Experimental study of interfacial structure of horizontal air-water two-phase flow in a 101.6 mm ID pipe

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The current work seeks to investigate the interfacial structure and establish an extensive experimental database in horizontal air–water two-phase flow in a 101.6 mm inner diameter pipe. A wide range of flow configurations are studied including bubbly, plug and slug flows. A flow visualization study using the high-speed video camera enables qualitative description of bubbly-to-plug and bubbly-to-slug transitions, while the database of local time-averaged two-phase flow parameters obtained by the four-sensor conductivity probe enables quantitative study on the evolution of the flow. Detailed measurements across the flow area are performed for nine test conditions at three different axial locations downstream of the inlet. Using this database, the effects of superficial liquid and gas velocities, and development length on the evolution of interfacial structure are investigated. Similar characteristics are observed as in a counterpart 38 mm ID horizontal two-phase flow facility, which include (1) the bubbles are found to be more concentrated near the top wall in bubbly flow as superficial liquid velocity decreases at a constant superficial gas velocity, while increasing superficial gas velocity promotes the growth of bubble layer thickness; (2) in bubbly-to-plug transition, the void fraction of small bubbles decreases and the size of small bubbles increases, while in bubbly-to-slug transition, opposite trends are observed. Meanwhile, different characteristics on the evolution of the interfacial structure are also observed, which indicates the effect of increasing pipe diameter. The bubbly-to-plug/slug transition is found to shift to higher superficial liquid velocities as pipe diameter increases. It is observed that the gas phase is more concentrated near the top wall in the large diameter pipe. As a result, the distance between bubbles is smaller and there is a higher chance for bubbles to coalesce into large bubbles. The critical void fraction where the bubbly-to-plug/slug transition initiates decreases as pipe size increases.