Two-phase flow in a vertical concentric annulus: Pressure drop and flow configuration

This paper presents experimental investigation of flow configurations and pressure drop of single-phase water flow and two-phase air-water flow in a vertical annulus. The annular test section had a concentric geometry with a casing and tubing diameter of 50 and 33.7 mm, respectively. The superficial velocity conditions of the liquid and gas were ranged 0.08–1.56 and 0–3.56 m/s, respectively. The combination of these superficial velocities produces the bubbly, slug and churn flow regimes. The identification of the flow patterns shows that the Mishima and Ishii model is the most relevant to highlight the flow transition. The measured friction factors were compared to prediction models from the literature. It was deduced that the model proposed by Gunn and Darling underestimates the liquid friction factor in the annulus. The measured pressure drops and the dimensionless pressure gradient evolution exhibits different slopes that characterize each flow pattern. The standard deviation and structure frequency describe specific ranges for each flow pattern. These two parameters can also be used for the prediction of flow patterns.