The CFD Simulation Of Stirred Tank Bioreactor

Stirred tank bioreactor is widely used in many biochemical processes as ferment and cell culture. Although there are lots of theoretical and experimental study, the study of mixing and design methods are not developed well up to now. The semi-empirical methods are still the main tools for design and scale-up industry processes. To meet the purpose for optimal design, scale-up and fully understand the processes occurring in stirred tank bioreactor, there are need for careful experimental measurements and mathematical models to measure and describe the characteristics of flow in such reactors. Computational Fluid Dynamics(CFD) for the study of flow and mixing characteristics in stirred tank bioreactor is carried out more and more frequently. In this study, based on the function provided by the commercial CFD code (FLUENT), three-dimensional flow fields and shear stress are carefully studied, including the influence of turbulent models to the computational results. It is found that the results of velocity field using RNG k-εturbulent model are in good agreement with experimental data. Most of the turbulent kinetic energy is in the field of stirrer. Although RNG k -ε turbulent model is good for velocity distribution, its results of turbulent kinetic energy is worse than the standard k-εmodel. Most of the shear stress is in the field of stirrer too. The gas-liquid flow in the stirred tank bioreactor was simulated too. The model is three-dimensional and the impeller region is included using a Multiple Frames of Reference method. It is found that the axial gas velocities in the impeller discharge stream are overpredicted. The flow characteristics below and above the impeller are well predicted. But the results of gas fractions are lower than experimental data. Coupled and segregated solution of momentum and mass equation were adopted when studying the mixing process in stirred tank bioreactor. The calculated concentration response curve is consistent with the literature data. Both methods predict the same change rule of mixing time. But the value of mixing time from coupled solution is lower than that from segregated one. Coupled solution needs much more computational efforts than the segregated. It has shown that mixing process depends on the flow field used for mixing calculation. The value of mixing time also depends on detecting and feeding location.