Application with turbo atomizing sprayer

The uniformity of vertical distribution of the syrup in turbo atomizers is still a challenge for producers. Sometimes due to lack of adequate adjustments, but often also due to poorly designed equipment.

When applying pesticides to tree crops, one of the factors that most affect their efficiency and effectiveness is the uniform distribution of wind and spray flow throughout the plant canopy. Pesticide applications have increasingly gained attention from farmers, society, institutions responsible for environmental protection and food safety, labor inspection bodies and, mainly, consumers.

The application of pesticides is an agricultural practice that requires a lot of knowledge from the agents involved in its execution. A trained applicator can contribute significantly to the quality of the application, but simply training the operator does not guarantee success in phytosanitary treatments. It is also necessary that the sprayers are in satisfactory maintenance and use conditions to carry out the activities, in order to improve the quality of operations.

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In recent years, the methodologies and equipment used in the application of pesticides have evolved considerably. However, many improvements can still be made in relation to existing flaws in the construction projects of these machines. There is, therefore, a need to carry out tests on these equipment to find solutions for using the air current and increasing the sprayer's operating efficiency, which is technically, economically and environmentally reliable.

Hydropneumatic sprayers are equipped with spray tips to divide the syrup into drops and a fan to transport the drops to the interior of the plant's canopy, through air movement within the tree canopy. The air current drives the droplets into the canopy through its turbulent movement. However, energy is required to operate the fan and much of this is lost due to the distribution of the air column. There are design alternatives available on the market with different capacity for using the air flow and syrup.

Plant canopy varies with age and plant species. Therefore, it is necessary for the direction of the air column to be adjusted by the operator, in order to provide greater volume and air flow in places where the canopy is denser. The selection of the tips arranged on the bar can be carried out taking into account the architecture of the canopy, which can produce and direct drops of larger diameter towards the upper part and smaller diameter towards the lower part of the canopy, depending on the leaf mass of the crop in question. (Figure 1).

The air flow in hydropneumatic sprayers has the important function of moving the leaves in order to allow the droplets to be deposited in the lower canopy. In addition to this function, the air flow must help the uniform distribution of the drops, since in the case of axial fans the air is swirled to mix the drops and distribute them better on the plant. The air speed varies with the height of the fan depending on its design, which makes the distribution and penetration of droplets a problem that must be solved. Figure 2 shows the air speed taken at 0,50 meters, vertically from the most prominent tip of the bar, aiming to identify the behavior of the air in the plant canopy. This sample found that on the right side the speed is greater in the lower middle third, while on the left side the speed is greater in the upper central part of the cup.

In Figure 3, it is possible to see the data where the speed was taken radially to the spray bar, aiming to identify whether the air flow had the same speed in this position radial to the fan.

The distribution of the air flow, by the fans, has the function of displacing the mass of air stopped inside the plant canopy and introducing a new mass of air loaded with droplets. In this study of air speed, it was possible to verify that the tips arranged on the bar, in the shape of a semi-arc, do not have the same distance in relation to the target, as the tips of the lower and upper part of the bar are further away from the plant canopy. This is one of the reasons, together with the lower air velocity, for spray deposition to be lower in the upper part of the plants.

In Brazil, there are still no studies that accurately indicate an ideal range for air flow when spraying tree plants. Orchards are generally not pruned and this is an indication that the ideal volume of air, necessary to drive drops into the plant canopy, is greater than that recommended in Europe.

These results demonstrated that the air distribution was uneven vertically in the nozzle bar, mainly due to the construction design of the axial fans. The speed values, in relation to the study in the radial plane, were higher in the position relative to tip seven on both sides, due to the proximity of the anemometer to the top of the bar.

The intensity of the air flow is determined by the air speed generated by the turbine, directly influencing the vertical distribution of the applied liquid. Different baffle designs and characteristics have been developed for airflow sprayers. Therefore, the height of the turbine can influence the efficiency of the application in relation to the plant. The greater or lesser height of the turbine can prevent the spray from reaching leaves in different positions in the canopy. Therefore, the greater the distance between the spray tips and the target, the lower the air's capacity to transport the droplets and the greater the probability of evaporation and drift.

It is possible to build a simple and relatively cheap structure that can be built by the producer to check the distribution of the syrup vertically. Using this structure, it was possible to observe that at the ends of the lower part of the bar the amount of product is much greater than at the top when using equal ends, which indicates that it is necessary to change the tip depending on the canopy architecture.

In Figure 4, it is possible to observe that in those tips up to two meters high the volume collected reached approximately 200ml, however, above this height practically no liquid was collected after five minutes of spraying. However, coffee plantations, for example, reach a height of 4,5 meters and the deposit at the top is very small.

The coefficient of variation for boom sprayers is around 7%, when compared to that obtained in hydropneumatic sprayers equipped with an axial fan, the coefficient of variation was 136%, 136% and 141% for pressures of 633kPa, 844kPa and 1.055 kPa, respectively. Spraying on trees depends on the geometry of the canopy and requires that the spray volume is sometimes greater in the upper canopy of the plant. The farmer, through the selection of tips, can change the volume applied at each level of the canopy. However, the influence of the fan can cause irregularity in the distribution of syrup. This occurs because most of the droplets are directed downwards, taking the same direction as the air flow.

Cleyton Batista de Alvarenga (UFU); Mauri Martins Teixeira (UFV);Paula Cristina Natalino Rinaldi (UFRRJ); Robson ShigueakiSasaki (IF-Southeast MG)

Article published in issue 148 of Cultivar Máquinas.