cen58933_ch10

# 1011 which gives revert turbulent 00690 lkl pr05 tsat

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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 (10-29) Nondimensionalized heat transfer coefficients for the wave-free 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 (10-30) 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) (10-31) where D is the diameter of the horizontal tube. Equation 10–31 can easily be modified for a sphere by...
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