CFD Modelling of Direct Contact Condensation in Suppression Pools by Applying Condensation Models of Separated Flow
Tanskanen, Vesa (2012-04-13)
Väitöskirja
Tanskanen, Vesa
13.04.2012
Lappeenranta University of Technology
Acta Universitatis Lappeenrantaensis
Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-265-222-5
https://urn.fi/URN:ISBN:978-952-265-222-5
Tiivistelmä
The condensation rate has to be high in the safety pressure suppression pool systems of
Boiling Water Reactors (BWR) in order to fulfill their safety function. The phenomena
due to such a high direct contact condensation (DCC) rate turn out to be very challenging
to be analysed either with experiments or numerical simulations. In this thesis, the
suppression pool experiments carried out in the POOLEX facility of Lappeenranta University
of Technology were simulated. Two different condensation modes were modelled
by using the 2-phase CFD codes NEPTUNE CFD and TransAT. The DCC models applied
were the typical ones to be used for separated flows in channels, and their applicability to
the rapidly condensing flow in the condensation pool context had not been tested earlier.
A low Reynolds number case was the first to be simulated. The POOLEX experiment
STB-31 was operated near the conditions between the ’quasi-steady oscillatory interface
condensation’ mode and the ’condensation within the blowdown pipe’ mode. The condensation
models of Lakehal et al. and Coste & Lavi´eville predicted the condensation
rate quite accurately, while the other tested ones overestimated it. It was possible to get
the direct phase change solution to settle near to the measured values, but a very high
resolution of calculation grid was needed.
Secondly, a high Reynolds number case corresponding to the ’chugging’ mode was simulated.
The POOLEX experiment STB-28 was chosen, because various standard and highspeed
video samples of bubbles were recorded during it. In order to extract numerical
information from the video material, a pattern recognition procedure was programmed.
The bubble size distributions and the frequencies of chugging were calculated with this
procedure. With the statistical data of the bubble sizes and temporal data of the bubble/jet
appearance, it was possible to compare the condensation rates between the experiment
and the CFD simulations.
In the chugging simulations, a spherically curvilinear calculation grid at the blowdown
pipe exit improved the convergence and decreased the required cell count. The compressible
flow solver with complete steam-tables was beneficial for the numerical success of
the simulations. The Hughes-Duffey model and, to some extent, the Coste & Lavi´eville
model produced realistic chugging behavior. The initial level of the steam/water interface
was an important factor to determine the initiation of the chugging. If the interface
was initialized with a water level high enough inside the blowdown pipe, the vigorous
penetration of a water plug into the pool created a turbulent wake which invoked the
chugging that was self-sustaining. A 3D simulation with a suitable DCC model produced
qualitatively very realistic shapes of the chugging bubbles and jets. The comparative FFT
analysis of the bubble size data and the pool bottom pressure data gave useful information
to distinguish the eigenmodes of chugging, bubbling, and pool structure oscillations.
Boiling Water Reactors (BWR) in order to fulfill their safety function. The phenomena
due to such a high direct contact condensation (DCC) rate turn out to be very challenging
to be analysed either with experiments or numerical simulations. In this thesis, the
suppression pool experiments carried out in the POOLEX facility of Lappeenranta University
of Technology were simulated. Two different condensation modes were modelled
by using the 2-phase CFD codes NEPTUNE CFD and TransAT. The DCC models applied
were the typical ones to be used for separated flows in channels, and their applicability to
the rapidly condensing flow in the condensation pool context had not been tested earlier.
A low Reynolds number case was the first to be simulated. The POOLEX experiment
STB-31 was operated near the conditions between the ’quasi-steady oscillatory interface
condensation’ mode and the ’condensation within the blowdown pipe’ mode. The condensation
models of Lakehal et al. and Coste & Lavi´eville predicted the condensation
rate quite accurately, while the other tested ones overestimated it. It was possible to get
the direct phase change solution to settle near to the measured values, but a very high
resolution of calculation grid was needed.
Secondly, a high Reynolds number case corresponding to the ’chugging’ mode was simulated.
The POOLEX experiment STB-28 was chosen, because various standard and highspeed
video samples of bubbles were recorded during it. In order to extract numerical
information from the video material, a pattern recognition procedure was programmed.
The bubble size distributions and the frequencies of chugging were calculated with this
procedure. With the statistical data of the bubble sizes and temporal data of the bubble/jet
appearance, it was possible to compare the condensation rates between the experiment
and the CFD simulations.
In the chugging simulations, a spherically curvilinear calculation grid at the blowdown
pipe exit improved the convergence and decreased the required cell count. The compressible
flow solver with complete steam-tables was beneficial for the numerical success of
the simulations. The Hughes-Duffey model and, to some extent, the Coste & Lavi´eville
model produced realistic chugging behavior. The initial level of the steam/water interface
was an important factor to determine the initiation of the chugging. If the interface
was initialized with a water level high enough inside the blowdown pipe, the vigorous
penetration of a water plug into the pool created a turbulent wake which invoked the
chugging that was self-sustaining. A 3D simulation with a suitable DCC model produced
qualitatively very realistic shapes of the chugging bubbles and jets. The comparative FFT
analysis of the bubble size data and the pool bottom pressure data gave useful information
to distinguish the eigenmodes of chugging, bubbling, and pool structure oscillations.
Kokoelmat
- Väitöskirjat [1037]