---

In the present study two-phase flow within the effervescent atomizer has been simulated by the volume of fluid interface tracing model using 0.08%, 0.32%, 1.24%, and 4.9% gas-to-liquid mass ratios and 0.38 L/min liquid flow rate. The purpose of this simulation is to study two-phase flow regimes within the effervescent atomizer and their effect on the atomization quality. This study also considers the gas-liquid interface instabilities in different two-phase flow regimes inside the atomizer. The compressibility of gas phase which is rear in literature survey included in gas-to-liquid mass ratios of 1.24% and 4.9%, due to the high gas phase velocity in constant liquid flow rate and high gas-to-liquid mass ratios. The effect of gravitational force is considered in all simulations. The results of the simulation indicate that by increasing the gas-to-liquid mass ratio, the two-phase flow regime inside the discharge passage transfers from bubbly flow regime with long bubbles to annular flow regime. In addition to decreasing the liquid film thickness coming out from discharge orifice (during transform of the flow regime from bubbly flow to annular flow), the liquid interface instabilities increase in the annular flow regime and besides, where segregated ligaments from the liquid interface become shorter, thinner and more unstable. This type of regime is the most efficient flow behavior for the effervescent atomizer.

---

The present study investigates the effect of the mixing chamber length on the effervescent atomizer internal two-phase flow and the liquid film thickness at the exit of the atomizer at different gas-to-liquid mass ratios. Therefore, the internal flow of this atomizer simulated for three different lengths of the mixing chamber, at the gas-to-liquid mass ratios of 0.08%, 0.32%, and 1.24% and at the liquid flow rate of 0.38 L / min by the volume of fluid interface following model. The simulation results show that the mixing chamber length does not have much effect on the dominant flow regime in the discharge passage. However, by increasing the mixing chamber length, the two-phase flow inside this chamber more expanded before entering into the discharge passage. Therefore, the two-phase interface instabilities in the discharge passage are lower for the atomizer with the longer mixing chamber. In addition, based on the measuring results of the liquid film thickness at the exit of the atomizer, the effect of the mixing chamber length on the thickness of this film depends on the gas-to-liquid mass ratio. Increasing the mixing chamber length at low gas-to-liquid mass ratio increases the liquid film thickness at the exit of the effervescent atomizer. While at high gas-to-liquid mass ratio, it's inverse. At middle gas-to-liquid mass ratio, the changes of the liquid film thickness at the exit of the atomizer with the mixing chamber length do not show a steady trend.