Showing papers in "Canadian Journal of Chemical Engineering in 2002"

Compatibilization of Polymer Blends

Abstract: Most polymer blends are immiscible and need to be compatibilized. The compatibilization must accomplish: (i) optimization of the interfacial tension; (ii) stabilize the morphology against high stresses during forming; and (iii) enhance adhesion between the phases in the solid state. Compatibilization is accomplished either by addition of a compatibilizer or by reactive processing. This review will focus on the three aspects: description of the interphase, compatibilization by addition and reactive compatibilization.

Diffusivity of CO2, CH4, C2H6 and N2 in athabasca bitumen

Abstract: Experimental data for the diffusivity of carbon dioxide, methane, ethane and nitrogen in Athabasca bitumen are presented in the range 25–90°C at 4 and 8 MPa. The diffusivity of these gases has been determined as a function of gas concentration in bitumen using a non-intrusive experimental method. The diffusivity of gas in general is found to increase with temperature and pressure, and is a unimodal function of concentration. A correlation is provided for the average diffusivity of these gases as a function of temperature. On presente des donnees experimentales pour la diffusivite du dioxyde de carbone, du methane et de l'azote dans du bitume d'Athabasca dans la gamme de 25–90°C a 4 et 8 MPa. La diffusivite de ces gaz est determinee en fonction de la concentration de gaz dans le bitume a l'aide d'une methode experimentale non intrusive. II ressort qu'en general la diffusivite du gaz augmente avec la temperature et la pression et qu'elle est une fonction unimodale de la concentration. On propose une correlation pour la diffusivite moyenne de ces gaz en fonction de la temperature.

Quantitative Analysis of Mixer-Type Rheometers using the Couette Analogy

Abstract: A procedure based on a Couette analogy, to quantitatively analyze torque/rotor speed data in order to extract viscosity/shear-rate curves using non-conventional geometries is presented. It is first validated using a relatively simple geometry for which the equivalent internal radius used in the analogy can be analytically obtained. The results showed that the equivalent internal radius depends only slightly on the nature of the fluid and that there is an optimal radial position r* in the analog Couette gap where the calculations can be easily performed for computing the viscosity/shear-rate data from torque/rotational speed data. The experimental results with complex geometries and complex fluids are found to coincide, within experimental errors, with those obtained using standard geometries over a wide range of shear rates. The approach is also found to be very useful to evaluate shear-rate and viscosity data in Couette viscometers when large gaps are used with non-Newtonian fluids. Nous presentons une procedure basee sur une analogie Couette, permettant d'analyser de facon quantitative des donnees couple-vitesse angulaire de rotor afin d'extraire des rheogrammes dans des geometries non conventionnelles. Cette procedure est tout d'abord validee a l'aide d'une geometrie simple pour laquelle un calcul analytique du rayon interne equivalent est possible. Les resultats montrent que ce dernier depend peu de la nature du fluide et qu'il existe une position radiale optimale, r*, dans l'entrefer Couette virtuel permettant de calculer simplement les valeurs de viscosite-vitesse de cisaillement a partir des donnees de couple-vitesse angulaire de rotor. Les resultats experimentaux obtenus a l'aide de geometries complexes et des fluides non-newtoniens complexes coincident, aux erreurs experimentales pres, avec ceux obtenus a l'aide de geometries conventionnelles, sur une large place de vitesses de cisaillement. Cette procedure s'est averee particulierement utile pour des viscosimetres de Couette a entrefer large.

Bubble coalescence and its effect on dynamic foam stability

Abstract: The size of bubbles generated using a single-hole sparger, a multi-hole sparger and a flotation cell were measured. While the size of bubbles generated from the single-hole sparger does not depend on frother concentration, the bubble size strongly depends on frother concentration when the multi-hole sparges, or flotation cell, are utilized. The bubbles size ceases to depend on frother at the concentrations exceeding the value characteristic for each frother and referred to as the critical coalescence (CCC). All the bubble size vs. frother concentration curves converge on a single curve. Aqueous solutions of the frothers that are characterized by low CCC values from foams quite stable under dynamic conditions. Since bubble coalescence can be inhibited by frother concentrations exceeding the CCC, sparing systems can be studied and compared only at frother concentrations that exceed CCC. On a mesure la taille des bulles produites par un aerateur a orifice unique, un aerateur a orifices multiples et une cellule de flottation. Alors que la taille des bulles produites avec l'aerateur a orifice unique n'est pas liee a la concentration d'agent moussant, la taille des bulles depend fortement de la concentration d'agent moussant dans le cas des aerateurs a orifices multiples ou de la cellule de flottation. La taille des bulles cesse d'ede la valeur caracteristique de chaque agent moussant (concentration de coalescence critique ou CCC). Toutes les courbes de taille des bulles par rapport a la concentration d'agent moussant se superposent. Les solutions aqueuses des agents moussants qui sont caracterises par de faibles valeurs de CCC forment des mousses plutot stables dans des conditions dynamiques. Considerant que la coalescence es bulles peut etre inhibee par des concentrations d'agent moussant excedant la CCC, les systemes de dispersion peuvent etre etudies et compares seulemetn a des concentrations d'agent moussant qui excedent la CCC.

