Flow regime transitions in a bubble column

- Flow transitions in a bubble column are identified based on the pressure fluctuation.
- Up to four flow regimes can be observed.
- Different analysis methods show systematic differences.
- The Kolmogorov entropy is most accurate in determining the main flow transition.

In a 0.102 m ID bubble column, various techniques for flow regime identification based on pressure fluctuation measurement were applied: standard deviation, fractal analysis, Kolmogorov entropy KE and power spectral density. The superficial gas velocity reached up to 0.2 m s−1 and the pressure was varied up to 2 MPa. Up to four flow regimes could be identified: intermittent, homogeneous, transition and heterogeneous flow. KE shows a sharp minimum at the end of the homogeneous regime and start of the transition or heterogeneous regime, respectively. Overall, KE is the most accurate method to determine this main transition. The fractal analysis shows a minimum at a clearly lower gas velocity. The standard deviation and the power spectral density are less accurate than KE but more convenient since the value obtained in a single measurement could be compared to a threshold.

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