GAS HOLDUP DISTRIBUTIONS IN LARGE-DIAMETER BUBBLE-COLUMNS MEASURED BYCOMPUTED-TOMOGRAPHY

Using the computed tomography (CT) and computer automated radioactive particle tracking (CARPT) facilities at the Chemical Reaction Engineer ing Laboratory (CREL), time-averaged gas holdup distributions and liqu id recirculation velocities were measured in a 44 cm diameter bubble c olumn for air-water and air-drakeoil systems at 2, 5, and 10 cm/s supe rficial gas velocities, which cover bubbly, transition and chum-turbul ent flow regimes, respectively. Gas holdup was found to increase only slightly with the increase in axial distance from the distributor, but increased significantly with the increase in superficial gas velocity , as expected. A lower gas holdup was observed in the air-drakeoil sys tem than in the air-water system. This could be predominantly attribut ed to the formation of large bubbles in the former case due to the hig her viscosity of drakeoil (approximately 0.03 Pas ( = 30 cp)). At high superficial gas velocities, the time-averaged cross-sectional gas hol dup distributions were almost symmetric for both air-water and air-dra keoil systems. However, at 2 cm/s superficial gas velocity, an asymmet ry in the holdup distribution was observed, which manifested itself in an asymmetric liquid recirculation pattern. At all gas velocities, th e radial gas holdup distribution for the air-water system was steeper than that for the air-drakeoil system, yielding steeper radial liquid velocity profiles. Comparison of the gas holdup obtained in the 44 cm diameter column and that obtained in a 10 cm diameter column is discus sed. (C) 1998 Elsevier Science Ltd. All rights reserved.