CFD Modeling of Shear-Rate Distribution in a Bubble Column Bioreactor: Influence of Bubble Diameter and Lift Force

Shear rate (γ̇) is a critical parameter for evaluating the bioreactor performance. Average shear rate ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>γ̇</mml:mi> <mml:mrow><mml:mi>a</mml:mi> <mml:mi>v</mml:mi></mml:mrow> </mml:msub> </mml:math> ) traditionally characterizes the shear environment, allowing comparisons among different bioreactor designs based on microorganism morphology and viability. This study presents an innovative approach using computational fluid dynamics (CFD) to assess the influence of lift force on both maximum <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>γ̇</mml:mi> <mml:mi>max</mml:mi></mml:msub> </mml:math> and average ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>γ̇</mml:mi> <mml:mrow><mml:mi>a</mml:mi> <mml:mi>v</mml:mi></mml:mrow> </mml:msub> </mml:math> ) shear rates in a bubble column bioreactor. By employing a two-fluid Eulerian model for gas-liquid multiphase simulations, the research explored a range of specific air flows ranging from 1 to 5 vvm, specific flow rate per volume of medium, which corresponds to the superficial velocities of 4.57 to 22.86 m/s and varied average bubble diameters. Notably, including the lift force amplified the impact of bubble diameter variations on local velocity gradients, significantly affecting shear rates. The findings suggest that <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>γ̇</mml:mi> <mml:mi>max</mml:mi></mml:msub> </mml:math> may serve as a superior metric for comparing bioreactor performance, providing a robust framework for the optimization of biotechnological system design.