Experimental study on the radial distribution of the main transition velocities in bubble columns

Abstract

The effect of the radial position on the main transition velocities in bubble columns has not been reported in the literature hitherto. In this paper, the information entropies IE were extracted in a new way from local gas holdup fluctuations measured by a wire-mesh sensor at different radial positions in both small (0.15 m in ID) and large (0.4 m in ID) bubble columns. On the basis of well-defined local minima in the IE profiles, the transition velocities Utrans at the different radial positions were identified successfully. It was found that in the small column the first transition velocity Utrans,1 (corresponding to the end of the gas maldistribution regime) was somewhat lower in the center of the column as compared to the wall. In the large column, the Utrans,1 value in the center was somewhat higher than the one at the wall. The second transition velocity Utrans,2 (corresponding to the onset of the churn-turbulent regime) in the small column was slightly higher at the core of the column. In the large column, the Utrans,2 value was changing constantly from UG=0.089 m/s to 0.101 m/s and vice versa. The IE results showed that only at the fifth radial position in the small column and at the third and fourth radial positions in the large column there was a division of the transition regime into first and second transition sub-regimes.