Viscous effects on gas-liquid hydrodynamics for bubble size determinations in different Newtonian and non-Newtonian fluids using a CFD-PBM model

Often, culturing during bioprocessing generates severe conditions that modify the viscosity of the culture media. The change in viscosity leads to different microenvironments governed by viscous effects-mediated hydrodynamics. For example, different bubble size distributions are dispersed inside a bioreactor due to viscous effects. Traditionally, the mathematical modeling framework used in numerical simulation of the bubble size distribution in (bio)reactors is based on breakup and coalescence models valid only in the inertial subrange of turbulence. Hence, applying the traditional models for breakup and coalescence in viscous fluids can result in inaccurate model predictions because the dissipation subrange of turbulence is not considered. This work focuses on the numerical prediction of the bubble size in a stirred bioreactor using the concept of the complete energy spectrum of turbulence to enable viscous effects in the breakup and coalescence models. The breakup and coalescence models are used within the population balance equation (PBE), coupled with computational fluid dynamics (CFD). The emphasis of the PBE-CFD simulations is placed on gas-liquid hydrodynamics aspects related to viscous Newtonian and non-Newtonian fluids applications. In bioreactor zones where viscosity effects occur, the use of the complete energy spectrum of turbulence facilitates the calculation of the transition between dissipation and inertial subranges of turbulence. It is shown that the numerical simulations captured viscous effects-mediated hydrodynamics. Considering these findings, using the complete energy spectrum of turbulence in PBE-CFD simulations is a promising approach for numerical bubble size prediction.