SFM_web - ENU 4134 Separated Flow Model(s) D. Schubring...

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Unformatted text preview: ENU 4134 Separated Flow Model(s) D. Schubring September 18, 2009 Modeling of Two-Phase Flow I Averaging, averaged parameters (2) I Transport equations (2) I Homogeneous equilibrium model (1+) I Separated flow model(s) (1+) I Choked (critical) flow (1+) Separated Flow Model(s) In the SFM, the velocities of liquid and vapor are no longer assumed equal, although thermal equilibrium is still assumed. To close the model, we need some relation to replace v f = v g . In general, these relations are termed void fraction correlations or (as in T&K), void-quality-slip relations . General Void-Quality-Slip Relations Some relations among void fraction, { } , flow quality, x , slip ratio, S = { v v } / { v l } , and volumetric fraction of vapor, { } , are general and have provided as part of Chapter 5. These include: S = x 1- x l v 1-{ } { } (1) { } = 1 1 + 1- x x g f S (2) { } = 1 1 + 1- x x g f (3) These relations are always true. You should be very adept as using these as needed. Closure Equation Three closure relations will be explored in this course: I HEM, in which S = 1. I The Martinelli-Nelson void fraction, in which { } is correlated as a function of pressure and quality for steam-water only . I The drift flux model. Martinelli-Nelson Void Fraction Figure 11-17, page 497. Martinelli-Nelson Void Fraction Remarks I Only applicable to steam-water I Require reading off of a chart and interpolation I No dependence on mass flow rate, which is seen in real data I No consideration of surface tension effects Drift Flux Model...
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SFM_web - ENU 4134 Separated Flow Model(s) D. Schubring...

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