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Impeller Speed (impeller + speed)

Distribution by Scientific Domains

Chemistry	56%
Life Sciences	18%

Selected Abstracts

Critical Impeller Speed for Suspending Solids in Aerated Agitation Tanks

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2002
Yonggang Zhu
Abstract Systematic measurements have been carried out in agitated gas-liquid-solids systems to determine the just off-bottom suspension speed. A variety of solids sizes, solids concentrations, impeller sizes and tank sizes are used. The difference between the just off-bottom suspension speeds with and without gas sparging does not show a linear relationship with the gassing rate and the relation is system-dependent. The relative just off-bottom suspension speed RJSS = Njsg / Njs is found to be dependent only on the just suspension aeration number Najs = Qg / NjsD3 and, for DT6 impellers, the relation is RJSS = 1 + mNanjs with the values of 2.6 and 0.7 for m and n, respectively. The relation is independent of the impeller size, solids size, solids loading and tank size, and can be used to scale up laboratory data to full-scale mixing vessels. Data from different studies support the present findings. Des mesures systématiques ont été effectuées dans des systèmes gaz-liquide-solides agités afin de déterminer la vitesse de suspension minimale au-dessus du fond du réservoir. Diverses tailles de solides, concentrations de solides, dimensions de turbines et dimensions du réservoir sont utilisées. La différence entre les vitesses de suspension minimale avec et sans aspersion de gaz ne suit pas une relation linéaire avec la vitesse de gazage et la relation est dépendante du système. On a trouvé que la vitesse relative de suspension minimale au-dessus du fond RJSS = Njsg / Njs est dépendante uniquement du nombre d'aération en suspension Najs = Qg / NjsD3 et que, pour les turbines DT6, la relation est RJSS = 1 + mNanjs, avec des valeurs pour m et n de 2,6 et 0,7, respectivement. La relation est dépendante de la dimension de la turbine, de la taille des solides, du chargement en solides et de la dimension du réservoir, et elle peut être utilisée pour mettre à l'échelle des données de laboratoire pour les mélangeurs en pleine grandeur. Des données provenant de diverses études appuient les présentes conclusions. [source]

Parametric Study of Blade Tip Clearance, Flow Rate, and Impeller Speed on Blood Damage in Rotary Blood Pump

ARTIFICIAL ORGANS, Issue 6 2009
Nahn Ju Kim
Abstract Phenomenological studies on mechanical hemolysis in rotary blood pumps have provided empirical relationships that predict hemoglobin release as an exponential function of shear rate and time. However, these relations are not universally valid in all flow circumstances, particularly in small gap clearances. The experiments in this study were conducted at multiple operating points based on flow rate, impeller speed, and tip gap clearance. Fresh bovine red blood cells were resuspended in phosphate-buffered saline at about 30% hematocrit, and circulated for 30 min in a centrifugal blood pump with a variable tip gap, designed specifically for these studies. Blood damage indices were found to increase with increased impeller speed or decreased flow rate. The hemolysis index for 50-µm tip gap was found to be less than 200-µm gap, despite increased shear rate. This is explained by a cell screening effect that prevents cells from entering the smaller gap. It is suggested that these parameters should be reflected in the hemolysis model not only for the design, but for the practical use of rotary blood pumps, and that further investigation is needed to explore other possible factors contributing to hemolysis. [source]

Microencapsulation of hydrophilic solid powder as fire retardant agent with epoxy resin by droplet coalescence method

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008
Masanori Takahashi
Abstract To give water resistance to Bistetrazol,diammonium (BHT,2NH3) as a fire retardant agent, microencapsulation with epoxy resin was tried by the droplet coalescence method. In this method, two kinds of epoxy resin droplets were prepared; one is the larger epoxy resin droplet containing BHT,2NH3 as a core material and the other the smaller droplets containing Imidazole as a gelation agent. The larger epoxy resin droplets were made to coalesce with the many smaller droplets during the microencapsulation process to prepare microcapsules. In the experiment, the agitation velocities for preparation of the droplets and for coalescence were mainly changed. With increase in the impeller speed, the content of core material increased, became maximum because of increase in the coalescence frequency, and then decreased because of breakup of droplets. With increase in the impeller speed, the leakage ratio of core material decreased, became minimum, and then increased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008. [source]

