Impingement and breakup characteristics of free opposed impinging jets with unequal nozzle diameter

Abstract

The free opposed impinging jets with unequal nozzle diameter is developed to improve mixing efficiency at unequal flowrates for liquid–liquid reactions. The liquid sheet breakup characteristics and droplet behavior are investigated using particle image velocimetry. Water, 40w% glycerol-water (40G), and 50% glycerol-water (50G) under different jet velocities and nozzle diameters are studied for comparison, the correlation equations are obtained and the errors are analyzed. When the jet velocity increases, the liquid sheet breakup mode exhibited a closed-rim mode, open-rim mode, rimless mode, wave or ligament mode, and fully developed mode for water and 40G under a nozzle diameter of 1.5–2 mm, and the first four modes were observed with the high viscosity liquid (50G) or under a large nozzle diameter (2–3 mm). As the jet velocity increases, the dimensionless breakup length increases sharply at the closed-rim and open-rim modes, and then decreases at the rimless mode. The sheet thickness, Sauter mean diameter, average droplet diameter, and droplet velocity decrease, and the droplet size becomes more uniform with increasing jet velocity. However, the opposite variation trend is observed with increasing viscosity and nozzle diameter, and the effect is more significant at u < 4.25 m/s. The droplet average diameter increases at u = 2.12 m/s and 3.18 m/s and decreases at u ≥ 4.25 m/s downwards along y-axis due to the coalescence and secondary breakup of droplets. The droplet velocity becomes lower as droplets move downwards along y-axis from −40 mm to −50 mm due to the dissipation of momentum. The results reveal that the increase of viscosity and nozzle diameter has a negative effect on liquid sheet and droplet behavior at low jet velocities. The rimless mode is the key mode affecting the transition of the sheet breakup mechanism, and after this mode, the negative effects of viscosity and nozzle diameter weaken due to the high momentum, which promotes the breakup of the liquid sheet and droplets. It will provide theoretical support for the mixing mechanism with unequal flowrates, and is helpful to expand the application of free opposed impinging jets.