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Unformatted text preview: ENU 4134 – Regime Maps D. Schubring July 28, 2010 Learning Objectives I 1fi Characterize the various regimes of twophase flow I 1fii Use flow regime maps (empirical and modelbased) to identify flow regime(s) present in twophase system I 1fiii Identify the importance of coherent structures (waves, droplets, bubbles, etc.) in twophase flow and in the differentiation among regimes Empirical Analysis of TwoPhase Fluid Mechanics Motivation: for many applications, the analytical twophase 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 regimespecific models/correlations to predict quantities of interest ( dP / dz , etc.). The most important regimes (bubbly and annular) are given most of the regimespecific coverage. Bubbly is key in BWR cores and annular flow is key in SG’s and some accident scenarios. 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. 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 regimebased model is used. Gravity also leads to strongly timevarying parameters ( e.g. , liquid that has negative velocities at times in churn flow). Flow Regimes in Vertical Flow – Hewitt and Hall Taylor Bubbly, slug, churn, annular Flow Regimes in Horizontal Flow – Barnea Regime Identification Subjective – clear tube and see what’s there....
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This note was uploaded on 02/07/2011 for the course ENU 4134 taught by Professor Schubring during the Spring '11 term at University of Florida.
 Spring '11
 Schubring

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