Etude de l'oxydation du pentachlorophénol dans différentes géométries de réacteurs à ultrasons de haute fréquence

The determination of the key geometric parameters used for high-frequency sonoreactor modeling has been studied. The methodology allowing the characterization of the different reactors built in our laboratory has been defined. The methods are: calorimetry, determination of the residence time distributions, the observation of the chemiluminescence of luminol and the degradations of a prototype molecule: pentachlorophenol. After characterization of the studied reactors, it seems that volumetric power, with equivalent emitting system, is the major parameter of the reactor's performance.     

Formation de nano‐gouttelettes d'eau au sein d'un éjecteur à air induit: Une étude qualitative par visualisation de l'écoulement

This paper deals with the formation of water nano‐droplets in an induced ejector. The two processes of formation which occur simultaneously when the ejector is fed with humid air are clearly shown with flow visualization. A brief analysis of the light scattered by the droplets generated by condensation within the flow reveals that their mean diameter does not exceed 0.1 μm.     

Régimes d'écoulement et mesure de l'épaisseur d'un film liquide ruisselant autour d'un tube horizontal

The flow characteristics and film thickness have been studied experimentally for the case of a falling liquid film flows on a horizontal cylinder. The optical method based on laser‐induced fluorescence is presented in this paper. All tests have been conducted with the adiabatic water/fluorescence mixture at atmospheric pressure. Five falling‐film modes are observed for different liquid mass flow. The wavelengths have been measured for each film Reynolds number value for droplet and column modes. The transitions between different falling‐film modes are studied and the hysteresis phenomenon is observed. The measured dimensionless wavelengths are compared to the results of Hu and Jacobi (1998). The experimental results show the local evolution of film thickness around the cylinder. They are compared to the results of Rogers and Goindi (1989), Rogers (1986) and Chyu and Bergles (1987). The local measurements of film thickness are correlated by including the effects of film Reynolds number.     

Distribution des temps de séjour en écoulement tourbillonnaire annulaire induit par une entrée tangentielle du liquide

In this work, a thorough model for the flow in annular cell provided with various feed systems, based on an experimental determination of the residence time distribution, was presented for values of the Reynolds number in the range 100 to 5000. Using the plug flow model with axial dispersion, followed by a series of perfectly stirred plug-reactors, it was shown that the non-maintained swirling flow induced by a tangential inlet exhibits a very pronounced piston behavior in conjunction with a stirred zone due to the flow inlet/outlet system in the cell. When an axial inlet or an inlet perpendicular to the cell was used, the percentage of the overall reactor volume having a plug flow with respect to the one with a tangential inlet was decreased.     

Étude comparative de flux et de performances lors du traitement d'effluent papetiers par bioréacteur à membranes

The goal of this study was to evaluate the role of the membrane within a membrane bioreactor (MBR) and to model the flux. Two models developed for external membrane bioreactor enabled the evaluation of the importance of mixed liquor suspended solids. The effect of backwash was also quantified. A performance comparison of two membrane bioreactors using membranes with different pores demonstrated the predominant importance of the sludge layer (deposited at their surface and inside of the membranes) versus the pore size.     

Réacteur électrochimique à lit granulaire transporté

This work deals with an electrochemical reactor composed of a solid granular matrix located in a conical vessel. The solution to be treated flows through the reactor by forced convection. This mode of operation allows the solid matrix to move downwards because of gravity, assures good cohesion, hence good conductivity. The numerical solution of the differential equations obtained from the mass and charge balances permits the determination of the concentration, current and potential distributions in the case where the granular bed is kept fixed; the moving bed configuration is also discussed. The concentration development (plug flow reactor) and the influence of liquid and solid flow rates are discussed and illustrated in the case of selective copper recovery from dilute solutions (< 500 ppm) in a sulfuric acid medium. Finally a reactor design diagram for such devices is proposed.     

Contrôle hydrodynamique de l'evaporation d'un film liquide ruisselant sur une paroi isotherme à symétrie de révolution dans un courant d'air humide

A thin-film evaporation from a surface of a axisymmetrical body in a humid air stream was studied using a finite difference method associated with Thomas' algorithm. The surface of the body is supposed isothermal. The variability of physical properties is taken into account, and a steady-state and laminar regime is supposed. The influence of the main parameters of the system on the evaporation is determined, especially the wall profile. It is shown that, for certain conditions of calculation, it is possible to find a flat ellipsoid of revolution offering a uniformly accessible wall between the pole and the equator.     

