Comparison between average shear rates in conventional bioreactor with Rushton and Elephant ear impellers

• Published in: Chemical engineering science Vol. 90; pp. 92 - 100
• Main Authors: Bustamante, M.C.C., Cerri, M.O., Badino, Alberto C.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 07-03-2013
• Subjects: agitation; air flow; Biochemical engineering; Bioreactors; cells; chemical engineering; Correlation; Ear; Elephantidae; Fluid dynamics; Fluid flow; fungi; Impellers; Mass transfer; Mixing; Momentum transfer; Non-Newtonian fluids; oxygen; rheological properties; Turbulence; Turbulent flow; Mixing; Momentum transfer; Non-Newtonian fluids; Bioreactors; Biochemical engineering; Mass transfer
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2012.12.028

As an alternative to the Rushton turbine impeller (RT), the Elephant ear impeller (EE) has been indicated as suitable for the cultivation of shear-sensitive cells such as animal cells and filamentous fungi. In the present work the average shear rate (γɛav) was evaluated and compared in a conventional bench-scale stirred-tank bioreactor, using different impeller configurations such as the Rushton turbine and the Elephant ear turbine in the down-pumping (EEDP and up-pumping (EEUP) modes. Based on recent methodology, correlations to estimate the average shear rate (γɛav) were obtained for the different impellers according to the rotational impeller speed (N), specific air flow rate (φair), and rheological properties of non-Newtonian pseudoplastic fluids. Values of γɛav predicted by the proposed method were within the range of values calculated by the correlations found in the literature, indicating that the proposed method generates reliable values of γɛav. The γɛav values obtained for the RT and EEDP impellers increase with the increase of N and decrease with the increase of φair for all non-Newtonian fluids. In contrast, for the EEUP impeller γɛav values decrease with the increase of N and φair. The negative influence of φair in γɛav at constant agitation (N) for all impellers was attributed to the increase of the gas hold-up by the increase of φair. EE impellers generated values of γɛav lower than that observed in the system equipped with the RT impeller. EEUP was the impeller that combined good oxygen mass transfer and low shear, appropriate characteristics for its use in bioprocesses involving shear-sensitive microorganisms. The importance of the correlations developed in the present work is that they allow estimation and comparison of the shear conditions in cultures as a function of the operating conditions (N, φair), rheological properties of the fluid (K and n), and volumetric oxygen transfer coefficient (kLa) in conventional bioreactors equipped with different impeller configurations in turbulent flow regime.
▸ Average shear rate (γɛav) was evaluated in stirred-tank with Rushton turbine and Elephant ear impellers. ▸ We propose correlations for γɛav as function of operating conditions and rheological properties. ▸ We have verified that EE impellers generate the lowest values of γɛav. ▸ Elephant ear up-pumping mode impeller (EEUP) combined good oxygen mass transfer and low shear.