Environmental Technology

CFD modeling of gas-liquid multi-impeller stirred bioreactors

A computational model was developed to predict the flow characteristics of the gas–liquid flows generated by multiple impellers in a bioreactor. The aim of this work is to gain insight in the flow regimes and prediction of hydrodynamics parameters, gas holdup, local bubble-size distributions and mixing time in a vessel agitated by dual Ruston turbine impellers. Eulerian multiphase and population balance equation-multiple size group (MUSIG) models have been implemented. Breakup and coalescence of bubbles are modeled fundamentally using isotropic turbulence theory. The flow regimes predicted by numerical simulations were validated with experimental results. The gross flow characteristics like fractional gas hold-up, and mixing time have been measured and compared with numerical simulations.

The gas-liquid flows generated by two six-bladed Ruston turbines in a stirred reactor were simulated for a single volumetric gas flow rate () of 0.5 vvm and for three impeller rotational speeds (N) equal to 250, 350, 450 rpm respectively and the flow regimes obtained by numerical simulation along with the experimental findings are shown in Figure (a), (b) and (c). The flow regimes represented in the figure corresponds to the FF, DL and DD flow regimes respectively, where F stands for flooding regime, L stands for loading regime and D represents the fully dispersed regime.

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