Progress in understanding and modelling of annular two-phase flows with heat transfer

Highlights: • Research on annular two-phase flow with heat transfer. • Mechanistic modelling of dryout and post-dryout heat transfer. • Calculations of wall temperature in the post-dryout region. • Multidimensional CFD model of annular two-phase flow and heat transfer. - Abstract: Annular two-phase flows with heat transfer play important role in many industrial applications. In particular, thermal margins of Boiling Water Reactors (BWR) are entirely determined by this type of flow and heat transfer conditions. To avoid dryout, a liquid film must be present on heated rods of BWR fuel assemblies during normal operation. The present paper describes the recent progress in understanding and modelling of the governing phenomena of annular two-phase flow and heat transfer. A special attention has been devoted to experimental observations that have the most significant influence on the adopted modelling approach. The primary goal is to pave a path to mechanistic modelling of dryout and post-dryout heat transfer applicable to nuclear fuel assemblies. Current Computational Fluid Dynamics (CFD) approaches to model the governing phenomena are presented and their further improvements are suggested.