Experimental Investigations on Onset of Slugging in Horizontal Air-Water Two-Phase Flow

Flow visualisation experiments are reported on two-phase air-water flow through a 25 mm internal diameter, 8 m long horizontal pipeline in order to analyse the onset and evolution of slug flow over a wide range of superficial Reynolds number of liquid (Re-SL) and gas Reynolds number (Re-SG). The visualised images reveal that slug is formed when the amplitude of wavy interface increases over a stratified film and blocks the gas. As the slug passes the liquid level behind the slug significantly drops. Liquid level of this thin film is then observed to rebuild its level in a time whose order of magnitude is equal to the inverse of the slug frequency. Interfacial structures of slugs are analysed in terms of non-dimensional liquid height at five different axial locations along the test rig. Effect of inlet gas and liquid flow rates on the slug initiation and growth is also illustrated in terms of Re-SL and Re-SG.