Void fraction under high pressure, low flow conditions in rod bundle geometry

Void-fraction data are reported from a series of high pressure, low heat and mass flux experiments. Testing was performed in a heated vertical rod bundle with internal dimensions similar to a PWR fuel bundle. The results are of interest in analyses of small break loss of coolant accidents. The experiments showed that, at a given pressure, void-fraction data could be fitted to a drift-flux equation with a constant drift-velocity. The drift-velocity was observed to decrease with increasing pressure and was independent of void fraction: a characteristic normally associated with churn-turbulent flow. However, relevant drift-flux correlations found in the literature gave relatively poor predictions of void fractions. The best predictions were obtained from an empirical correlation based on dimensional analyses. (orig.)