Pressure Effects on Low-Liquid Loading Two-Phase Flow in Near-Horizontal Upward Inclined Pipe

The present work presents experimental and modeling studies of low liquid loading gas-liquid flow in slightly upward inclined pipes with relatively large diameter and high system pressure. These conditions are common in wet gas transport pipelines in oil and gas systems. Earlier studies were conducted at lower pressures and/or smaller diameter pipes.;Experimental results were obtained for an 85 m long, 0.155 m ID upward inclined pipe at an angle of 2º from horizontal. The flowing fluids are Isopar L as the liquid phase and Nitrogen as the gas phase. System pressures of 1.48, 2.18 and 2.86 MPa were considered resulting in gas densities of 17, 23 and 32 kg/m3, respectively. Superficial liquid velocities varied from 0.01 to 0.05 m/s, while superficial gas velocities varied from 1.5 to 16 m/s. Observed flow patterns were pseudo-slugs, stratified and annular. Pressure gradient, liquid holdup, entrainment flux and entrainment fraction were measured. A wire-mesh sensor was used to obtain the liquid and gas geometric distribution in the pipe cross-sectional area over time, as well as interfacial wave celerity, pseudo-slug translational velocity and interfacial roughness. Capacitance probes distributed along the test section were used to obtain pseudo-slug frequency and translational velocity at different locations through the pipe. Flow was visualized with both high-speed and high-resolution cameras.;This study presents a new model for pressure gradient calculations at the stratified-annular pattern transition region. The model considers the fact that the interface shape is flat for larger diameter pipes. A thin liquid film is formed at the gas-wall interface due to the entrained droplets deposition. This thin liquid film is responsible for an increased gas-wall friction factor. The friction factor is modeled based on a liquid mass balance at a pipe cross-sectional area, where atomization and deposition of liquid droplets occur, as well as liquid drainage through the pipe walls. Based on interfacial roughness measurement from this and past studies, the interfacial friction factor is assumed as a constant value. The rate of atomization equation is modified to better describe entrainment data obtained at high pressure systems. Final model shows a fair prediction with the acquired and literature data.