(697b) Modeling Gas-Liquid Mass Transfer Using a Discrete Bubble Method: An Application to Bioreactors

Computational Fluid Dynamics (CFD) has been used in bioreactor engineering in general but most of the publications focus on studying single phase fluid mixing pattern and impeller power draw. These calculations provide details in fluid field and liquid-liquid mixing pattern. However, it has been challenging to effectively simulate gas bubble evolution as a secondary phase and O₂/CO₂ mass transfer phenomena that occurs on the gas-liquid interface around the bubbles. In this study, the physical process of mass transfer between the gas bubbles and bulk liquid is modeled using a Lattice-Boltzmann’s approach i that significantly simplifies the multiphase model setup. The rate of mass transfer across the gas-liquid boundary is determined using correlations developed for turbulent flow that were previously reported in publications. The bubble specific surface area, [m²/m³], which indicates the area per unit volume of the gas-liquid interface was calculated by solving the two-phase fluid model using a discrete bubble approach. The resulting overall volumetric mass transfer coefficient was then determined.

The mass transfer calculation for both O₂ and CO₂ was performed for lab scale Applikon 3L bioreactors with two distinct impeller and sparger setups. The model predicted mass transfer rates based on simulated probe reading were compared to experimentally determined data from previous studies. The model predicted mass transfer rates of CO₂ and O₂ agrees well with experimentally determined values in both reactor setups over a wide range of impeller agitation rate and airflow rate. The model was also used to help understand the impact of Applikon 3 L reactor setup to fluid flow and mass transfer.