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 U trans at the different radial positions were identified successfully. It was found that in the small column the first transition velocity U trans,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 U trans,1 value in the center was somewhat higher than the one at the wall. The second transition velocity U trans,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 U trans,2 value was changing constantly from U G =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.

The Limerick bubbly flow rig: Design, performance, hold-up and mixing pattern

“…24). These capillaries increase the pressure drop in order to allow lower flow rates without the occurrence of weeping (or gas maldistribution [46]) for the following reasons: (1) to improve the gas distribution across the 98 needles per chamber to ensure that every needle receives the same flow rate (see also Appendix A.1) and emits bubbles at a similar rate and (2) to increase the pressure ratio P R, which is defined in Muilwijk and Van den Akker [25] as a ratio of the surface tension pressure to the pressure drop over the nozzle, to operate under constant flow condition and therefore, reducing the weep point.…”