Numerical investigation of azimuthal heat conduction effects on CHF phenomenon in rod bundle channel

Abstract

In CFD simulations of boiling flow and CHF phenomenon, the solid domains are usually neglected to reduce the complexity and computational time. However, based on the simulation of three test sections, the azimuthal heat conduction in the solid domains is found to have a significant influence on the numerical results, especially on the wall temperature distribution. This technical note tries to give the researchers some suggestions about the azimuthal heat conduction effects on boiling flow by CFD simulation of steady state flows in vertical pipes and rod bundle geometry. The CFD modeling methodology was developed using FLUENT. Eulerian two-phase flow is used to model the flow and heat transfer phenomena of boiling flow. Three boundary conditions are tested to investigate the effect of azimuthal heat conduction. The results show that the three boundary conditions are nearly equivalent to each other for subcooled boiling flow in centrosymmetric and non-centrosymmetric geometry, like vertical pipe and rod bundle. But for the CHF phenomenon in rod bundle, the simplified BC overestimates the azimuthal inhomogeneity and the peak temperature of the rod surface. During this process, azimuthal heat conduction plays a key role in this result. The conclusions require researchers should model the entire domain in the CFD simulation and set the heating boundary according to the experiment as accurately as possible to better predict the flow and heat transfer characteristics in the boiling flow.