A numerical simulation using commercial software (Fluent) is conducted to analyze the two-phase air–water flow in a straight pipe with an inner diameter of 1 mm. The superficial velocity for the liquid phase is fixed at 2 m/s, while the superficial velocity for the gas phase is ranged from 0.1 to 10 m/s. Within two decades of the superficial velocity ratios of gas to liquid (vgs/vls) range, it is found that the dependence of the volume fraction of the liquid phase at the statistically stationary state (ϕLs) on vgs/vls can be divided into two regimes. When the flow transitions to slug and annular-like flows, ϕLs(vgs/vls) approximately follows a power-law relationship with a scaling exponent of −0.35. Additionally, it is found that the drift-flux theoretical model can effectively predict ϕLs(vgs/vls). Simultaneously, the relation between the time for the initial mixing process (ts) and vgs/vls also exhibits two regimes. For bubbly flow, ts(vgs/vls) approximately follows ts∼(vgs/vls)−0.25. As the flow transitions to slug and annular-like flows, the scaling exponent of ts(vgs/vls) decreases to −0.7. Furthermore, it is revealed that in the transition range from bubbly to churn flow (0.1 ≲ vgs/vls ≲ 1), the dependence of the mean bubble length lb on vgs/vls follows lb∼(vgs/vls)1.6. Finally, through the analysis of the probability density function of the pressure drop, it is indicated that slug and annular-like flows exhibit significant intermittent fluctuations. This study reveals various laws of void fraction, flow structures of the continuous bubble, and pressure drop vs vgs/vls under zero gravity, providing insight for applications of two-phase flow under microgravitational environments.
Wang et al. (Thu,) studied this question.