Flow Pattern and Mixing in the Multi‐Turbine Agitated Bioreactor Filled with Poly(γ‐Glutamic Acid) Solution

We investigated the flow pattern and mixing behavior of a poly(γ‐glutamic acid) (γ‐PGA) solution in a bioreactor equipped with two Rushton turbines by simulation and experiment. Computational fluid dynamics (CFD) is used to solve the three‐dimensional hydrodynamics in the bioreactor and to obtain the flow patterns and tracer concentration at every point. The flow circulation patterns by inter‐impeller clearance and viscosity and their effects on overall mixing time were studied. Based on the results we can conclude that the impeller clearance should not be larger than 0.2 D for the efficient mixing under non‐aerated condition when the liquid viscosity is above 20 cp, which corresponds to concentrations of 20 g/L or above for γ‐PGA.