Plug and slug flows exist over a wide range of flow conditions in horizontal two-phase flow, which are characterized by the alternating appearance of elongated bubbles that occupy the upper portion of the pipe and liquid regions that occupy the entire cross-sectional area of the pipe.&nbsp; Due to the quasi-periodic gas pocket, plug and slug flows are inherently unsteady with a large variation of mass flow rate, pressure, and velocity in both radial and axial directions even when the gas and liquid flows supplied to the systems are steady.&nbsp; This can cause severe vibrations of the support structure, pipe corrosion, pipe fatigue, and destruction.&nbsp; Such an unstable nature of horizontal plug and slug flows must be considered in the design of two-phase flow systems.The current work performs air-water experiments in three different pipe sizes of 38 mm, 51mm, and 102 mm to investigate the frequencies of plug and slug bubbles in horizontal flows.&nbsp; The local four-sensor conductivity probe is used to establish experimental data for large elongated bubbles.&nbsp; The investigated conditions focus on a relatively high superficial liquid velocity region (1.0 m/s ≤ jf ≤ 4.0 m/s), where limited experimental data are available in the literature.&nbsp; The investigated superficial gas velocity (jg) ranges from 0.19 m/s to 3.0 m/s.&nbsp; In total, 19 conditions are studied.&nbsp; To identify the elongated plugs and slugs, the local four-sensor conductivity probe is located near the top wall.&nbsp; Based on the flow visualization study, the stable plug and slug bubbles cannot be shorter than a pipe diameter.&nbsp; Therefore, a chord length greater than a pipe size is used as a criterion to pick up the elongated plug and slug bubbles.&nbsp; Using the obtained data, the frequencies of plug and slug bubbles are analyzed.&nbsp; For the investigated conditions, the Strouhal number (St) ranges from 0.03 to 1.68, while the St of the existing data in the literature are generally below 0.1.&nbsp; It is found that the frequency of elongated bubbles increases as jf increases, but first increases then decreases as jg increases.&nbsp; This indicates that large elongated bubbles start to coalesce once jg reaches a certain value.&nbsp; This threshold has a higher value of jg than the plug to slug transition point.&nbsp; In addition, the frequency decreases as pipe size increases. The existing correlations in the literature are evaluated using the newly collected data.&nbsp; It is found that the St number-based correlations can predict the data will higher accuracy.&nbsp; New correlations are developed using the new data and they can predict the frequency with an absolute average percentage difference of ±20%.

Frequency of Plug/Slug Bubbles in Horizontal Air-Water Two-Phase Flow

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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