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Unformatted text preview: ENU 4134 – Regime Mapping Example – D. Schubring 1 Using a ﬂow regime map
Repeating needed data from our SFM example:
For the following conditions, compute the void fraction with the indicated models:
m = 0.15 kg s−1
˙ (1) 2 A = 1cm (2)
−2 Gm = 1500 kg m s −1 (3) x = 0.125 (4) ◦ (5) Tsat = 270 C The liquid and vapor densities, along with pressure, need to be obtained using steam tables as:
ρv = 28.1 kg m−3 (6) −3 (7) Psat = 5.505 M P a (8) ρf = 768 kg m We assumed churn ﬂow. Is this actually the regime present? Plot the ﬂow on the Hewitt and
Roberts map (Figure 117, page 469)? If this ﬂow is undergoing boiling, what regimes will it pass
2
through (i.e., compute ρl jl2 and ρv jv as a function of x)? Figure 1: Figure 117, page 469, T&K ENU 4134 – Regime Mapping Example – D. Schubring 2 Dropping brackets... (this becomes more common as we go through the term)
1500 = ρv jv + ρf jf
ρv jv
x=
ρf jf + ρv jv
1500x = ρv jv (9)
(10)
(11) 1500 (1 − x) = ρf jf
2
ρv jv =
2
ρf jf = (12) 15002 x2 = 8.1 × 104 x2
ρv
15002 (1 − x)2
= 2930 (1 − x)2
ρf (13)
(14) For x = 0.15:
2
ρv jv = = 8.1 × 104 × 0.152 = 1820
2
ρf jf (15) 2 = = 2930 (1 − 0.15) = 2120 (16) Figure 2 shows the results. The ﬂow in question (x = 0.15) is not in the churn regime, but
rather in the annular or wispyannular regime. At most qualities, this ﬂow is annular – typical of
relatively low pressure ﬂows. At higher pressure, lower density ratios allow for bubbly ﬂow at a
slightly higher quality. x=0.15 Figure 2: Conditions shown on the HR map. Indicated points (from topleft to bottomright): x =
0.95, 0.85, 0.75, 0.65, 0.55, 0.45, 0.35, 0.25, 0.15, 0.05, 0.01. ...
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 Fall '11
 Schubring

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