### Browsing by Author "Wierink, Gijsbert Alexander"

Now showing 1 - 2 of 2

###### Results Per Page

###### Sort Options

Item A computational framework for coupled modelling of three-phase systems with soluble surfactants(Aalto University, 2012) Wierink, Gijsbert Alexander; Heiskanen, Kari, Prof.; Materiaalitekniikan laitos; Department of Materials Science and Engineering; Kemian tekniikan korkeakoulu; School of Chemical Technology; Heiskanen, Kari, Prof.Bubble-particle interaction is a key phenomenon in many industrial applications, for example in mineral froth flotation. Flotation systems are typically characterised by high void fraction of dispersed phases and often multiple surface active compounds are present. The complexity of bubble-particle interaction has lead researchers to develop simplified models for dilute systems and typically physical and physico-chemical aspects are left out. This work discusses a modelling framework for analysis of bubble-particle interaction in the presence of soluble surfactants. The model includes full momentum coupling between gas, liquid, and solid phases using a coupling between Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM) named CFDEM. CFDEM is an open source modelling framework where the CFD code OpenFOAM and the DEM code LIGGGHTS interact. To accommodate topological changes of the bubble surface during break-up and coallescence the Volume Of Fluid (VOF) method was used. Solid particles are tracked in a Lagrangian frame of reference and experience forces due to collisions and the presence of the gas-liquid interface. A comprehensive model has been developed where particle-interface forces are modelled as a hyperbolic function of the gradient of the phase fraction. Particles can be captured within the interfacial region and can detach from the bubble when the balance of forces so dictates. DLVO and non-DLVO forces, as well as inertial forces, form part the total stress balance and contribute to the momentum equation of all phases. Variable interfacial tension is taken into account by implementation of a volumetric transport equation for soluble surfactant in the bulk fluid and within the interfacial gas-liquid region. The method is fully mass conservative and combines higher order physical momentum coupling with physico-chemical momentum. The sub-models used need further study, but to the authors knowledge the model presented is the first to couple all momenta in a comprehensive modelling framework for bubble-particle interaction. The main value of this work is that the computational framework is modular and easily extensible to include more accurate sub-models. The Lagrangian particles are in fact dynamic lists that can be populated by the properties appropriate to the system. These properties accommodate further development and help to identify future research needs in the field of flotation modelling.Item Modeling and validation of flows in a low speed centrifugal separator(2006) Wierink, Gijsbert Alexander; Turunen, Janne; Niitti, Timo; Materiaalitekniikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Heiskanen, KariThe aim of this Master's thesis is to assess the possibilities of Computational Fluid Dynamics (CFD) modelling in FLUENTr to predict fluid flow behaviour in a low speed centrifugal separator. From literature it is known that model limitations of the basic k-e turbulence model lay predominantly in the field of prediction of confined swirling flow behaviour. In this thesis CFD modelling of pipe flow and swirling annular flow is done in FLUENTr and validated by flow visualization experiments. The study includes a discussion of the fundamental physical theory behind the behaviour of fluid flows and particles in them and a low speed integrated centrifugal separator is introduced. With the theoretical insights, the classification mechanism of the device is explained. Subsequently the physical theory is used to explain the working of CFD flow modelling and what can be achieved. Also, a concise overview of the available techniques of flow visualization is given. In the experimental part of the thesis first a well established flow phenomenon, Reynolds' pipe flow experiment, is CFD modelled in FLUENTr and then validated by a flow visualization experiment. FLUENTr's flow predictions for pipe flow fit experimental data especially well for more turbulent flow conditions; a good result for modelling the turbulent swirling annular flows in the main experiment. With this practical experience gained the proposed centrifugal separation device was modelled in FLUENTr and parallel to that a flow visualization experiment run. Physical assumptions of the standard k-c turbulence modelling algorithms suggest model limitation especially in the type of flows encountered in the device studied. However, the model validation experiment indicates that CFD flow modelling of this type can in fact predict confined swirling flows fairly accurate. The model fit to the validation experiment was found to have a fractional bias of maximum 0.257 with common values well below 0.2. The average hit rate of CFD prediction to experimental data varied between 0.77 to 0.85 for low flow rate and between 0.75 and 0.92 for higher flow rates; unity being a perfect match. It can be concluded that strongly turbulent, confined swirling flows can be predicted well by the standard k-c turbulence model in CFD modelling and that accuracy even increases for increasing turbulence. Further development lays mainly in the investigation of this type of fluid flows in different geometric configurations and up-scaling.