Modelling of gas-liquid stirred tanks is very challenging due to the presence of strong bubble-liquid interactions. Depending upon the needs and desired accuracy, the simulation may be performed by considering one-way, two-way, three-way or four-way coupling between the primary and secondary phase. Accuracy of the prediction on the two-phase flow generally increases as the details of phase interactions increase but at the expense of higher computational cost. This study deals with two-way and three-way coupling of gas-liquid flow in stirred tanks which were then compared with results via four-way coupling. Population balance model (PBM) based on quadrature method of moments (QMOM) was implemented in a multi-compartment model of an aerated stirred tank to predict local bubble size. The multi-compartment model is regarded as three-way coupling because the local turbulent dissipation rates and flow rates were obtained from a two-way computational fluid dynamics (CFD) simulation. The predicted two-phase flows and local bubble size showed good agreement with experimental data.
Dry reforming of methane (DRM) appears as a promising process for the industrial production of syngas in comparison to other conventional reforming technologies. However, DRM process suffers from catalyst deactivation induced by carbonaceous species which reduces the catalyst lifespan. Currently, catalytic designs in DRM have trended towards the incorporation rare-earth metals. As such, ceria (Ce) based catalyst has recently attracted research interest for its key feature to mitigate catalyst deactivation owing to its complementary redox and oxygen storage properties for the removal of surface carbon deposit. The present short review summarizes on the recent catalytic performance of Ce-based catalyst and impact of ceria redox on the DRM mechanism. The utilization of oxygen vacancies introduced by the Ce redox support enhances the catalytic activity by providing additional bifunctional sites and intermediate species to facilitate the surface reaction rate. This perspective will elucidate the role of oxygen vacancies in Ce supports and fine tune the catalytic performance of DRM for industrial applications.
Abstract. This paper concerns with the experimental measurement and computational fluid dynamics simulation on local hydrodynamics of a gas-liquid internal-loop airlift reactor. The aim of this work is to study the sensitivity of the drag models and the significance of considering the lift force on the predictive accuracy of the simulation. The experimental analysis was carried out using laser Doppler anemometry at three different heights (i.e. Y = 0.20 m, 0.30 m and 0.38 m) across the riser and downcomer at volumetric flow rate of 0.30 m 3 /h to provide validation for the simulation results. A transient three-dimensional gasliquid internal-loop airlift reactor was carried out using FLUENT 16.2 by implementing the two-fluid model approach. The Eulerian-Eulerian multiphase and standard k-İ dispersed turbulence model were employed in this study. Results suggest that the spherical drag model performed poorly and that the drag model governed by Rayleigh-Taylor shows promising accuracy in the prediction of overall mean axial liquid velocity. On the other hand, the consideration of lift model shows slightly improvement in accuracy. These findings may serve as a guidance for future scale-up and design of airlift reactor studies
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