(601d) Fundamental Experimental Analysis of Single Bubble Breakup in Stirred Tanks By 3D-Particle Tracking

Fundamental experimental analysis of single
bubble breakup in stirred tanks by 3D-particle tracking

Frederic
Krakau,
Matthias Kraume

Chair
of Chemical and Process Engineering, Technical University Berlin, D-13355 Berlin,
Germany

Bubble size distributions are a key parameter for the
performance and efficiency of multiphase gas/liquid systems. The bubble size
distribution results from the contrasting phenomena breakup and coalescence and
directly influences the interphase contact area or rather the mass transfer
between disperse and continuous phase.

A promising option, to reduce the effort for
dimensioning and predict the behavior of gas/liquid systems, is to use
computational fluid dynamics (CFD) simulations in combination with the
population balance equation (PBE) framework. For breakup and coalescence, the
PBE framework uses sub models. These models are often limited to very specific process
parameters and sometimes even predict contradictory behavior. Although a large
number of models exists in literature, there is a lack of experimental data
available. To gain a deeper understanding of the breakup and coalescence phenomena
and to improve existing models further experimental investigations are
essential.

Whereas breakage and coalescence proceed
simultaneously in gas/liquid systems, it is necessary to consider them
separately for the detailed understanding of the underlying effects. In this work,
a bottom-up approach is applied to examine the single bubble breakup process in
the stirred tank. The influence of process parameters, such as injection
location or power input, on the fluid particle breakup is analysed for a
Rushton turbine. A fully automated setup including two high-speed cameras is
used for the serial generation and three-dimensional observation of bubble
breakup trajectories. The additional analysis software tool allows an unbiased
evaluation of the trajectories and ensures high repetition rates necessary for
the statistical analysis. Quantitative breakup parameters, such as the initial
breakup location, the initial- and final breakup time or the initial- and final
daughter size distribution, are analysed based on the three-dimensional bubble
breakup trajectories.

Fig. 1: Three-dimensional single bubble
breakup trajectory with breakup into two daughter bubbles