Flow regime transitions in a bubble column

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 K-E 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. ICE shows a sharp minimum at the end of the homogeneous regime and start of the transition or heterogeneous regime, respectively. Overall, ICE 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 K-E but more convenient since the value obtained in a single measurement could be compared to a threshold. (C) 2017 Elsevier Ltd. All rights reserved.