Local measurements of upward air–water two-phase flows in a vertical 6×6 rod bundle

A 3 m high vertical rod bundle flow channel consisting of 6×6 rods with the rod diameter of 10 mm and the pitch of 16.7 mm and a channel box with the cross section of 100 mm × 100 mm was used to study the local two-phase flow characteristics under influences of the 36 rods and the channel box. The air and water were selected as the two-phase working fluids in the present experiments. A double-sensor probe installed at the axial position of z/D_H = 149 and six evenly-installed differential pressure (DP) gauges measured the upward-moving two-phase flow in the rod bundle flow channel under the atmospheric condition. Since the local parameters of void fraction, interfacial area concentration (IAC), bubble diameter, and gas velocity are essential to know the internal structures of the two-phase flow, their data at 16 points within an octant symmetric triangular area of the flow channel cross section were collected by the double-sensor probe under various flow conditions in the experiments. The local measurements of double-sensor probe were found to agree well with the void fractions from the DP gauges and the superficial gas velocity from a gas flowmeter. Both the measured void fractions and IACs displayed a transition from radial wall-peaking profile to radial core-peaking profile in the low superficial liquid velocity flow conditions and pure radial wall-peaking profiles in the high superficial liquid velocity flow conditions. The measured Sauter mean diameters showed their radial wall-peaking profiles with the peaking degree decreasing with the increasing superficial gas velocity in both the low and high superficial liquid velocity flow conditions. The measured gas velocities in the main flow direction showed a transition from a radial nearly-flat profile or a radial mid-peaking profile to radial core-peaking profiles in the low and high superficial liquid velocity flow conditions. The area-averaged void fractions and IACs integrated from their measured local values were respectively compared with the predictions of existing drift-flux and IAC correlations. The comparison results showed that the drift-flux correlation of Ozaki et al. (2013) and the IAC correlation of Shen and Deng (2016) give the reasonable prediction and can be recommended for the predictions of the void fraction and the IAC respectively in the bubbly flows in the rod bundle flow channel.