Microbial Microbial production of gamma linolenic acid:

With an aim to undertake the scale-up studies on the production of gamma linolenic acid, experimental and CFD modeling of gas dispersion in a dual Rushton turbines stirred bioreactor were performed. Experiments were carried out to identify various flow regimes in a dual Rushton turbines stirred bioreactor for different gas flow rates and impeller speeds. Three hydrodynamic flow regimes were identified namely; FF, DL and DD regimes. FF meant that the upper and lower impellers were in the flooding (F) regime; DL meant that the upper impeller was in the dispersion (D) regime and the lower impeller was in the genomics loading (L) regime; and DD meant that the upper and lower impellers were in the dispersion (D) regime. The commercial CFD code, CFX was used to predict local bubble-size distributions and local volume fraction in the dual turbines stirred bioreactor for different agitator speeds and gas flow rates. Eulerian multiphase and population balance equation-multiple size group (MUSIG) models were implemented and the breakup and coalescence of bubbles were modeled fundamentally using isotropic turbulence theory. The flow regimes predicted by numerical simulations were validated with the experimental results. At 450 rpm, complete dispersion was seen in the fermenter. The CFD simulation showed that the bubble size in the fermenter varied between 2-8 mm and was dominated with mean bubble size of 4 mm. The CFD simulation gave the gas hold value of 0.06 compared to the experimental value.The gas hold-up capacity of the fermenter increased with an increase in stirring speed. All the flow regimes and data obtained under the experimental conditions were successfully modelled using the CFD. The flow regimes were similar to the flow patterns obtained under the experimental conditions

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