Two-phase flow in large annular ducts is very common in industrial applications. Nevertheless, many two-phase-flow phenomena in such a geometry have not been fully understood. This article addresses an investigation on the effects of duct geometry and liquid viscosity on vertical upward annular-duct...

Two-phase flow in large annular ducts is very common in industrial applications. Nevertheless, many two-phase-flow phenomena in such a geometry have not been fully understood. This article addresses an investigation on the effects of duct geometry and liquid viscosity on vertical upward annular-duct two-phase flows. Compressed air and tap water or mineral oil were the working fluids. Three oil viscosity ranges were tested, from 30 to 400 mPa·s. A 10.0-m-long inclinable experimental setup was designed and built for the experiments conducted in two equivalent geometries. The first is made of a 95-mm-inner-diameter circular pipe (called the reference pipe), and the second is a concentric annular duct with 95-mm hydraulic diameter, the same diameter as the reference pipe. The radial geometries were similar to those observed in oil wells. Flow patterns, total pressure drop, and in-situ volumetric fractions were obtained. According to the results, the standard hydraulic diameter might not be appropriate for the modeling of vertical gas/liquid flow in large annular ducts

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