Study on Droplet Breakup and Liquid Film Distribution in Nuclear Cyclone Steam-Water Separator

Cyclonic steam–water separators are widely used in nuclear steam generators due to their compact structure and high separation efficiency. The internal swirling flow field governs droplet breakup and liquid film distribution, and thus limit separation performance, but the evolution of the flow field and its influence on such behaviors remain insufficient. This paper combines numerical simulation and high-speed imaging experiments to investigate the flow field evolution, droplet breakup, and liquid film distribution patterns during cyclonic steam–water separation. The results indicate that the swirling flow field gradually develops from its initial establishment into a quasi-steady state within 0.1–0.5 s. The flow velocity is predominantly distributed within 9–24 m/s. The high-velocity zone migrates along the swirling direction, accompanied by an intensified radial pressure gradient with local pressure differences of 60–100 Pa. The evolution of the pressure and velocity fields within local high-shear regions dominates the energy transport process of the gas–liquid two-phase flow. Under the action of the high-speed swirling gas phase, droplet breakup exhibits multistage characteristics, including liquid column deflection (We < 2.67), ligament stripping (2.67 < We < 6.59), and bag-type breakup (We is the Weber number). Concurrently, the sidewall region demonstrates a significant capturing effect on droplets, resulting in a localized and discontinuous liquid film distribution. This work provides theoretical support for the optimization of cyclonic steam–water separators, facilitating higher separation efficiency and operational safety in nuclear systems.