A = Af + Ar = 0.1815 m2/m .
The heat transfer coefficient for the horizontal (unfinned) surface of the tube is given by
eq 91
g (ρl - ρv ) kl hfg
1/ 4
3
hh = 0.728
= 1540 W/m2 K .
νl (Tsat - Tb ) dr
Beatty-Katz model:
The average fin height over the diameter do is
(
)
Lf = π do - dr 4do = 0.0046 m .
2
2
The heat transfer coefficient for the fin surface is
g (ρl - ρv ) kl hfg
1/ 4
3
hf = 0.943
= 2719 W/m2 K .
νl (Tsat - Tb ) Lf
Because ηf = 1, η = 1 from eq 93. Thus the Beatty-Katz model, eq 90 becomes
A
Ar
h = hh
+ hf f = 2487 W/m2 K .
A
A
The enhancement ratio is
h
h
=
= 1.63 .
hp hh
Based on the envelope area over the fins, πdoL, the average heat transfer coefficient is
h = 7568 W m2 K .
Webb et al. model:
For the Adamek condensate film profile, the Webb et al. model uses eq 97 for hf. Thus
1/ 4
σhfgθmSm
ξ+1
k
⋅
hf = 2.419 l
= 4696 W/m2 K .
3
νlkl (Tsat - Tb ) (ξ + 2)
Sm
The average interfin spacing s is calculated by assuming the fin to have an average
thickness of (0.38 + 0.23)/2 = 0.305 mm. Thus
s = 1.032 mm.
The flooding angle β can now be calculated using eq 89:
4σ
β = cos-1 1 -
= 41.44 degrees or 0.72 radians .
doρl gs
Finally using eq 98 and neglecting the last term, h is given by
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