Design and hydraulic performance test of a jet-impingement sprinkler at low pressure

An asymmetric impinging jet collision mode is adopted to design the jet impingement sprinkler. By using the secondary jet to collide with the main jet, the movement and fragmentation mode of the main jet are changed to optimize the dispersion effect of the jet. The main body structure of the sprinkler is similar to that of a traditional impact sprinkler to meet the wetted radius requirements. The focus of the study is on the structure of the secondary nozzle, including the inner diameter of the secondary spray tube, the elevation angle of the secondary nozzle, the length of the secondary spray tube, and the inlet cone angle of the secondary nozzle. The sprinkler is made of aluminum alloy material and designed with a segmented structure plug-in design to avoid changes in the jet direction caused by threaded connections. The wetted radius and Christiansen's uniformity coefficient are selected as evaluation indicators. The wetted radius is calculated using interpolation algorithms, and the Christiansen's uniformity coefficient is calculated by using MATLAB program and a interpolation mathematical model to calculate the radial water application rate distribution for the square layout scheme. The experiment is conducted in a windless experimental hall, and the influence of various geometric parameters of the secondary nozzle on the water application rate distribution is evaluated through comprehensive evaluation of the wetted radius and Christiansen's uniformity coefficient using the CRITIC weighting method.According to the experiment, the coefficient of variation of flow rate for the nine different combinations of structures under different pressures is less than 2%. It can be concluded that the four structural parameters changed in this study do not affect the flow rate. By analyzing the average flow rate of the nine combinations, it is found that the flow rate is proportional to the pressure, and the flow rate at each test pressure is greater than 0.08 m³/h, which means that the wetted radius of the sprinkler is the farthest distance from the centerline of the sprinkler to the point where the water application rate is 0.26 mm/h. By comprehensive scoring, the optimal structural combination for the full pressure range of 150～300 kPa is secondary spray tube length of 20 mm, secondary nozzle inlet cone angle of 55°, inner diameter of secondary spray tube of 6 mm, and secondary nozzle elevation angle of 33°. A comparison experiment of the water hydraulic performance between the jet impinging sprinkler and the non-impinging sprinkler shows that the jet impinging sprinkler has a longer wetted radius and a slightly different water application rate distribution. Hydraulic performance tests were conducted on the optimal structure and the traditional 15PY2 sprinkler. It was observed that, under low pressure, the wetted radius of the jet impinging sprinkler decreased, while the Christiansen’s uniformity coefficient increased. Under medium pressure, the wetted radius increased, and uniformity improved. Moreover, the comprehensive performance of the jet impinging sprinkler was found to be superior to that of the traditional 15PY2 sprinkler under a full pressure range of 150 to 300 kPa. Finally, a comparison was conducted to analyze the droplet size distributions of the traditional 15PY2 sprinkler and the jet impingement sprinkler in the anterior middle and posterior sections. The results show that the jet impingement sprinkler produces larger droplet diameters at 150 and 250 kPa in the anterior middle section of the wetted radius. However, in the posterior section, it only exhibits larger droplet diameters at 150 kPa. At 250 kPa, the droplet diameters are smaller. The obtained structure and conclusions of the study provide a reference for future research on the hydraulic performance affected by jet impingement.