CFD Numerical Simulation On Flow And Mass Transfer In Airlift Bioreactor

The airlift bioreactor has been being the focus of the bioreactor research for itspredominant fluid mixing performance and widely using foreground. While itsstructure choosing, designing and scale-up are still depended only on experimentalvalidation and expert experience, lacking in support of theories and consuming muchmoney and time. Being used to analyze the flow, mixing and mass transfer charactersof fluid, Computational Fluid Dynamics (CFD) can not only save a lot of resource,but also get some important local data that cannot be gathered in experiment. NowCFD technology is regarded more and more in the fields of the reactor designing andoptimization.For studying on fluid flow and mass transfer in the airlift bioreactor in detail andgroping after a theory of airlift reactor designing and scale-up, the major work of thispaper are summarized as follows:(1) Based on the analysis of fluid flow in airlift bioreactor, a turbulent two-fluidmodel was proposed. The model takes into account bubble break-up and coalescencein the reactor, velocity slip and interaction between gas and liquid. Besides, thenumerical model is combined with two-film model to describe the oxygen masstransfer process.(2) In order to simulate the gas input equipment of airlift bioreactor, FORTRANprograms were used to simulate the gas sparger and subroutine USRINT andUSRSRC were used to replace the source terms of model equations, while gas-roomwas simply excluded during defining computational space.(3) The established model equations were solved by means of CFX-4.4. Theprofiles of flow field, local gas holdup, bubble diameter and dissolved oxygenconcentration, etc. were gained, and the flow and mass transfer in reactor wereshowed roundly. The simulation results reveal that the airlift bioreactor hascharacteristics such as well macro-mixing, low dead-zone volume, and small shearstress.(4) An experimental system of 30L airlift internal loop bioreactor was designed - III -ABSTRACTand manufactured. The liquid velocity and dissolved oxygen concentration weremeasured by PIV system and dissolved oxygen probe respectively. The comparisonbetween experimental data and numerical results reveals that they have samedevelopment trends though there exist biggish warp.Multiple-phase flow and mass transfer in bioreactor is a complex question in theapplication of CFD technology. Although biggish warp exists between experiment andsimulation, the value is less than that of present reported. In contrast to conventionalstudy, this paper provided more information of flow and mass transfer in airliftbioreactor, which can be directly used to design and scale up airlift bioreactor. In aword, CFD technology is a kind of potentially valuable method for studying on theflow and mass transfer in airlift bioreactor.