Effect of process parameters on characteristic distribution of droplets generated by internal mixing air-mist nozzle

Abstract

The cooling intensity of high-temperature slab critically depends on the ability of droplets to penetrate the vapor film, which is governed by the velocity and size of droplets. These characteristics, in turn, are significantly influenced by the nozzle design and process parameters. However, the specific relationship between distribution uniformity of droplet velocity and droplet size and process parameters remains insufficiently characterized. In this study, a typical internal mixing air-mist nozzle of secondary cooling zone was taken as the research object, the velocity and size of droplets across the spray zone were systematically measured, and the effects of spray distance, air pressure and water pressure on these droplet characteristics distributions were thoroughly analyzed. Key findings reveal that the droplet velocity decreases radially from the spray center toward the edges. Simultaneously, the distribution range of droplet diameter and the Sauter mean diameter (d₃₂) exhibit a non-monotonic trend, initially decreasing before increasing. Increasing the spray distance expands the droplet dispersion but reduces both the droplet velocity and d₃₂ in the center zone. The higher air pressure and lower water pressure facilitate higher droplet velocities in the center zone, leading to a decrease in overall droplet diameter and d₃₂. It is evident that air pressure emerges as the primary factor influencing the nozzle atomization performance. Notably, while increasing air pressure or decreasing water pressure diminishes the horizontal uniformity of the droplet vertical velocity component, it markedly improves the uniformity of d₃₂ distribution. Optimal horizontal uniformity of the mean impact Weber number of droplets was observed at an air pressure of 0.3 MPa and a water pressure of 0.4 MPa, as well as at an air pressure of 0.4 MPa and a water pressure of 0.5 MPa.