Fiber suspensions in complex geometries: Flow/orientation coupling

Abstract: A Galerkin finite element solution is developed for the flow of fiber suspensions Primary variables are velocity, pressure, and a second-order tensor describing the fiber orientation The model treats the orientation as three-dimensional, includes fiber—fiber interaction effects, and uses an orthotropic closure approximation The flow and orientation are strongly coupled through an orientation-dependent constitutive equation We explore the effect of this coupling on the fluid mechanics of fiber suspensions by studying three flows: an axisymmetric contraction, an axisymmetric expansion, and a center-gated disk Coupling enhances the corner vortex in the contraction, in quantitative agreement with published experiments and calculations The expansion results demonstrate that the aligned-fiber approximation is not valid for this flow In the center-gated disk the effects of coupling are modest and are only noticeable near the center of the disk This supports the use of decoupled models for injection molding in thin cavities On a mis au point une methode de resolution par elements finis de Galerkin pour l'ecoulement de suspensions de fibres Les variables primaires sont la vitesse, la pression et un tenseur de second ordre decrivant l'orientation des fibres Le modele traite l'orientation comme etant tridimensionnelle, inclut les effets d'interaction entre les fibres et utilise une approximation de fermeture orthotropique L'ecoulement et l'orientation sont fortement couples par une equation constitutive dependante de l'orientation Nous explorons l'effet de ce couplage sur la mecanique de fluide des suspensions de fibres en etudiant trois ecoulements : une contraction axisymetrique, une expansion axisymetrique et un disque crante centre Le couplage ameliore le vortex du coin dans la contraction, ce qui concorde quantitativement avec les experiences et les calculs publies Les resultats de l'expansion demontrent que l'approximation des fibres alignees n'est pas valable pour cet ecoulement Dans le disque crante centre, les effets du couplage sont modestes et ne se remarquent que pres du centre du disque Cela vient defendre l'utilisation de modeles decouples pour le moulage sous pression dans les cavites minces

Fundamentals of bitumen coking processes analogous to granulations: A critical review

Abstract: A number of coking processes use hot particles to heat liquid bitumen or petroleum residue to cause cracking reactions. These particles may be mineral or coke solids. Interactions of these particles, in fluid beds, moving beds and other types of contactors, are governed by the liquid films on the particle surfaces. This paper explores the analogy between granulation and coking, and suggests that the key relationships that will govern the behavior of wet particles in coking processes are the Stokes number of the particles, the thickness or the liquid films, and the diameter and surface roughness of the particles. The implications for distribution of liquid feed in the reactor, fouling, and defluidization or bogging are discussed. This analysis suggests experiments that can be performed under non-reactive conditions with scaled variables in order to study phenomena that cannot be observed in situ in high-temperature cracking processes. Plusieurs procedes de cokefaction utilisent des particules chaudes pour chauffer les residus liquides de bitume ou de petrole et provoquer des reaction de craquage. Ces particules peuvent etre des solides de mineraux ou de coke. Les interactions de ces particules, dans les lits fluides, les lits mobiles et autres types de contacteurs, sont gouvernees par les films liquides a la surface des particules. On explore dans cet article cett analogie entre la franulation er la cokefaction et on suggere que les principales relations qui gouverneront le comportement de particules, l'epaisseur des films liquides ainsi que le diametre et la rugosite de surface des particules. On examine les repercussions sur la distribution de l'alimentation liquide dans le reacteur, le refoulement, la defluidisation ou l'enlisement. On propose dans cette analyse des experiences qui peuvent etre realisees dans des conditions non reactive avec des variavles mises a l'echelle dans le but d'etudier les phenomenes qui ne peuvent pas etre observes in situ dans des procedes de craquage a haute temperature.

Polymer‐Clay Nanocomposites Based on Blends of Polyamide‐6 and Polyethylene

Abstract: The preparation of polyamide-6/clay, high-density polyethylene/clay, and high-density polyethylene/ polyamide-6/clay nanocomposites is considered. X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier Transform Infrared (FTIR) measurements show that the clay enhances the crystallization of the γ-form of polyamide-6. The clay also acts as a nucleation agent and causes a reduction of spherulitte size. Scanning electron microscopy (SEM) analysis of fracture surfaces shows that the clay reduces the PA-6 particle size in the HDPE/PA-6/clay nanocomposites and changes the morphology. Mechanical properties and the effect of maleated polyethylene are also reported.

