Two-phase flow patterns in large diameter vertical pipes

An experimental investigation of adiabatic upward co-current air-water two-phase flow has been carried out to determine the flow patterns in a 12.2=m-high and 250=mm nominal diameter vertical pipe. The visual observations of flow patterns were supplemented by statistical analysis of the time-averaged void fraction determined by pressure drop method. Four flow patterns were identified in the vertical test section, namely dispersed bubbly, bubbly, agitated bubblyand churn/forth flow within the experimental superficial velocity range ( j(a) = 0.18-2.2 m/s and j(w) = 0.18-1.2 m/s). Conventional slug flow consisting of smooth bullet-shaped bubbles (Taylor bubble) and liquid slugs was never observed; instead, agitated bubbly flow was the most dominant flow pattern in relevant superficial velocity range. On the basis of the visual and statistically extracted information, a flow pattern map was developed and compared with the existing flow pattern maps. Available flow regime transition models compared against the present experimental data yielded poor agreement with none of the existing models predicting the transitions as a whole. A satisfactory agreement was obtained with other large diameter studies with inconsistencies mainly attributable to confusion in the identification of the flow patterns. (c) 2013 Curtin University of Technology and John Wiley & Sons, Ltd.