atw 2017-06

atw Vol. 62 (2017) | Issue 6 ı June
| | Fig. 6.
Predicted and experimentally determined heat transfer coefficients in the
condensation region for film condensation.
| | Fig. 7.
Comparison of the overall heat transfer rates between the predicted and
experimentally determined results (left), and variation of total thermal
resistance of a TPCT assembly vs. air weight fraction in a pressure tank (right).
RESEARCH AND INNOVATION 417
| | Fig. 8.
Comparison of the overall heat transfer rates between the predicted and experimentally determined results (Left), Variation in total thermal resistance of a TPCT
assembly vs air weight fraction in the pressure tank (Right).
The correlation reported by
Rohsenow was compared with the
experimental data, as shown in
Figure 7. Most heat transfer coefficients
of the experimental results are
much lower than those obtained by
the correlations. In this study, city
water was used as a coolant in the
experiment, and the scale generated
on the pipe surface effected as insulation.
If the accident sequence determines
that the designed water sources
are not available in sufficient quantity,
or at a sufficient rate, any water source
should be used without delay. It is
quite possibly that the city water may
be used during an accident when the
water sources are not available. For
conservatism, city water was used as a
coolant, and this condition causes the
experimental data to be much lower
than the predicted values.
The input heat transfer rates versus
the temperature difference between
the inner pressure tank and coolant
are plotted in Figure 8, and total
thermal resistance is obtained from
Eq. 9 and also presented in Fig. 8.
It shows that the concentration of
non-con densable gas in the containment
is key factor which affects total
thermal resistance and the performance
of the MPHP when the MPHP is
implemented in actual NPPs.
4 Conclusion
An analysis of experimental data and
comparison to existing widely used
correlations lead to the following
conclusions:
1. Measured heat transfer coefficients
in each region and the overall heat
transfer rate are higher than the
predicted values. This shows that
the theoretical results are conservative
when a MPHP is implemented
in an actual NPP. Additionally,
the key factor that affects the
total thermal resistance of a MPHP
assembly is non-condensable gas
concentration in the containment.
2. The experiment results show that
a TPCT consists of a 1-m long
boiling and condensation region,
respectively, and can transfer at
least 45 kW/m 2 of heat flux.
3. Based on the measured heat flux
and heat transfer capacity, a MPHP
assembly consists of 1-m long
boiling and condensation pipes,
respectively, and has about 2,000
pipes with an overall diameter of
about 1.75 m to provide 50 % heat
removal capacity. In the case of
100 % heat removal capacity, it
has 4,500 pipes and the overall
diameter is about 2.4 m.
4. Precise calculations using computer
code simulate the behavior
(pressure, temperature) of the
containment atmosphere when
the novel PCCS is in operation and
to account for other heat sources
than the decay power.
5. The development of average parameters
(lumped parameter method)
and performing param etric studies
to account for the effects of increasing
heat pipe length and array size
(steam access from the containment
to pipes). The air weight fraction
was con sidered to be up to 0.5 w/o
in this experiment, and thus this
effect was considered roughly in
this experiment.
6. Because of the large added mass
(cylindrical wall extension and/
or water tanks on the dome top,
cooling water, MPHP assemblies
with water, and their accessories),
an additional seismic evaluation of
the containment (concrete walls
and dome) is necessary.
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