Dispositif de déposition de couches de suspensions de céramiques appliqué à la stéréolithographie

A system to coat uniform layers of ceramic suspensions has been developed for rapid prototyping applications. The metering system is made of a gas injection nozzle which height, angle of attack and pressure can be adjusted. The coated layer homogeneity and the process reproducibility have been studied. The effect of each parameter on the coated layer thickness has been characterized using a design of experiments approach and a reliable mathematical model is proposed to optimze the coating system.     

Modélisation Mathématique de la Décantation de la Boue Rouge

A good performance of the solid‐liquid unit operation is required for the economical exploitation of the Bayer process. A computational fluid dynamics (CFD) model simulating the operation of the last washing stage mud thickener of a large Canadian alumina plant is presented. The parametric study of the impact of changes in four parameters shows that the diameter of flocculated red mud particles, the feed flow rate and the radius of the feed well are critical parameters for the operation of the thickener.     

Méthodologie d'étude et de modélisation de la déphosphatation d'effluents aqueux

Due to phosphorus impact on water pollution, a P‐recovery process by calcium phosphate precipitation was developed. The reactor process is a fluidized bed in which phosphate precipitates continuously and coats sand grains. The pilot unit can treat synthetic wastewater flow rates ([P] = 50 mg/l) of about 0.1 m3/h. A two‐stage methodology is proposed to understand the physicochemical phenomena. Fluidized bed precipitation modeling involves thermodynamical concepts taking into account the various calcium phosphates that can precipitate vs. operating conditions (PH, [P], [Ca], T). Coating modeling is performed by a first‐order kinetics reaction between fines and sand grains, combined with a network of ideal reactors representing system hydrodynamics.     

Modéalisation de la copolyméarisation éathylégne α-oléafine par catalyse ziegler—natta

A copolymerization model of ethylene and a α-olefin describing the monomer uptake and the quality of the polymer produced, namely M_n, M_w, M_z, the distribution of molecular weight, short branching index and double bonds, is presented. This model assumes the existence of several types of active sites (2 or 3) and do not involve any limiting diffusion. It is applied to ethylene and butene-1 bulk copolymerization at high pressure and high temperature. Parameters are identified with CSTR experiments.     

Modélisation de la cinétique de biodégradation de phénol par granules aérobies

This work describes a model of the biodegradation of phenol carried out by aerobic granules. These granules were obtained by culturing an activated sludge supernatant in a sequencing batch reactor fed with a synthetic waste water and subsequently, by acclimation to phenol (100 mg/L). The kinetics of phenol biodegradation by the aerobic granules was investigated over a wide range of initial phenol concentrations (40–1112 mg/L) in shake‐flask cultures. A Haldane‐type model was adjusted to the experimental results, which depicts successfully the phenol biodegradation profiles in the entire range of initial concentrations studied by using only one set of parameters. It is our view that the proposed model could contribute to the knowledge about the ability of aerobic granular systems to biodegrade toxic, inhibitory compounds such as phenol.     

L'électrolyseur dans l'optique de la dynamique des procédés

This article written for the non-specialists reviews the various methods for modeling electrolyzer behavior. Deterministic and stochastic models are discussed and the adaptation of process dynamic to electrolysers is emphasized.     

Étude hydrodynamique des lits fluidisés sous vide et sous haute température

After having analyzed the few literature results concerning fluidized beds hydrodynamics under reduced pressure, new theoretical elements are proposed which provide an estimation of the beginning and finishing fluidization velocities. Numerous experimental results(U_mfapp, U_mb, U_mp, ?_mf, ?_mb, ?_mp), obtained at 20 and 500°C, are then presented for several sub-atmospheric pressures. Finally, f& the first time, at leastto our knowledge, by high frequency recording pressure drops through the bed, the influence of pressure decreases on the hydrodynamics is accurately analyzed.     

