Experimental And Simulation Studies On Flow Field Characteristics Of Shaking Bioreactors

With the increasing attention of people in the field of health care,the demand for biomedical products gradually increases.One of the important steps is to prepare various biological products through cell culture.As core equipment to maintain cell growth in vitro,the flow field characteristics of bioreactors are important factors affecting its performance.Shaking bioreactors are new type of animal cell culture equipment,which have high oxygen transfer efficiency and low shear strain rate,and have wide application prospects.However,it is difficult to get analytical solution by theoretical calculation method since the flow field in bioreactors is complicated.Therefore,it is of great significance to carry out experimental and simulation studies on flow field characteristics of shaking bioreactors.In this paper,CFD model of shaking bioreactors was established by the combination of experiment and numerical simulation.The influences of working volume,shaking frequency,shaking radius,bottom structure and baffle on mixing,oxygen transfer and shear strain rate of flow field in bioreactors were investigated.The main achievements are as follows:(1)Gas-liquid two phase flow model of the shaking bioreactors was established,and the gas-liquid interface was tracked by Volume of Fluid(VOF)model.Rotational motion of liquid was simulated by RNG k-?turbulence model,and dynamic mesh technology was applied to update the calculation domain.Comparisons between experimental results of flow characteristics and simulated data under different working conditions were conducted.It is shown that simulated free-surface shapes and liquid levels data are in good agreement with experiment results,which verifies the validation of numerical simulation model.(2)The Effects of process parameters on the flow characteristics of shaking bioreactors were studied.As shaking frequency is increased,axial exchange rate of liquid increases,implying a better convective diffusion effect.Meanwhile,volumetric oxygen transfer coefficient(k _La)and average shear strain rate(SSR)increase with shaking frequency;On the other hand,both convection diffusion and turbulent diffusion are degraded with working volume since volumetric power consumption decreases with working volume,resulting in a reduction in k_La and average SSR value;Shaking radius has positive effect on liquid velocity but no significant effect on flow characteristics of bioreactors.(3)The influences of four bottom shapes,such as conical bottom,ellipsoid bottom,flat bottom and sphere bottom,on flow characteristics of shaking bioreactors were studied.The results show that turbulent kinetic energy and k_La value of bioreactors with conical bottom and ellipsoid bottom are significantly larger than those of bioreactors with flat bottom and sphere bottom.The difference of SSR in four bioreactors is not significant,and it is all distributed in the low range,which is acceptable for cell cultivation.(4)The influences of half bottom cone angle on flow characteristics were studied.The results show that both turbulent kinetic energy and oxygen transfer capacity increase first and then decreases as the half cone angle is increased from 30°to 60°,and there is a peak at 50°.The velocity gradient distribution of flow field in shaking bioreactors with different half cone angles is close,and the average shear strain rate change little.(5)Numerical studies on the flow field of vertical,inclined,horizontal baffle bioreactors were carried out.The comparison results show that both three kinds of baffles have broken the quasi steady state flow of no baffle bioreactors,and forming an irregular gas-liquid interface.A significant increase in turbulence parameters and oxygen transfer capacity is also observed.The average SSR of flow field in three baffle bioreactors increase significantly,but it is still distributed in the low range.