Scale-up in laminar and transient regimes of a multi-stage stirrer, a CFD approach

A multi-stage industrial agitator system adapted to the mixing of a mixture whose viscosity varies during the process has been characterized by using CFD. In the entire study the mixture is supposed to have a Newtonian behavior even though it is rarely the case. It is shown that the well-adapted propeller is able to e7ciently blend high viscous media provided the Reynolds number is not too low. A scale-up study of the agitated system has also been carried out by respecting the classical scale-up rules such as the geometrical similarity and the conservation of the power per volume in the particular case of viscous media. Using an Eulerian approach, the hydrodynamics of three di9erent scales with geometrical similarity have been numerically characterized by the energy curve (power number versus Reynolds number) and by the Metzner and Otto constant in which both are required for scale-up procedure. Experimental power measurements have been carried out at the smaller scale so that simulations have been partially validated. New hydrodynamic criteria have also been introduced in order to quantify the =ows in the case of a multi-stage stirrer running at low Reynolds number. It has been shown how this hydrodynamic di9ers dramatically from one scale to another when scale-up at constant energy per volume is applied. From the CFD results, recommendations about the widely used scale-up rules have been suggested and modi>cations of stirring geometry have been proposed in order to reduce the =ow pattern variations during scale-up. ? 2002 Elsevier Science Ltd. All rights reserved

Optimal rates of convergence for persistence diagrams in Topological Data Analysis

Computational topology has recently known an important development toward data analysis, giving birth to the field of topological data analysis. Topological persistence, or persistent homology, appears as a fundamental tool in this field. In this paper, we study topological persistence in general metric spaces, with a statistical approach. We show that the use of persistent homology can be naturally considered in general statistical frameworks and persistence diagrams can be used as statistics with interesting convergence properties. Some numerical experiments are performed in various contexts to illustrate our results

Investigation by laser doppler velocimetry of the effects of liquid flow rates and feed positions on the flow patterns induced in a stirred tank by an axial-flow impeller

The (ow patterns established in a continuously-fed stirred tank, equipped with a Mixel TT axial-(ow impeller, have been investigated bylaser Doppler velocimetry, for a high and a low value of mean residence time—mixing time ratio. The pseudo-two-dimensional axial– radial-velocityvector plots, as well as the spatial distributions of the tangential velocitycomponent and the velocitypro;les around the impeller, show that the interaction between the incoming liquid and the liquid entrained bythe agitator rotation cause the (ow pattern in the vessel to become stronglythree-dimensional, especiallyin the region between the plane, where the feeding tube lies, and the 180◦-downstream plane. The increase in the liquid (ow rate and the location of the feed entryboth a$ect the (ow pattern, with the latter having a more pronounced e$ect. The overall process, in this mode of operation, depends upon the appropriate con;guration and choice of parameters: for conditions corresponding to high liquid (ow rates, the (ow patterns indicate the possibilityof short-circuiting, when the liquid is fed into the stream being drawn bythe agitator and when the outlet is located at the bottom of the vessel

Effect of repeated exposure to AQUI-S® on the viability and growth of Neoparamoeba perurans

Peer reviewedPublisher PD

Alternate operating methods for improving the performance of a continuous stirred tank reactor

The effect of the pumping direction of an axial flow impeller, the feeding rate and the number of feed inlets on the operation of a continuously-fed stirred tank has been studied using CFD. The flow patterns generated by the up-pumping and down-pumping impeller, under both ‘typical’ and ‘intensified’ operating conditions, are compared. The effect of various tank configurations on the performance of the vessel is assessed by analysing the flow and power numbers, as well as the concentration field of a non-reactive tracer. Furthermore, the inlet feed jets are reduced using traditional jet similarity analysis and are compared with that of a typical round jet. The results show that up-pumping impellers improve circulation in the upper part of the tank and reduce shortcircuiting of the feed stream with only a small increase in power consumption. Furthermore, by using multiple feed inlets to increase the total throughput capacity, the amplitude of torque fluctuations is decreased and impeller bypassing is also decreased. The ensemble of conclusions suggest that the throughput capacity and mixing quality of a CSTR can be improved, without problems of short-circuiting, by employing up-pumping impellers coupled with multiple surface feed points

