Page 139 - Applied Process Design For Chemical And Petrochemical Plants Volume III

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104 Applied Process Design for Chemical and Petrochemical Plants

Figure 10-53A. Determine the inside heat transfer coefficient for
superheated steam. (Used by permission: Ganapathy, V. Hydrocarbon
Processing, Sept. 1977. ©Gulf Publishing Company, Houston, Texas.
All rights reserved.) ©Figure 10-53C. Determine the inside heat transfer coefficient of
common liquids. (Used by permission: Ganapathy, V. Hydrocarbon
Processing, Sept. 1977. ©Gulf Publishing Company, Houston, Texas.
All rights reserved.)

1
minimum spacing of / 5 the shell diameter or 2 in.,
whichever is larger. Baffles spaced equally to shell diameter
are found to give good average performance, and this guide
is often used in estimating the initial spacing for baffles.
Where possible the baffle spacing and percent baffle cut
should provide equal flow area. This is of particular impor-
tance in pressure drop calculations. Figure 10-59 is useful
for this equalization.
Shell-side film coefficients can be conveniently obtained
25
from the charts of Chen, Figures 10-60, 10-61, and 10-62.
38
These are based on Donohue’s equation
0.6 c p 0.333 0.14
h o D o D o G w
0.22a b a b a b (10-61)
K a k a w
Figure 10-53B. Determine the inside heat transfer coefficient of com-
mon gases (Used by permission: Ganapathy, V. Hydrocarbon Pro- Equivalent tube diameter for shell-side heat transfer cal-
cessing, Sept. 1977. ©Gulf Publishing Company, Houston, Texas. All culations is used by permission from Kern and Kraus. 206
rights reserved.)
The volumetric equivalent diameter, d e in., is again cal-
culated on the basis of 4 the hydraulic radius; see Figure
10-56.
cut. If twice the number of baffles is used for a fixed fluid
flow, the velocity across the tube bundle is doubled, and the d e 4 free area , in. (10-62)
increase in film coefficient is about 44%. However, the pres- wetted perimeter
sure drop will approach four times its value before doubling
the number of baffles (see Figure 10-57). (a) Equivalent Diameter, D e , for Annulus
Figure 10-58 illustrates a low pressure drop baffle arrange-
2 2 4 1flow area2
ment. Each situation must be examined, as no generalities D e D 2 D 1 4r h (10-62A)
will solve all detailed designs. Baffles should be held to a D 1 1wetted perimeter2