Title: A Mechanistic Model for Gas-liquid Two-phase Flow in Slightly Inclined Pipes: To Improve Predictions of Flow Patterns and Pressure Drops.
Abstract: This paper describes experimental and modeling studies to investigate the behavior of gas-liquid two-phase flow in horizontal and slightly inclined pipelines. The studies were performed with experimental data newly obtained at over 1000 flow conditions that were designed to cover all the flow patterns. The experiments were conducted at a test loop of a 54.9mm diameter, 105.0m long pipeline, with 0, 5, and 10 degree inclination of the test section.A new mechanistic model for horizontal and slightly inclined flow was developed implementing transition criteria between the flow patterns, correlation for liquid holdup, and flow models for pressure drop computation. The criteria for the transition boundaries between flow regions were determined for eight flow patterns matching the predicted flow patterns with the experimental observations. For stable dispersed bubble flow, constraints on the bubble size were additionally applied. At the transition between stratified and non-stratified flow, we added such a criterion that slug flow can remain stable at much lower flow rates of liquid. The froth flow region was newly modeled to reproduce the experimental observations between annular and slug flow.The pressure drops were computed for individual conditions of the experimental measurements. Excellent performance of the model was demonstrated by good agreements between the computed results and the experimental data. Correct identification of the flow pattern is crucial for accurate estimation of pressure drops, particularly for those near the transition boundaries. Use of appropriate friction factors is of primary importance for pressure drop calculations in any of the flow patterns.