Based on their experimental work, Kazeminejad (1987) and Coney et al. (1989b) pre-
sented the following correlations for the convective heat transfer coefficient for vertical
rectangular fins.
Blunt-edged dry fin:
0.60
U D
hDh
= 0.590 ∞ h
(80)
νa
ka
Blunt-edged wet fin:
0.69
U D
hDh
= 0.231 ∞ h
.
(81)
νa
ka
Elliptical-edged dry fin:
0.60
U D
hDh
= 0.420 ∞ h
.
(82)
νa
ka
Elliptical-edged wet fin:
0.69
U D
hDh
= 0.146 ∞ h
.
(83)
νa
ka
Optimum fin design
This section considers the design of optimum dimensioned fins for use in a moist air
stream. The discussion will be based on the works of Kilic and Onat (1981) and Toner et al.
(1983), and will cover longitudinal fins of rectangular and triangular profiles.
Rectangular fins
Kilic and Onat (1981) considered a vertical rectangular fin as shown in Figure 16a, and
modified the classical convecting fin equation to allow for simultaneous heat and mass
transfer. The modified equation can be expressed as
B
2 (T - T ) - m fg
hh
d2Tf
=m f
Pva - P exp A -
(84)
a
Tf
dx2
hR vTa
where m = 2h / kw
hm = mass transfer coefficient
Rv = gas constant for water vapor
Pva = partial pressure of water vapor at temperature T,
P = total pressure
A and B = constants.
A model similar to eq 84 has also been used by Karniven et al. (1990) to study moisture
on fins. The Karniven et al. model allows for radiative heat transfer in addition to convec-
tive heat and mass transfer. Furthermore, the model considers a partially wet fin rather
than a fully wet fin, and also determines the line separating the wet and dry regions.
27
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