Document Type : Research Article
Authors
1 Department of Biosystems Engineering, Faculty of Agriculture, University of Kurdistan,Sanandaj.Iran
2 Department of Physics,Faculty of Science,University of Kurdistan, Sanandaj, Iran
Abstract
Introduction
Due to the increasing need for agricultural products, protection of products against pathogens and preventing them from being wasted is important. Study on droplets charging systems are important because of its influence on the reduction of chemicals and the increase of droplet deposition on the target. Conventional sprayers in Iran have many disadvantages such as drift, environmental pollution, lack of complete and homogeneous coverage on spraying surface, phytotoxicity and crop losses. Therefore, evaluation of new spraying methods and using a variety of electrical sprayers as alternatives to conventional spraying is essential. The aim of this study is design, construction and optimization of performance of electrodynamic head of atomizer motorized knapsack sprayer, and study of the effects of the parameters of angle of the target position, spraying distance and wind speed on the performance of the electrodynamic head in the atomizer.
Materials and Methods
Experiments were performed in agricultural machinery workshop at The Department of Biosystems Engineering of University of Kurdistan, Iran, with atomizer motorized knapsack sprayer equipped with electrodynamic head. The effect of some factors, including wind speed, angle of the target position and spraying distance to the target were investigated on deposition and coverage percentage, uniformity of spraying. These effects were investigated to determine the uniformity coefficient of total spraying. Design Expert 8.0.6 Trial software was used to design the experiments and to analyze data based on central composite design. The investigated factors and levels were: distance of nozzles from the target (at three levels of 2, 4, and 6 m), angle of the target position (at three levels of 0, 45, and 90 degree), and wind speed (at three levels of 2.5, 3, and 3.5 m/s). Water sensitive paper cards were used to evaluate the quality of spraying spread. The cards were scanned and magnified with an Olympus SZX12 Stereo Microscope equipped with objective lens of X1 and total magnification of 7X. The characteristics of droplets size were determined using MountainsMap Trial and Deposit Scan softwares.
Results and Discussion
The maximum value of the total spraying uniformity coefficient is equal to 1.95 for the spraying angle of 0 degrees, the distance of 6 meters and the speed of 3.5 meters per second. Meanwhile, the lowest value of the spray uniformity coefficient of 1.18 was obtained in the test conditions of 90 degrees, the distance of 2 meters and speed of 2.5 meters per second respectively. Based on analysis of variance for the interaction model of two factors (F value less than 0.0001, explanation coefficient 0.9435, absolute explanation coefficient 0.9174, standard deviation 0.0564 and coefficient of variation 3.609%). It can be stated this model is highly accurate in predicting the uniformity of the total spraying, and the linear components of spraying angle and spraying distance, as well as the interaction of spraying angle × spraying distance and spraying distance × wind speed had a significant effect on the uniformity of the total spraying (p<0.05). Nevertheless, the linear component of wind speed and the interaction between wind speed and spray angle had no significant effect on the changes in the uniformity coefficient of the total spray. According to the variance analysis table (F-value values), the effect of spraying distance on the spraying uniformity coefficient is far greater than the effect of spraying angle. It has been observed that by increasing the spraying distance and decreasing the spraying angle, the spraying uniformity coefficient will increase. It can also be stated that the linear components of spraying angle and spraying distance, the interaction component of spraying angle × spraying distance and the square power of the components of spraying distance and air speed have a significant effect on the coverage of the spraying surface. The values of R2, Adj-R2, CV and Press for the model adapted to the test data of leaf surface coverage percentage were obtained as 0.9929, 0.9865, 4.87% and 188.61%, respectively. Also, the amount of misfit for the mentioned mathematical model is significant (p<0.05). This indicates the appropriate accuracy of the model in predicting the amount of water sensitive paper cover. Among the three input variables, the spraying distance has the greatest effect on the amount of water sensitive paper cover.
Among the three input variables, the spraying distance has the greatest effect on the amount of water sensitive paper cover. At high levels of the spraying angle, especially at the spraying angle of 90 degrees, the spraying amount has decreased with the increase of the distance. At the spray angle (angle of the target position) of 90 degrees, by increasing the distance from 2 to 4 meters, the spray uniformity coefficient has increased from 1.18 at a wind speed of 2.5 ms-1 to 1.84 at a wind speed of 3.5 ms-1. Increasing the distance between the sprayer and the target decreased the amount of surface coverage on the target. The uniformity of particle settlement on the bottom surface of the target was relatively the same in electrodynamic spraying. This is despite the fact that at low levels of the spraying angle (for example zero-degree angle) the spraying amount increases at first with the increase of the spraying distance from 2 to 3 meters and then decreases with a sharp slope. According to the contours of spray surface changes, all wind speed levels in the spray distance range of 4 to 6 m with the increase of the spray angle, show no change in the spray surface value (p< 0.05). Meanwhile, in the spray distance range of 2 to 4 m, with the increase of the spraying angle, the amount of spraying surface has increased significantly (p<0.05).
Conclusion
In order to improve the performance of atomizer motorized knapsack sprayer, an electrodynamic spraying head was designed and built, and its performance was optimized using the central composite design of the response surface method(RSM). During the research process, the influence of the independent parameters such as the distance of the nozzle in relation to the target, the angle of the target position and the wind speed on the variables, including spraying uniformity, the percentage of the spraying surface and the percentage of changes in the total spraying coefficient were discussed and investigated. The results of the research led to the determination of the 3.5 ms-1 wind speed, 2.5 m sprayer distance and 90º spraying angle with 0.792 desirability, which were considered as the optimal performance conditions of the electrodynamic spraying head. The results of laboratory validation for optimal conditions show that the amount of uniformity of total spraying and the percentage of spraying surface are equal to 28.27% and 1.65%, respectively.
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