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INTRODUCTION
In the energy balance of agricultural sprayers assisted by air flow, it is suggested that between 50 and 65% of the power in these equipment is used to move the fan that produces the air flow. At work, a power balance of the TYME 2091 sprayer is carried out, considering the power shot, the power liquid pump and the power in fan. The aerodynamics of the air flow from the fans in agricultural sprayers is essential to achieve efficient tree coverage. The magnitude of the flow and speed of the fan air are parameters that decide on the transfer of the pesticide drop to the tree, because it influences its speed, direction and size, as corroborated Delele et al. (2005), when he expresses that the air velocity generated by the air stream-assisted sprayers determines the destination of the pesticide droplets. On the other hand, works by Herrera et al. (2004), have related the parameters of the fan with the quality of the sprinkling, so the knowledge of these will allow an adequate exploitation of the sprayer. The parameters of the fan are closely linked to its power consumption and in turn decide on the quality of the sprinkler, so the study of the aerodynamics of the air flow is important to achieve low energy consumption and maintain the quality of the treatment. Researchers in recent years have developed computational fluid dynamics (CFD) models, looking for a way to solve this problem with more agility and fewer resources for experimentation. The work with CFD has been complemented with experimental field trials of Walklate et al. (1996); Xu et al. (1998); Herrera et al. (2004); Delele et al. (2007). More recent studies in CFD with results validated in a controlled way were carried out by Tsay et al. (2004); Han et al. (2014). In this work, the effect of the variation of the air speed at the fan outlet on the aerodynamics of the air flow during the work process of the sprayer will be analyzed through the use of computer simulation (CFD) and as variables Answers will analyze the deviation and scope of the air flow through the interpretation of the velocity graphs of the modelling results. These results are complemented with the control of the quality of the sprinkling in the variables studied. Quality evaluations are carried out in the field using hydrosensitive cards, in which the covered area is measured using Imagej, the image treatment program. Conclusions are reached about the relationship of the fan parameters, the aerodynamics of the air flow and the quality of the spray, allowing the selection of the working regime with the lowest power consumption.
MATERIALS AND METHODS
The model for the study is based on the parameters of the TEYME 2091 sprayer fan, which has an axial fan with radial outlet model "PVS-900" with a diameter of 900 mm. Fan outlet speeds of 18, 22 and 27 m/s will be evaluated, maintaining the outlet width of the fan diffuser and considering the sprayer with a translation speed of 2.18 km/h. Figure 1 shows the sprayer used as a reference for modeling.
Table 1 shows the parameters of the fan, air speed at the outlet, air flow and power consumed, in the variants to be evaluated with the movement speed of the sprayer of 2.18 km/h. The data of the ventilator parameters are taken from the data provided by the manufacturer.
| Fan parameters | Airspeed in; m/s | Airflow in; m3/h | Power in; kW |
|---|---|---|---|
| V-1 | 18 | 46 789 | 9,75 |
| V-2 | 22 | 56 959 | 18,04 |
| V-3 | 27 | 69 095 | 31,05 |
Energy balance
The energy balance is made from the power consumption of the sprayer, the power consumption in the shot, the power consumed by the pump to move the liquid to the nozzles where the drop is produced and the power consumption of the fan which produces the air stream for the transfer of the drops towards the tree.
Power consumption in the shot
Determination of the shot force, N.
Power consumed in the draft, kW.
Hydraulic power consumed by the pump, kW.
Pump power, kW.
For the analysis of the energy balance, a Pareto diagram will be made to compare the power consumption in the agricultural sprayer.
Modeling of the air stream
The computational modeling analysis was carried out using the ANSYS 16.0 program, which bases its numerical analysis on the solution of the moment and continuity equations that are applied to the air flow dynamics. Figure 2 shows the computational domain where the fluid moves for CFD modeling, this element shows the mesh that defines 489 nodes and 443 elements for the development of the Navier-Stokes equations. In the modeling, the properties of air as a fluid were density of 1,225 kg/m3 and viscosity of 1,7894 x 10-5 kg/m.s. As response variables, the deviation and scope of the air flow will be analysed through the interpretation of the velocity distribution graphs.
Measurement of spray quality
The way to quantify the quality of the spraying is by evaluating the coverage of the tree by the pesticide drops, in addition to determining the size and number of drops. Currently there are different technologies available in image analysis that can determine the coverage percentage safely. Samples are taken from the pesticide deposit on the tree with hydrosensitive cards, they are placed on the plant by the beam and the underside of the leaves in different positions. The evaluation was made in citrus plantations of the Jagüey Grande enterprise, maintaining similar conditions for the three variants studied. In the analysis of the hydrosensitive cards to measure the coverage, the Imagej image treatment program was used.
RESULTS AND DISCUSSION
Power consumption calculation results
In the theoretical calculation of the pulling power (Ntiro), the full mass of the sprayer 3 405 kg was taken from the technical specifications of the sprayer and a rolling coefficient of f = 0.05 was selected. In the theoretical calculation of the (Npump), a flow rate of 70 L/min, a pressure of 20 bar and an efficiency of ηtotal = 0.82 was selected as its working regime.
Table 2 shows the results of the power consumed in the sprayer, in the draft, in the pump and the fan for the different working regimes.
