Gas holdup in bubble columns at elevated pressure via computed tomography

Gas holdup in a pressurized bubble column (pressures from 0.1 to 0.7 MPa) was studied in a laboratory scale vessel (diameter 0.162 m) with air–water system over a range of superficial gas velocities (0.02–0.18 m/s) using non-invasive γ-ray based Computed Tomography (CT). It was found that the cross-sectional average gas holdup increases with pressure, as well as with superficial gas velocity. At all operating conditions, the azimuthally averaged radial gas holdup profiles exhibit a characteristic shape with greater gas holdup in the column center than by the walls. It is also observed that with an increase in pressure, the transition to churn-turbulent regime characterized by the change of the radial gas holdup profile from relatively flat to almost parabolic, is delayed to higher superficial gas velocities. The average cross-sectional gas holdup at each operating condition was compared with predictions of existing correlations and large discrepancies in predictions (as high as 300%) were found.