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The flow mechanism of internal two-phase flow atomization remains unclear despite its widespread applications. A newly outside-in-liquid (OIL) atomizer is designed to investigate the two-phase flow mechanism inside the effervescent atomizer in this work. Numerical simulation is used to study the internal flow characteristics of the OIL atomizer under different gas–liquid mass flow ratios (GLRs). The findings indicate that the volume-of-fluid (VOF) model and compressible Euler method effectively capture the intricate evolution of the internal flow. The cavitation phenomenon occurs before the gas phase reaching the orifice. Subsequently, the cavitation phenomenon disappears as the gas phase flows downstream into the orifice. At different GLRs, the gas phase before reaching the mixing chamber is a single separated bubble. However, the final flow patterns are mainly annular flow, which is most obvious at high GLR. Increasing the GLR can increase the gas void fraction in the orifice. Furthermore, the gas void fraction will reach the peak faster and then remain stable. The two phases are accelerated after entering the orifice. Among them, the flow velocity of gas phase is much higher than that of liquid phase. This research demonstrates the notable impact of GLR on the internal flow. Furthermore, it addresses the existing research gap in this aspect of internal flow. [ABSTRACT FROM AUTHOR]

A high-speed backlight system was adopted to investigate the evolution process of the inside-out-gas (IOG) effervescent atomizer and subsequent influence on spray morphology. The results show that bubble flow and annular flow are the most obvious flow patterns when the liquid flow rate is 20 g/s. During the transition from bubble to annular flow, slug flow occurred at gas–liquid mass ratio (GLR) of 3.2%. The annular flow was observed when the GLR further increased to 6.4%. In particular, when the mixing chamber is in a large bubble flow, an annular flow can still be formed at the orifice for the small exit diameter. For the annular flow, a relatively stable spray cone angle was observed. On the contrary, the slug flow has a greater oscillation for the spray cone angle. It was found that bubble flow in the orifice has little effect on atomization effect. For the spray cone angle, the oscillation in the slug flow is larger. Furthermore, the effects of GLR and liquid injection pressure drop are carefully considered in the empirical formula fitting compared to the widely used empirical formula. The empirical formula of the discharge coefficient of the effervescent atomizer is fitted, which provides fast data support for engineering applications. [ABSTRACT FROM AUTHOR]