On the stratification criterion in the CATHARE code

In the CATHARE code, the stratification criteria consider both the stability of the stratified flow regime and the stability of a bubbly flow. This paper focuses on the transition from bubbly to stratified flow. It can be modelled by considering the balance between buoyancy that induces bubbles to rise and accumulation of gas phase at top of the pipe and turbulence that mixes bubbles. A ratio of a turbulent velocity to a free bubble rise velocity is used to determine the flow regime. A new model is proposed based on METERO test data which may reduce code uncertainty. (author)