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Development of a Mean Bubble Size Correlation under Pool Scrubbing Conditions
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The fission product filtration capability of pool scrubbing is an uncertain factor in severe accident risk analysis. Limited discussions on aerosol transportation phenomena exist due to insufficient understanding of aerosol mass transfer from single bubbles and bubble plume behavior. This study aims to investigate aerosol transportation during pool scrubbing by integrating individual bubble mass transfer into the overall bubble plume.
Decontamination factor (DF) measurements were conducted for various nozzle submergences, followed by analysis of bubble diameter distributions in the corresponding bubble plume. Findings revealed that the MELCOR model overestimates bubble break-up, contrary to the expected positive impact on DF. To address this discrepancy, a computational fluid dynamics simulation was employed to analyze mass transfer coefficients considering different bubble diameters and aerosol properties. By integrating the mass transfer of single bubbles, the discrepancy in the DF tendencies was attributed to the underestimation of aerosol mass transfer coefficients in individual bubbles.
Calculating the bubble diameter accurately is crucial for predicting the De-contamination Factor (DF) in pool scrubbing codes. Currently, empirical correlations that depend on flow regimes and conditions are used to estimate bubble diameters in pool scrubbing codes, leading to a discrepancy between predicted and experimental DFs. The Interfacial Area Transport Equation (IATE) has the potential to improve the DF estimations in pool scrubbing codes as it can dynamically calculate the bubble diameter by estimating Interfacial Area Concentration (IAC) through mechanistically modeled bubble breakup and coalescence mechanisms. However, most of these models were developed for fully developed pipe flow conditions, which are not suitable for pool scrubbing gas-liquid flow conditions. To evaluate the IATE's applicability in pool scrubbing geometries, the OpenFOAM Computational Fluid Dynamics (CFD) code was used to investigate the hydrodynamics of a high inlet velocity pool scrubbing experiment on a large scale. The investigated bubble interaction mechanisms showed that the models heavily rely on the effects of Shear Induced Turbulent (SIT) through turbulent velocity fluctuations, although Bubble Induced Turbulent (BIT) is more dominant in pool scrubbing conditions. It was found that a relatively lower critical Weber number is required for bubble breakup mechanisms to take effect in pool scrubbing geometries, and only area averaging leads to missing information in pool scrubbing geometries due to its scale, therefore, void weighted area averaging must be used. The SMD calculated using IATE and experimental results showed relatively good agreement near the exit, but IATE overestimated the SMD in the transition and downstream region.
Although gas–liquid bubbly flows are encountered in various engineering fields, there are very few established theoretical foundations on the interfacial area concentration, which have been supported by extensive experimental data. From this point of view, a simple equation for the interfacial area concentration has been derived from the interfacial area transport equation. The derived theoretical equation has been modified to obtain experimentally supported predictive correlation. The obtained interfacial area correlation was validated by 459 data sets measured in bubble columns and forced convective bubbly flows under various conditions. These data sets covered extensive loop and flow conditions such as channel geometry (circular or rectangular channel), channel hydraulic equivalent diameter (9.0–), flow direction (vertical or horizontal flow), superficial gas velocity (0.000788–), and superficial liquid velocity (0.00–). The extensive database also covered wide ranges of physical properties such as liquid density (684–), liquid viscosity (0.410–), and surface tension (20.0–). An excellent agreement was obtained between the developed semi-theoretical correlation and 459 data within an average relative deviation of ±22.0%.
This paper presents an assessment of various models which can be used for the multidimensional simulation of multiphase flows, such as may occur in nuclear reactors. In particular, a model appropriate for the direct numerical simulation (DNS) of multiphase flows and a mechanistically based, three-dimensional, four-field, turbulent, two-fluid computational multiphase fluid dynamics (CMFD) model are discussed. A two-fluid bubbly flow model, which was derived using potential flow theory, can be extended to other flow regimes, but this will normally involve ensemble-averaging the results from direct numerical simulations (DNS) of various flow regimes to provide the detailed numerical data necessary for the development of flow-regime-specific interfacial and wall closure laws.
- Y Abe
- K Fujiwara
- S Saito
- T Yuasa
- A Kaneko
Y. Abe, K. Fujiwara, S. Saito, T. Yuasa, A. Kaneko,
Bubble Dynamics with Aerosol during Pool Scrubbing, NED.
337 (2018) 96-107.
- A Behzadipour
- A H Azimi
- I E Lima Neto
A. Behzadipour, A.H. Azimi, I.E. Lima Neto, Effect of
grid-screen on Bubble Characteristics of Vertically
Discharged Bubble Plumes, CES. 253 (2022) 117545.
- A H Azimi
- A Behzadipour
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A.H. Azimi, A. Behzadipour, I.E.L. Neto, Effects of Air
Discharge on Bubble Dynamics in Vertically Discharged
Bubble Plumes, Chemical Engineering Science. 268 (2023)
118440-118440.