Paste Extrusion of Polytetrafluoroethylene (PTFE) Fine Powder Resins

Abstract: The rheology of non-melt processible polytetrafluoroethylene (PTFE) pastes has been studied using a capillary rheometer. It was found that fibrils of submicron dimensions are created during PTFE paste processing, which are responsible for the final strength of the extrudate. The mechanism of fibrillation is explained in terms of the unwinding of crystallites. To describe the effects of die design, a simple mathematical model has been developed. The model takes into account the elastic-plastic (strain hardening) and viscous nature of the material in its non-melt state. The model predictions are found to be consistent with experimental results obtained from macroscopic pressure drop measurements and flow visualization experiments.

Pressure buildup in gas-liquid flow through packed beds due to deposition of fine particles

Abstract: In order to understand the increase in pressure drop in hydrotreating reactors due to deposition of fine solids, experiments were conducted with a model suspension of kaolin clay in kerosene. The suspension was circulated through packed beds of catalyst pellets in the trickle-flow and pulse-flow regimes, and the increase in pressure drop measured as a function of particle concentration in the bed. The increase in pressure drop was linear with particle concentrations over the range 0–60 kg.m−3. A consistent approach to modeling the pressure drop behavior was to determine an effective porosity of the packed bed as a function of the concentration of fine particles, then use this porosity in the Ergun equation as a basis for calculating the two-phase pressure drop. Afin de comprendre l'augmentation de perte de charge causee par le depot de solides fins dans les reacteurs d'hydrotraitement, des experiences ont ete menees avec une suspension modele d'argile de kaolin dans du kerosene. On a fait circuler la suspension dans des lits garnis de pastilles de catalyseur en regime a ecoulement ruisselant et a ecoulement pulse et on a mesure l'augmentation de perte de charge en fonction de la concentration de particules dans le lit. L'augmentation de la perte de charge est lineaire pour des concentrations de particules se situant dans la gamme de 0–60 kg.m−3. Une facon coherente de modeliser le comportement de la perte de charge consiste a determiner une porosite effective du lit garni en fonction de la concentration de fines, puis d'utiliser cette porosite dans l'equation d'Ergun comme base pour calculer la perte de charge diphasique.

Synthesis of Oligoester α,ω‐diols by Alcoholysis of PET through the Reactive Extrusion Process

Abstract: The alcoholysis of PET with diols in the presence of dibutyltinoxide was carried out in a twin-screw extruder with residence times of 1 min and without solvent. The reaction led to scissions of PET chains and to the synthesis of oligoester α,ω-diols with average number molecular weights of about 1000 g·mol—1 characterised by conventional techniques such as NMR, SEC and MALDI-TOF. The alcoholysis kinetics was studied with a rheological tool under selected conditions, and it was shown that this reaction is quite compatible with the residence times in an extruder. This study clearly shows that the oligoesters synthesised by reactive extrusion have characteristics similar to the oligoesters synthesised by batch processes over many hours. Furthermore, the melting temperature of these oligoesters can be controlled between room temperature and 220°C by using diols with different structures for the alcoholysis. L'alcoolyse du PET en presence d'oxyde de dibutyletain et d'α,ω-diols est menee au sein d'une extrudeuse bi-vis sur des temps de sejour de l'ordre de la minute. La reaction, entrainant des coupures de la chaine PET, transforme le polymere en oligoesters, α,ω-diols de masse molaire moyenne en nombre egale a 1000 g·mol—1, caracterises a l'aide de techniques classiques: NMR, SEC, MALDI-TOF. Le suivi de la viscosite du melange reactif au cours du temps donne une bonne estimation de la cinetique d'alcoolyse du PET et montre que les temps de reaction sont bien compatibles avec les temps de sejour au sein d'une extrudeuse. Les obligomeres produits par alcoolyse du PET au sein de ce reacteur continu ont les memes caracteristiques que ceux issus des procedes “batch” durant plusieurs heures. Il est possible en outre de controler la temperature de fusion des oligoesters diols en jouant sur la nature des diols utilises pour l'alcoolyse.

Gas hold-up in stirred tank reactors

Abstract: Based on a study of the gas hold-up data for stirred tank reactor generated in the present work and the data available in the literature for large stirred tank reactors (T = 0.57 m to 2.7 m) equipped with disc turbines and pitched blade downflow turbines a correlation is presented which reliably predicts gas hold-up data over wide range of system configurations and operating parameters. The parameter used, N/N-cd, relates gas hold-up at impeller speed N with respect to the gas hold-up at minimum impeller speed for complete dispersion of the gas, N-cd, It is shown that the gas hold-up data of different workers when compared on the basis of N/N-cd, shows unanimity.

