TU Berlin

Chair of Chemical & Process EngineeringDipl.-Ing. Frederic Krakau

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Dipl.-Ing. Frederic Krakau



Verfahrenstechnik I

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.


Whereas 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).

Fig. 1: Trajectory of bubble broken into five daughter bubbles

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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