Assessment of advanced boiling flow and heat transfer models for PHWR conditions

Abstract

This paper presents an assessment of advanced two-phase flow and wall boiling models for prediction of critical heat flux (CHF) of the annular-flow liquid-film dryout type, which is typically encountered in boiling water and pressurized heavy water reactors (BWRs and PHWRs). The advanced multiple flow regime (MFR) model in the CFD code Siemens STAR-CCM+ was used in conjunction with the RPI wall boiling model to predict the heat transfer leading to CHF. The CFD predictions were assessed against selected simple-geometry CHF tests with water flowing through a heated tube, with inside buttons simulating appendages, at high operating pressures relevant to the PHWR flow conditions. Comparing the CFD predictions against experimental dryout powers, it was found that the RPI wall boiling model in conjunction with the MFR model resulted in a closer agreement with the measurements. However, the application of the RPI wall boiling model along with the conventional Eulerian multiphase model resulted in relatively poor predictions of dryout power. Overall, the results obtained in this study underpredict the experimentally reported dryout powers. It was also observed that both models performed better at the higher mass fluxes than at the lower mass fluxes.