atw 2017-12

atw Vol. 62 (2017) | Issue 12 ı December
it is still in the subcritical state.
Hence the fluid remains in the mixture
region in the outlet of the test
section.
3.3 Natural circulation flow
at supercritical pressure
When the average pressure is raised
above the critical point, the coolant is
considered to be in a supercritical flow
state. The results of the natural circulation
flow are shown in Figure 6
and Figure 7.
As shown in Figure 6 and 7a, the
black curve represents the value of
heating power, and the blue curve
represents the mass flow rate of the
natural circulation. In Figures 6 and
7b, the black curve represents the
temperature at the outlet of the test
section, and the red curve represents
the inlet temperature for the test
section. When the system pressure is
maintained at 23.5 MPa during the
initial (low power) phase of heating,
there is a lower temperature at the
outlet of the test section. As the
heating is continued, there is a rapid
increase in the temperature of the test
segment. The temperature rises much
more slowly, as it approaches the
pseudo-critical point. By increasing
the heating power to a further extent,
there is a periodic oscillation in the
power value. There is also a periodicity
in the temperature of the
fluid, when the outlet temperature (of
the test section) reaches near the
pseudo- critical point. The fluctuation
con tinues with a certain frequency/
amplitude during this period.
As the system pressure is maintained
at 26.1 MPa, there is a great
amount of fluctuation in heating
power of the test section, followed
by a corresponding fluctuation in the
natural circulation flow rate. As the
heating power is decreased, there is a
reduction in the value of the natural
circulation flow rate. When the system
pressure is much higher (in the supercritical
state), there is an increase in
the fluctuation of the flow rate, with
longer cycle periods. At this pressure,
temperature at the outlet of the test
section reaches 400 °C. At this temperature,
the coolant is above the
RESEARCH AND INNOVATION 727
| | Fig. 6a.
Natural circulation mass flow trend (Pressure = 23.5 MPa).
| | Fig. 6b.
Natural circulation temperature variation trend (Pressure = 23.5 MPa).
| | Fig. 7a.
Natural circulation mass flow trend (Pressure = 26.1 MPa).
| | Fig. 7b.
Natural circulation temperature variation trend (Pressure = 26.1 MPa).
| | Fig. 8a.
Transition of natural circulation stability.
| | Fig. 8b.
Temperature trend during transition of the natural circulation stability.
Research and Innovation
Supercritical Water Natural Circulation Flow Stability Experiment Research ı Dongliang Ma, Tao Zhou, Bing Li and Yanping Huang