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 12.2m high and 250mm 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. Five flow patterns were identified in the vertical test section namely – dispersed bubbly, bubbly, agitated bubbly, churn/froth flow within the experimental superficial velocity range (ja = 0.18-2.2m/s and jw = 0.18-1.2m/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. Based on the visual and statistically extracted information, a flow pattern map was developed and compared to 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.