Transfert photonique dans un photoréacteur à écoulement tourbillonnaire

Photonic transfer has been analyzed for two hydrodynamic conditions in an annular photoreactor: a swirling decay- ing flow generated by a tangential inlet, and an axial flow generated by a radial inlet. The photonic transfer coefficient was determined by carrying out the homogeneous photoreduction of potassium ferrioxalate. A comparison of the two hydrodynamic conditions is made in aqueous solution and in a suspension of black carbon in order to reduce the light penetration depth. The last condition emphasizes the interest in using tridimensional flow to design a photoreactor.     

Etude de l'influence des paramètres de fonctionnement d'un réacteui électrochimique à lit fixe conique

The recovery of metallic ions from dilute solutions has been carried out with a three-dimensional electrode. This work follows a study of electrochemical reactors with transported beds enclosed in a conical vessel. It deals more precisely with the influence of flow direction (upwards or downwards) and the cone angle when a reactor is working at the limiting diffusion current. The results of this study permit to define the geometric parameters determining the most efficient operation of the reactor.     

Modélisation de l'efficacité de filtration d'un échangeur cyclone

This work is a modelling of the Aireco® filtration system. This heat exchanger, with particle catching capabilities, is made of a cyclonic body which contains refrigerated coils. The water vapour contained in the gas to be treated condensed on the coils surface. Our modelling considers two main capture surfaces: the entry zone in which particles are collected by inertial impaction and the cyclonic body in which particles diffused by centrifugal force is the main phenomena. We found that these considerations explain our experimental results with an accuracy more than 90%, when the Aireco® is on a normal point of working.     

Ecoulement de fluides newtoniens et non newtoniens à travers des lits fixes stratifiés

Fixed beds of plate shape particles have been studied in two different “flow-particle” configurations. From pressure drop measurements performed for a Newtonian fluid flow, two characteristic structural parameters have been determined by using a capillary - type model. The differences concerning the hydrodynamic behaviour of the two configurations are discussed and a factor characterizing the bed anisotropy is proposed. A dimensionless equation allowing the pressure drop determination for Newtonian and non-Newtonian purely viscous fluid flow in the two configurations, for a large range of Reynolds numbers, is proposed and tested with experiments.     

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.     

Ordonnancement à court-terme d'un atelier discontinu de chimie fine

The objective of this paper is to use production engineering concepts to solve scheduling problems encountered in chemical engineering. The studied case is the multipurpose (or job-shop) chemical batch plant involving the most complex specific constraints which can be found practically: various products to be manufactured, different synthesis sequences, presence of intermediate products, various storage policies, mass balances, utilities, effluent limitation,… The development of a discrete-event simulation model of a fine chemistry plant is proposed in this paper. Use of the model and simulation results are then analyzed. Attention is focused on applications which seem interesting from a production management viewpoint but also from chemical engineering concepts (plant design, effluent treatment, stability et storage of reaction intermediates…).     

Evolution axiale du coefficient de transfert de matière en colonne à bulles et en lit fluidisé triphasique

Liquid phase volumetric mass transfer coefficients for oxygen are determined in a three-phase fluidized bed and in a bubble column. The concept of exponential decreasing axial variation of volumetric mass transfer coefficient leads to a better representation of oxygen concentration profiles inside the column. Compared to the bubble column, k_la axial variations are more important in the lower part of the fluidized bed column, where solid particles increase the coalescence phenomenum, particularly with viscous liquids.     

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.     

Effet de la pression sur la transition ruisselant-pulsé dans les réacteurs catalytiques à lit fixe arrosé

The effect of pressure on transition displacement between trickle and pulsed regimes (TPR: trickle-pulsed transition) in catalytic trickle bed reactors (CTBR) is not properly predicted by existing theoretical models and empirical correlations. Based on high pressure TPR data available to date, a modified Charpentier diagram is proposed to quantify directly the effect of pressure in non-foaming systems.     

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.