Statistical tool combined with image analysis to characterize hydrodynamics and mass transfer in a bubble column

Image analysis technique has been proved to be very effective in the quantification of particles size and morphology distributions in different work areas. In the present work this technique was combined with the discriminant factorial analysis (DFA) in order to allow the automatic identification of single bubbles (isolated bubbles without influence of surrounded bubbles) in multiphase systems. With the previous methodology it has been possible to distinguish online and automatically among three different classes of bubbles (single bubbles and medium complexity and large complexity bubbles groups), allowing for the first time the computation of the local bubble population complexity in the system. The automatic and correct characterization of the single bubbles allowed the correct determination of bubble size and, consequently, the specific interfacial area a at different experimental conditions. Agreement between automated and manual classification, measured in terms of a performance index, is 98% for single bubbles identification. Further, the present work describes the application of such methodology to the study of temperature, type of gas sparger, and liquid phase properties (viscosity and surface tension) influence on the individual components of volumetric liquid side mass transfer coefficient, kLa. The results show that the different experimental parameters and liquid properties act by a particular way on kL and a.

► New tool, for automatic identification of single bubbles in multiphase systems.
► The outputs are: bubble size and morphology, a and local complexity of the system.
► Information very useful for a better knowledge of hydrodynamic influence on kLa.
► kL is strongly influenced by the presence of bubbles groups.
► Agreement between automated and manual classification is 98% for single bubbles.