This study investigates wave-stratified flow in a horizontal pipe at high pressure, and flow characteristics are obtained, such as flow pattern map, liquid film thickness, and pressure drop. Compared with a flow pattern map of a gas-liquid two-phase flow carried out at atmosphere, stratified flow zone is depressed with increasing system pressure and the critical gas superficial velocity decreases for smooth-wave-stratified flow transition, while the critical liquid superficial velocity increases for stratified-intermittent transition. On one hand, the compressed air results in an increase in momentum transfer between gas and liquid phases, which accounts for the smaller gas superficial velocity that is encountered in both smooth-wave and stratified-annular flow transition at higher pressure. One the other hand, it slows down the liquid below the crest, and it makes the interface wave crest unstable and split for the vortex shedding behind the wave crest, which accounts for flow regime transition in gas-liquid two-phase flows in pipelines. As a result, stratified-intermittent flow transition is depressed and delayed. The pressure influence on the liquid film profile is analyzed, and relationships between film thickness and dimensionless numbers are studied, such as liquid Weber number and gas Weber number. Friction factors on different interfaces at high pressure are studied, and new empirical formulas are deduced.

A model is proposed for liquid film profile prediction in gas-liquid two-phase flow, which is able to provide the film thickness along the circumferential direction and the pressure gradient in the flow direction. A two-fluid model is used to calculate both gas and liquid phases’ flow characteristics. The secondary flow occurring in the gas phase is taken into account and a sailing boat mechanism is introduced. Moreover, energy conservation is applied for obtaining the liquid film thickness distribution along the circumference. Liquid film thickness distribution is calculated accordingly for different cases; its values are compared with other models and available experimental data. As a result, the newly proposed model is tested and good performances are demonstrated. The liquid film thickness distribution in small pipes and inclined pipes is also studied, and regime transition is revealed by liquid film profile evolution. The observed inflection point demonstrates that the liquid film thickness decreases steeply along the circumference, when the circle angle ranges between 30° and 50° for gas-liquid stratified flow with small superficial velocities.