Some characteristics of gas-liquid two-phase flow in vertical large-diameter channels

In engineering fields such as power generation systems (nuclear and thermal power plants), chemical processing, oil industry and so on, large-diameter channels have been extensively used to increase the mass, momentum and heat transport capability of the working fluid. Compared with small-diameter pipes, two-phase flow in the large-diameter channels shows more complicated flow characteristics. Much larger cap bubbles can exist and the interfacial instability prevents the large cap bubbles from forming large stable Taylor bubbles. So, the flow regimes and the radial void fraction profiles are different and the relative velocities between the two phases are significantly increased compared to those in small-diameter pipes. This paper reviews the recent progress in the research on two-phase flows in large-diameter channels. Recent progress on the state-of-the-art tool of four-sensor probe is explained and the necessary two-group bubbles can be classified through the measured bubble diameter, instead of the present method using bubble chord length, in 3-dimensional two-phase flow. The databases on the flows in large-diameter channels are presented and their typical multi-dimensional characteristics are discussed in detail. The most updated constitutive equations covering flow regime transition criteria, drift-flux correlations, interfacial area concentration (IAC) correlations and one- and two-group interfacial area transport equation(s) (IATE(s)) are summarized and their merits and drawbacks are analyzed. The important assumption that the area-averaged interfacial velocity weighted by IAC is equal to the area-averaged gas velocity weighted by void fraction in the 1D IATE has been confirmed by the present newly-obtained experimental data. The 1D numerical simulations of multi-dimensional two-phase flows in large-diameter channel are reviewed. Finally, the future research directions are suggested.