Computational Assessment of Turbulent Eddy Impact on Hydrodynamic Mixing in a Stirred Tank Bioreactor with Vent based Impellers

Homogeneity and efficient oxygen transfer are crucial for aerobic cultures, which is popularly performed in Stirred Tank Bioreactors, through internal mechanical agitation of the impellers.Although there are a number of impeller designs for achieving this purpose, there are still concerns about the ability of the impellers to yield homogeneity and mitigate or eliminate stagnant zones.In this study, a novel impeller design, with auxiliary agitators in form of vents, was introduced and evaluated for small lab-scale bioreactors. For the evaluation, 3D models of a single and double impeller configurations, placed in two different bioreactors were developed. Computational fluid dynamics was employed to carry out the hydrodynamic simulation using k-epsilon standard model in the bioreactors.Computational variables such as the flow velocity, streamlines, pressure and wall shear stress on the shaft and impellers, eddy viscosity, turbulence eddy dissipation and turbulence kinetic energy were obtained and compared in both bioreactors to evaluate the performances at speeds of 50, 100, and 150 revolutions per minute.A comparison of the results with traditional segment-segment and segment-Rushton impellers shows that our double impeller configuration performs more desirably at speeds ranging from 100 to 150 RPM. Homogeneity was also achieved in both bioreactors, and there was significant reduction of stagnant zone less than 99 percentage in the double impeller configuration and significant mitigation in the single impeller agitation.