Écoulement de Taylor‐Couette en géométrie finie et à surface libre

The reactors of Taylor‐Couette type are relatively recent application in the engineering processes field. The stability and the flow structure in this device are examined under the effect combined of the free surface and the fluid's height in annular space. The exploitation of the flow regimes is carried out according to the number of Taylor for various values of aspect ration Γ. By means of ultrasonic velocimetry (UPV) we determine axial average velocity profile and the axial wavelength. We also carry out the spectral analysis by Fourier's fast transform of the fluctuations associated with the average velocity values in order to analyze the flow structure. We particularly aim for checking the presence or the absence of the azimuth wave according to the filling height and the rotational velocity imposed. We highlight the effects of free surface and aspect ratio on the conditions of appearance of the second instability ( wavy mode). The analysis of the fluctuation shows that the appearance of the azimuth wave regime (Wavy mode) is delayed when the aspect ration decreases. Below a critical value noted Γc = 10, the azimuth wave regime is not observed any more.     

La modélisation de la turbulence dans une enceinte avec ouvertures et sources chaudes localisées

The air circulation inside an enclosure with multiple openings and local heat sources was studied by means of a mathematical model. After a number of comparisons to studies in an experimental apparatus, it was concluded that a turbulence model should be introduced in order to improve the mathematical simulation. Two turbulence models, one based on the algebraic and the other on the differential (K-?-G) model of the turbulent viscosity, were investigated. The differential model provided only small improvements in the results and increased the running costs substantially when compared to the algebraic model. Hence the utilisation of the differential model was not justified in these simulations. The combined effect of the forced convection through the enclosure and the natural convection from the heat sources was simulated in an attempt to study the air circulation and the air temperature inside the building of an aluminum reduction plant.     

Analyse des interactions fluide-paroi dans un système ouvert a partir de la connaissance de la distribution des temps de sejour. Application aux dépôts d'aérosols par thermophorèse

In an open material system where the residence time distribution of a fluid is known, it is possible, using micromixing Zwietering' model to predict the results of linear interaction between the fluid and the wall of system but also for the aerosol particles transported by the fluid flow. This methodology is applied for aerosol deposition by thermophoresis in cylindrical pipe with constant wall temperature. The interpretation of experimental results in laminar flow shows that, for Knudsen numbers between 0.2 and 1.0, the thermophoresis coefficient must be calculated by Talbot' correlation. Finally, in transition flow, the aerosol mass deposition by thermophoresis and turbulent diffusion becomes probably minimal.     

Modélisation de la cinétique morphologique en corrosion générale et en corrosion localisée

Two theoretical methods have been proposed to investigate the evolution of the interface shape. The first one enables to relate the various types of overall morphological evolution (roughness levelling and increase) and the driving force intensities to the nature of the physical chemistry occurring at the interface and its neighbourhood. The second one deals with the quantitative characterization of local morphological evolutions, in particular in stress corrosion. It allows the determination of crack initiation and propagation kinetics from morphological information gathered with samples     

Augmentation,par régénération électrochimique du substrat,de la production d'une biomasse (thiobacillus ferrooxidans DSM 583) pour un procédé biologique de récupération de métaux

A bioelectrochemical reactor regenerates the substrate of the acidophilic bacterium Thiobacillus ferrooxidans DSM 583 (ferrous ions). This reactor uses a through-flow porous fixed bed or carbon as cathode. A linearizing non-linear regulator insures an efficient control of the intensity imposed to the electrochemical reactor. The protein concentration, correlated to the biomass concentration, is 6.4 fold increased for a 55 h growth, including a 20 h electrolysis. The metal tolerance and the metal fixation capacity of a T. ferrooxidans biomass are presented both for solutions including one or two metallic ions and an industrial waste. A bioelectrochemical process based on these characteristics is proposed for removing metal ions from wastes.     