Fonctions pragmatiques et prosodie de enfin en français spontané

National audienceCet article cherche à rendre compte de la forme enfin en français parlé contemporain, d'un point de vue pragmatique et prosodique. Dans un premier temps, nous tentons de dégager les fonctions que enfin assume et dans un second temps, nous tentons de mettre en évidence des configurations prosodiques qui le caractérisent. L'objectif de ce travail est d'examiner la façon dont la prosodie contribue à l'interprétation pragmatique de enfin.Les données sont extraites d'un corpus de 4 conversations de 20 minutes chacune, dans lesquelles enfin a toujours un statut de particule. Les paramètres prosodiques observés sont la durée, les pauses, la configuration intonative, et la réalisation phonétique de la forme. Les résultats montrent que la prosodie joue un rôle pour distinguer des statuts sémiotiques différents de la forme analysée (particule vs. non particule). Au sein des particules, les résultats montrent également qu'on peut distinguer les enfin ayant une valeur d'évaluation de la planification du discours à un niveau global, et ceux ayant une valeur d'évaluation plus locale correspondant à une opération de correction

PIV measurements in an aerated tank stirred by a down- and up-pumping axial flow impeller

Liquid phase hydrodynamics in an aerated tank stirred by a down- and an up-pumping pitched blade turbine have been investigated using Particle Image Velocimetry. The effect of agitator configuration and the gas phase on the mean velocity fields and turbulent quantities in the vessel have been investigated. The global mean gas holdup has also been evaluated for the two pumping conditions. For the gas flow rate used, the presence of gas only slightly alters the liquid flow patterns produced by both the down- and up-pumping configurations and causes a general decrease in the mean liquid velocities. The turbulent kinetic energy in the impeller discharge region was not affected by the presence of gas, but in the bulk of the tank, aeration caused a decrease in this value. Global gas holdup was found to be ~36% greater for the up-pumping impeller and a large amount of gas was found to be entrained by the primary circulation loop

CFD analysis of industrial multi-staged stirred vessels

This paper presents tools for analysis of CFD results adapted for flows in multi-stage stirred vessels through out two industrial cases. Those tanks fitted with double-flow impellers are used first to cool down highly viscous resins and subsequently for indirect emulsification. Since the simulation of these processes in their whole complexity would be unrealistic, it considers single-phase flows without heat transfer. The result analysis in order to prove that the mixing and the circulation are effective is not usual; in these cases, the circulation and impeller numbers are not adapted. The average axial flow numbers are relevant of the circulation in the whole tank and of the connection between the flows produced by the propellers in the given configuration. The velocity profiles give relevant results, but are not sufficient whereas the particle tracking validates that the propellers do not work together in one case and do work together in a second one

Flow Induced by Dual-Turbine of Different Diameters in a Gas-Liquid Agitation System: the Agitation and Turbulence Indices

Flow induced by a dual turbine stirred tank was characterized measuring local velocities with a LDV and drawing the main velocity fields and the maps of turbulence intensities. The hydrodynamic regime studied in all the experiments was the so-called merging flow regime. Two impeller configurations were studied. In the first one, two disk style turbine of the same dimensions (configuration A) were used, while in the second one, the dimensions of the upper turbine were 20 % proportionally smaller than those of the lower turbine (configuration B). The agitation and turbulence indices were used to evaluate, as a first order approximation, the power consumption distribution between convective and turbulent flows. The comparison of the two-phase agitation systems studied showed that configuration B seems to be more efficient than configuration A, since both induce a similar global convective flow, but the first one assures a significant reduction of power consumption. The distribution of power consumption between convective and turbulent flows was evaluated using the agitation index and a new global parameter: turbulence ind

Approche hydrochimique de la dégradation mécanique du versant instable de Séchilienne

National audienceLa chimie des eaux est un signal très fin qui permet la localisation dans le temps et dans l'espace de l'arrivée des eaux d'infiltration à l'origine des impulsions mécaniques des instabilités de versant. Il s'agit de comprendre comment s'organise la relation complexe entre altération chimique, modifications hydromécaniques et fragilisation/mouvements du versant rocheux instable. Pour cela, un suivi hydrogéochimique des eaux souterraines a été mis en place depuis 2010 sur le site de Séchilienne (France). La conductivité électrique est représentative du signal chimique engendré par la dégradation du massif. L'acquisition en continu de ce paramètre est pertinente pour le site de Séchilienne et peut se substituer au suivi chimique. L'avantage de l'acquisition de cette donnée est triple, ce qui peut en faire un outil pour la gestion du risque : mesure en temps réel, avec un pas de temps très fin et mise en œuvre peu coûteuse