atw 2017-06

atw Vol. 62 (2017) | Issue 6 ı June
RESEARCH AND INNOVATION 416
Test case
Heat
input,
kW
Initial
absolute
pressure,
MPa
The predicted Air
weight fraction
at steady state,
w/o
10-#1 10 0.1 0.4
10-#2 0.14 0.45
10-#3 0.21 0.5
15-#1 15 0.1 0.35
15-#2 0.15 0.4
15-#3 0.22 0.45
20-#1 20 0.1 0.3
20-#2 0.16 0.35
20-#3 0.27 0.4
25-#1 25 0.1 0.25
25-#2 0.18 0.3
25-#3 0.29 0.35
30-#1 30 0.1 0.2
30-#2 0.14 0.25
30-#3 0.2 0.3
Area of
interest
| | Tab. 2.
Test matrix.
• Temperature profile according to the heat
input and initial air pressure
• Pressure profile in the pressure tank
Region Correlation Author
Inside
pressure tank
Inside
boiling region
of pipe
Inside
condensation region
of pipe
Inside
coolant tank



| | Tab. 3.
Heat transfer correlations for predicted value compared with the experiment results.
Uchida
Tagami
Kataoka
Murase
Imura
Nusselt
Rohsenow
The test conditions are listed in
Table 2. Test cases 10-# to 30-#
were performed to evaluate the heat
removal performance in the pressure
vessel. Heat input flowed from 10 kW
to 30 kW in each case. As mentioned
above, non-condensable gases greatly
affect the heat transfer inside the
containment because they depend
only on natural circulation, and no
power supply or fan operation for
forced circulation is possible. Furthermore,
as the MPHP assembly consists
of a multitude of long pipes, the
lengths and radial locations of
the pipe in the assembly are expected
to have a significant effect on the
passage of steam to pipes. Therefore,
the increase in concentration of noncondensable
gases owing to steam
condensation in the pipe array was
considered. For this reason, the
weight fraction range of air is determined
to be from 0.2 to 0.5 w/o.
3 Results and discussions
The empirical correlations compared
with the experimental results are
presented in Table 3. The four correlations
based on steam condensation
with non-condensable gas were chosen
for a comparison with the experimental
data. These correlations are only
dependent on the con centration of
non- condensable gas, and thus are selected
to compare with the data. [7, 8]
As shown in Figure 4, all correlations
compared with the experimental
data tend to under predict the
measured values. These correlations
were developed for steam condensation
with non-condensable gas on a
long vertical plate. In this study, the
geometry of the condensation area
making contact with a steam and air
mixture is of a cylinder type, and it
shows that air weight accumulated
on the pipe surface is lower than
pre dicted. Thus, steam condensates
better than the predicted models.
The correlation reported by Imura
et al. was compared with the experimental
data, as shown in Figure 5.
The Imura et al. correlation tends to
under predict the measured values
though the heat transfer coefficients
in the boiling region, and predictions
generally show reasonable agreement
with the majority of the points being
within the 35 % band.
The correlation reported by Nusselt
was compared with the experimental
data. This correlation covers all data
within ±10 %, as shown in Figure 6,
and shows very good agreement with
the measurements.
| | Fig. 4.
Predicted and experimentally determined heat transfer coefficients in the
pressure tank for steam condensation with non-condensable gas.
| | Fig. 5.
Predicted and experimentally determined heat transfer coefficients in the
boiling region for full pool boiling mode with distilled water.
Research and Innovation
Experimental Investigation of a Two-Phase Closed Thermosyphon Assembly for Passive Containment Cooling System ı Kyung Ho Nam and Sang Nyung Kim