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222 Applied Process Design for Chemical and Petrochemical Plants

efficiency. Weighted fin efficiency is expressed by Kern and
Kraus 206 as:

f s f – s o –
w (10-235)
s f – s o –
where s f fin surface per ft of pipe length
s o plain pipe surface per ft length
w weighted fin efficiency, fraction, from Figure 10-147
f fin efficiency, fraction [(tan h) (mb)]/(mb)
tan h hyperbolic tangent
1/2
m fin performance factor [(2h)/k m o ] , ft 1
b fin height, ft
2
h heat transfer coefficient, Btu/(hr) (ft )(°F)
k m metal thermal conductivity, Btu/(ft) (hr)(°F)
Figure 10-145. Generalized design evaluation of low-finned tubes o fin width, ft, at fin base
and fluid heat exchangers. (Used by permission: “An Opportunity.”
Wolverine Tube, Inc.)

1
Figure 10-146. Weighted efficiencies of low-finned tubing of 11, 16 and 19 fins per in. length, / 16 -in. high, radial. (Used by permission: Engi-
nd
neering Data Book, 2 Ed., ©1960. Wolverine Tube, Inc.)