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Extraction of both information and reconstruction entropies from ultrafast x-ray tomography data in a bubble column

Nedeltchev, S.; Hampel, U.; Schubert, M.

Due to the complex hydrodynamics of bubble columns, there are no reliable methods for identification of both main transition velocities. In addition, it is not clear which type of signal is most suitable for flow regime identification. In this work, both the information entropies (IE) and reconstruction entropies (RE) have been extracted for the first time from tomographic raw images obtained by means of ultrafast X-ray tomography. The time series have been recorded with a sampling frequency of 1000 Hz in a bubble column (0.1 m in ID) operated with an air-deionized water system under ambient conditions. The main transition velocities Utrans in two semi-rings from the cross-section of the bubble column have been identified based on both the IE and RE values calculated from 5 signal reconstructions. In each semi-ring the RE algorithm has been applied to two different cases for signal’s processing. In the centrally located smaller semi-ring the two main Utrans values were successfully identified at 0.04 and 0.1 m/s. In the surrounding larger semi-ring the onsets of the transition and heterogeneous regimes occurred at 0.03 and 0.09 m/s. The results imply that following the above-described approaches the main transition velocities can be extracted from any part of the column’s cross-section.
In summary, this work demonstrates that the ultrafast X-ray tomography data can be used for flow regime identification in a bubble column provided that the hidden information in the time series is quantified by both the IE and RE algorithms.

Keywords: Bubble columns; Information entropies; Reconstruction entropies; Ultrafast X-ray tomography; Hydrodynamic regimes; Transition velocities

Involved research facilities

  • TOPFLOW Facility
  • Lecture (Conference)
    13th International Conference on Gas–Liquid and Gas–Liquid–Solid Reactor Engineering (GLS-13), 20.-23.08.2017, Bruxelles, Belgium
  • Chemical Engineering Science 170(2017), 225-233
    Online First (2017) DOI: 10.1016/j.ces.2017.03.020
    Cited 12 times in Scopus

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