Novel Identifier of Transitions in Bubble Columns Operated with Water and Aqueous Alcohol Solutions

The accurate identification of the transition velocities Utrans in bubble columns (BCs) is important for their effective design, operation, and scale‐up. In this work, a novel parameter, namely, the new hybrid index (NHI), was developed and successfully applied to gas holdup and pressure fluctuations recorded in various BCs operated with water and aqueous solutions of alcohols (ethanol and propan‐2‐ol). The first Utrans was identified on the basis of a well‐pronounced local NHI minimum, whereas the second Utrans was distinguished by the point from which the NHI profile levels off. It was concluded that the main Utrans depend on the type of gas‐liquid system and sparger used. A set of several Utrans is reported. The new hybrid index (NHI) was developed to identify flow regimes in bubble columns. The first transition (end of homogeneous regime) is precisely identifiable by a pronounced local NHI minimum. However, the onset of the heterogeneous regime is not so clear. The point at which the NHI profile levels off marks the second transition, i.e., the onset of liquid macrocirculation and bubble coalescence.