Classification of primary breakup modes for dual gas-assisted annular sheet nozzles

This study aims for the systematic characterization of the primary breakup pattern of gas-assisted annular sheet nozzles featuring two co-flowing gas streams (dual gas-assisted annular sheet nozzles). Three nozzles with different liquid sheet thickness (1–3 mm) but constant gas orifice areas were applied. Water was used as liquid phase. The liquid as well as both gas streams were varied independently. Primary breakup was captured utilizing high-speed imaging. Besides known breakup modes already described in literature, new modes were observed and described as function of inner/outer gas momentum flow rate and liquid velocity for each sheet thickness. Breakup modes were categorized into bubble-induced modes - characterized by the formation of a bubble - and non-bubble-induced modes, where bubble formation is suppressed. A comprehensive mapping and detailed description of the primary breakup of dual gas-assisted annular sheet nozzles is presented, offering new insights into the interplay between gas and liquid flow rates and nozzle geometry. Furthermore, an empirical approach was developed to calculate the inner and outer gas momentum flow rates required to achieve technically relevant breakup regimes across varying liquid mass flow rates. These findings establish a basis for liquid mass flow scaling and support the design and optimization of atomization systems for technical applications. • New breakup modes for dual gas-assisted sheet nozzles are identified. • Formation of a bubble significantly influences breakup patterns. • Breakup maps link flow conditions and nozzle design to breakup modes. • Applying and predicting breakup modes for nozzle design based on operating conditions.