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270 Applied Process Design for Chemical and Petrochemical Plants

Table 10-53
Estimating Factors, 1-in. O.D. Tube 2 / 8 -in. Spacing
3
Depth, tube rows 4 6 8 10 12
Typical standard FV, ft/min** 595 540 490 445 405
2
2
Ft surface/ft face area 5.04 7.60 10.08 12.64 15.20
2
Weight lb/ft face area 75 88 115 131 147
**FV face velocity.
Used by permission: Smith, E. C. Chemical Engineering, V. 65, p. 145,
©1958. McGraw-Hill, Inc. All rights reserved.

Figure 10-188. Optimum bundle depth. (Used by permission: Smith,
E. C. Chemical Engineering, V. 65, Nov. ©1958. McGraw-Hill, Inc. All
rights reserved.)

This can be converted to finned surface by ratio of
finned/bare surface areas.
e. Calculate face area, FA 2 : Figure 10-189. Outside fin film, coefficient for air-fin exchangers.
(Used by permission: Hajek, J. D. Compiled from manufacturer’s data,
A
FA 2 FA 1 , (from Table 10-53) (10-306) private communications, now deceased.)
surface area
a b
face area Balance these to obtain practical or standard size
units. Bundle widths are usually 4 ft, 6 in. and 7 ft, 6 in.
Where subscript 2 refers to second or check calculation, and 1
j. Calculate hp requirements from Figure 10-190;
refers to original trial.
read surface area/hp or read Figure 10-189 for pres-
f. If FA 2 FA 1 , proceed with detailed design.
sure drop for certain tube arrangements.
If FA 2 FA 1 , reassume new air outlet temperature
and repeat from (a). total surface, A
HP (10-308)
g. For detailed check: surface area>hp
Assume tube-side passes and calculate h i , h io in the 1ACFM21p t 2
usual manner. Also: HP (10-309)
16,35621e f 21e d 2
From air velocity, ft/min, calculate quantity and
film coefficient considering fin efficiency. p v 0.1 in. water, usually
Figure 10-189 may be used directly to obtain effec- p s 0.2 to 0.25 in. water at 500 ft/min FV for each 3
tive outside fin coefficient, h o , based on the bare rows of tubes
tube surface. Recalculate overall U. If this value dif- p t p v p s , in. water
fers greatly, unit should be calculated until balance e r 0.65 usually
is reached. e d 0.95 usually
h. Calculate tube-side pressure drop in usual manner,
k. Approximate weight:
including loss in headers.
i. Determine unit plan size: (face area)(weight/face area) (10-310)
p v velocity pressure, in. water
Width=
p s static pressure, in. water
face area p t total pressure, in. water
assumed tube length 1usually 4 ft, 6 in. min. through 30 ft2 ACFM actual CFM at fan intake
FA face area of air cooled exchanger tube bundle,
(10-307)
length width, ft 2