CFD simulations of steam-water flow with condensation

Gas-liquid two-phase flows have become increasingly important in engineering equipment and technology (e.g. in chemical or process industries). Depending on mass flow rates, geometry and the fluid properties, different flow regimes can occur (e.g. bubble flow, stratified flow, droplet flow etc.). The current project focuses on stratified two-phase flows with heat and mass transfer across a moving interface due to direct contact condensation (DCC) in horizontal pipes or channels. In case of direct contact condensation, the resistance to condensation heat transfer considerably lower compared to film-wise condensation. Hence, DCC allows a considerably better heat exchange between the phases. Direct contact condensation is used in a variety of heat transfer devices (such as direct contact condensers), which offer the possibility of increased per-formance. DCC has also been of major importance in connection with the analysis of nuclear reactor safety systems, in particular during two-phase pressurized thermal shock (PTS) scenari-os. PTS occurs when there are large thermal loads on the Reactor Pressure Vessel wall during an accident. Therefore, the modeling of direct contact condensation is a task of considerable im-portance. Condensation phenomena depend on the turbulence in the liquid phase. To consider pronounced 3D effects and local phenomena CFD methods need to be used. Generally, two-phase CFD models are not yet mature and have to be qualified for two-phase flows. The work aims at the development and validation of CFD models for two-phase stratified flows including heat and mass exchange between the phases. A promising model development strategy implies experimental data with high resolution both in space and time for the entire domain of interest. To investigate two-phase PTS scenarios with DCC, the TOPFLOW-PTS experiments were carried out at the TOPFLOW test facility of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) [1]. The goal of the paper is to present the CFD simulations of a TOPFLOW-PTS steam-water experiment and to discuss the limits of the models used.