Improved design and testing of the low-pressure end sprinkler nozzles for light and small pan irrigation sprinklers

Abstract: Light and small pan sprinklers have been suitable for irrigation in the small and scattered fields in rural China. Excellent prospects can be widely expected for popularization and application in recent years. Taking the Nelson R55 rotary refracting sprinkler as a prototype, this study aims to design a series of rotary refracting end nozzles using the working principles of secondary fragmentation, face slot diversion, rotary jet and non-full circle restricted spraying. A Creo software modeling and laser rapid prototyping were used to produce the solid nozzle, thereby improving the spraying range, sufficient water fragmentation, and uniformity of combined spraying under low-pressure conditions. The water distribution of the end sprinkler was measured under constant spraying. The combination of the end sprinkler and the middle sprinkler water was superimposed to calculate the uniformity of the sprinkler water distribution under mobile spraying. A multi-objective comprehensive evaluation of the end sprinkler was carried out to determine the optimal design parameters of the sprinkler using the principal component analysis, where the uniformity, average sprinkler intensity, and total width were used as the evaluation indicators. Research results showed that: 1) The ratio of the sprinkler surface and groove diversion was adjusted at the near and far end of the water distribution, where the optimal presented the uniform and concentrated surface-groove distribution. 2) The same stream cross-sectional form of the sprinkler presented with the increase in the surface groove ratio, where the intensity of peak sprinkler was reduced by 13.12%-73.62%. The same surface groove ratio of the sprinkler and semi-circular flow path decreased by 36.88%-62.17%, compared with the V peak sprinkler intensity. Once the "surface-groove" diversion ratio tended to be equal, the water distribution at the end of the unit was more uniform, indicating less impact on the overall spraying quality of the unit. 3) The optimal operating parameters of the sprinkler nozzle were selected with the 1:1 diversion ratio, uniform and concentrated distribution of curved surfaces and grooves, semi-circular flow channel cross-sectional form, and non-circular nozzles with a speed of 100-120 r/min. In this case, the sprinkler range reached 10.3 m. In the improved sprinkler nozzle, the combination uniformity of light and small pan sprinkler under low-pressure conditions of 0.10 MPa increased by 32 percentage point, compared with the R55 type end sprinkler. The control width of the unit increased by 38.5%. The flow rate increased by 5.2 m3/h. The low-pressure end nozzle can effectively enhance the spraying width of the unit, and has high adaptability with the central nozzle, thereby achieving the dual objectives of energy-saving and quality irrigation. This finding can provide a theoretical basis for the design of low-pressure rotary nozzle and efficient irrigation of sprinklers.