Design and test of goose-neck long-range air-assisted sprayer for nursery

Plant nursery presents the characteristics of close planting. It is difficult for the traditional air-assisted sprayer to take into account the dual requirements of "long spray range and uniform droplet deposition", which leads to the problems of low deposition and drift.A goose-neck long-range air-assisted sprayer for nursery was designed based on CFD simulation and free submerged jet theory. The three-outlet flow guide device, as the core component of the sprayer, has outlets A, B, and C. Air outlet A adopts a circular arc shape, while air outlet B and air outlet C are gradually expanding circular arc tubes. The three air outlets are interconnected and correspond to different areas, which can meet the requirements of far-range spray operation. The optimized curvature radius parameters are conducive to maintaining a uniform and stable flow state of airflow. Based on the free submergence jet theory, the air outlet and fan parameters were determined, and airflow field distribution measurement experiments were conducted. when the fan speed is no less that 2 200 r/min, the airflow speed can fit the spraying requirement as far as 20 m. The average airflow speed was 2.33 m/s at a height of 0.8 m ; the airflow speed was 1.74 m/s at 20.0 m. The variation coefficient of airflow speed at different heights was less than 30%, indicating that the energy attenuation rate was slow and uniform, and the airflow could carry droplets to spray far away at a uniform speed. The droplet deposition test shows that the variation coefficient of the droplet deposition amount of the goose-neck long-range nursery air spray is 28.87%. To ensure the reliability of our findings,a comprehensive field test of the sprayer were conducted. Citrus seedlings, with an average height of 80 cm, were chosen as the test subjects, and the test was carried out in the nursery of the Citrus Research Institute of Chongqing Southwest University. Following the guidelines of GB/T17997-2008, the droplet deposition effect and drift rate at various distances were tested .The experimental results show that the fan speed of the sprayer is 2 400 r/min and the driving speed is 1 m/s; the droplet deposition tends to be less-more-less with the increase of distance. The droplet coverage rates of the upper and lower leaves of the canopy were 51.93% and 24.38%, respectively, and 42.99% and 19.26%, respectively. The average droplet deposition on the front and back leaves of the upper canopy was 13.34 and 2.82 µL/cm², respectively, and that on the lower canopy was 5.44 and 2.63 µL/cm², respectively, which met the requirements of plant protection spraying operation. It can be seen that the sprayer shows good spray range performance and droplet deposition uniformity, which can meet the agronomic requirements of the complex planting environment in the nursery and the industrial standards of the air-assisted sprayer. At present, in Chinese nurseries such as citrus, pear, and apple, etc, manual machinery accounts for a large proportion of spraying equipment, and the demand for specialized sprayers is becoming increasingly urgent. Due to the close planting mode of the nursery, it can be considered that the two modes of spray with high clearance spraying and long-range airflow-assisted spraying have application prospects. Compared with high-clearance spraying, long-range airflow-assisted spraying has the characteristics of high operating efficiency and good horticultural trafficability and is more suitable for small and medium-sized nurseries. However, improving the delivery distance of aerosol flow while ensuring good uniformity of droplet deposition is still a challenge. The results of this study can provide a new idea for developing a long-range air-assisted sprayer for nurseries.