Resumen de Cfd modelling of multiphase turbulent flows in a bubble column reactor
This work presents numerical study turbulent two-phase flows in a 3D bubble column reactor using different models at different scales. The focus is first set on the hydrodynamics, flow regime transitions and mass transfer using the Euler-Euler mixture k-ε model at a wide range of superficial gas velocities. The emphasis is to assess the performance of this model and the analysis of the flow regime transitions and the transient flow behavior inside the bubble column reactor. A quantification of the interfacial forces at different parts of the reactor were presented. Different models of the overall mass transfer coefficient estimation, namely the slip penetration model and the eddy cell model, are compared against the experimental data to analyze the mass transfer. The results reveal some of the characteristic features of homogeneous and heterogeneous flow regimes on the liquid circulation, gas holdup, turbulent fluctuations and gas-liquid mass transfer.
For transient and turbulent flow regimes, Euler-Euler large eddy simulations were used for a reliable scale resolution. The flow is more dynamic, and more details of the instantaneous local flow structure have been obtained including large-scale structures and vortices developed in the bubble plume edge. The power spectra for were analyzed for both high and low frequencies regions at different gas velocities.
In addition to the different scale simulations, the three-dimensional Euler-Euler large eddy simulation model was used to calculate large-scale structures and their interaction with bubbles at inlet superficial gas velocities where vortical-spiral and turbulent flow regimes occur. We use a conditional sampling procedure of liquid velocity and gas hold-up time series to identify and educe the development of coherent flow structures which consists in a pair of counter-rotating vortices convected in a staggered pattern along the column in both the vortical-spiral and central plume regions. The yielded averaged topology of the three-dimensional large-scale structures which was reconstructed and visualized using iso-surfaces.
