Flow Characteristics and Evolution Mechanisms of a Liquid–Liquid Compound Jet

The disintegration and evolution of liquid–liquid compound jets significantly impact the mixing and mass transfer of two-phase fluids, yet the underlying mechanisms remain unclear. In this study, the flow characteristics and evolution mechanisms of a compound jet were investigated by using high-speed imaging. Three types of inner fluid structures were identified: liquid droplets, liquid dumbbells, and liquid ligaments, among which liquid dumbbells and ligaments were transitional inner fluid structures. Liquid dumbbells evolve into droplets through pinch-off or recoil, whereas liquid ligaments first contract into liquid dumbbells and then undergo a similar evolution to form droplets. A model was developed to investigate the competing mechanisms between pinch-off and recoil in the evolution of liquid dumbbells. The effects of flow rate ratio, flow velocity, interfacial tension, and liquid viscosity on the mean droplet diameter ( d 32 ) and jet breakup length ( L ) were systematically examined. Based on the experimental results, correlations for predicting d 32 and L were proposed, with deviations within ± 10% and ± 20%, respectively.