| Low liquid loading gas-liquid two-phase flow in near-horizontal pipes has been studied both experimentally and theoretically. A new state-of-the-art, air-oil test facility was designed, constructed and operated. A transparent test section (50.1-cm ID x 19-m long) could be inclined within ±2° from the horizontal. Mineral oil was used as the liquid phase (μL = 5.66 mPa.s, ρL = 877 kg/m3, and σ = 30 dynes/cm at 23.9°C) and air was used as the gas phase. The measured parameters included gas flow rate, liquid flow rate, pressure, differential pressure, temperature, liquid holdup, liquid film flow rate, droplet entrainment fraction, droplet deposition rate and liquid film thickness at the bottom of the pipe.; A surprising phenomenon was observed; at high gas velocities (annular flow), liquid film flow rate, liquid holdup and pressure gradient decreased as liquid velocity increased. The reason is believed to be the effect of droplet entrainment on the gas stream. Countercurrent flow and vortices in the liquid film were observed in upward inclined flows. Gas bubbles were observed in the liquid film at all five inclination angles. A two-fluid model was developed for low liquid loading flows. New correlations were proposed for the interfacial friction factor. The effect of droplet entrainment on the interfacial friction factor is also evaluated. The predictions of liquid holdup and pressure gradient from the new models matched well with the experimental data. |
