The effects of pressure and pipe diameter on gas-liquid two-phase flow behaviors were investigated experimentally and theoretically for horizontal and slightly inclined pipelines. Experimental data of flow pattern, pressure drop and liquid holdup were acquired in the wide range of the gas and liquid flow rates in a large diameter (106.4 mm) pipe for different pressures (592 and 2060 kPa) and different inclination angles (0°, 1°, and 3°). To evaluate effects of the pipe diameter, our previous experimental data of low pressure (490 kPa) and small diameter (54.9 mm), were also used. Based on analysis of the experimental observations, a flow pattern map was developed for each pressure, pipe diameter, and inclination.

Major phenomena identified in data analysis include: Pressure and pipe diameter clearly affect the flow pattern transition boundaries. The high pressure tends to shift the boundaries to the lower side of superficial gas velocity in the flow pattern maps. In the large-diameter-pipe experemints, stratified flow was observed at higher superficial liquid velocities than in small diameter. The gas flow rate and inclination angle showed influences on liquid holdup and pressure drop behavior. The average pressure did not show large influences on liquid holdup and pressure drop.

Based on the experimental data, a mechanistic model was developed incorporating transition criteria for eight flow patterns, and individual flow models for estimating liquid holdup and pressure drop. The results predicted by the individual models demonstrated excellent agreements with the experimental data for each pressure and each inclination angle.

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