Heat and Mass Transfer
An experimental investigation of heat transfer
and flow friction characteristics of louvered fin surfaces
by the modified single blow technique
K. C. Leong, K. C. Toh
Abstract
This paper describes the development of an
experimental facility to determine the heat transfer and
flow friction characteristics of heat exchange surfaces by
the modified single blow technique and the application of
this transient technique to evaluate the performance
characteristics of louvered fin heat exchangers. The reli
ability of implementing the modified single blow technique
on the developed test facility is borne out by the good
agreement in the heat transfer and flow friction data for
the parallel plate test core when compared with theoretical
and empirical correlations available in the literature. Per
formance evaluation of two louvered fin surfaces used
mainly for cooling of large land and marine based elec
trical power generator sets is carried out and compared
with similar louvered fin surfaces available in the litera
ture. On the basis of dimensionless area and power factors,
it was found that the flat fin is slightly superior in overall
performance than its corrugated counterpart for low
Reynolds numbers. Both surfaces are however inferior in
performance when compared with the flat fin surface of
Achaichia and Cowell and the corrugated fin surface of
Davenport. Use of the
j/f
ratio as an approximate figure of
merit led to an inaccurate assessment of the performance
of the louvered fin heat exchanger surfaces evaluated in
this study.
List of symbols
A
c
exchanger minimum freeflow area (m
2
)
A
fr
exchanger frontal area (m
2
)
A
s
total exchanger surface area (m
2
)
C
specific heat (J/kg
±
K)
D
h
hydraulic diameter, 4
A
c
L
=
A
s
(m)
G
mass velocity,
_
m
=
q
o
A
fr
(kg/m
2
±
s)
h
convective heat transfer coefficient (W/m
2
±
K)
k
thermal conductivity (W/m
±
K)
K
c
;
K
e
entrance and exit pressure loss coefficients
L
length of test core (m)
M
s
mass of solid (kg)
_
m
mass flow rate (kg/s)
P
pressure (N/m
2
)
p
fan power (W)
q
heat transfer rate (W)
T
temperature (K)
v
fr
frontal velocity (m/s)
h
time (s)
s
i
time constant of inlet fluid temperature response
(s)
q
m
mean fluid density (kg/m
3
)
q
o
porosity of solid matrix
D
P
pressure drop across test core (N/m
2
)
Dimensionless groups
f
Fanning friction factor
j
Colburn
j
factor, StPr
2
=
3
NTU
number of heat transfer units,
hA
s
=
_
m
f
C
f
Nu
Nusselt number,
hD
h
=
k
f
Pr
Prandtl number,
l
C
f
=
k
f
Re
Reynolds number,
GD
h
=
l
St
Stanton number,
h
=
GC
f
T
²
f
Dimensionless fluid temperature,
T
f
³
T
i
=
T
fm
³
T
i
T
²
s
Dimensionless solid temperature,
T
s
³
T
i
=
T
fm
³
T
i
x
²
Dimensionless length variable,
x
=
L
k
Longitudinal heat conduction parameter of solid
material,
k
y
A
fr
q
o
=
_
m
f
C
f
L
h
²
Dimensionless time,
_
m
f
C
f
h
=
M
s
C
s
s
²
i
Dimensionless time constant,
_
m
f
C
f
s
i
=
M
s
C
s
Subscripts
av
average value
ex
experimental values
f
fluid (air)
fm
final steadystate value
i
initial value
or
orifice plate
s
solid
th
theoretical values
Superscript
²
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 Spring '09
 serhatyeşilyurt
 Heat Transfer, Cowell, Kays WM, Achaichia

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