Fabrication by three-phase emulsification of pellicular adsorbents customised for liquid fluidised bed adsorption of bioproducts

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2003
Mohsen Jahanshahi
Abstract A novel dense pellicular adsorbent, custom-designed for liquid fluidised bed adsorption of protein bioproducts, has been fabricated by coating zirconia,silica particles with agarose gel in a three-phase emulsification process. A slurry feedstock comprising solid zirconia,silica particles (120 µm average diameter) suspended in an aqueous solution of agarose was emulsified in an oil,surfactant mixture in a stirred vessel to yield composite droplets. These were subsequently stabilised by cooling to form spherical pellicular particles characterised by a porous, pellicular coat cast upon a solid core. The impact of agitation speed, surfactant concentration, oil viscosity and slurry composition upon the pellicle depth and overall particle diameter was investigated. Pellicle depth decreased with increasing impeller speed and decreased oil viscosity, whilst increased slurry viscosity enhanced that parameter. Initial increases from low concentrations of Span 80 surfactant (0.1% w/v oil) reduced the depth of the agarose pellicle, but the highest values investigated (1.5% w/v oil) promoted particle aggregation. The fluidisation behaviour of particles fabricated under various conditions was characterised by the measurement of expansion coefficients and axial dispersion coefficients for the liquid phase when operated in a standard fluidised bed contactor. Both parameters were found to be comparable or superior to those reported for conventional, composite fluidised bed adsorbents. The controlled coating of porous agarose upon a solid core to yield specific pellicular geometries is discussed in the context of the fabrication of adsorbents customised for the recovery of a variety of bioproducts (macromolecules, nanoparticulates) from complex particulate feedstocks (whole broths, cell disruptates and unclarified bio-extracts). Given the agreement between the size of the pellicular particles and the trends expected from theory, the large-scale manufacture of such particles for customised industrial use is recommended. Copyright © 2003 Society of Chemical Industry [source]

Agitation and mobilization of thixotropic liquids

AICHE JOURNAL, Issue 9 2010
J. J. Derksen
Abstract Direct numerical simulations of transitional and turbulent flows of purely viscous thixotropic liquids in stirred tanks have been performed. The simple thixotropy model used is based on the notion of a network in the liquid with an integrity that builds up with finite rate under quiescent conditions, and breaks down under liquid deformation. We solve a transport equation for the network integrity which is two-way coupled to the lattice-Boltzmann-based flow solver. The liquid's time scale characterized by the dimensionless Deborah number shows a profound impact on the level of mobilization and the flow patterns in the mixing tanks, especially if the time scale of the liquid is of the same order as the circulation time in the tank. It is also demonstrated to what extent increasing the impeller speed improves mobilization and mixing. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

Review on Mixing Characteristics in Solid-Liquid and Solid-Liquid-Gas Reactor Vessels

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2005
Gopal R. Kasat
Abstract Mechanically agitated reactors with single and multiple impeller systems are used in the industry for the various three-phase mixing processes such as crystallization, fermentation, and hydrogenation, etc. The paper reviews the experimental work reported in the literature along with different techniques used for the measurement of the specific quantities such as minimum or critical impeller speed for solid suspension. The work critically surveys the literature and makes specific recommendations for the use of appropriate correlations and conditions to be used for the success of such equipment. This assessment will put all the relevant literature on a common footing and will help to validate work reported earlier. Les réacteurs agités mécaniquement munis d'une seule turbine et de turbines multiples sont utilisés dans l'industrie pour divers procédés de mélange triphasiques, tels que la cristallisation, la fermentation, l'hydrogénation, etc. On examine dans cet article les travaux expérimentaux présentés dans la littérature scientifique ainsi que les différentes techniques utilisées pour la mesure de quantités spécifiques, telle la vitesse de turbine minimale ou critique pour la suspension de solides. On effectue une étude critique de la littérature scientifique et on propose des recommandations pour le choix de corrélations et conditions appropriées pour une bonne utilisation de cet équipement. Cette évaluation mettra toutes les publications pertinentes à un même niveau et aidera à valider le travail présenté antérieurement. [source]

