Water-sheet atomization and spray characterization from convergent nozzles

This study investigates atomization in water-sheet sprays issued from convergent nozzles. High-speed shadowgraphy is used to map breakup regimes, and laser diffraction is used to quantify droplet-size distributions across systematic variations of the flow rate, nozzle outlet aspect ratio, and convergent angle. Within the Weber number-angle (We–θ) space, two stable regimes and a third, unstable one are identified, with the latter exhibiting chaotic atomization and further subdividing into three sub-regimes. The droplet-size distributions are often bimodal, with a large-drop peak linked to rim-driven pinch-off and a fine-drop peak associated with sheet-driven atomization. Moreover, power-law correlations are developed for breakup length, Sauter mean diameter (d32), and number-mean diameter (d10). These scalings reflect the interplay of inertia, surface tension, and viscosity, where stronger aerodynamic/viscous forcing (higher capillary number) yields finer sprays (smaller d32 and d10) while pushing breakup downstream, with the nozzle geometry modulating these trends: larger outlet aspect ratios slightly lengthen breakup yet suppress droplet sizes, whereas larger convergent angles shorten breakup and further reduce characteristic diameters. These results provide a predictive framework for estimating breakup length and droplet sizes across various operating conditions, enabling the design of compact sheet-spray devices.