A simple correlation for gas bubbles rising in power‐law fluids

Abstract: Recently, the author (Rodrigue, 2001 a, b) proposed a generalized correlation for the steady rise of gas bubbles in uncontaminated viscous Newtonian fluids of infinite extent. It is the purpose of this note to show that this model can be modified for inelastic non-Newtonian power-law fluids. Using data taken from six different studies, it is shown that the modified model can predict quite nicely the bubble velocity for these non-Newtonian inelastic fluids. Recemment, l'auteur (Rodrigue, 2001 a,b) a propose une correlation generalisee pour l'ascension stable de bulles de gaz dans les fluides newtoniens visqueux non contamiees dans une colonne infinie. On se propose dans cet article de montrer que ce modele peut etre modifie pour les fluides de loi de puissance non newtoniens inelastiques. A l'aide des donnees venant de six etudes differentes, on montre que le modele modifie peut predire assez bien la vitesse des bulles pour ces fluides non newtoniens inelastiques.

γ-Alumina supported Cu-Ni bimetallic catalysts: Characterization and selective hydrogenation of 1,3-butadiene

Abstract: Addition of a second metal often improves the selectivity of a supported catalyst for the hydrogenation of 1,3-butadiene. Catalysts containing 15 wt% Ni and varying amounts of Cu were prepared and characterized by TPR, XRD and XPS. The Cu-Ni interaction affects the reduction behavior of the catalysts. TPR result shows that the synergetic effect of copper and nickel modifies the capability of metal to combine with hydrogen in bulk phase. The Ni 2p spectra in XPS shows significant shifts toward lower binding energies with increasing copper loading. From XRD results it is represented that aggregation of nickel occurs more easily due to the copper addition. The adding of copper on Ni/Al 2 O 3 makes the conversion rate decreased and increases the selectivity to 1-butene.

Influence of horizontal return bend on the two‐phase flow pattern in a 6.9 mm diameter tube

Abstract: The two-phase flow pattern for air-water mixtures inside a 6.9 mm U-tube is reported to have curvature ratios of 3˜7.1. At a lower total mass flux of 50 kg/m2·s and a quality of 0.1, or at a larger curvature ratio of 7.1, no influence on the flow patterns is seen. However, if the curvature ratio is reduced to 3, the flow pattern in the recovery region just after the return bend is temporally turned from stratified flow into annular flow. For a quality larger than 0.4, the annular flow pattern prevails in the entire tube. For G = 400 kg/m2·s and x < 0.01, the size of the plug in the downstream is usually larger than that in the upstream due to the coalesce in the return bend. This coalescence phenomenon continues to further increase the total mass flux at the lower quality region. For a total mass flux above 500 kg/m2·s, the bubbly flow pattern in the upstream region may become intermittent. Le profil d'ecoulement biphasique pour des melanges air-eau dans un tube en forme de U de 6,9 mm presente, selon les donnees, des rapports de courbure de 3-7,1. Pour un flux massique total inferieur de 50 kg/m2·s et une qualite de 0,1, ou pour un rapport de courbure superieur de 7,1, aucune influence sur les profils d'ecoulement n'est constatee. Cependant, si le rapport de courbure est reduit a 3, le profil d'ecoulement dans la region de recuperation juste apres le coude se modifie temporairement, passant d'un ecoulement stratifie a un ecoulement annulaire. Pour une qualite superieure a 0,4, le profil d'ecoulement annulaire est present dans toute la conduite. Pour G = 400 kg/m2·s et x < 0,01, la taille du bouchon dans l'ecoulement descendant est habituellement plus grande que celle observee dans l'ecoulement ascendant du fait de la coalescence dans le coude de retour. Ce phenomene de coalescence continue a accroitre davantage le flux massique total dans la region de qualite inferieure. Pour un flux massique total au-dessus de 500 kg/m2·s, le regime d'ecoulement a bulles dans la region ascendante peut devenir intermittent.