Scalar mixing measurements in a continuously operated stirred tank

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2001
Markus F. W. Distelhoff
Abstract An LIF (Laser induced flourescence) line scan system was used to obtain unobtrusive scalar concentration measurements in a continuously operated stirred tank agitated by a radial flow Rushton turbine and an axial flow 60°-pitched blade impeller. A better blending process was generally achieved in the axial flow field, with macro- and micromixing in the radial flow field being most complete with fluid injected into the radial discharge jet, and in the axial flow field with fluid injected from above into the rotating impeller. Local concentration levels and fluctuations scaled with the feed pipe flow rate, and the degree of concentration uniformity throughout the tank scaled with the impeller speed and increased with the cube of the power input. On a utilisé un scanneur LIF (fluorescence induite par laser) afin d'obtenir des mesures non invasives de concentration scalaire dans un réservoir agité par une turbine Rushton à écoulement radial et une turbine à pales inclinées à 60° à écoulement axial fonctionnant en continu. On obtient généralement un meilleur procédé de mélange dans le champ d'écoulement axial, le macro et micro-mélange dans le champ d'écoulement radial étant plus complet lorsque le fluide est injecté dans la zone de refoulement radial, et dans le champ d'écoulement axial lorsque le fluide est injecté au-dessus de la turbine. Les niveaux de concentration locaux et les fluctuations sont corrélés au débit de la conduite d'alimentation, et le degré d'uniformité des concentrations dans le réservoir est fonction de la vitesse de la turbine et augmente avec le cube de l'apport de puissance. [source]

Fluid-Borne entities in the impeller stream of a rushton turbine

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2000
Larry A. Glasgow
Abstract The breakage or disintegration of suspended entities by energetic fluid motions in stirred tanks is an essential aspect of many operations in the chemical process industries. However, the hydrodynamic inhomogeneity of such tanks makes it extremely difficult to characterize the stresses experienced in any simple manner. This work provides a determination of both the location and the frequency of interaction of spherical fluid-borne entities with the discharge of a Rushton turbine. These data show how both particle size and impeller speed affect the severity of the exposure, setting the groundwork for improved descriptions of the dynamic behaviour of the particle size distribution in a wide variety of dispersed-phase processes. La rupture ou la désintégration de particules suspendues par des déplacements de fluides énergé-tiques dans des réservoirs agités est un aspect essentiel de nombreuses opérations des industries de procédés chimiques. Toutefois, la non-homogénéité hydrody-namique de ces réservoirs rend extrçmement difficile la caractérisation des forces en jeu par une méthode simple. On détermine dans ce travail la position et la fréquence d'interaction de particules sphériques transpottées par le fluide dans la zone de refoulement d'une turbine Rushton. Ces données montrent comment la taille des particules et la vitesse de la turbine influent toutes deux sur la sévérité de l'exposi-tion, jetant ainsi les bases pour améliorer la description du comportement dynamique de la distribution de taille des particules dans un large éventail de procédés en phase dispersée. [source]

Parametric Study of Blade Tip Clearance, Flow Rate, and Impeller Speed on Blood Damage in Rotary Blood Pump

New milliliter-scale stirred tank bioreactors for the cultivation of mycelium forming microorganisms