Influence du dodecyl sulfate de sodium sur la tension interfaciale du système biphasé butanol-eau

Interfacial tension between the two phases formed by the partially miscible system composed of butanol-1 and water has been investigated. Using the method of drop volume tensiometry, the effect of a surface-active agent, sodium dodecyl sulfate, on interfacial tension was investigated. Addition of surfactant to the butanol-rich phase, which forms the droplet, has been found to bring about a decrease in interfacial tension the magnitude of which was influenced by the time of contact. When the surfactant was added to the aqueous (bulk) phase, the decrease in interfacial tension was greater and it was equal to that observed when the surfactant was added to both phases. It is concluded that the orientation of phases in the instrument has an important effect on the apparent interfacial tension observed.     

Corréation entre la stabilité colloïdale de la matière première et le degré de dispersion du noir de carbone

The evolution of carbon black technology allows, at present, various hydrocarbon products as fillers in complex mixtures. The fillers investigated in this work are made of a blend of five products from different origins. The objective of this work is the study of the correlation between the colloidal stability of the filler and the quality of the carbon black, as well as the relation between the degree of dispersity of the carbon black and the resin tensile strength.     

Le cyclone: Un réacteur chimique. Application à la réaction de décarbonatation de NaHCO3

The purpose of the present paper is the experimental and theoretical study of the behaviour of the cyclone working as a chemical reactor. The model reaction is the decarbonation of NaHCO₃. Thanks to the use of scale-up relationships previously determined, it is possible to derive kinetic constants in good agreement with other published values obtained under quite different conditions. The measurements are performed in a wide range of experimental conditions (particle size, residence time of particles, cyclone wall temperatures, solid flow rate). The paper emphasizes two possible fields of utilization for the cyclone: a device for the measurement of kinetic constants, a processing reactor operating with high throughput of solids.     

Etude numérique et paramétrique de la combustion de particules d'aluminium

Several numerical models have been investigated to study the reactivity of aluminium particles coming from the combustion of solid propellants in spatial launchers. The Law model has been rapidly selected as it yields a continuous model from an aluminium drop to an oxide drop. The model also gives the residue size at the end of the combustion process. This could explain the scaling observed in the rocket engines. In order to study the coupling between the flow and the combustion, the combusion of aluminium drops has been widely analyzed with 0D computation. The main mechanisms of the combustion process have been identified.     

Modèles Hydrodynamiques pour la Séparation des Courants dans un Décanteur Pilote

Despite of its general use in industry, particle sedimentation is still a not well understood unit operation. Hydrodynamics is complex in essence, mainly because the possible volumes are depending on the operating conditions, which in turn has consequences on the stability of the equipment in unsteady state conditions.     

Simulation bidimensionnelle de phénomènes de convection naturelle et forcée en formulation primitive

The air circulation, and the temperature and pressure profiles were simulated in two dimensions using a hybrid finite difference method which combines the MAC method and the stream function/vorticity approach. Three different flow problems were solved: (i) forced convection in a closed cavity; (ii) natural convection in a closed cavity; and (iii) forced and natural convection in a cavity with localised openings and hot sources. The results for the first two problems were compared to the literature and the results for the third problem were compared to data obtained from an experimental apparatus.     

Analyse Expérimentale et Numérique du Comportement de Membranes Thermoplastiques en ABS et en HIPS dans le Procédé de Thermoformage

In this work, we are interested, on the one hand in the characterization of circular polymeric ABS and HIPS membrane under biaxial deformation using the bubble inflation technique, on the other hand in modelling and numerical simulation of the thermoforming of ABS and HIPS materials using the dynamic finite element method. Hyperelastic models (Mooney‐Rivlin, Ogden) are considered. First, the governing equations for the inflation of a flat circular membrane are solved using a variable‐step‐size‐finite difference method and a modified Levenberg‐Marquardt algorithm to minimize the difference between the calculated and measured inflation pressure. This will determine the material constants embedded within the models used. For numerical simulation, the lagrangian formulation together with the assumption of the membrane theory is used. Moreover, the influence of the hyperalastic model on the thickness and on the stress distribution in the thermoforming sheet are analysed for ABS and HIPS materials.