Implementation of an improved interfacial mass and energy transfer model in RETRAN-3D

RETRAN 3D MOD002.0 includes a five-equation flow field model to extend the code's analytical capabilities to situations in which thermodynamic nonequilibrium phenomena are important. Evaluation of this model's performance against several depressurization and repressurization transients has shown severe numerical and convergence problems related to the calculation of the interfacial energy and mass transfer. To remove these code limitations, a new interfacial mass and energy transfer model has been developed and implemented in RETRAN-3D. This model calculates the phase change based on the net heat transfer to the liquid-vapor interface at saturation. The heat transfer for each phase is equal to the product of the interfacial area density, a heat transfer coefficient, and the difference between the interface and the bulk temperature of the respective phase. A flow regime map based on the work of Taitel and Dukler is used to identify the flow regime in a control volume and to select the appropriate correlations for these quantities. Assessment of the new model's performance includes the simulation of an experimental depressurization transient, OMEGA test 9; a turbine trip transient in a BWR/4; and a very fast depressurization transient, the Edwards pipe problem. The results are free from the previous numerical problems and show a good agreement with experimental values.