Drying of solids in vacuum fluidized bed

Abstract: A drying process in a fluidized bed under vacuum conditions is experimentally and theoretically studied. A fluidized bed operating in reduced pressure presents a possibility for a better quality of production, with safer process conditions. A mathematical model is developed for the reduced-pressure drying process in a fluidized bed. Some parameters were analyzed by comparing experimental results with model predictions. The predictions from the model agreed quite closely with the experimental data. The results showed that a decrease in pressure reduces the interparticular resistance. A good agreement was also found applying the model to data, at atmospheric pressure, from other authors. On a etudie de maniere theorique et experimentale le procede de sechage en lit fluidise dans des conditions de vide. Un lit fluidise fonctionnant a pression reduite s'avere une possibilite pour une meilleure qualite de production, avec des conditions de procede plus sures. Un modele mathematique a ete etabli pour le procede de sechage a pression reduite dans un lit fluidise. On a analyse certains parametres en comparant les resultats experimentaux et les predictions du modele. Les predictions du modele concordent plutot bien avec les donnees experimentales. Les resultats montrent qu'une diminution de la pression entraine une reduction de la resistance interparticulaire. On a egalement trouve un bon accord en appliquant le modele aux donnees d'autres auteurs obtenues a la pression atmospherique

A review of techniques for instrumentation design and upgrade in process plants

Abstract: This article is a review of the area of optimal instrumentation location in process plants for both grassroots designs and upgrades. Emphasis is put in methods for monitoring purposes and based on the cost minimization model. These methods are mostly related to data reconciliation paradigms and include especial consideration to the detection of gross errors. Connections between this model and other models based on other objective functions and goals are analyzed. Finally, the emerging field of sensor design for efficient process fault detection is briefly covered. On passe en revue dans cet article la problematique du positionnement optimal de I'instrumentation dans les usines dans le cas de nouveaux procedes ou d'amelioration de procedes existants. L'accent est mis sur les methodes destinees au contrǒle et basees sur un modele de minimisation des coǔts. Ces mehodes renvoient surtout a des paradigmes de reconciliation des donnees et portent une attention particuliere a la detection des erreurs globales. Les relations entre ce modele et les autres modeles reposant sur d'autres fonctions objectives sont analysees. Enfin, le domaine emergent de la conception des senseurs pour la detection efficace des defauts de procede est examine brievement.

Prediction of Gas-Phase Adsorption Isotherms Using Neural Nets

Abstract: This study investigated a number of models (the modified Sips', Dubinin-Astakhov's, VSM theory, the generalized Khan et al.'s model and a simple artificial neural network (ANN)) to predict the effect of temperature on equilibrium adsorption of hydrocarbon gases and vapors on activated carbon. Published data on the adsorption of methane, ethane and propane on activated carbon at 311 K to 505 K were used to estimate the parameters of the conventional models and train the network. Then, the conventional models and the ANN were used to predict the isotherm at a single temperature for each adsorbate, and these results were compared with experimental data. It was found that the ANN model had a lower mean relative error than the conventional models. On examine dans cette etude plusieurs modeles (le modele Sips modifie, le modele de Dubinin-Astakhov, la theorie VSM, le modele de Khan et al. generalise et un reseau neuronal artificiel simple (ANN)), afin de predire l'effet de la temperature sur l'adsorption a l'equilibre des gaz et des vapeurs d'hydrocarbures sur le carbone active. On a utilise des donnees publiees sur l'adsorption du methane, de l'ethane et du propane sur du carbone active a des temperatures entre 311 K et 505 K pour estimer les parametres des modeles conventionnels et entrainer le reseau. Les modeles conventionnels et l'ANN ont ensuite ete utilises pour predire l'isotherme a une seule temperature pour chaque adsorbat, puis les resultats ont ete compares aux donnees experimentales. On a trouve que le modele ANN avait une erreur relative moyenne plus faible que les modeles conventionnels.

Prediction of gas hold-up in a bubble column filled with pure and binary liquids

Abstract: A dimensionless correlation for gas hold-up in a bubble column filled with pure liquids and binary mixtures has been developed. The criteria of bubble coalescence in pure liquids and foamability of binary mixtures have been included successfully in the proposed correlation. For the first time, comprehensive data of gas hold-up with respect to concentration in four binary systems are presented. The often-reported enhancement of gas hold-up in aqueous alcohol mixtures has been observed experimentally. The proposed correlation is able to predict successfully the trend of gas hold-up enhancement with respect to concentration. The estimated values are found to be within 7% of the measured values.

Evolution of chemistry, morphology and rheology of various polymer systems along a twin-screw extruder

Abstract: Intermeshing twin-screw extruders have been recently identified as useful in special application niches such as the extrusion of PVC dry blends (counter-rotating machines) and compounding operations (co-rotating machines) Thus, it is of interest to study the mechanical and/or chemical effects that occur along the screw axis of the extruders, since they will dictate the characteristics and performance of the final material This work aims at illustrating the usefulness of a simple experimental tool recently developed for the study of the physical, chemical and morphological evolution along the extruder of polymer based systems, data being presented and discussed for a number of composites and blends Les extrudeuses bi-vis engrenees ont aujourd'hui trouve des niches d'application propres, telles que l'extrusion des melanges secs de PVC (machines contre-rotatives) et les operations de compoundage (machines co-rotatives) Ainsi, il est interessant d'etudier les effets mecaniques et/ou chimiques qui surviennent le long de l'axe des vis des extrudeuses, puisque ceux-ci dicteront les caracteristiques et la performance du materiel final Ce travail vise a illustrer l'utilite d'un outil experimental simple developpe recemment pour l'etude de l'evolution physique, chimique et morphologiques le long de l'extrudeuse pour des systemes polymeriques, des donnees etant presentees et examinees pour plusieurs composites et melanges

