CFD Simulation of Average and Local Gas–Liquid Flow Properties in Stirred Tank Reactors with Multiple Rushton Impellers

Abstract

In this article, computational investigation of the gas-liquid ow in stirred tank with multiple Rushton impellers was carried out. Experimental results of average and local details of gas-liquid ow characters were reported, including gas-holdup, bubble Sauter diameter, speci c area and mass transfer coe cient. Thoroughly interphase momentum transfer models including drag and non-drag models were investigated, together with four mass transfer coe cient models using commercial CFD software ANSYS CFX 12.0. Among the drag models tested, the modi ed Brucato model showed more accurate results than others, while non-drag models showed slight e ects on the average ow and local ow characters. For accurate local ow simulation, the population balance model (PBM) showed quite sensitive e ect on the local gas distribution. Simulation of interphase mass transfer with eddy cell model showed the most agreement with experimental measured data. Additionally, two advection schemes were employed and compared with each other to test their ability to get more accurate simulation result.

Numerical and experimental assessment of a miniature bioreactor equipped with a mechanical agitator and non‐invasive biosensors

“…Ranganathan and Sivaraman found that both the slip velocity model and eddy cell model could predict the mass transfer parameter well. We have previously proven that the simulation of interface mass transfer with the eddy cell model showed the best agreement with experimentally measured data . Thus the eddy cell model was applied in this work as where K = 0.4 is the model constant, D L is the diffusion coefficient of oxygen (2.01 × 10 −9 m 2 s −1 at 20 °C) and ϵ is the turbulence dissipation rate in the liquid phase …”

“…Impeller rotation was modeled with the multi‐reference frame (MRF) . For gas–liquid flow, the interphase force, especially the drag force, plays a key role in the accurate prediction of gas distribution and further affects the prediction of mass transfer . Previously, we have demonstrated that the modified Brucato drag model showed more accurate results than other drag models such as the Grace drag model, Ishii–Zuber drag model and Tomiyama drag model .…”

“…We employed here the same model for simulating the interphase drag force: where F D is the drag force, α g and α l are the gas and liquid volume fractions respectively, ρ l is the liquid density, d is the air bubble size, u l and u g are the liquid and gas velocity vectors respectively and C D,lg is the drag coefficient. The latter is modeled by the modified Brucato drag model given by where λ is the Kolmogorov length scale and C D is the drag coefficient of a single bubble in the stagnant liquid: Here Re b is the bubble Reynolds number and Eo is the Eötvös number given by …”

“…48,49 Previously, we have demonstrated that the modified Brucato drag model showed more accurate results than other drag models such as the Grace drag model, Ishii-Zuber drag model and Tomiyama drag model. 48 Similar results were also found by Ranganathan and Sivaraman. 46 We employed here the same model for simulating the interphase drag force:…”

The Process of the Intensification of Coal Fly Ash Flotation Using a Stirred Tank

“…The flow structure in stirred tanks is three-dimensional, complex and has high shear. The computational fluid dynamics (CFD) simulation is used to promote the study of the fundamental phenomena, which could provide the flow field information in the stirred tank [18]. As we know, the large eddy simulation (LES) could obtain the precision flow field information, and its computational consumption is between the direct numerical simulation (DNS) and the Reynolds-averaged Navier-Stokes equations (RANS) [19].…”