ABSTRACT
Two-phase flow in circular tubes is found in a wide range of industrial applications, including oil/gas pipelines and systems with evaporation (such as thermosyphon reboilers in the process industry and water-tube boilers in the power generation industry) and condensation (in-tube condensation in shell-and-tube heat exchangers and air-cooled heat exchangers, for instance). Though downward flows are important (particularly in condensation applications), they have been the subject of much less investigation than have vertical upflows. Studies of flow patterns in co-current downward flow are reported by Golan and Stenning, Barnea et al., and Crawford et al. The most important feature of such flows is the greater propensity to annular flow compared to upward flow systems. There has been a great deal of interest in flow pattern maps for horizontal flows, particularly on the onset of intermittent flows. Even small deviations of the channel from the horizontal can have a dramatic effect on the transition to slug flow.
