Effects of nozzle diameter on water distribution for rotating spray-plate sprinkler

This study aims to deeply understand the influence of nozzle diameter on the water distribution characteristics of rotating spray plate sprinklers. The experiment was carried out in a windless indoor environment. An R3000 rotating spray plate sprinkler was selected as the research object with the 6-groove red spray plate and 36 nozzles (diameter 1.79-9.92 mm). The water distribution characteristics of rotating spray plate sprinkler under three working pressures of 98, 196, and 294 kPa were tested using radial collector arrays method. The results show that the radial water distribution patterns of 9#-38# nozzle (diameter 1.79-7.54 mm) presented a double hump curve under 98 kPa working pressure condition, while the patterns of 40#-50# nozzle (diameter 7.94-9.92 mm) was a single hump curve. The radial water distribution patterns of all nozzles showed a single hump curve under the working pressure of 196 and 294 kPa. The maximum was all the same as the radial position in the radial water distribution curves with the different diameter nozzles, which was basically the same as the first peak position under the working pressure of 98 kPa. The position was usually between 1.3 and 3.5 m away from the nozzle. The maximum and average values of water application rate increased with the increase of nozzle diameter. It was found that the maximum water application rate presented an exponential relationship with the nozzle diameter using curve fitting. An exponential relationship was found in the average value of water application rate with the nozzle diameter. The coefficients of determination (R2) of the fitting formulas were above 0.95. There was exponentially related to the maximum and average value of water application rate and the nozzle diameter. However, the universal index relationship was further verified by the other structural forms of spray-plate. The spray radius was 4-7 m when the working pressure was 98 kPa. The spray radius was 5.5-9 m when the working pressure was 196 kPa. When the working pressure was 294 kPa, the spray radius was 5-9 m. There was no monotonic increase in the spray radius with the increase of nozzle diameter, while the nozzle diameter exceeded 7.54 mm (38# nozzle). The test showed that a parabolic model was established to determine the variation of the spray radius with the nozzle diameter under pressure. Three prediction models only applied to the rotating spray-plate sprinkler with a nozzle diameter of less than 7.54 mm. The prediction error was large after exceeding the diameter. There was a uniform decrease in the water distribution for the rotating spray plate sprinkler with the increase in working pressure. The water distribution uniformity of the single nozzle was more than 60%, under the pressure condition of 98 kPa, except for the 9# and 10# nozzle (diameter 1.79 and 1.98 mm). The water distribution of the R3000 rotating spray-plate sprinkler was approximately triangular (single hump curve) or a triangular combination distribution (double hump curve). The flow rate of nozzle was determined by the working pressure and nozzle diameter. The uniformity, the characteristics of the water distribution and the spraying radius depended on the structure and speed of the spray plate. Therefore, flat or multi-peak water distribution was the key goal to design the spray-plate structure in the rotating spray plate sprinkler for better spraying performance. The finding can provide the technical basis and reference for the optimization design, engineering application and product localization of low-pressure rotating spray plate sprinklers. © 2022 Chinese Society of Agricultural Engineering. All rights reserved.