BIOTECHNOLOGY & BIOENGINEERING, Issue 3 2010
Ralf Hortsch
Abstract A novel milliliter-scale stirred tank bioreactor was developed for the cultivation of mycelium forming microorganisms on a 10 milliliter-scale. A newly designed one-sided paddle impeller is driven magnetically and rotates freely on an axis in an unbaffled reaction vessel made of polystyrene. A rotating lamella is formed which spreads out along the reactor wall. Thus an enhanced surface-to-volume ratio of the liquid phase is generated where oxygen is introduced via surface aeration. Volumetric oxygen transfer coefficients (kLa),>,0.15,s,1 were measured. The fast moving liquid lamella efficiently prevents wall growth and foaming. Mean power consumption and maximum local energy dissipation were measured as function of operating conditions in the milliliter-scale stirred tank bioreactor (V,=,10,mL) and compared to a standard laboratory-scale stirred tank bioreactor with six-bladed Rushton turbines (V,=,2,000,mL). Mean power consumption increases with increasing impeller speed and shows the same characteristics and values on both scales. The maximum local energy dissipation of the milliliter-scale stirred tank bioreactor was reduced compared to the laboratory-scale at the same mean volumetric power input. Hence the milliliter impeller distributes power more uniformly in the reaction medium. Based on these data a reliable and robust scale-up of fermentation processes is possible. This was demonstrated with the cultivation of the actinomycete Streptomyces tendae on both scales. It was shown that the process performances were equivalent with regard to biomass concentration, mannitol consumption and production of the pharmaceutical relevant fungicide nikkomycin Z up to a process time of 120,h. A high parallel reproducibility was observed on the milliliter-scale (standard deviation,<,8%) with up to 48 stirred tank bioreactors operated in a magnetic inductive drive. Rheological behavior of the culture broth was measured and showed a highly viscous shear-thinning non-Newtonian behavior. The newly developed one-sided paddle impellers operated in unbaffled reactors on a 10 milliliter-scale with a magnetic inductive drive for up to 48 parallel bioreactors allows for the first time the parallel bioprocess development with mycelium forming microorganisms. This is especially important since these kinds of cultivations normally exhibit process times of 100,h and more. Thus the operation of parallel stirred tank reactors will have the potential to reduce process development times drastically. Biotechnol. Bioeng. 2010; 106: 443,451. © 2010 Wiley Periodicals, Inc. [source]

Encapsulation of adult human mesenchymal stem cells within collagen-agarose microenvironments,

BIOTECHNOLOGY & BIOENGINEERING, Issue 4 2005
Anna Batorsky
Abstract Reliable control over the process of cell differentiation is a major challenge in moving stem cell-based therapies forward. The composition of the extracellular matrix (ECM) is known to play an important role in modulating differentiation. We have developed a system to encapsulate adult human mesenchymal stem cells (hMSC) within spherical three-dimensional (3D) microenvironments consisting of a defined mixture of collagen Type I and agarose polymers. These protein-based beads were produced by emulsification of liquid hMSC-matrix suspensions in a silicone fluid phase and subsequent gelation to form hydrogel beads, which were collected by centrifugation and placed in culture. Bead size and size distribution could be varied by changing the encapsulation parameters (impeller speed and blade separation), and beads in the range of 30,150 microns in diameter were reliably produced. Collagen concentrations up to 40% (wt/wt) could be incorporated into the bead matrix. Visible light and fluorescence microscopy confirmed that the collagen matrix was uniformly distributed throughout the beads. Cell viability post-encapsulation was in the range of 75,90% for all bead formulations (similar to control slab gels) and remained at this level for 8 days in culture. Fluorescent staining of the actin cytoskeleton revealed that hMSC spreading increased with increasing collagen concentration. This system of producing 3D microenvironments of defined matrix composition therefore offers a way to control cell-matrix interactions and thereby guide hMSC differentiation. The bead format allows the use of small amounts of matrix proteins, and such beads can potentially be used as a cell delivery vehicle in tissue repair applications. © 2005 Wiley Periodicals, Inc. [source]

CFD Investigation of the Mixing of Yield-Pseudoplastic Fluids with Anchor Impellers

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2009
P. Prajapati
Abstract The study was carried out to simulate the 3D flow domain in the mixing of pseudoplastic fluids possessing yield stress with anchor impellers, using a computational fluid dynamics (CFD) package. The multiple reference frames (MRF) technique was employed to model the rotation of the impellers. The rheology of the fluid was approximated using the Herschel,Bulkley model. To validate the model, the CFD results for the power consumption were compared to the experimental data. After the flow fields were calculated, the simulations for tracer homogenization were performed to simulate the mixing time. The effects of impeller speed, fluid rheology, and impeller geometry on power consumption, mixing time, and flow pattern were explored. The optimum values of c/D (impeller clearance to tank diameter) and w/D (impeller blade width to tank diameter) ratios were determined on the basis of minimum mixing time. [source]

Simulation of Barium Sulfate Precipitation using CFD and FM-PDF Modeling in a Continuous Stirred Tank

