Log law of the wall revisited in Taylor-Couette flows at intermediate Reynolds numbers

We provide Reynolds averaged azimuthal velocity profiles, measured in a Taylor-Couette system in turbulent flow, at medium Reynolds (7800 < Re < 18000) number with particle image velocimetry technique. We find that in the wall regions, close to the inner and outer cylinders, the azimuthal velocity profile reveals a significant deviation from classical logarithmic law. In order to propose a new law of the wall, the profile of turbulent mixing length was estimated from data processing; it was shown to behave nonlinearly with the radial wall distance. Based on this turbulent mixing length expression, a law of the wall was proposed for the Reynolds averaged azimuthal velocity, derived from momentum balance and validated by comparison to different data. In addition, the profile of viscous dissipation rate was investigated and compared to the global power needed to maintain the inner cylinder in rotation

EVALUATING THE ROLE OF GEOMETRICAL FEATURES OF A TAYLOR VORTEX BIOREACTOR TO CULTURE ANIMAL CELLS BY USING COMPUTATIONAL FLUID DYNAMICS

International audienceTaylor bioreactor is fast becoming the next bioreactor to culture animal cells due to milder shear and homogenous flow structures throughout the bioreactor in comparison to the traditional stirred tank. However, there is not much information in the literature about how geometrical aspects of the Taylor bioreactor may affect the culture of animal cells which could result in poor efficiency. As a result, six different geometrical conditions of Taylor bioreactor are presented, related to off-bottom clearance and the external cylinders' bottom shape, after conducting a detailed grid and time-step independence study and validating with experimental results. Simulations were conducted at Reynolds number of 12077 and Taylor number of 5331 with a radius ratio of 0.84 and aspect ratio of 19.8. Throughout the bulk zone equivalent of 80 % of the gap-width, the mean velocity was found to be around 50 % of the maximum with similar gradients which is encouraging for cultivating of animal cells in Taylor bioreactor in comparison with spinner flask and stirred tank bioreactors where the gradients are much less uniform. Curved bottom surfaces of the external cylinder and higher off-bottom clearance areas adversely affect the flow structures creating dead-zone areas in the off-bottom clearance area

Feasibility of the taylor vortex flow bioreactor for mesenchymal stromal cell expansion on microcarriers

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Recombinant rabies virus glycoprotein synthesis in bioreactor by transfected Drosophila melanogaster S2 cells carrying a constitutive or an inducible promoter

S2 cell populations (S2AcRVGP2K and S2MtRVGP-Hy) were selected after transfection of gene expression vectors carrying the cDNA encoding the rabies virus glycoprotein (RVGP) gene under the control of the constitutive (actin) or inductive (metallothionein) promoters. These cell populations were cultivated in a 1 L bioreactor mimicking a large scale bioprocess. Cell cultures were carried out at 90 rpm and monitored/controlled for temperature (28 degrees C) and dissolved oxygen (10 or 50% air saturation). Cell growth attained similar to 1.5-3 x 10(7) cells/mL after 3-4 clays of cultivation. The constitutive synthesis of RVGP in S2AcRVGP2K cells led to values of 0.76 mu g/10(7) cells at day 4 of culture. The RVGP synthesis in S2MtRVGP-Hy cell fraction increased upon CuSO(4) induction attaining specific productivities of 1.5-2 mu g/10(7) cells at clays 4-5. RVGP values in supernatant as a result of cell lysis were always very low (<0.2 mu g/mL) indicating good integrity of cells in culture. Overall the RVGP productivity was of 1.5-3 mg/L. Our data showed an important influence of dissolved oxygen on RVGP synthesis allowing a higher and sustained productivity by S2MtRVGP-Hy cells when cultivated with a DO of 10% air saturation. The RVGP productivity in bioreactors shown here mirrors those previously observed for T-flasks and shaker bottles and allow the preparation of the large RVGP quantities required for studies of structure and function. (C) 2010 Elsevier B.V. All rights reserved.FAPESP[02/09482-3]FAPESP[07/52264-0]FAPESP[05/51746-6]CNPqButantan Foundatio