4.0
100
80
2.0
60
40
0.1
0.8
Tube 1
Tube 1
2
2
3
3
0.6
4
4
5
5
0.4
20
200
400
600
800 1000
200
300
400
500
600 700
2 /s)
2/s)
G (kg/m
G (kg/m
Figure 25. Condensation heat transfer coeffi-
Figure 26. Pressure drop during the conden-
cient for condensation of steam in internally
sation of steam in internally finned horizontal
finned horizontal tubes. Adapted from Royal
tubes. Adapted from Royal and Bergles (1978).
and Bergles (1978).
the same, but the heat transfer performance of tube 3 is superior to that of tube 4. Clearly,
the area ratio is not the controlling factor. The pressure drop characteristics (Fig. 26) show
that the highest pressure drop occurs in tube 3.
Based on their experimental data, they proposed a correlation that represented 95 % of
the data within 30 %. The Royal-Bergles correlation is
1.91
0.8
e2
dhGl
k
0.33 160
+ 1
h = 0.0265 l
(103)
sd
Prl
l
h
dh
where s is the average fin spacing. It is important to note that this correlation was derived
for steam at 1.0 bar and may not be accurate for other fluids or pressures. Furthermore, the
correlation does not account for the surface tension effects or the temperature gradients in
the fin.
Luu and Bergles (1979) tested the tubes of Table 4 with R-113 as the condensing fluid,
and found that tube 2, with shortest fins and highest number of fins, exhibited the best
heat transfer performance at low flow rates. At high mass flow rates, the measured heat
transfer coefficient ranged between 70 and 120 % of the smooth tube value. In a subse-
quent paper, Luu and Bergles (1980) tested eq 103 against their R-113 data and found it to
be unsatisfactory. A new correlation was
developed to predict condensation of R-113
Table 4. Geometric data for internally
in internally finned tubes. However, this
finned tubes.
correlation overpredicted the data of Said
α
Tube
do
e
n
and Azer (1983), who therefore developed
()
no.
(mm)
(mm)
A/Ap
their own correlation. In doing so, they ex-
1
15.9
--
--
--
1.00
cluded the data of Luu and Bergles which
2
15.9
0.60
32
2.95
1.70
was rather unfortunate. Kaushik and Azer
3
12.8
1.74
6
5.25
1.44
(1988) applied regression analysis to the
4
12.8
1.63
6
0
1.44
5
15.9
1.45
16
3.22
1.73
steam data of Royal and Bergles (1978), the
42
Previous Page
