Study on bubbly and cap-bubbly flow in a square channel using dual wire-mesh sensors

The experiments of co-current vertical upstream air-water two-phase flow in a 66 mm × 66 mm square channel were carried out. The superficial liquid velocity ranges from 0.765 m/s to 1.53 m/s and the superficial gas velocity ranges from 0.0215 m/s to 0.313 m/s, including bubbly flow and cap-bubbly flow. A dual wire-mesh sensors (WMSs) was used to measure the bubbles in the two-phase flow. The local superficial gas velocity from the dual WMSs was compared with the rotameters and most results were within the deviation of 5%. It can ensure the measurement accuracy of the WMSs. The experimental results include the void fraction projection, sectional averaged void fraction variation, time-averaged void fraction profile, gas velocity profile, and the bubble size distribution. Within the range of flow conditions of this paper, the void fraction was relatively uniformly distributed among the cross-section in the bubbly flow and core peak in the cap-bubbly. Both cross-correlation velocity and bubble velocity were used to calculate the gas velocity profiles. Since the bubble lateral displacement, the cross-correlation method trend to miss the correlation caused by small bubbles and get a higher velocity. Bubble velocity was recommended to be used for determining gas velocity profiles. The results of void fraction profiles, gas velocity profiles, and bubble size distributions can be used for the validation of two-phase models of CFD codes. The void fraction predictions of two drift-flux correlations were compared against the experimental data and both models provided reasonable prediction accuracy.