Fluid dynamics investigation of variant impeller combinations by simulation and fermentation experiment

Fluid dynamics in three bioreactors equipped with different impeller combinations were investigated by Computational Fluid Dynamics (CFD) modeling, and avermectin fermentation experiments by Streptomyces avermitilis were also conducted in these bioreactors. Down-pumping propeller (DPP), 6-curved-blade disc turbine (6CBDT) and 6-arrowy-blade disc turbine (6ABDT) were combined to form different impeller combinations, which were tested in this work. The results of simulation showed that impeller combination consisting of upper two DPP and one bottom 6CBDT could provide the modest flow field environment for avermectin fermentation among the tested impeller combinations. Mass transfer study showed that even if the same impellers were used, different impeller combinations gave different KLa value. It was shown that same “radial flow impeller” such as 6ABDT or 6CBDT used in this work would produce the same shear force in the impeller sweeping zone, but it was different for the “axial flow impeller” such as DPP used in this work, which produced different forces at different mounting positions. The relationship between the fluid dynamics and the fungal cell physiological situation was also discussed based on results of simulation and experiments.