The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform
Frantisek Rieger - One of the best experts on this subject based on the ideXlab platform.
-
effect of particle content on Agitator Speed for off bottom suspension
Chemical Engineering and Processing, 2002Co-Authors: Frantisek RiegerAbstract: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, 2000Co-Authors: Frantisek RiegerAbstract: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, 1995Co-Authors: Frantisek Rieger, Václav SinevičAbstract: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 - One of the best experts 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, 2016Co-Authors: A W Nienow, Q. A. Rafiq, T. R. J. Heathman, K. Coopman, C. J. HewittAbstract: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, 1998Co-Authors: A Amanullah, B Tuttiett, A W NienowAbstract: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 - One of the best experts 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, 2007Co-Authors: A Ghionzoli, Waldemar Bujalski, R K Grenville, Alvin W Nienow, R W Sharpe, Alessandro PagliantiAbstract: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.
A Amanullah - One of the best experts on this subject based on the ideXlab platform.
-
Agitator Speed and dissolved oxygen effects in xanthan fermentations
Biotechnology and Bioengineering, 1998Co-Authors: A Amanullah, B Tuttiett, A W NienowAbstract: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.
T.d. Wheelock - One of the best experts on this subject based on the ideXlab platform.
-
Coal beneficiation kinetics of a gas-promoted oil agglomeration process
1996Co-Authors: F. Zhang, T.d. WheelockAbstract:The kinetics of a gas-promoted oil agglomeration process were investigated by monitoring the change in the turbidity of an aqueous particle suspension as the particles were agglomerated with heptane in a closed tank fitted with baffles and an Agitator. Measured amounts of air and heptane were added to a suspension of Pittsburgh No. 8 coal under vigorous agitation. The subsequent rate of change of particle concentration was taken to be an indication of the rate of agglomeration. The rate was found to be proportional to the particle number concentration raised to a power and dependent on Agitator Speed and the amounts of air and oil added.
-
Development of a gas-promoted oil agglomeration process. Technical progress report, October 1, 1993--September 30, 1994
1994Co-Authors: T.d. WheelockAbstract:During the first year of the project two model mixing systems, which differed in size but were similar in design, were constructed and tested. The systems were equipped for measuring Agitator Speed and torque and for measuring the turbidity of coal particle suspensions undergoing agglomeration. Preliminary measurements of aqueous suspensions of coal particles showed that the Beer-Lambert law applies to such suspensions at least for low concentrations. Therefore, the measured turbidity can be used as an indicator of particle concentration and a means for monitoring the progress of oil agglomeration. However, the method is not applicable for large particle concentrations so a different technique was tested for monitoring the agglomeration of large concentrations. This technique involves measuring Agitator torque and observing changes in torque while Agitator Speed is held constant. The results of preliminary tests of the technique were encouraging. In these tests significant changes in Agitator torque were observed when particle agglomeration took place as long as solids concentration of 25 w/v % or more were utilized. A number of agglomeration tests were conducted using either one or the other of the two monitoring techniques. Both methods showed that even very small amounts of air can promote the oilmore » agglomeration of coal particles suspended in water. Even the amount of air dissolved in water at room temperature and pressure can affect the process providing the air is displaced from the solution by a slightly soluble agglomerant such as heptane. The apparent rate of agglomeration was observed to increase as more air was introduced and also as Agitator Speed was increased.« less
-
Development of a gas-promoted oil agglomeration process. Technical progress report, December 1, 1993--February 28, 1994
1994Co-Authors: T.d. Wheelock, J. Drzymala, F. ZhangAbstract:The overall purpose of this research project is to carry out the preliminary laboratory-scale development of a gas-promoted, oil agglomeration process for cleaning coal using model mixing systems. A model mixing system has been previously designed and constructed for conducting oil agglomeration tests in such a way that Agitator Speed and torque can be measured as well as agglomeration performance. Equipment is also provided for monitoring the progress of agglomeration during a batch test. This equipment includes a photometric dispersion analyzer for measuring the turbidity of the particle suspension. In order to measure the turbidity a small stream of material is withdrawn from the mixing tank and conducted through an optical cell associated with the photometric dispersion analyzer. The material is then returned to the mixing tank. A peristaltic pump located between the optical cell and the mixing tank is used for circulating the material. During the past quarter a series of shakedown test were carried out to calibrate the equipment and to determine some of its operating characteristics. The accuracy of the Agitator Speed and torque measuring instrument was checked. Also the gas dispersing effectiveness of the mixing system was investigated. In addition, the effects of Agitator Speed andmore » solids concentration on Agitator torque and power requirements were studied.« less
