Impact of heat-exchanging tube configurations on the gas holdup distribution in bubble columns using gamma-ray computed tomography

An advanced gamma-ray computed tomography (CT) technique was used for the first time to visualize and quantify the impacts of the presence of heat-exchanging tubes and their configurations on the gas-liquid distributions and their profiles in a 6-inch (0.1524 m O.D.) Plexiglas® bubble column in an air-water reactor. Two superficial gas velocities (i.e., 0.2 and 0.45 m/s) were employed to simulate the churn turbulent flow regime. To investigate the impact of vertical internals configurations, three arrangements (i.e., hexagonal, circular without a central internal, and circular with a central internal) were employed in addition to the column with no internals. Using the same sized vertical internals and the same occluded cross-sectional area (CSA), it was found that the configuration of the vertical internals significantly impacted the gas holdup distribution over the CSA of the column. All studied superficial gas velocities resulted in symmetrical gas holdup distributions over the CSA of the bubble columns without vertical internals; however, the columns equipped densely with vertical internals did not have symmetrical gas holdup distributions. The presence of an extra central tube in the circular configuration played a key role in the gas-liquid distribution over the CSA of the bubble column. The hexagonal configuration had the advantage of providing the best spread of the gas phase over the entire CSA of the column. Gas holdup values at the wall region of the bubble column increased with the addition of vertical tubes in all investigated configurations. However, a remarkable increase in the gas holdup values was obtained with the hexagonal configuration. The experimental data (i.e., gas holdup distributions and their diametrical profiles) can help to evaluate and validate three-dimensional (3-D) computational fluid dynamics (CFD) simulations to better predict the hydrodynamic parameters involved in these types of reactors.