The present study investigates the main flow regime boundaries in a bubble column with internals based on a novel statistical-chaotic method. The latter was applied to gas holdup fluctuations recorded by means of a wire-mesh sensor (8×8 wires). The bubble column (0.1 m in I.D.) was operated with an air-deionized water system at ambient conditions. Thirty-seven vertical tubes (arranged in a square pitch with a diameter of 8×10⁻³ m) were installed as internals.

Based on an original combination of statistical and chaotic parameters, it was found that in the core of the bubble column with internals, the first transition velocity U_trans-1 (end of homogeneous regime) occurred at a superficial gas velocity U_G of 0.06 m/s, the second transition velocity U_trans-2 (end of heterogeneous regime) appeared at U_G=0.13 m/s. At these critical velocities, the new parameters exhibited well pronounced minima. In the column’s core, the existence of a transition flow regime was not identified. In the annulus of the bubble column with internals, three transition velocities (at U_G=0.03, 0.06 and 0.10 m/s) were identified. The first transition velocity identified the end of the gas maldistribution regime. The second and third critical velocities distinguished the ends of the homogeneous and heterogeneous regimes, respectively.

The processing of the gas holdup data in the entire cross-section of the column revealed that the U_trans-1 and U_trans-2 values occurred at somewhat lower U_G values (0.05 and 0.08 m/s). These critical gas velocities identified both the lower and upper boundaries of the transition regime.