Gas–liquid atomization physics of fan-shaped nozzles: Pressure threshold and droplet penetration characteristics

Abstract

Spray cooling is a key secondary cooling technique for continuous casting. The water penetration ratio, a critical parameter for calculating the heat transfer coefficient between sprayed water and slab surfaces, is governed by nozzle water pressure, air pressure, and spray height. This study focuses on fan-shaped air–water nozzles and develops a three-dimensional flow-field simulation coupled with multiphase flow and discrete phase models. The numerical model is validated via a self-built test platform, with a maximum prediction error of 3.33%. We systematically investigate droplet size, velocity distribution, and water penetration ratio under various pressure conditions. The results show that higher water pressure intensifies primary and secondary atomization, moving the initial droplet breakup upstream and causing non-monotonic changes in droplet diameter and axial velocity. Within 0–98 mm spray height, rising air pressure makes droplet diameter increase first and then decrease, while axial velocity rises continuously. As the air–water ratio increases from 1.0 to 2.0, the penetration ratio declines steadily with growing spray height. Two critical pressure thresholds are identified: 0.20 MPa for water pressure and 0.15 MPa for air pressure, which explain asymmetric droplet dispersion from distorted flow fields of fan-shaped nozzles. For the first time, a linear correlation between penetration ratio and spray height is established. This work provides theoretical support and quantitative references for optimizing secondary cooling parameters in continuous casting.