A CRITERIA FOR DETERMINING THE TRANSITION BETWEEN THE HOMOGENEOUS AND THE HETEROGENEOUS FLOW REGIMES IN TWO-PHASE BUBBLE COLUMNS

Bubble columns are widely used in various engineering disciplines, such as chemical engineering, mineral processing, and biotechnology. Their notable advantage lies in their substantial contact area between the gas and liquid phases, which facilitates efficient heat and mass transfer processes. This study investigates the stability of the homogeneous flow regimes in bubble columns under various operational conditions, including scenarios with and without an imposed liquid flow inside the column. The drift flux model, augmented by certain assumptions, emerges as a useful tool to achieve this objective. It is utilized here to classify whether the system operates within a stable homogeneous flow regime or is susceptible to transitioning into the heterogeneous flow regime. A description based on a balance of forces acting on the bubble allows to determine the system’s characteristic curve. The intersection between the operative condition curve and the characteristic curve of the system determines the operating point of the given system. It is noteworthy that a single operative condition curve may yield multiple operative points. However, beginning with the continuity equations and utilizing the drift flux, it can be proved that not all these points are stable operating points. Finally, the drift flux theory is used to predict the global gas holdup in the homogeneous flow regime. The results of the proposed methods are compared with available experimental data concerning bubble columns operating in batch, co-current, and counter-current mode.