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Computer‐automated radioactive particle tracking (CARPT) data obtained in a 0.162 m air‐water bubble column operated at ambient pressure have been analysed. The superficial gas velocity (Ug) has been varied in the range 0.02‐0.12 m/s under constant liquid height 1.04 m. A perforated plate (82 holes ø 0.4 mm, free plate area 0.05 %) distributor has been used. The Kolmogorov entropy (KE) vs. Ug allows identification of the transition velocity (Utrans = 0.064 m/s) between bubbly and transition regimes. KE models for both regimes have been also developed. The quality of mixedness (QM) concept shows that QM(upper zone) ⊕ QM(lower zone) at Utrans = 0.064 m/s.

The Kolmogorov entropy (KE) algorithm was applied successfully to single source c-ray Computed Tomography (CT) data measured in a 0.162 m ID bubble column equipped with a perforated plate distributor (163 holes ·˘1.32 mm). Dried air was used as the gas phase and Therminol LT (q L = 886 kg m -3 , l L = 0.88 · 10 -3 Pa s, r = 17 · 10 -3 N m -1 ) was used as a liquid phase. Three different pressures, P, of 0.1, 0.4, and 1.0 MPa were examined. At each pressure the superficial gas velocity, u G , was increased stepwise by steps of 0.01 m s -1 up to 0.2 m s -1 . The average absolute deviation (AAD) was also used as a robust statistical criterion for regime transition. At all three pressures, based on the sudden changes in both the AAD and KE values, the boundaries of the following five regimes were identified: dispersed bubble regime, first and second transition regimes, coalesced bubble regime consisting of four regions (called 4-region flow), and coalesced bubble regime consisting of three regions (called 3-region flow). The existence of these regimes has already been documented. As the pressure increases, the transition velocity between the dispersed bubble and first transition regimes and the transition velocity between coalesced bubble (4-region flow) and coalesced bubble (3-region flow) regimes shift to higher u G values. On the other hand, at P = 0.4 MPa the second transition regime starts earlier. In addition, at P = 1 MPa the transition to coalesced bubble (4-region flow) is delayed.

When Higbie's penetration theory is applied to calculate k L -values for ellipsoidal rather than spherical bubbles, some correction factor needs to be introduced. In a recent paper, such a correction factor (less than unity) was derived for the homogeneous flow regime, based on k L a-data measured in 1-butanol, toluene, ethanol, and tap water: f c = 0.211 Eo 0.63 . In the present work, the validity of this approach is further tested on k L a-data published for ethylbenzene, xylene, tetralin, anilin, nitrobenzene, 1,2-dichloroethane, 1,4-dioxane, 2-propanol, benzene, ligroin, and ethyl acetate. The full data set involving 79 experimental k L a-values at homogeneous flow in 14 organic liquids and tap water, is correlated with a 8.7 % mean error in the following modified form: f c = 0.185 Eo 0.737 .

A new semi-theoretical approach for prediction of gas holdups in the homogeneous flow regime is suggested. The model is based on two different expressions for the gas-liquid interfacial area. It is argued that in the case of oblate ellipsoidal bubbles (formed in the homogeneous regime) some correction factor should be introduced in order to render both expressions equivalent. The correction term is correlated to Eötvös number and a dimensionless gas density ratio. The method was capable of predicting 386 experimental gas holdups measured in 21 organic liquids, 17 liquid mixtures and tap water with an average relative error of 9.6%.