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Experimental study on bubbly flow transition in vertical annular gap bubble column
conference contributionposted on 15.08.2011 by Fahd M. Al-Oufi, Iain W. Cumming, Chris Rielly
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Mean and local gas void fractions in vertical upward, two-phase flows contained within the annular gap between two concentric tubes are presented. For a given gas superficial velocity, jg, the mean void fraction, , was found to decrease as the diameter ratio of the two tubes approached unity (i.e. for narrower gaps). Moreover, was significantly lower than that obtained in an open tube at the same jg. Two explanations were proposed: (i) large bubbles, generated in the annular gap, destabilised the flow, and (ii) the driftflux distribution parameter in an open tube was different to that in an annular gap, which results in a different mean . It was shown that injection of large bubbles into a homogeneous flow led to an early transition. Furthermore, the void fraction profiles in the annular gaps depended on both jg and the gap geometry
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