Mass Transfer Study of the Oxygen Transfer in a Stirred Tank Reactor Using Population Balance Modelling
In the present paper, the oxygen dispersion in a laboratory scale (3 liters) bioreactor is modeled using open source Computational Fluid Dynamic (CFD) package OpenFOAM (Open-source Field Operation And Manipulation). The combined effect of the bubble breakup and coalescence in the tank is accounted by a novel method of Population Balance Model (PBM) called Extended Quadrature Method of Moments (EQMOM). The three-dimensional simulation is made within a Multiple Reference Frame (MRF), which is a well-established method for the modeling of mixers, also ofter referred to as CSTRs (Continuous Stirred Tank Reactors). Dispersed gas and bubbles dynamics in the turbulent flow are modeled using Eulerian-Eulerian (E-E) approach with mixture k- turbulent model. A modified Tomiyama drag coefficient was used for the momentum exchange, as well. Parallel computing is employed to make efficient use of computational power to predict the spatial distribution of gas phase fraction, Sauter mean bubble diameter (d32), Number Density Function (NDF), oxygen mass fraction in water and flow structure. The numerical results are compared with experimental data, and good agreement is achieved. The results are discussed based on an impeller rotational speed (50 rpm) with different volumetric mass transfer coefficients.
Keywords: Stirred Tank; Bubbly Flow; OpenFOAM; Computational Fluid Dynamic (CFD); Population Balance Model (PBM)