Suitability of drift-flux models, void-fraction evolution, and 3-D flow pattern visualization during stationary and transient flashing flow in a vertical pipe

An assessment of void-fraction correlations and drift-flux models applied to stationary and transient flashing flows in a vertical pipe has been performed. Experiments have been carried out on a steam/water loop that can be operated both in forced- and natural-circulation conditions to provide data for the assessment. The GE-Ramp and Dix models are found to give very good predictions both for forced- and natural-circulation flow conditions, in the whole range of measured void fractions. Advanced instrumentation, namely, wire-mesh sensors, has been used to obtain a detailed picture of the void-fraction development in the system. On the basis of experimental data, a three-dimensional visualization of the transient flow pattern during flashing was achieved. A transition of the flow pattern between bubbly and slug/churn regimes was found.