An experimental study of vertically upward air-water two-phase slug flow using hot-film anemometry

Wang, Guanjun (2001) An experimental study of vertically upward air-water two-phase slug flow using hot-film anemometry. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

An experimental study has been conducted to investigate two-phase slug flow and the closure problem of two-phase flow models. To investigate the problem experimentally, a 3-inch ID and 180-foot long close loop re-circulation multiphase flow research facility was constructed at the Fluids Laboratory, Memorial University of Newfoundland (MUN). Accurate instrumentation of this facility makes it suitable for both conducting multiphase flow research and testing multiphase flow measurement systems. A new flow pattern map has been developed based on dimensional analysis. The functional equation governing the flow pattern formation was analyzed to yield the proper dimensionless plotting parameters. The use of these parameters makes the resultant flow pattern map independent of flow geometry and fluid physical properties. Data collected from the MUN flow loop as well as from the literature were used to generate the new flow pattern map. Flow pattern boundaries were systematically determined using a pattern recognition technique. -- The second part of this study is focused on vertically upward concurrent slug flow. A simultaneous flow measurement system using both dual-probe hot-film anemometry and high-speed flow visualization was used to obtain the quantitative flow information. To discriminate the signal into the gas and liquid phases, a combined amplitude and first-order time derivative phase detection method has been developed. The void fraction of the flow was estimated from the resultant phase indicator function. An innovative data reduction technique using wavelet analysis combined with the phase detection method was developed to decompose the original signals into signals corresponding to air slugs and small air bubbles. This technique results in two velocities corresponding to slugs and bubbles from cross-correlation analysis of the discriminated signals. Slug/bubble velocities, slug/bubble sizes, slug/bubble frequencies and slug/bubble void fractions were also estimated from the decomposed signals. Slug flows under a variety of flow conditions were investigated to yield a detailed description of the flow. The calculated mean velocities of air slugs, bubbles and liquid slugs are slightly lower than those predicted by the correlations in literature. Necessary modifications of these models were, therefore, recommended. Models for predicting void fraction, slug void fraction, slug/bubble dimensions and bubble frequency were also developed. The results obtained from the hot-film signal processing technique were verified by the two image processing methods. -- A technique for approximating the interfacial area concentration from a single normal probe was proposed in this study. Comparison of the measurements conducted in this study with the reported interfacial area concentration models developed based on bubble flow indicates that these models are not suitable for slug flow. An interfacial area concentration model was, therefore, formulated for slug flow based on the synthesis method. The proposed correlation indicates that the interfacial area concentration is closely related to flow and fluid properties. In summary, the study presented in this thesis provides a detailed quantitative flow description and information for formulating accurate constitutive equations for vertically upward air-water two-phase slug flow.

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