Improved modelling of the unsteady-state behaviour of an immobilized-cell, fluidized-bed bioreactor for phenol biodegradation

Abstract: The dynamic response of an immobilized-cell, fluidized-bed reactor (ICFBR) to step changes in phenol loading was investigated at 10°C for a pure culture of Pseudomonas putida Q5, a psychrotrophic bacterium. A novel dynamic model was developed and tested to simulate the response of all four key process variables: the bulk phenol concentration, the suspended biomass concentration, the concentration profile of the substrate in the biofilm and the biofilm thickness. Accurate model predictions required the use of kinetics, determined using cells which were not acclimated to the post-shock reactor conditions (‘unacclimated’ cells) and the implementation of a specific-growth-rate suppression factor to account for the unbalanced growth situations experienced during the transient response periods. On a etudie, a 10°C et pour une culture pure de Pseudomonas putida Q5, une bacterie psychotrope, la reponse dynamique d'un reacteur a lit fluidise et a cellules immobilisees (ICFBR) pour des changements en echelon du chargement de phenol. On a mis au point et teste un nouveau modele dynamique dans le but de simuler la reponse des quatre variables principales du precede: la concentration en masse de phenol, la concentration de biomasse suspendue, le profil de concentration du substrat dans le biofilm et l'epaisseur du biofilm. Les predictions precises du modele ont necessite l'utilisation de la cinetique determinee a l'aide des cellules qui n'etaient pas acclimatees aux conditions du reacteur apres le choc (cellules « non acclimatees ») ainsi que l'application d'un facteur de suppression de vitesse de croissance specifique afin de prendre en compte les situations de croissance non equilibrees vecues durant les periodes de reponse transitoire.

Drop Deformation and Breakup Mechanisms in Viscoelastic Model Fluid Systems and Polymer Blends

Abstract: This paper reviews the dispersion mechanisms in viscoelastic systems under relatively high shear rate conditions. In particular, two non-Newtonian deformation and breakup mechanisms were revealed by flow visualization in a transparent Couette shearing setup. The first one is the dispersed droplet elongation perpendicular to the flow direction. This was observed only for viscoelastic drops and had been associated to normal force buildup in the droplet. The second deformation/breakup mechanism was observed in very high viscosity ratio polymer systems. It consists in erosion at the drop surface. Clouds of very small ribbons and sheets were developed around the drop then stretched and finally broken into very small droplets, rapidly distributed in the matrix. Cet article examine les mecanismes de dispersion dans les melanges viscoelastiques a des taux de cisaillement relativement eleves. Deux nouveaux mecanismes de deformation et de rupture de gouttes viscoelastiques ont ete reveles en utilisant un montage de visualisation transparent de type Couette. Le premier mecanisme est l'orientation de l'axe principal de la goutte perpendiculairement a la direction de l'ecoulement, phenomene qui n'a ete observe que pour des gouttes viscoelastiques. Ce phenomene a ete relie au developpement de forces normales (elasticite) a l'interieur de la goutte. Le second mecanisme de deformation/rupture a ete observe avec des systemes de polymeres fondus possedant des rapports de viscosite eleves. Il consistait en une erosion de la surface de la goutte generant ainsi un nuage de gouttelettes et de minces feuillets autour de la goutte principale. Ces derniers s'etiraient suite a l'ecoulement de la matrice et finissaient par etre brises en gouttelettes tres fines rapidement dispersees dans la matrice.

Experimental research on drag reduction by polymer additives in a turbulent pipe flow

Abstract: In order to investigate the effects of injection position to drag reduction as well at further the effects of polymer additives on turbulent structures, LDA messurements of turbulent pipe flows were conducted. The amount of drag reduction grows with the increase of the Reynolds number, and injecting the polymer at the centre of pipe is more effective than at the wall. Due to the addition of polymer solution, the axial, radial r.m.s. velocity fluctuations and Reynolds stress decrease over the entire pipe cross-section, the time auto-correlation coefficients of axial and radial velocity fluctuation at the centre of pipe decay more slowly, the number of spectrum peaks is decreased, and the peak shifts towards lower wave numbers

Prediction of dispersed phase holdup in a modified multi‐stage bubble column scrubber

