Three dimensional CFD simulation of heat and mass transfer in passive heat removal systems

The current job is presenting the CFD- modelling and simulation of condensation inside passive heat removal systems. Designs of future nuclear boiling water reactor concepts are equipped with emergency cooling systems which are passive systems for heat removal. The emergency cooling system consists of slightly inclined horizontal pipes which are immersed in a tank of subcooled water. At normal operation conditions, the pipes are filled with water and no heat transfer to the secondary side of the condenser occurs. In the case of an accident the water level in the core is decreasing, steam comes in the emergency pipes and due to the subcooled water around the pipe, this steam will condense. The emergency condenser acts as a strong heat sink which is responsible for a quick depressurization of the reactor core when any accident happens. The actual project is defined to model the phenomena which are occurring inside the emergency condensers. The focus of the project is on detection of different morphologies such as annular flow, stratified flow, slug flow and plug flow and also modeling of the laminar film which is occurring during the condensation near the wall.
The condensation procedure inside the pipe can be divided to two steps. The first step is the wall condensation and the second step is the direct contact condensation (DCC). The Algebraic Interfacial Area Density (AIAD) concept is used in order to model the interface between liquid and steam. In the next steps the Generalized Two-Phase Flow (GENTOP) model will be used to model also the dispersed phases which are occurring inside the pipe. Finally, the results of the simulations will be validated by experimental data which will be available in HZDR. In this paper the results of the first part has been presented.