Local and Area-Averaged Flow Structure of Air-Water Two-Phase Flow in a Vertical Annulus

The flow structure of gas-liquid two-phase flow has been investigated in a vertical annulus channel. The annulus consisted of a geometry where the inner diameter was 19.1 mm and the outer diameter was 38.1 mm. The total height of the test section was 4.37 m. Experiments were conducted for nineteen inlet flow conditions. These flow conditions covered bubbly, cap-slug, and churn-turbulent flows. The local flow parameters, such as void fraction, interfacial area concentration, and bubble interface velocity, were measured at nine radial positions within the gap of the annulus at z/D_h = 230 of the test section. Radial distributions of these parameters were interpreted in terms of turbulent velocity profile, lift and wall forces. In addition, the local measurements were used to calculate distribution parameter, C₀ in drift-flux model, and area averaged interfacial area concentration. Ishii’s (1977) model was modified and a new correlation of C₀ was proposed based on the experimentally obtained C₀ values. The area-averaged interfacial area concentration (IAC) values were compared with the most widely used models (Ishii and Mishima, 1980; Spore et al., 1983; Hibiki and Ishii, 2002). The advantages and drawbacks of these models were highlighted.