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Agitator Speed

The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform

Frantisek Rieger – 1st expert on this subject based on the ideXlab platform

  • effect of particle content on Agitator Speed for off bottom suspension
    Chemical Engineering and Processing, 2002
    Co-Authors: Frantisek Rieger


    This paper deals with the effect of particle content on Agitator Speed for off-bottom suspension. The measurements were carried out with a pitched six-blade turbine characterized by Agitator to vessel diameter ratio d/D=0.3 in dish bottomed vessel equipped with four baffles. The resulting equation for off-bottom suspension was obtained in a wide range of particle sizes for volumetric particle content up to 20%.

  • effect of particle content on Agitator Speed for off bottom suspension
    Chemical Engineering Journal, 2000
    Co-Authors: Frantisek Rieger


    This paper deals with the effect of particle content on Agitator Speed for off-bottom suspension. The measurements were carried out with a pitched six-blade turbine in a flat-bottomed vessel equipped with four baffles. An equation for off-bottom suspension Speed was obtained for volumetric particle content up to 45%.

  • Suspension of Solid Particles
    Collection of Czechoslovak Chemical Communications, 1995
    Co-Authors: Frantisek Rieger, Václav Sinevič


    The results of Agitator Speed measurements for complete suspension of solid particles reported earlier were completed by new measurements in larger vessel and with smaller particles and with particles of different density. Good agreement between earlier and new results justifies the applicability of the correlation proposed for calculation of critical Agitator Speed.

A W Nienow – 2nd expert on this subject based on the ideXlab platform

  • Mixing theory for culture and harvest in bioreactors of human mesenchymal stem cells on microcarriers
    Theoretical Foundations of Chemical Engineering, 2016
    Co-Authors: A W Nienow, Q. A. Rafiq, T. R. J. Heathman, K. Coopman, C. J. Hewitt


    The use of human mesenchymal stem cells (hMSCs) in regenerative medicine is a potential major advance for the treatment of many medical conditions, especially with the use of allogeneic therapies where the cells from a single donor can be used to treat ailments in many patients. Such cells must be grown attached to surfaces and for large scale production, it is shown that stirred bioreactors containing ~200 μm particles (microcarriers) can provide such a surface. It is also shown that the just suspended condition, Agitator Speed N _JS, provides a satisfactory condition for cell growth by minimizing the specific energy dissipation rate, ε_T, in the bioreactor whilst still meeting the oxygen demand of the cells. For the cells to be used for therapeutic purposes, they must be detached from the microcarriers before being cryopreserved. A strategy based on a short period (~7 min) of very high ε_T, based on theories of secondary nucleation, is effective at removing >99% cells. Once removed, the cells are smaller than the Kolmogorov scale of turbulence and hence not damaged. This approach is shown to be successful for culture and detachment in 4 types of stirred bioreactors from 15 mL to 5 L.

  • Agitator Speed and dissolved oxygen effects in xanthan fermentations
    Biotechnology and Bioengineering, 1998
    Co-Authors: A Amanullah, B Tuttiett, A W Nienow


    Agitation Speed affects both the extent of motion in Xanthan fermentation broths because of their rheological complexity and the rate of oxygen transfer. The combination of these two effects causes the dissolved oxygen concentration and its spatial uniformity also to change with Agitator Speed. Separating these complex interactions has been achieved in this study in the following way. First, the influence of agitation Speeds of 500 and 1000 rpm has been investigated at a constant nonlimiting dissolved oxygen concentration of 20% of air saturation using gas blending. Under these controlled dissolved oxygen conditions, the results demonstrate that the biological performance of the culture was independent of agitation Speed as long as broth homogeneity could be ensured. With the development of increasing rheological complexity lending to stagnant regions at Xanthan concentrations >20 g/L, it is shown that the superior bulk mixing achieved at 1000 rpm, compared with 500 rpm, leading to an increased proportion of the cells in the fermentor to be metabolically active and hence higher microbial oxygen uptake rates, was responsible for the enhanced performance. Second, the effects of varying dissolved oxygen are compared with a control in each case with an Agitator Speed of 1000 rpm to ensure full motion, but with a fixed, nonlimiting dissolved oxygen of 20% air saturation. The specific oxygen uptake rate of the culture in the exponential phase, determined using steady-state gas analysis data, was found to be independent of dissolved oxygen above 6% air saturation, whereas the specific growth rate of the culture was not influenced by dissolved oxygen, even at levels as low as 3%, although a decrease in Xanthan production rate could be measured. In the production phase, the critical oxygen level was determined to be 6% to 10%, so that, below this value, both specific Xanthan production rate as well as specific oxygen uptake rate decreased significantly. In addition, it is shown that the dynamic method of oxygen uptake determination is unsuitable even for moderately viscous Xanthan broths. © 1998 John Wiley & Sons, Inc. Biotechnol. Bioeng.57: 198–210, 1998.

A Ghionzoli – 3rd expert on this subject based on the ideXlab platform

  • the effect of bottom roughness on the minimum Agitator Speed required to just fully suspend particles in a stirred vessel
    Chemical Engineering Research & Design, 2007
    Co-Authors: A Ghionzoli, Waldemar Bujalski, R K Grenville, Alvin W Nienow, R W Sharpe, Alessandro Paglianti


    Abstract In this work, the effect of the vessel bottom roughness on the suspension of solid particles in stirred tank reactors is investigated. The experiments were performed in a baffled vessel, which was mechanically stirred with a 45° pitched blade turbine. In order to evaluate the influence of the bottom roughness on particle suspension, four bottoms of different roughness and 8 different sets of spherical particles were used. The density of the solid particles, ρs, ranged from 2500 kg m−3 to 8743 kg m−3 and they were characterized by narrow size distributions with a mean diameter, dp, from 128 μm up to 1850 μm. Measurement of the minimum impeller Speed for ‘just complete suspension’, Njs, showed that the roughness of the bottom had a significant influence. The precise effect depends on the particle size compared to the size of the roughness elements and to the Kolmogoroff microscale, λK.