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Extraction in pump-mixers with presence of solid phase

Subject Area Chemical and Thermal Process Engineering
Hydraulic and Turbo Engines and Piston Engines
Term from 2017 to 2022
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 395373747
 
Final Report Year 2023

Final Report Abstract

A common project from Prof. H.-J. Bart, TU Kaiserslautern (TUK) - focused on experimental side - and Prof. R. Skoda, Ruhr Univ. Bochum (RUB) - focused on simulations - has been launched for the analysis of extraction processes in pump-mixers in presence of solids. By a combined experimentalnumerical method, the complex behaviour of pump-mixing was investigated. In literature, almost no data exist in respect to local analysis of pump-mixer performance, as only integral data (e.g. mean Sauter diameter) is given. In that respect it was necessary to generate a comprehensive database (1) of transient local data (drop size distributions - DSD, velocity and pressure fields) of a pump-mixer for the first time. In a step-by-step approach it started with batch followed by a continuous setup, also including first experiments in liquid-liquid- solid multiphase systems. Thus, initially literature data on local velocity fields has been exploited by adopting the design and operation range of this literature setup. Thereby, valuable data e.g., on the local turbulence field complemented the own multi-phase experiments and simulations. In that respect at TUK a flexible setup for batch and continuous operation was developed and equipped with sophisticated particle analytics. Albeit the focus was still on two-phase liquid-liquid systems without solids, orientating experiments in three-phase systems were performed at TUK. Here, an in-house convolutional neuronal network program in combination with the modified patented optical probe proved to be very effective to evaluate the DSD also in three-phase systems (2). The setup allows a variation of different influencing factors such as location of the impeller, impeller speed, phase ratio and fraction of solids. At RUB, 3D simulations were performed complementarily to the experiments. The focus was the assessment of multi-phase turbulence models and the validation of the coupled CFD-PBM (population balance model) 3D simulation method (3). Crucial shortcomings of existing droplet kernels could be identified, which hindered us to extend the two-phase simulations to the addition of a solid phase. Instead, a strategy of kernel adjustment based on locally measured DSD has been proposed, and a self-developed SAS (scale-adaptive turbulence model) (4) has been identified as an accurate and still not too expensive turbulence model with scale-resolving capabilities. In the extension period, both, turbulence modelling and kernel development will be extended to the presence of solids. The developed coupled 3D CFD-PBM code is generic and should be also applicable to gas-liquid and later gas-liquid-solid systems (heterogeneous catalysed oxidation, hydrogenation, etc.) as an outlook for further research.

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