Flow regime transitions in a bubble column

Abstract 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. K E shows a sharp minimum at the end of the homogeneous regime and start of the transition or heterogeneous regime, respectively. Overall, K E 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.