Transition of plug to slug flow and associated fluid dynamics

• Published in: International journal of multiphase flow 2017-05, Vol.91, p.63-75
• Main Authors: Thaker, Jignesh, Banerjee, Jyotirmay
• Format: Article
• Language: English
• Subjects: Flow visualization; Local measurement; Plug flow; Slug flow; Transition
• ISSN: 0301-9322; 1879-3533
• DOI: 10.1016/j.ijmultiphaseflow.2017.01.014

•Transition of plug to slug flow is analysed by flow visualization and local velocity measurements using LDV.•LDV measurements show a large velocity difference between liquid slug and liquid film regions.•Higher translational velocity of elongated bubble (due to high ReSG) results in sudden increment in liquid plug/slug velocity.•Higher interfacial shear between liquid film and slug bubble leads to secondary flow structures near bubble tail.•Secondary flow structures (swirls) results in detachment of small bubbles from plug bubble tail leading to transition. Transition of plug to slug flow is associated with bubble detachment from elongated bubble tail or bubble entrainment inside the liquid slug. The mechanism responsible for this transition was earlier identified by Ruder and Hanratty (1990) and Fagundes Netto et al. (1999) based on the shape of the hydraulic jump observed at elongated bubble tail region. The transition mechanism reported by Ruder and Hanratty (1990) and Fagundes Netto et al. (1999) was only based on their flow visualization study. Plug to slug transition and associated dynamics of bubble detachment from the elongated bubble is analysed in the present paper using flow visualization and local velocity measurements. Experiments are reported for 13 different inlet flow conditions of air and water phases. Images of plug/slug flow structures are captured at a rate of 4000 FPS using FASTCAM Photron camera and the local values of axial liquid velocity are measured using LDV system synchronised with a 3D automated traverse system. LDV measurement of local liquid velocity in the liquid slug and liquid film establishes the reason for detachment of bubbles from the slug bubble tail.