Liquid hold-up and phase split have been measured to study flow pattern dynamics around a vertical dividing junction with 0.005 m internal diameter pipes. Liquid phase viscosities were varied systematically between 1 mPa s and 36 mPa s. Test matrix implemented varied between 0–32 m/s for gas superficial velocity and 0.003–1.3 m/s for liquid superficial velocity respectively. Dynamic signals were acquired during the passage of gas–liquid two-phase flow employing electrical resistance between pairs of flush-mounted ring conductance probes located around the junction. The time varying void and phase split data have been examined at a number of levels. First, information about distribution of phases and flow pattern classification along each segment of the pipe is presented using probability Density Function (PDF) generated from time varying void fraction. PDF characteristic signature exhibits lower peaks and a marked shift towards decreasing void fraction as liquid viscosity increases. For a viscous liquid phase, bubbly flow approaching the junction changes to slug flow pattern after splitting at the junction in the vertical direction. Flow pattern in the horizontal side arm remains inevitably stratified irrespective of increase in liquid viscosity. At another level, liquid hold-up and phase split were examined. This analysis reveals additional flow assurance details. Liquid hold-up was seen to increase with increase in both liquid viscosity and gas take-off at the horizontal segment of the junction. However, effect of liquid viscosity only become significant when gas take-off exceeds a threshold of 0.40. Plot of the liquid hold-up against mixture velocity at various take-offs and different liquid viscosities fingerprints churn-annular transition boundary around gas superficial velocity of 15 m/s.

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