Air-water two-phase flow in a rolling 3 × 3 rod bundle under stagnant condition

Experimental investigation on adiabatic air-water two-phase flow in a 3 × 3 rod bundle subjected to rolling motion under stagnant condition was carried out. The gas superficial velocity jg is from 0.024 m/s to 0.95 m/s, and the rolling period and amplitude range from 8 s to 16 s and from 5° to 15°, respectively. The results showed that the additional pressure drop introduced by rolling motion could be neglected compared with gravitational pressure drop. Rolling motion leads to the void fraction decreasing and the gas rising velocity increasing at low gas flow rate, while the influence at high gas flow rate is not significant. The transient gas flow rate, void fraction and gas rising velocity oscillate apparently in the region of jg < 0.086 m/s, whereas their fluctuations in the region of jg > 0.086 m/s are insignificant. In addition, the increase in rolling amplitude or the decrease in rolling period make the fluctuation amplitudes of the void fraction and gas rising velocity increasing. Though Wilson (1965) model provides fair predictions on the averaged values of the two parameters above, it cannot predict their transient values in rolling motion, for which a new correlation is given based on the Wilson model (1965) in the region of jg < 0.086 m/s.