Atomization characteristics of normal flat fan nozzle and air induction nozzle under high speed airflow conditions

Abstract: Flat fan nozzles and air induction nozzles are often used in ground spraying. Although the atomization characteristics of these 2 kinds of nozzles in low speed flow were studied sufficiently, their high speed atomization characteristics were still not very clear. The objectives of this research were to assess the atomization characteristics of the LU-120-03 normal flat fan nozzle and the IDK-120-03 air induction nozzle, and their suitability in agricultural aerial spray application. The experiment was conducted in the IEA-I high speed wind tunnel at National Engineering Research Center of Intelligent Equipment for Agriculture (NERCIEA) with Marvern Spraytec laser diffraction system. The measurement point was set at 0.15, 0.25 and 0.35 m away from the orifice of the nozzle which was 0.1 m outside the exit of the tunnel. The wind speed range was from 121.7 to 305.5 km/h, and the tube pressure was set to be 0.3, 0.4 and 0.5 MPa. The nozzle was installed on an electric lifting platform which could be traversed vertically so that the entire spray plume could be sampled by the laser diffraction system. Three replications for each nozzle/pressure tested were taken, and the standard deviation of volume middle diameter of droplets was required to be less than or equal to 5% of the mean. The results of the experiment to the LU-120-03 nozzle showed that when the wind speed increased from 150 to 305 km/h, the volume middle diameter of the droplets decreased from 210 to 130 μm. The relative span of the droplets was found to slightly increase from 1.3 to 1.5 with the increase of the wind speed when the tube pressure exceeded 0.4 MPa. The volume middle diameter of the droplets was also found to be related to the tube pressure. When the wind speed was less than 250 km/h, the increase of the tube pressure could decrease the volume middle diameter of the droplets. However, it would increase the volume middle diameter slightly when the wind speed exceeded 280 km/h. The main reasons of the droplet atomization were also discussed, and the aerodynamic shear stress was believed to be one of the most important reasons. Droplets generated by the IDK-120-03 nozzle had a different behavior. The volume middle diameter of the droplets decreased rapidly (by about 70%) when the wind speed increased from 120 to 305 km/h. Meanwhile, it was not affected by the tube pressure. The relative span of the droplets was mainly affected by the wind speed. When the wind speed was less than 220 km/h, the relative span of the droplets was in proportion to the wind speed. When the wind speed exceeded 220 km/h, the relative span of the droplets decreased slightly with the increase of the wind speed. The increase of the tube pressure could also increase the relative span of the droplets slightly. The measuring distance from the orifice of the nozzle was also found to be important to the diameter and relative span of the droplets. In our results, 0.35 m away from the orifice of the nozzle was a proper measuring point, at which the droplets were fully atomized.