Effects of Different Nozzle Orifice Shapes on Water Droplet Characteristics for Sprinkler Irrigation

Abstract

In common irrigation systems, sprinklers are mounted with circular nozzles, but innovative noncircular nozzles can save water and energy by improving fragmentation in a low–intermediate pressure irrigation system. In order to investigate the effects of nozzle orifice shapes (circular, square, and equilateral triangular) on droplet characteristics, experiments using high-speed photography and water droplet spectrum measurement were performed. Using ImageJ to observe with the overlapped droplets and using the self-compiled programs of MATLAB to observe the morphology of droplets, we extracted the outlines of droplets. In addition, several empirical formulas for the prediction of droplets were obtained by way of a regression analysis of the experimental data. In particular, the shape coefficient of the nozzle orifice and the operating pressure of the nozzle were added to these formulas as variable factors to make them applicable to a variety of nozzles and working conditions. The results show that with the increase in shape coefficient, the jet atomization intensifies, and the droplets breaking from the jet will be dense and uniform. The velocity distribution of the droplets conforms to exponential functions (R2 > 0.7). The prediction formulas of diameter and kinetic energy were established with coefficients of determination exceeding 0.95. In low pressure conditions, the specific power multiplies at the end of spraying, and the maximum is proportional to the nozzle orifice coefficient. The impact-driven arm compensates for the disadvantage of the noncircular nozzles with the high irrigation-specific power, by producing a wider diameter gradient of droplets. Therefore, innovative sprinklers based on noncircular nozzles can be applied in a low–intermediate pressure system to increase water use efficiency, reduce energy consumption, and reduce costs.