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Rushton Turbine (rushton + turbine)
Selected AbstractsA simplified procedure to identify trailing vortices generated by a Rushton turbineAICHE JOURNAL, Issue 2 2007Renaud Escudié First page of article [source] Size distributions and stability of toluene diluted heavy oil emulsionsAICHE JOURNAL, Issue 3 2006Chandra W. Angle Abstract The sizes and stability of oil droplets created from various concentrations of heavy oil-in-toluene at a fixed oil:water ratio were investigated during turbulent flow in model process water. The Reynolds number (Re) ranged from 17,000 to 34,500 and was obtained by stirred tank mixing with a Rushton turbine. The droplet sizes were monitored using laser light scattering. Results showed that at high Re and low oil concentrations (that is, low drop-surface coverage), breakage of the droplets was the dominant process, but as Re was reduced, coalescence was dominant. Droplets were less prone to breakage as the oil concentrations in toluene increased, and droplet sizes approached a steady state quickly during mixing. Their size distributions broadened and stability increased as heavy oil in toluene increased. Stability was attributed to a surface coverage by asphaltenes and the consequent interfacial elasticity that provided resilience to breakage. Equilibrium interfacial tension ,E was determined by fitting a diffusion-limited kinetic mathematical model to the data. The Gibbs adsorption model gave a monolayer surface coverage of 3 nm2/mol asphaltenes, consistent with other published results. High zeta potential of the droplets also hindered coalescence. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source] Enhanced mixing of Newtonian fluids in a stirred vessel using impeller speed modulationTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2009Wei M. Yek Abstract This paper reports on an experimental study of mixing intensification using speed modulation of a six-blade Rushton turbine in a stirred vessel. Mixing times were measured using a non-intrusive technique based on direct visualisation of an acid-base reaction in a Newtonian fluid. The impeller speed modulation was achieved by using two waveforms: a square wave and a sine wave. The amplitude was fixed between a maximum Reynolds number of Remax,=,60 and minimum Reynolds numbers of Remin,=,40 or 30. The wave periods were varied (10, 20, or 40,s) in order to compare the effects of unsteady stirring on mixing performance. It was observed that a square wave protocol with the shortest wave period and the larger amplitude resulted in the shortest time to destroy the observed isolated mixing regions (IMRs), which are known to exist in stirred vessels operating at low Reynolds number. However, the sine wave protocol led to a slow diffusive mechanism in which IMR structures reached an asymptotic volume and remained visible even after several hours. The results are presented and discussed using digital photographs taken at different time intervals during experimentation. Ce papier présente une étude experimentale concernant l'intensification du mélange en modulant la vitesse d'une turbine de type Rushton a six palettes dans une cuve agitée. Les temps de mélanges sont mesurés avec une technique non-intrusive basée sur la visualisation directe d'une réaction acide-base au sein d'un fluide Newtonien. La modulation de la vitesse de la turbine a été realisée en utilisant deux formes d'ondes: une onde carrée et une onde sinusoidale. L'amplitude de chaque onde a été fixée entre un nombre de Reynolds maximal de Remax,=,60 et un nombre de Reynolds minimal de Remin,=,40 ou 30. Les périodes des ondes étaient variées (10, 20 ou 40,s) dans le but de comparer les effets du mélange non-stationnaire sur les performances du systeme. Il a été observé que le protocole suivant l'onde carrée avec la periode la plus courte et l'amplitude la plus large produisait le temps le plus court necessaire pour la destruction des zones de mélanges isolées (IMRs), dont l'éxistense est connue dans les cuves a mélange opérant aux nombres de Reynolds bas. Toutefois, le protocol suivant une onde sinusoidale a conduit a un mechanisme de diffusion lent dans lequel les IMRs atteignies un volume symptotique et sont restées visibles après plusieurs heures. Les résultats sont présentés and discutés en utilisant des photographes digitales prises à des intervales de temps differents durant les éxperiences. [source] Scalar mixing measurements in a continuously operated stirred tankTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2001Markus 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 turbineTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2000Larry 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] Simulation of Barium Sulfate Precipitation using CFD and FM-PDF Modeling in a Continuous Stirred TankCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2007Z. 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] Oil and fungal biomass dispersion in a stirred tank containing a simulated fermentation brothJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2001Ma Soledad Córdova-Aguilar Abstract The production of ,-decalactone by the filamentous fungus Trichoderma harzianum involves four phases (oil,water,air,mycelium) and its dispersion is crucial during fermentation. Oil and biomass (when present) dispersion, as a function of the volumetric power drawn (P/V), was characterized, in two; three- and four-phase systems agitated with Rushton turbines. Trichoderma harzianum mycelium was used as the solid phase in the four-phase system. Two stages of the fermentation were simulated: the beginning (15% oil and 1.4,kgm,3 of mycelium) and the end (2% oil and 10.6,kg,m,3 of mycelium). In the two-phase system, the use of exhausted broth achieved higher oil dispersions at low P/V values as compared with distilled water. Aeration decreased the oil dispersion for the high-oil system, but enhanced oil dispersion for the low-oil system. Compared with the P/V used in the actual fermentation (0.2,kW m,3), a high segregation of the system was observed for the high-oil/low-biomass system, due to the difficulty of mixing the thick oil,air emulsion present at the top of the tank. The system simulating the end of the fermentation reached almost complete homogeneity of oil and biomass, a phenomenon due to the high biomass/oil ratio and the biomass acting as an oil carrier. © 2001 Society of Chemical Industry [source] New milliliter-scale stirred tank bioreactors for the cultivation of mycelium forming microorganismsBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2010Ralf 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] Power consumption and maximum energy dissipation in a milliliter-scale bioreactorBIOTECHNOLOGY PROGRESS, Issue 2 2010Ralf 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] Particle Flow Modelling in Slurry-Fed Stirred VesselsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 3 2004F. Scargiali Abstract Despite its importance, experimental information on the Residence Time Distribution (RTD) of solid particles in continuous-flow stirred vessels is still scant. In this work, experimental data on particle RTD in a high-aspect-ratio vessel stirred by three equally-spaced Rushton turbines, obtained by means of Twin Systems Approach (TSA), are employed to assess the suitability of the well known Axial-Dispersion Model to describe particle behavior in the investigated system. The data analysis and model parameter assessment are preceded by a discussion on the utility of self-recirculated systems in carrying out experiments concerning continuous slurry-fed apparatuses. In particular, the suitability of single recirculated systems is discussed and a way to extract numerical RTD data from the relevant experiments is proposed. The advantages and disadvantages of employing instead a couple of twin systems, as it was actually done to obtain the experimental data employed in this work, is shortly discussed. [source] Fluid-Borne entities in the impeller stream of a rushton turbineTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2000Larry 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] | |||||||||||||