Numerical Simulation of Subchannel Flow Boiling Using Five-Component Wall Boiling Model and iMUSIG Model

Abstract Boiling heat transfer of subchannel has significant influence on nuclear reactor thermal-hydraulic performance. Employing the Euler-Euler two-fluid approach in computational multi-fluid dynamic (CMFD) simulations, this study conducts a high-fidelity multi-fluid simulation on subchannels. Utilizing the OECD/NRC NUPEC PWR Subchannel and Bundle Tests (PSBT) benchmark, four subchannels are numerically simulated: a typical central subchannel, a central subchannel with a thimble, a side subchannel, and a corner subchannel. The simulation model integrates a five-component wall boiling model and an inhomogeneous multiple size group (iMUSIG) model in OpenFOAM v6, capturing phenomena like bubble sliding, size variability, coalescence, and breakup. Turbulence is modeled using the standard k-ϵ and Sato models, the latter incorporating an additional turbulent viscosity term for bubble-induced turbulence. The study compares cross-sectional averaged void fractions at measurement planes and analyzes key bubble dynamics parameters, including bubble departure and lift-off diameters, wall heat flux partitioning, and bubble size distribution. The results have shown the promising accuracy of the five-component wall boiling model coupled with the iMUSIG model in predicting the void fraction.