| Present biotechnological applications demand large amounts of low-cost and high-quality products. This can only be obtained if processes developed at laboratory scale are accurately translated to full industrial scale. But because of the emergence of scale-up effect, it is likely that conditions in laboratory-scale cultures will differ from those at pilot-plant and production scale. In addition to altering culture variables, changing scales can also affect the degree of homogeneity, with the concomitant appearance of environmental gradients. In this work, two methods were utilized to study fluid dynamics of the Heterogeneities in the reactor.In 200L reactor, Computational Fluid Dynamics (CFD) simulation combined with experiments was utilized to determine the Gas-liquid two-phase impeller system. They could eliminate the degree of homogeneity within the reactor with low power consumption and good Gas-Liquid Dispersion.In this paper, Scale-down method was introduced to simulate the heterogeneities in large-scale bioreactor by constructing Scale-down system. The characteristic parameters of fluid dynamics in Scale-down system, such as mixing time and residence time distribution, were measured to initiate to us in the fluid dynamics character. The results show that tm was mainly influenced by circulation flow and PFR form. Plug flow feature in the PFR was maintained with high circulation flow, large PFR volume and small diameter. Virtual volume (Vvrit) was introduced to analyze the mixing time character. RTD experiments validate the existence of dead zone or backmixing. It was also stated that fluid dynamics character in the PFR was affected by circulation flow and diameter. But influence was reduced when PFR account for a small proportion. Based on experiments, fluid flied and hydrodynamic parameters within Scale-down system were proved by CFD simulation. Our conclusions were validated by simulation results to supply fermentation test with a solid theoretical basis...
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