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5. RegimeMaps_web - ENU 4134 Regime Maps D Schubring...

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ENU 4134 – Regime Maps D. Schubring July 28, 2010
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Learning Objectives I 1-f-i Characterize the various regimes of two-phase flow I 1-f-ii Use flow regime maps (empirical and model-based) to identify flow regime(s) present in two-phase system I 1-f-iii Identify the importance of coherent structures (waves, droplets, bubbles, etc.) in two-phase flow and in the differentiation among regimes
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Empirical Analysis of Two-Phase Fluid Mechanics Motivation: for many applications, the analytical two-phase parameters ( { α } , S , etc.) from the first few lectures are hard/impossible to evaluate. It is often easier to develop empirical models based on a particular flow regime, in which certain effects are expected to be dominant. Such an approach proceeds in two stages: (1) identify or model or otherwise determine the flow regime (these slides) and (2) apply regime-specific models/correlations to predict quantities of interest ( dP / dz , etc.). The most important regimes (bubbly and annular) are given most of the regime-specific coverage. Bubbly is key in BWR cores and annular flow is key in SG’s and some accident scenarios.
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Flow Regime Maps I Outline of horizontal and vertical flow regimes seen in these maps. I Mapping coordinates. I Example horizontal and vertical maps. I Vertical flow map of Taitel et al. – theoretically determined transitions. I Concluding remarks.
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Horizontal vs. Vertical Flow In horizontal flow, gravity acts perpendicular to the direction of flow As a result, parameters in horizontal flow (local velocity, void fraction, wall shear, etc., etc.) are often functions of θ . In vertical flow, gravity acts parallel to the direction of flow. This adds an additional “source” of pressure drop ( ρ m g ) and emphasizes the importance of { α } , even when a regime-based model is used. Gravity also leads to strongly time-varying parameters ( e.g. , liquid that has negative velocities at times in churn flow).
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Flow Regimes in Vertical Flow – Hewitt and Hall Taylor Bubbly, slug, churn, annular
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Flow Regimes in Horizontal Flow – Barnea
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Regime Identification Subjective – clear tube and see what’s there.
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