Effects of Liquid Viscosity on Agricultural Nozzle Droplet Parameters

To discuss the effects of pesticide viscosity on the atomisation characteristics of an agricultural nozzle, glycerite with different mass fractions was prepared to replace the pesticide. First, the atomisation region of the nozzle was meshed and sized. Second, the speed and kinetic energy of the droplets at different positions in the atomisation region were measured by Phase Doppler Anemometry. The results demonstrated that the Sauter mean diameter, volume mean diameter and arithmetic mean diameter of droplets first decreased and then increased gradually in the axial direction of the atomisation region. Surface waves of a certain pattern were formed on the liquid surface, which was ejected by the disturbance of external air resistance. As the distance increased, the amplitude increased and the wave crest was broken into small droplets. These droplets then collided and agglomerated into large droplets under the effect of gravity. Droplets had an approximately symmetric distribution on the radial direction of the atomisation region, and the droplets were small in the middle and large at the two ends. The droplet size was positively related to the radial distance. Compared with the droplet speed at the two ends, the droplet speed at the axis was higher and the droplet size was smaller. Moreover, the kinetic energy of the droplets along the axial direction decreased sharply and then increased slowly. Droplets with high viscosity at the near end of the nozzle had small kinetic energy, and the effects of liquid viscosity on the atomisation characteristics of a nozzle could not be neglected. The droplet kinetic energy slightly increased at the far end.

Simulation and experimental research on droplet flow characteristics and deposition in airflow field

In order to study the motion law of droplet flow under the airflow action of long-range air-blast sprayers,a CFD-based 3D model was established for the air-blast sprayer duct and its external airflow field,and the discrete phase model was introduced to simulate the motion of droplet flow in the airflow.The simulation data of the droplet flow trajectory,droplet flow parameters and droplet deposition were obtained by establishing the monitoring sections and bilateral coupling calculation in the airflow field.Results showed that gravity had an obvious effect on droplets and large droplets settled faster.Some of the larger droplets were formed by polymerization in droplets motion.The smaller droplets were transported further along with the airflow,and the long-range sprayer has a significant effect on the directional transport of small droplets.Besides,the spraying swath in the direction perpendicular to the range enlarged gradually with the increase of the spraying range.At the end of the range,the diffuse and drifting of the droplets were dominant.Given that the outlet airflow velocity of the sprayer duct was 25.01 m/s and the spray pressure 1.8 MPa,the maximum motion distances of aerosol,mist,fine mist and coarse mist in the airflow field were 18.5 m,19.5 m,17.5 m and 10.5 m,respectively.Droplet size and number as well as number density and volume density of droplet flow on all monitoring sections showed a regression function with changes in the distance of the spraying range.The simulation results of the model adopted in this paper were verified by Chi-square test between the simulation results of the droplet deposition and the spray measurement results.Research results provide a new method for the study of orchard air-blast spraying technology and references for the optimization of spraying technology.