Unformatted text preview: f enhancement depends on the Reynolds number.
Based on his experimental studies, Kutateladze (1963, Ref. 15) recommended
the following relation for the average heat transfer coefficient in wavy lamiRe 1800,
nar condensate flow for
l and 30
hvert, wavy Re kl
1.08 Re1.22 g
5.2 2
l 1/3 30 , Re 1800 (1025) l A simpler alternative to the relation above proposed by Kutateladze (1963,
Ref. 15) is
hvert, wavy 0.8 Re0.11 hvert (smooth) (1026) which relates the heat transfer coefficient in wavy laminar flow to that in
wavefree laminar flow. McAdams (1954, Ref. 2) went even further and
suggested accounting for the increase in heat transfer in the wavy region by
simply increasing the heat transfer coefficient determined from Eq. 10–22 for
the laminar case by 20 percent. Holman (1990) suggested using Eq. 10–22
for the wavy region also, with the understanding that this is a conservative
approach that provides a safety margin in thermal design. In this book we will
use Eq. 10–25.
A relation for the Reynolds number in the wavy laminar region can be
determined by substituting the h relation in Eq. 10–25 into the Re relation in
Eq. 10–11 and simplifying. It yields
Revert, wavy 4.81 3.70 Lkl (Tsat
l h*
fg Ts) g 1/3 0.820 , 2
l v l (1027) Turbulent Flow on Vertical Plates At a Reynolds number of about 1800, the condensate flow becomes turbulent.
Several empirical relations of varying degrees of complexity are proposed for
the heat transfer coefficient for turbulent flow. Again assuming
l for
simplicity, Labuntsov (1957, Ref. 17) proposed the following relation for the
turbulent flow of condensate on vertical plates:
hvert, turbulent 8750 Re kl
58 Pr 0.5 (Re0.75 g
253) 2
l 1/3 , Re 1800
l (1028) cen58933_ch10.qxd 9/4/2002 12:38 PM Page 539 539
CHAPTER 10
1.0
Pr = 10 Eq. 1024 5
h (νl2/g)1/ 3
————
—
kl 3
Eq. 1025 2
1
Eq. 1028 Wavefree
laminar
0.1
10 Wavy laminar
30 100 Turbulent
1000 1800
Re 10,000 FIGURE 10–26
Nondimensionalized heat transfer
coefficients for the wavefree laminar,
wavy laminar, and turbulent flow
o...
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This note was uploaded on 01/28/2010 for the course HEAT ENG taught by Professor Ghaz during the Spring '10 term at University of Guelph.
 Spring '10
 Ghaz

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