| Summary: | The influence of the recently identified hydrodynamic flow regimes on the prediction of gas hold-up and liquid circulation velocity in airlift reactors has been investigated. Some hydrodynamic models based on momentum balance are considered. Experiments were conducted on a pilot plant, external loop airlift reactor using air-water system. The generalised equation of Joshi and Lali for the homogeneous regime predicts the overall gas hold-up in this region with satisfactory accuracy and the difference between the experimental and predicted values is lower than ± 8%. Hsu and Dudukovic model predicts the liquid circulation velocity based on the gas hold-up correlations proposed for the homogenous, transition and heterogeneous flow regimes and two-phase friction factor with satisfactory accuracy (within 4.9 %). The results also show that the friction factor has pronounced effect on the model predictions. It would appear, also that the characterisation of various flow regimes has profound effect on the predictions of these important design parameters. Superposition approach is implemented to develop a correlation for the prediction of the axial gas hold-up in the riser as a function of the height and superficial gas velocity. The proposed correlation gives an average error of 4.7%. Keywords: Airlift reactors, flow regimes, gas hold-up, liquid circulation
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