efficient enough. While the use of electrostatic spraying is way more effective. On which the technologies are improving day by day and they are getting better and better.
Electrostatic sprayers save time labor, fuel and pesticide. Although they are a bit pricy and can’t reach high trees. Still future calibrations can be made to suite them according to the needs. When using electrostatic sprayers, the weather conditions must also be in notice.
To make the electrostatic spraying more accurate sensors\ image analyzers can be used to enhance the targeted spraying of the pesticide liquid, the sensors would detect when the nozzle is pointed at the crops and when it is not and stop\start the spraying process immediately, although it would increase the cost but it would reduce the contamination of the surrounding area. Also, for the problem of short range, new models\designs of nozzles can be introduced to increase the range at which the sprayer can shot the pesticide which would make it easier to reach high trees and other such places.
How to use benefit irrigation system with electrostatic in future?
In order to save and use less resources we can use sprinkle, drip n tickle and subsurface system to give pesticide to crops. In this method we will give them the opposite charge to the nozzle and the crop. When the water will come out from bottom of the crop it will go towards the opposite (actually the targeted area). SPRINKLING from the bottom help to give pesticide above and below the leaves. It also uses less water and material and covers a large area. This thing also not uses petrol to minimize greenhouse effect.
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