An air-assisted electrostatic nozzle uses a combination of air-assisted atomization and electrostatic spray technology. This article optimizes the existing air-assisted electrostatic nozzles in terms of structural design to obtain a higher charge-to-mass ratio and a smaller droplet size. The optimized air-assisted electrostatic nozzle was studied experimentally, and the effects of liquid pressure, air pressure and applied voltage on the droplet size and charge-to-mass ratio were investigated. Comparing the effects of air pressure, liquid pressure and applied voltage on the charge-to-mass ratio and droplet size, the relationship curves of the droplet size and charge-to-mass ratio under each voltage were fitted using the Rayleigh charge limit theory. For a higher CMR during the spray operation, applied voltages between 2.5 kV and 3 kV, an air pressure between 0.4 bar and 0.6 bar, and a liquid pressure of less than 0.9 bar could be chosen. The optimized air-assisted electrostatic nozzles not only have small droplets but also have high charge-to-mass ratios, reducing the need for pesticide use and thus protecting human health and the environment.
Air-assisted spraying technology is widely used in orchard sprayers to disturb canopy leaves and force droplets into the plant canopy to reduce droplet drift and increase spray penetration. A low-flow air-assisted sprayer was developed based on a self-designed air-assisted nozzle. The effects of the sprayer speed, spray distance, and nozzle arrangement angle on the deposit coverage, spray penetration, and deposit distribution were investigated in a vineyard by means of orthogonal tests. The optimal working conditions for the low-flow air-assisted sprayer working in the vineyard were determined as a sprayer speed of 0.65m/s, a spray distance of 0.9m, and a nozzle arrangement angle of 20°. The deposit coverages of the proximal canopy and intermediate canopy were 23.67% and 14.52%, respectively. The spray penetration was 0.3574. The variation coefficients of the deposit coverage of the proximal canopy and intermediate canopy, which indicate the uniformity of the deposition distribution, were 8.56% and 12.33%, respectively.
The dynamic evaporation of single droplets was investigated under controlled conditions. In the evaporation process, a droplet was placed on a peach leaf surface. In this research, the relative humidity and temperature were kept constant, and the wind speeds and thiophanate-methyl concentrations varied. Based on these conditions, this study aimed to determine the droplets’ dynamic transforming characteristics, including the contact angle, the height of the droplets, and the evaporation rate. Five concentrations and five wind speeds were chosen, and pure water droplets at different wind speeds were used as a control group. All single droplets were generated by a syringe. The results showed that the pure water and thiophanate-methyl droplets’ evaporation mode was CCR (constant contact radius) mode. An increase in the wind speed accelerated the evaporation process, when the wind speed was 0 m/s, the evaporation was the longest, and the shortest evaporation was achieved with 2.0 m/s wind speed. An increase in wind speed enhanced the pure water droplets’ dynamic evaporation process with a maximum enhancement ratio of 3.44 times in the present work. Under the same conditions, the thiophanate-methyl droplets’ evaporation time was shorter than that of the pure water droplets. For thiophanate-methyl droplets, the higher the concentration, the shorter the dynamic evaporation process. A 1250 ppm thiophanate-methyl solution with 2.0 m/s wind speed, had an evaporation ratio that was 2.83 times greater than that measured with 0 m/s wind speed. These results could benefit farmers by suggesting that they should adjust the concentration of thiophanate-methyl depending on the wind speed in order to reduce pollution.
High clearance sprayer is a high-efficiency pesticide application machine in orchard management. In this paper, operational safety of high clearance sprayers is validated by using finite element simulation and vibration testing. The 3D model of the frame is simplified by using shell units instead of solid units, the static performance of high clearance sprayer frames under static full load and ultimate torsional conditions was studied by means of finite element simulation tests, the mechanical properties of the frame under step excitation were studied by multi-body dynamic simulation test. The simulation results show that, at a safety factor of 1.5, the maximum stress extremes in the frame are within the safe permissible stress range. During the dynamics analysis, a tire-ground contact simplified model was proposed. The results of the modal analysis show that the inherent frequency distribution of the high clearance sprayer is compact, and the vibration test has measured a large difference between the engine vibration frequency with the inherent frequency of the frame, this means that resonance will not occur. The theoretical analysis shows that the designed high clearance sprayer meets the requirements of large cross-row field operations, the study provides a reference for the overall design of the high clearance sprayer.
To realize the online evaluation of spray quality, an online measuring system for spray coverage and deposition quality is developed. The measuring theory of spray coverage and deposition quality on an LWS (leaf wetness sensor) surface is analyzed. When the spray conditions are constant, there is a linear correlation between the spray coverage on the sensor surface, the spray deposition quality and the LWS output voltage increment. The results of calibration experiments show that when the spray conditions are constant, the coefficient of determination R2 of the regression curves between the sensor output voltage increment and the spray coverage on the sensor surface is more than 0.75, and the coefficient of determination R2 of the regression curves between the sensor output voltage increment and the spray deposition quality on the sensor surface is more than 0.90. Based on ZigBee wireless sensor technology, this paper reports an online measuring system for spray coverage and deposition quality at multiple points in the field. The test results show that the online measuring system has good uniformity. Field test results show that the LWS voltage increment and the coverage rate of water-sensitive paper have a good correlation, and the measuring results of the spray deposition quality trend are in good agreement. The fit of the spray deposition quality curves measured by the two methods was 0.8924. The research results in this paper can provide a reference for using LWS sensors to measure spray coverage and deposition quality.
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