Transition from Homogeneous to Heterogeneous Regimes

FIGURE 10.2 Typical variation of gas holdup with superficial gas velocity in a bubble column. (Reproduced from Ruzicka et al. 2003 with permission from Elsevier B.V. Copyright 2003 Elsevier B.V. http //www.joumals.elsevier.com/chemical-engineering-journal/) 

In their review, Shaikh and Al-Dahhan (2007) have listed the following different techniques used in the literature for studying the transition from homogeneous to heterogeneous regime  

Measurement of gas holdup as a function of the gas velocity Gas holdup can be measured by simply noting the static liquid and dispersion height, and 7/p, respectively. Gas holdup is then estimated from 

Temporal signatures of properties associated with the hydrodynamic state A number of techniques have been used to measure temporal signatures 

Advanced measuring techniques With the advent of sophisticated imaging and velocimetry techniques, better understanding of the flow behavior and consequently a better prediction of regime transition is possible. The techniques used in the literature are listed below with the corresponding references. Readers interested in a specific technique may refer to these references Electrical capacitance tomography (ECT) (Bennett et al. 1999 Tapp et al. 2003) Electrical impedance tomography (EIT) (Tapp et al. 2003) 

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The transition from homogeneous to heterogeneous regime in case of bubble columns was qualitatively described in the introduction. At a certain critical superficial gas velocity, a small disturbance in the hold-up profile sets in liquid circulation, which in turn magnifies the hold-up disturbance. In this way, the disturbance grows, and finally an approximately parabolic gas hold-up profile and intense liquid circulation develop, which are the characteristics of the heterogeneous regime. 

Transition from the homogeneous to the heterogeneous regime occurs as follows ... 

Shnip AI, Kolhatkar RV, Swamy D, Joshi JB. Criteria for the transition from the homogeneous to the heterogeneous regime in two-dimensional bubble column reactors. Int J Multiphase Flow 18 705-726, 1992. 

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