Effect of Fluid Properties on Flow Patterns in Two-Phase Gas−Liquid Flow in Horizontal and Downward Pipes

This paper investigates the effect of gas density and surface tension on flow pattern transitions in horizontal and near-horizontal pipes. Experiments were conducted at atmospheric conditions in a 12.75-m long pipe with a diameter of 0.024 m and downwardly pipe inclinations of 0°, 0.25°, and 1°. The effect of gas density was examined using CO2 and He gases and the effect of surface tension was examined using aqueous solutions of normal butanol. The various transitions were identified visually and by statistical analysis of film height measurements. Gas density strongly affects the transition to 2-D and K−H waves, whereas the transition from stratified to slug flow remains rather unchanged. Both wave transitions can be described satisfactorily by existing models in the literature with some modifications. A reduction in surface tension causes the transitions to 2-D waves to be shifted to much lower gas rates. For downward flows, as previously reported in the literature, even a small inclination can cause an expansion of the stratified flow regime. In this regime two different types of waves can be identified, which retain the 2-D and K−H wave characteristics observed in horizontal flow.