On the characteristics of the roll waves in gas–liquid stratified-wavy flow: A two-dimensional perspective

Abstract

The characteristics of the roll waves in the oil–gas, stratified-wavy flow are studied experimentally in a 0.152m ID horizontal pipe for superficial gas velocities between 7.45m/s and 12.62m/s at two different liquid superficial velocities, 1 and 2cm/s. The liquid holdup, liquid film height, wetted wall perimeter decrease with the increasing superficial gas velocity. The interfacial surface area is calculated from the distinct interface between the phases from the experimental data without any assumptions on the interface geometry. The variation of the interfacial surface area is found to be closely related to the liquid holdup.The region where the interface fluctuations spread in the pipe cross-section is analyzed. For low gas flow rates, a small region exists where the fluctuations are negligible implying a continuous liquid contact with the pipe bottom. However, an increase in the superficial gas velocity extends the spatial reach of the interface fluctuations very close to the pipe wall at the bottom where the continuous liquid region diminishes. For all experimental conditions examined, the interface fluctuations occurring at a frequency range of 10Hz<f<40Hz is hypothesized to be related to the capillary waves.At low superficial gas velocities, the roll wave topology is stretched toward the sides of the pipe. Moreover, the oscillations of these waves at different transverse locations are out-of-phase. With an increase in the gas flow rate, the wave oscillations are observed to be in-phase with each other and more coherent structures are detected.