The flat and curved interface models for gas-liquid separated flows in pipes are developed mostly from air-water flow experiments in low pressure

small diameter

horizontal or nearly horizontal pipes

which may not be suitable for high pressure

large diameter and undulating natural-gas-condensate pipelines.By use of methods for phase behavior and physical properties and coupled thermo-hydraulic computations

the suitability of these two mechanistic separated flow models to gas-condensate flow in long-distance

high-pressure

large-diameter and undulating pipelines was studied.Different combinations of friction factor correlations for the flat and curved interface models were embedded in thermo-hydraulic computations of an actual high-pressure

large-diameter

undulating natural-gas-condensate long-distance pipeline.The computational results of pressure drops and accumulated liquid contents for the flat gas-liquid interface model in this study agreed better with the field operating data than the curved interface model.