The Velocity Variation Characteristics of the Flow Field and the Related Structural Parameter Optimization of the Direct Jet Nozzle

The atomization of nozzles plays a crucial role in improving the efficiency of spraying for dust suppression. According to the inertia collision theory for dustfall, the droplets with small particles and high-velocity possess a greater capacity for capturing dust, which requires a relatively higher speed of spraying at the outlet of the nozzle. Along the line of dustfall-droplet-velocity-structure, this study employs COMSOL Multiphysics software to simulate the internal characteristics of velocity field for a direct jet nozzle under different pressures and confirms that the convergence angle α and length-to-diameter ratio C of the outlet channel are the two main structural factors affecting velocity variation. A single-factor test is conducted for studying the characteristics of fluid migration under different nozzle structure parameters, and it is found that with other parameters unchanged, the smaller α is, the more slowly the jet velocity increases in the axial direction, and the more stable the jet velocity becomes in the radial direction; while the smaller C is, the more rapidly the jet velocity increases in the axial direction, but there was no obvious variation in the radial direction. As the simulation results shows, when α = 30° or C = 2, the average velocity at the nozzle’s outlet reaches the highest level and the velocity at the outlet of the convergence angle also becomes higher. Phase Doppler interferometer can be used to measure the velocity variation in the spray field, and the nozzle’s atomization performance could be obviously improved by optimizing the shrinkage angle α. Therefore, the priority should be given to the value of α in designing dustfall nozzles.