Abstract: This paper reports on the experimental investigation carried out to evaluate fractional dispersed phase holdup for a gas-liquid mixture in a modified multi-stage bubble column (with contraction and expansion disks), which has been conceived, designed and fabricated as a wet scrubber for control of air pollution; in addition it has versatile use as a gas-liquid contactor in chemical process industries. A correlation developed for predicting fractional dispersed phase holdup has been found to be encouraging and highly significant from statistical analysis. On presente dans cet article une etude experimental visante a evaluer la retention en phase dispersee fractionnelle pour un melange gaz-liquide dans une colonne a bulles multi-etagee modifiee (munie de disques de contraction et d'expansion), qui a ete concue, fabriquee puis utilisee comme un eputateur en phase humide pour controle de la pollution atmosoherique. Cet epurateur presente en outre un usage polyvalent comme contacteur gaz-liquide dans les industries de procedes chimiques. La correlation etablie pour la prediction de la retention en phase dispersee fractionnelle s'avere encourageante et tres pertinente du point de vue de l'analyse statistique.

Rheological Behavior of Coating Colors: Influence of Thickener

Abstract: In this work we have investigated the effect of rheology modifiers on the rheological properties of concentrated (65 solids mass%) kaolin suspensions and six different coating colors. Measurements have been performed on kaolin-based suspensions, without rheology modifier and with either a classic cellulose thickener or associative polymers. It was noticed that suspensions containing a thickener had a much larger viscosity and storage and loss moduli than suspensions containing no rheology modifier. The enhancement of the rheological properties was found to be much more important for the suspensions containing the associative polymer. These observations have been related to steric stabilization of the suspensions, and to the occurrence of entanglements and bridging when the associative polymer was used as the thickener. The influence of the thickener on the rheological properties of the coating colors was found to be similar to that observed for the concentrated kaolin suspensions. Dans ce travail nous avons etudie l'effet des modificateurs de rheologie sur les proprietes rheologiques de suspensions concentrees de kaolin (concentration massique en solide de 65 %) et de six sauces de couchage industrielles. Des mesures ont ete effectuees sur les suspensions de kaolin, sans modificateur de rheologie et avec un epaississant classique de cellulose ou des polymeres associatifs. Nous avons pu observer que les suspensions contenant un epaississant ont eu une viscosite et des modules de conservation et de perte beaucoup plus importants que les suspensions ne contenant aucun modificateur de rheologie. L'augmentation des proprietes rheologiques s'est averee beaucoup plus importante pour les suspensions contenant le polymere associatif. Ces observations ont ete liees a la stabilisation sterique des suspensions et a l'occurrence d'enchevetrements et de ponts lorsque le polymere associatif est employe comme epaississant. L'influence de l'epaississant sur les proprietes rheologiques des sauces de couchage industrielles s'est averee semblable a celle observee pour les suspensions concentrees de kaolin.

A generalized equation for the prediction of melting temperatures of homopolymers and copolymers

Abstract: A generalized equation was derived to calculate the melting temperatures of homopolymers and copolymers. The Gibbs-Thomson equation for homopolymers and a modified application to copolymers were derived using the proposed equation. The melting temperature Tm0 in the Flory equation corresponds to the melting temperature TmC,∞ of copolymer crystals with stems of infinite length. Also, TmC,n*, the melting temperature for copolymer crystals with stems containing the maximum possible number of structural units, n*, should be used instead of Tm0 as the basis of supercooling in crystallization. The proposed equation shows good agreement with experimental data for α-alkene-ethylene homogeneous copolymers. Une equation generalisee a ete proposee pour calculer les temperatures de fusion d' homopolymeres et copolymeres. L'equation de Gibbs-Thomson pour les homopolymeres et une equation modifiee pour les copolymeres ont ete obtenues a partir de l'equation proposee. La temperature de fusion Tm0 dans l'equation de Flory correspond a la temperature de fusion TmC,∞ des cristaux de copolymeres ayant une taille infinie. De plus, TmC,n*, la temperature de fusion pour des cristaux de copolymeres contenant le nombre maximum possible d'unites structurales, n*, devrait etre utilisee a la place de TmO comme la base de sous-refroidissement pour la cristallisation. L'equation proposee est en bon accord avec les donnees experimentales pour les copolymeres homogenes d'α-alcene-ethylene.