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2007
Z. Wang
Abstract A mixing-precipitation model combining computational fluid dynamics (CFD), finite-mode PDF (probability density function) model, population balance and kinetic modeling has been proposed to simulate the barium sulfate precipitation process in a continuous stirred tank agitated by a Rushton turbine. The effect of various operating conditions such as impeller speed, feed concentration, feed position and mean residence time on the barium sulfate precipitation process is clearly demonstrated. It is shown that the mean crystal size increases by increasing the impeller speed and mean residence time. However, when the feed concentration is increased, the mean crystal size decreases. The predictions are in reasonable agreement with the experimental data in the literature. [source]

LDA Velocity Measurements of High-Viscosity Fluids in Mixing Vessel with Vane Geometry Impeller

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2007
Lidija Slemenik Perse
Abstract The object of this work was to measure the velocity field in non-Newtonian fluids inside mixing vessel. The six-bladed vane rotor used for mixing was designed from rotating vane geometry of a sensor system, commonly used for rheometrical measurements of complex fluids (Barnes and Nguyen, J. Non-Newtonian Fluid Mech. 98, 1-14 (2001); Schramm, 1994). During mixing, the viscosity was determined by measuring the torque at different impeller speeds, and compared to rheologically obtained shear dependent viscosity. The velocity field was determined by LDA measurements at twelve places inside mixing vessel. It was observed that axial and radial component of the velocity were insignificant at all measurement points. On the other hand, the results showed the periodic nature of tangential component of the velocity, which was confirmed with computer-aided visualization method. Ce travail avait pour objectif de mesurer le champ de vitesse dans des fluides non newtoniens dans un réservoir de mélange. Le rotor à six pales utilisé pour le mélange a été conçu d'après la géométrie des ailettes rotatives d'un système de senseurs, communément utilisés dans les mesures rhéométriques de fluides complexes (Barnes and Nguyen, J. Non-Newtonian Fluid Mech. 98, 1-14 (2001); Schramm, 1994). Lors du mélange, on a déterminé la viscosité en mesurant le couple à différentes vitesses de turbine, puis on l'a comparée à la viscosité de cisaillement obtenue rhéologiquement. Le champ de vitesse a été déterminé par des mesures LDA à douze positions dans le réservoir de mélange. On a observé que la composante axiale et radiale de la vitesse était négligeable pour tous les points de mesure. Par ailleurs, les résultats montrent la nature périodique de la composante tangentielle de la vitesse, ce qui est confirmé par une méthode de visualisation assistée par ordinateur. [source]

Power consumption and maximum energy dissipation in a milliliter-scale bioreactor

BIOTECHNOLOGY PROGRESS, Issue 2 2010
Ralf Hortsch
Abstract Mean power consumption and maximum local energy dissipation were measured as function of operating conditions of a milliliter-scale stirred tank bioreactor (V = 12 mL) with a gas-inducing impeller. A standard laboratory-scale stirred tank bioreactor (V = 1,200 mL) with Rushton turbines was used as reference. The measured power characteristics (Newton number as function of Reynolds number) were the same on both scales. The changeover between laminar and turbulent flow regime was observed at a Reynolds number of 3,000 with the gas-inducing stirrer on a milliliter-scale. The Newton number (power number) in the turbulent flow regime was 3.3 on a milliliter-scale, which is close to values reported for six-blade Rushton turbines of standard bioreactors. Maximum local energy dissipation (,max) was measured using a clay/polymer flocculation system. The maximum local energy dissipation in the milliliter-scale stirred tank bioreactor was reduced compared with the laboratory-scale stirred tank at the same mean power input per unit mass (,ø), yielding ,max/,ø , 10 compared with ,max/,ø , 16. Hence, the milliliter-scale stirred tank reactor distributes power more uniformly in the reaction medium. These results are in good agreement with literature data, where a decreasing ,max/,ø with increasing ratio of impeller diameter to reactor diameter is found (d/D = 0.7 compared with d/D = 0.4). Based on these data, impeller speeds can now be easily adjusted to achieve the same maximum local energy dissipation at different scales. This enables a more reliable and robust scale-up of bioprocesses from milliliter-scale to liter-scale reactors. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source]