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Unformatted text preview: f condensate on vertical plates. The physical properties of the condensate are again to be evaluated at the film
temperature Tf (Tsat Ts)/2. The Re relation in this case is obtained by substituting the h relation above into the Re relation in Eq. 10–11, which gives
Revert, turbulent 0.0690 Lkl Pr0.5 (Tsat
l h*
fg Ts) g
2
l 1/3 4/3 151 Pr0.5 253 (1029) Nondimensionalized heat transfer coefficients for the wavefree laminar,
wavy laminar, and turbulent flow of condensate on vertical plates are plotted
in Figure 10–26. 2 Inclined Plates
Equation 10–12 was developed for vertical plates, but it can also be used for
laminar film condensation on the upper surfaces of plates that are inclined by
an angle from the vertical, by replacing g in that equation by g cos (Fig.
10–27). This approximation gives satisfactory results especially for
60°.
Note that the condensation heat transfer coefficients on vertical and inclined
plates are related to each other by
hinclined hvert (cos )1/4 (laminar) Vapor
θ (1030) Equation 10–30 is developed for laminar flow of condensate, but it can also
be used for wavy laminar flows as an approximation. Inclined
plate Condensate 3 Vertical Tubes
Equation 10–22 for vertical plates can also be used to calculate the average
heat transfer coefficient for laminar film condensation on the outer surfaces of
vertical tubes provided that the tube diameter is large relative to the thickness
of the liquid film. 4 Horizontal Tubes and Spheres
Nusselt’s analysis of film condensation on vertical plates can also be extended
to horizontal tubes and spheres. The average heat transfer coefficient for film
condensation on the outer surfaces of a horizontal tube is determined to be FIGURE 10–27
Film condensation on
an inclined plate. cen58933_ch10.qxd 9/4/2002 12:38 PM Page 540 540
HEAT TRANSFER hhoriz 0.729 ) h* k3
fg l
Ts)D g l( l
l(Tsat 1/4 (W/m2 · °C) (1031) where D is the diameter of the horizontal tube. Equation 10–31 can easily be
modified for a sphere by...
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 Spring '10
 Ghaz

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