Application of dividing junction in sub-sea separation of a hydrocarbon well stream is becoming increasingly popular across the petroleum industry. They are often used in stage separation of a hydrocarbon well stream to reduce process load on a primary separator. Where the diameters of the pipes making up the junction are small, it is of particular interest to nano multiphase flow technology (NMFT) currently being advocated. While there is a body of data for small diameter dividing junctions, it is almost exclusively for air-water where the pattern before flow and after the junction in the vertical segment of the pipe is usually unchanged. Here, new data for air and more viscous liquid are presented. They have been acquired from electrical resistance measurements made between pairs of flush-mounted ring conductance probes located around the junction. Liquid phase viscosities were varied systematically between 1 mPa$·$s (water) and 36 mPa$·$s (water-glycerol mixture). The implemented test matrix varied between 0 – 32 m/s for gas superficial velocity and 0.003 – 1.3 m/s for liquid superficial velocity respectively. The internal pipe diameter making up the junction is 5 mm. The time varying void fraction obtained has been used to obtain probability density functions (PDF) to characterize the flow. PDF exhibit lower peaks and a marked shift in the direction of decreasing void fraction for more viscous liquid. Flow structure frequency was extracted from a detailed spectrum analysis (PSD) based on the fluctuation of void wave signals with time. The result shows that the dominant frequency of the flow structure increases as liquid viscosity increases. Analysis of the measured phase split data reveals additional flow assurance details. This study shows the effect of liquid viscosity becomes significant only when the gas taken off exceeds a threshold of 0.40. The plot of the liquid hold-up against the mixture velocity fingerprints churn-annular transition boundary around a gas superficial velocity of 15 m/s. The flow pattern approaching the junction changes after leaving the junction in the vertical run arm as liquid viscosity increases; however, an increase in liquid viscosity has no effect on flow pattern in the horizontal side arm.

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