Modelling and economic analysis of gas production from hydrates by depressurization method

Abstract: Gas production from a hydrate reservoir involves decomposition of the solid hydrate. An analytical model is developed to predict reservoir performance for gas production by the depressurization method from a hydrate reservoir containing associated free gas. The model is developed by combining the intrinsic kinetics of hydrate decomposition, which is of interest to chemical engineers, with gas inflow performance relationship and material balance equations. An economic analysis model is also developed and incorporated with the reservoir performance model. These models are used in a case study of gas production from a hydrate reservoir in the Alaskan North Slope. The results show that gas transportation cost is the main factor controlling feasibility of commercial gas production. The hydrate zone contributes significantly to overall reservoir performance by arresting pressure decline and maintaining gas production rate. La production de gaz a partir d'un reservoir d'hydrates fait intervenir la decomposition d'hydrates solides. On a mis au point un modele analytique afin de predire la performance du reservoir pour la production de gaz par la methode de la depressurisation a partir d'un reservoir d'hydrates contenant un gaz libre associe. Dans ce modele, on combine les cinetiques intrinseques de la decomposition des hydrates, ce qui est interessant pour les ingenieurs chimistes, avec la relation de performance du debit de gaz et les equations de bilans de matiere. Un modele d'analyse economique a egalement ete elabore et incorpore au modele de performance du reservoir. Ces modeles sont utilises dans une etude de cas sur la production de gaz a partir d'un reservoir d'hydrates du North Slope d'Alaska. Les resultats montrent que le couCt du transport de gaz est le principal facteur qui conditionne la faisabilite de la production commerciale de gaz. La region des hydrates contribue considerablement a la performance globale du reservoir en stoppant la chute de pression et en maintenant la vitesse de production de gaz.

A simple and effective model for cross-flow microfiltration and ultrafiltration

Abstract: A semi-theoretical unsteady-state model for the flux in cross-flow microfiltration and ultrafiltration has been developed. The model predicts fouling behaviour for a wide range of particle sizes and foulant concentrations. The developed model uses only two coefficients, k1 and k2, incorporating both the influences of the cake formation and the shear cleaning of the membrane, to describe flux decline. These two parameters were found to be almost independent of the operating conditions. The model provides both a fundamental understanding of the key physical phenomena governing flux decline and a rational basis for the design of an improved and modified cross flow filters. Un modele semi-theorique a l'etat non permanent a ete mis au point pour les ecoulements en microfiltration tangentielle et en ultrafiltration. Le modele predit le comportement d'encrassement pour une large gamme de tailles de particules et de concentrations des salissures. Ce modele emploie seulement deux coefficients, k1 et k2, incorporant les influences de la formation du gateau et le nettoyage par cisaillement de la membrane, afin de decrire le declin du flux. Ces deux parametres s'averent quasi independants des conditions operatoires. Le modele permet une comprehension fondamentale des principaux phenomenes physiques qui gouvernent le declin du flux et fournit une base rationnelle en vue de la conception de filtres tangentiels ameliores et modifies.

Extended kalman filter based nonlinear geometric control of a seeded batch cooling crystallizer

Abstract: A nonlinear dynamic model of a seeded potash alum batch cooling crystallizer is presented. The model of the batch crystallizer is based on the conservation principles of mass, energy and population. In order to maintain constant supersaturation, a nonlinear geometric feedback controller is implemented. It is shown that compared to a natural and a simplified optimal cooling policies, the nonlinear geometric control (NCC) leads to a substantial improvement of the final crystal quality. An extended Kalman filter (EKF) is used as a closed loop observer for this nonlinear system to predict the non-measurable state variables. It is found that the EKF is capable of effectively predicting the first four leading moments of the population density function. The effectiveness of the EKF based nonlinear geometric controller in the presence of plant/model mismatch is also studied. Simulation results show that the EKF based nonlinear geometric controller is reasonably robust in the presence of modeling error.

A Chemical Model for the Dispersion of Fillers in a Polymeric Matrix

Abstract: Particle size distribution affects strongly physical and mechanical properties of filled polymers. The proposed model uses agglomerate size population balance in its new mathematical formulation expressing agglomeration, break-up and erosion as an evolution of one particle subjected to mean-filed type interaction with others. The erosion parameters have been calculated with experiments in an internal mixer. Controlled breakup of agglomerates was carried out through capillary dies to evaluate breakup parameters. Calcium carbonate filled polypropylene system was used to validate the formulation. La distribution de taille des particules influe fortement sur les proprietes physiques et mecaniques des polymeres composites. Un modele base sur les bilans de population de taille des agglomerats est propose. La nouvelle formulation mathematique exprime l'agglomeration, la rupture et l'erosion en fonction de l'evolution d'une particule soumise a une interaction representative moyennee avec les autres. Les parametres d'erosion ont ete calcules lors d'experiences dans un melangeur interne. La rupture controlee des agglomerats a ete effectuee dans des filieres capillaires afin d'evaluer les parametres de rupture. La formulation est validee avec le systeme composite polypropylene-carbonate de calcium.