TABLE. 2 Results of the power consumed by the sprayer
| Fan parameters | Nshot in; kW | Npump in; kW | Nfan en; kW |
|---|---|---|---|
| V-1 | 1,012 | 2,84 | 9,75 |
| V-2 | 1,012 | 2,84 | 18,04 |
| V-3 | 1,012 | 2,84 | 31,05 |
In Figure 3, 4 and 5 the results of the table are shown in Pareto diagrams. In the same it is observed that in the power balance of the agricultural sprayer studied TYME 2109, the power consumed by the fan to produce the air current occupies 71.7, 82.4 and 89% of the total, for the variants V-1, V- 2 and V-3 respectively. The highest consumption is the fan, so in the analysis to obtain better energy performance indices in the sprayer, it is necessary to focus the work on the fan parameters to achieve a rational energy balance.
Airstream modeling results
In the results, the flow graphs obtained in the CFD modeling are analyzed for the three air outlet speeds studied, and the sprayer translation speed of 2.18 km/h. In general, for all the simulated variants of the outlet velocity and the translation of the sprayer in the flow graphs, the different regions of the current described by Abramovich et al. (1984) are defined for the turbulent free flows, forming a central nucleus of maximum speed that wears out as it moves away from the source of the current (red color), it is accompanied by transition zones with lower speed values than as the distance to the outlet decreases and the center line of the lateral flow as described (Schliting, 1972).
Figure 6 shows the results of the air current for air speeds at the fan outlet of 18.22 and 27 m/s, in this case in the simulation it is considered that the sprayer moves at a speed of 2.18 km/h in its work process, so the air flow is subjected to the perpendicular action of this speed.
FIGURE 6 Simulation of air flow with sprayer travel speed of 2.18 km/h for fan output speeds of 18, 22 and 27 m/s.
As can be seen in Figure 6, the central nucleus of the flow represented with red colour disappears at a distance of 0.06 m from the origin in all the variants studied. In the transitory zone of the air flow for the three speeds studied, the maximum speed line presents a deviation of 0.15 m with respect to the geometric axis of the computational domain and in the opposite direction to the movement of the sprayer. At a distance of 3.5 m from the fan outlet, the difference between the airflow speeds between V-1 and V-2 is 0.63 m/s, in this case the difference at the fan outlet is 4 m/s; This same analysis for the V-2 and V-3, at 3.5 m distance from the outlet the difference is 0.51 m/s and the outlet is 5 m/s, which shows greater losses in the flow with higher velocities at the beginning. Similar analyses are found in works by Endalew et al. (2010).
This indicates that for the sprayer travel speed of 2.18 km/h it can be considered to use lower output speeds due to the similarity in the structure of the current, this gives the possibility of working with a lower power consumption regime of the fan and thus obtaining more rational energy performance indices.
Quality results of spraying
Table 3 shows the coverage results of the plant with pesticide for the three variants studied. It is observed that the best results are obtained for the V-2 variant, with a coverage of 90.2% by the upper part of the leaf and 85.2% by the underside of the leaf, although in the other variants the values are not low, but if differ on the underside of the leaf.
TABLE 3 Results of the spray quality analysis
| Effectiveness of tree coverage by pesticide droplets in% at sprayer speed at 2.18 km/h | |||
|---|---|---|---|
| Speed at fan outlet | 18 m/s | 22 m/s | 27 m/s |
| Leaf beam | 86,4 | 90,2 | 80,8 |
| Leaf underside | 79,3 | 85,2 | 68,2 |
This result of the quality of the sprinkling is narrowing related to the parameters of the fan. The lowest results in tree coverage are obtained in the V-3 variant, associated with the highest air outlet velocity (27 m/s) and the highest air flow 69 095 m3/h. In the case of the higher air outlet speed of the fan, the air stream achieves the greatest range as seen in figure 6, but the results in the quality of the aspersion are lower; Similar results to these obtained Randall (1971), when he determined better results in the tree cover for greater air flow with lower air speed. This result is due to the fact that a higher speed in the flow of the sprayer results in the screen effect on the foliage, not allowing the pesticide liquid to penetrate into the tree or that the high speed when transporting the drop reaches energy values kinetics such that it does not allow it to settle on the foliage and thus have less coverage of the tree.
The results show that when selecting a sprayer operating regime, the fan output speed and flow and the sprayer travel speed must be taken into account. The fan as the greatest power consumer in the agricultural sprayer must achieve a rational work regime and thus obtain better energy performance indices.
In the tree coverage results, the best results correspond to the V-2 variant with a fan working regime with an air flow rate of 56 959 m3/h and an air outlet speed of 22 m/s. If the power consumption of the V-2 variant is analyzed with respect to the V-3 variant, it is possible to reduce the power consumed by the fan by 13 kW.
CONCLUSIONS
The fan is the highest power consumer with a range from 71 to 89% of the total sprayer, which indicates that in order to improve the energy performance index of this equipment, work must be done to obtain the most rational working parameters of this.
In the CDF flow modeling, greater losses in the fan air flow were shown with higher fan air outlet speeds in the variants studied.
The best results in tree coverage were obtained in the V-2 variant, with an air outlet speed of the fan of 22 m / s and an air flow of 56 959 m3 / h, which indicates better aerodynamic characteristics in the range and geometry in the air stream.
In the V-2 variant sprayer working regime it is possible to reduce the fan power consumption by 13 kW and thus achieve a better energy performance index of the sprayer.
