Study On Flow Characteristics Of Bioreactors With Curved Mixing Impeller

As the core device of cell culture in vitro,bioreactors play an increasingly important role in the field of biomedicine.The stirred bioreactor is the most widely used at present because of its simple structure,convenient operation and good cell adaptability.However,the flow field inside the reactor is complex,and the analytical solution cannot be obtained through theoretical calculation.Meanwhile,the shear force generated by mechanical stirring will cause damage to cells,so it is necessary to carry out detailed numerical simulation study on the flow characteristics inside the stirred reactor.In this paper,the flow characteristics of the bottom-entry bioreactor were simulated,the curved mixing impeller was developed,and the structure parameters of the impeller were optimized.The main research work and achievements of this paper are as follows:(1)A stirred bioreactor model was established,and numerical simulation of the flow field inside the reactor was carried out using the method of multiple reference frame(MRF).The simulated velocity field was compared with the experimental results,and a good agreement was found.The simulation results of Standard k-epsilon model,RNG k-epsilon model and Realizable k-epsilon were compared,and it was found that the difference between the results of RNG k-epsilon model and the values of experiment was larger than that of the other two turbulence models,and the simulated values of the static region were more accurate than that of the dynamic region.(2)The influence of four types of mixing impeller structure,including RT impeller,PBT impeller,EE impeller and B-EE impeller,on the flow characteristics of bioreactor was studied.The results showed that the reactor with B-EE impeller proposed in this paper has the highest average turbulence kinetic energy and the lowest shear rate,which represents good mixing performance and shear rate.So the B-EE impeller is the preferred impeller for cell culture bioreactors.The flow circulation inside the RT impeller reactor differs greatly from the other three types,and the flow circulation circle is smaller and mainly distributed in the area of the cylinder wall of the reactor,which is not conducive to the overall mixing of materials.Therefore,it is generally not suitable for the bottom-entry bioreactor.(3)The structure parameters of curved mixing impeller mainly include impeller sector width,diameter ratio of impeller and reactor and the angle between impeller and stirred shaft.In this paper,the influence of the structure parameters of the curved mixing impeller on the flow characteristics of bioreactor was analyzed by three factors and three levels of orthogonal test.In order to get good mixing effect and low shear rate,the optimal parameters of curved mixing impeller is finally decided as follows: the angle between impeller and shaft is 60 °,the sector width is 90 ° and the diameter ratio is 1/2.(4)The influence of stirred impeller speed(150rpm,200 rpm,250rpm,300 rpm,350rpm and 400rpm)on flow characteristics in the reactor was studied.It was found that the turbulence kinetic energy,turbulent dissipation rate and shear rate of the fluid in the reactor will get raised with the increase of velocity.The average shear rate was 14.4(1/s)at a speed of 250 rpm,which was most suitable for cell growth.To sum up,the curved mixing propeller proposed in this paper is suitable for bottom-entry bioreactor,which has the characteristics of good mixing performance and low shear rate,and has important reference value for the development of bioreactor.Subsequent studies can be carried out around the Particle Image Velocimetry(PIV)and Laser Doppler Anemometry(LDA).