Effect of Mixing Port Length on Internal Flow and Near-field Jet Characteristics of Twin-fluid Atomizers

Abstract

Twin-fluid atomizers are used to improve liquid atomization and spray dispersion to achieve higher combustion efficiency and reduce smoke emissions in a wide range of operations associated with industrial burners and gas-turbine combustors. This study aims to elucidate the effect of the mixing port length on the internal flow and atomization process, and to determine the optimum length of the mixing port within a wide operating range. A Volume of Fluid-Large Eddy Simulation (VOF-LES) method is conducted to investigate the multiphase flow behaviors in three types of twin-fluid atomizers with different mixing port lengths. Furthermore, the jet breakup processes are observed using a high-speed video camera. The results indicate that under a low liquid flow rate, annular flow occurred in the three types of atomizers. Moreover, the thickness of the annular liquid film becomes more uniform as the length of the mixing port increases. However, at high liquid flow rates, the jet behavior depends on the mixing port length. For the medium-length atomizer, the inner jet exhibits intense fluctuations and impinges on the inner wall of the mixing port, thus facilitating the breakup process. Among the three different mixing port lengths, the medium-length atomizer effectively strengthens the breakup of the jet, thus indicating that an optimal mixing port length exists for twin-fluid atomization. The results indicate that the jet flow behavior is affected significantly by the mixing port design, which feature different lengths, thus resulting in different levels of jet fluctuation and breakup processes