Numerical analysis of hydrodynamics in a mechanically agitated gas–liquid pseudophase system

Abstract

The paper presents the results of numerical simulations of hydrodynamics in a gas-liquid pseudophase system (sucrose solution with yeast suspension). The simulations were performed in a bioreactor with a working volume of 0.02 m 3 , equipped with a Rushton turbine or Smith turbine stirrers. The results of the study were developed in the form of vectors of liquid velocity and the contours of the analyzed magnitudes. Also, the local values of the gas holdup φ in the gas-liquid pseudophase system were presented. The results of numerical simulations of the gas holdup were compared to the results of my own experimental study. Keywords Bioreactor • Mixing • Gas holdup • Numerical modeling • Gas-liquid pseudophase system List of symbols B Width of the baffle (outer diameter of the tubular baffle), m D Diameter of the impeller, m d d Sparger diameter, m H Liquid height in the vessel, m h Distance between impeller and bottom of the vessel, m k c Consistency index, Pa s m1 m Flow index n Impeller speed, s −1 T Inner diameter of the agitated vessel, m V g Gas flow rate, m 3 s −1 z Axial coordinate, m Greek letters φ Gas holdup η Dynamic viscosity of the liquid, Pa s ρ Density of the liquid, kg m −3 k Interfacial tension, N m −1

Computational modelling of mixing tanks for bioprocesses: Developing a comprehensive workflow

“…The residual values should be verified and reported, which is not always done. [6,9,14,15,18,25,31,33] In this work, all the simulations reached residuals values below 10 À5 at every time step. From the graphs of the monitored variables, nonphysical oscillations and numerical instabilities were discarded.…”

“…The residual values should be verified and reported, which is not always done. [ 6,9,14,15,18,25,31,33 ] In this work, all the simulations reached residuals values below 10 −5 at every time step.…”

“…The grid quality is important in CFD models, however, few have reported quality indices. [ 31 ] We focused on three relevant metrics: orthogonal quality, aspect ratio, and skewness. The orthogonal quality ranges between 0–1; the minimum value should be larger than 0.01, with the average close to 1.…”

A CFD-PBM Coupled Method to Optimize a Pilot-Scale Stirred Bioreactor

“…These studies usually neglected the influence of bubble breakup and coalescence, and assumed constant bubble sizes during simulation. To overcome the limitation, some researchers combined the PBM and Euler–Eulerian approach to explore the impact of bubble coalescence and breakup on bubble size distribution. , Another issue is that most studies focused on the single-impeller systems, − while little attention was devoted to the bioreactors with multi-layered paddle structure. In addition, for studies of aerobic fermentation, due to the lack of detailed experimental data, only a few CFD studies ,, have dealt with similar systems.…”

Fluid Flow and Mixing Phenomena in Mechanically Agitated and Gas Stirred Ladle Systems and Their Comparisons

“…Extensive research on turbulent flow phenomena during inert gas and electromagnetic stirring have been carried out and reported in the literature. [1][2][3][4] In contrast, equivalent efforts on mechanically agitated systems, particularly in metallurgical engineering, [5][6][7] have been less common and include such studies as, the k-ε turbulence model-based calculations of flow and mass transfer phenomena 5) as well as numerical modelling of combined inert gas and mechanical stirring processes. 6) Several topics, of interest in the mechanically agitated systems, such as measurements of flow and turbulence, modelling criteria, comparison among different stirring techniques etc.…”