Effects of spraying angle and pressure on the droplet distribution of micro-sprinkling hose

A micro-sprinkling hose has been a promising type of equipment for water-saving irrigation, due to the cheap, easy to lay and pack up when working. The performance of the micro-sprinkling hose depends on the kinetic energy in the process of field irrigation. Correspondingly, the intensity of kinetic energy can be determined by the droplet distribution of spraying water in the air, where the irrigation water is sprayed from the thin pipe within regular orifices. There is also a different tolerance of various plant organs to the kinetic energy of droplets sprayed from the micro-sprinkling hose. Particularly, the plant height and the canopy coverage of crops vary greatly in each growth period. In this study, an indoor irrigation experiment was carried out to explore the influence of spraying angle and pressure on the droplet distribution of micro-sprinkling hose. An N44-5 micro-sprinkling hose was used, where "44" was defined as the folding diameter of 44 mm, and "5" was represented a group of five orifices on the pipe wall of the micro-sprinkling hoes. Four working pressures were set, including 20, 24, 28, and 32 kPa, expressed as P20, P24, P28, and P32. Three spraying angles were also set, including 40°, 60°, and two-angle combinations, expressed as A40, A60, and A4060. A total of 12 working conditions was completed in the entire experiment. The measuring points were arranged in the wet area of the micro-sprinkling hose. Then, the irrigation water was sprayed from the single or two holes of the micro-sprinkling hose under different conditions, where the spraying water droplets were passed through the measuring area of the instrument. An LPM instrument was developed to measure the droplet number, diameter, velocity, and irrigation intensity of the spraying water. The results showed that: 1) The irrigation intensity at A40 was relatively stable, with the production of working pressure, where the intensity was 17.9-23.0 mm/h. Meanwhile, the irrigation intensity decreased gradually, with the increase of the working pressure at A60. When the two angles were combined for the irrigation, the irrigation intensity of the micro-sprinkling hose presented an outstanding increase trend, where two peaks of irrigation intensity were generated. 2) The droplet diameter decreased under the same spraying angle, with the increase of working pressure. However, the diameter of single-hole spraying droplets in the micro-sprinkling hose decreased under the same working pressure with the increase of spraying angle. 3) Both spraying angle and working pressure posed great influences on the spatial velocity and droplet diameter distribution of the single hole spraying droplets in the micro-sprinkling hose. The diameter range of the droplet was 0-2.5 mm for the single hole with the micro-sprinkling hose, where the droplet diameter was concentrated in the range of 0.45-1.25 mm. This finding can provide promising theoretical support to design the micro-sprinkling hose.