International Science Index


Entropy Analysis in a Bubble Column Based on Ultrafast X-Ray Tomography Data


By means of the ultrafast X-ray tomography facility, data were obtained at different superficial gas velocities UG in a bubble column (0.1 m in ID) operated with an air-deionized water system at ambient conditions. Raw reconstructed images were treated by both the information entropy (IE) and the reconstruction entropy (RE) algorithms in order to identify the main transition velocities in a bubble column. The IE values exhibited two well-pronounced minima at UG=0.025 m/s and UG=0.085 m/s identifying the boundaries of the homogeneous, transition and heterogeneous regimes. The RE extracted from the central region of the column’s cross-section exhibited only one characteristic peak at UG=0.03 m/s, which was attributed to the transition from the homogeneous to the heterogeneous flow regime. This result implies that the transition regime is non-existent in the core of the column.

[1] R. Krishna and J. Ellenberger, “Gas holdup in bubble column reactors operating in the churn-turbulent flow regime”, AIChE Journal, vol. 42, pp. 2627–2634, 1996.
[2] P. M. Wilkinson, A. P. Spek and L. L. Van Dierendonck, “Design parameters estimation for scale-up of high-pressure bubble columns”, AIChE Journal, vol. 38, pp. 544–554, 1992.
[3] I. G. Reilly, D. S. Scott, T. J. W. De Bruijn and D. MacIntyre, “The role of gas phase momentum in determining gas holdup and hydrodynamic flow regimes in bubble column operations”, Can. J. Chem. Eng., vol. 72, pp. 3–12, 1994.
[4] S. Nedeltchev and A. Shaikh, “A new method for identification of the main transition velocities in multiphase reactors based on information entropy theory”, Chem. Eng. Sci., vol. 100, pp. 2–14, 2013.
[5] S. Nedeltchev, “New methods for flow regime identification in bubble columns and fluidized beds”, Chem. Eng. Sci., vol. 137, pp. 436–446, 2015.
[6] S. Nedeltchev, Th. Donath, S. Rabha, U. Hampel and M. Schubert, “New evidence for the mixing length concept in a narrow bubble column operated in the transition regime”; J. Chem. Eng. Japan, vol. 47, pp. 722–729, 2014.
[7] Y. Kawase, M. Moo-Young, “Characteristic mixing length in bubble columns”, J. Chem. Eng. Japan, vol. 69, pp. 1228-1231, 1991.