Flow visualization of ultrasound-modulated two-fluid atomization

In this paper, we present flow visualizations of viscous liquid jets near the nozzle tip using a 30-nanosecond pulse laser as verifications of the initial and the jet boundary condition of a traveling capillary wave. Specifically, a bright band near the nozzle tip is seen in both ultrasonic and ultrasound-modulated two-fluid (UMTF) atomization, but not in two-fluid atomization. The bright band can be attributed to scattering of laser light sheet by the capillary wave generated by the ultrasound on the intact liquid jet. Good agreement between the jet breakup time calculated from this measured band length and that predicted by the modified Taylor's dispersion relation has led to the conclusion that UMTF atomization occurs via Taylor-mode breakup of capillary waves. Note that UMTF atomization is capable of controlling the drop-size and size distribution of two-fluid atomization for uniform drop formation.