Dipl.-Ing. Frederic Krakau
- © Krakau, privat
Verfahrenstechnik I 
Projekt ProzessIngenieurWissenschaften - PIW 
Breakage phenomena in gas/liquid systems
Bachelor's / Master's Theses
Current offers for theses can be found here .
Stirred gas/liquid systems are a fundamental part
in many technical processes in the chemical-, oil-, pharma and food
industries. A decisive role in respect to performance and efficiency
of these processes plays the bubble size distribution (BSD). It
determines the interphase contact area and thus has a direct impact on
the mass transfer between the disperse and continuous phase. The
bubble size distribution results from the contrasting phenomena
breakup and coalescence.
At present the dimensioning of stirred tanks is still linked to significant experimental expenses. In many cases cost- and time- consuming preliminary investigations at pilot plant scale with original material systems are necessary. Computational fluid dynamics (CFD) in combination with population balance equations (PBE) are a promising option to reduce this effort and predict the behavior of gas/liquid systems. For breakup and coalescence the population balance equations are using breakage- and coalescence sub models. Although these models were investigated over the last decades, the up-to-date present models in literature often match only within very narrow ranges with experimental data and some even describe contradictory behavior regarding important process parameters. Therefore it is necessary to further develop the existing models and to get a more profound understanding of the bubble breakage and coalescence phenomena.
breakage and coalescence proceed simultaneously in a stirred tank, it
is important for the mathematical description and understanding of the
processes, to consider them separately. In order to develop predictive
models for bubble size distributions, a quantitative understanding of
bubble breakup is required. Despite plenty of existing literature
about single fluid bubble breakage, there is a lack of reliable
experimental data. Building on previous experimental research at the
chair of chemical and process engineering, for single drop breakage in
a special breakage channel with a simplified flow field,
investigations about single bubble breakup are now being carried out
in the stirred tank (see Fig. 1).
The influence of process parameters such as
geometry or stirrer speed on single bubble breakup is examined. The
process is recorded by a high speed camera (up to 150,000 fps),
whereat it is necessary to automate the evaluation of bubble breakup
to get quantitative variables such as breakup time, breakup location
or bubble size distribution.
For the final modeling of transient bubble size distributions on the basis of population balances the acquired experimental singe breakup results are applied. In the literature existing breakup models to calculate the particle size distribution are improved and further developed by comparison with experimental measured particle size distributions.
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