bluuebunny/crossref_metadata_2025 huggingface dataset:
Fiber Suspensions in Complex Geometries: Flow/Orientation Coupling
Authors: Verweyst Brent E. , Tucker Charles L.
Published: July 2010

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.
Numerical Analysis of the Coupling Between the Flow Kinematics and the Fiber Orientation in Eulerian Simulations of Dilute Short Fiber Suspensions Flows
Authors: Chinesta Francisco , Poitou Arnaud
Published: July 2010

This paper focuses on an accurate evaluation of short fibers suspensions models coupling the flow kinematics with the fiber orientation evolution. In coupled models the flow kinematics is usually solved using the finite element method, where the fiber orientation is introduced in the constitutive equation through its value in some points (nodes or integration points). In this paper we will compare in a simple steady shear flow, the exact solutions of the extra‐stresses associated with the fibers' presence with the numerical simulations obtained using both the method of characteristics and the discontinuous Galerkin's method to solve the equation governing the generalized gradient evolution, in order to avoid the introduction of any closure relation. The error introduced if a quadratic closure relation is considered in the constitutive equation will be also quantified.
Numerical Modelling of the Flow of Fibre Suspensions through a Planar Contraction
Authors: Azaiez Jalel , Guénette Robert
Published: July 2010

This study presents results of numerical simulations of the flow of fibre suspensions in a Newtonian fluid through a 4:1 planar contraction. Two approaches are adopted to determine the fibre orientation. The first one uses orientation tensors defined as dyadic products of the orientation vector, while the second one is based on the fibre aligned assumption. An implicit time discretization scheme and a mixed finite element method based on the introduction of the rate of deformation tensor as an additional unknown are used to obtain the steady‐state flow. The numerical technique we use allows us to examine the flow of fibre suspensions in both dilute and semi‐dilute regimes at high values of the parameters controlling inertial and fibre effects. The predicted flow patterns and fibre orientation are discussed, and a systematic comparison between the predictions of the two approaches is presented.
A Chemical Model for the Dispersion of Fillers in a Polymeric Matrix
Authors: Lozano Tomas , Lafleur Pierre G. , Grmela Miroslav
Published: July 2010

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.
Present Challenges in the Numerical Modeling of Polymer‐forming Processes
Authors: Vincent Michel , Vergnes Bruno , Demay Yves , Coupez Thierrey , Billon Noëlle , Agassant Jean‐François
Published: July 2010

The purpose of the present paper is to present an overview of the main progresses recently made in the numerical modeling of polymer‐forming processes and to describe the challenges to overcome in the near future. Examples are presented in different domains, such as die extrusion, injection molding, film processing, reactive extrusion and pipe reinforcement.
Paste Extrusion of Polytetrafluoroethylene (PTFE) Fine Powder Resins
Authors: Hatzikiriakos Savvas G. , Ariawan Alfonsius B. , Ebnesajjad Sina
Published: July 2010

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.
Yield Stress Measurement of Silicon Nitride Suspensions
Authors: Zhu Lixuan , Papadopoulos Kyriakos , De Kee Daniel
Published: July 2010

Yield stress values of silicon nitride suspensions were measured via a novel slotted plate device and a constant stress rheometer and the results were compared. Test platform velocity, associated with the slotted plate method, was found to have a substantial effect on dynamic yield stress but not on static yield stress. The effects of suspension concentration and temperature on yield stress values were investigated. Yield stress measurements on mixtures of silicon nitride and alumina particles, as well as creep tests were performed.
Rheological Behavior of Coating Colors: Influence of Thickener
Authors: Moan Michel , Page Agnès , Carreau Pierre J. , Heuzey Marie‐Claude
Published: July 2010

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.
Orifice Flowmeter for Measuring Extensional Rheological Properties
Authors: Carreau Pierre J. , Ascanio Gabriel , Brito‐De La Fuente Edmundo , Tanguy Philippe A.
Published: July 2010

Extensional rheological properties play an important role in processes in which the fluid is subjected to highly decelerated or accelerated flows. This paper describes an orifice flowmeter used to measure extensional properties of rheologically complex fluids at high strain rates. The operating principle of the flowmeter is based on the pressure drop due to the flow through a small size orifice. The flowmeter was first calibrated, by plotting the pressure drop‐flow rate curve of the orifice, in terms of a dimensionless Euler number versus Reynolds number. Newtonian fluids consisting of aqueous solutions of corn syrup were used as calibration fluids. The calibration curve was then used to determine the apparent extensional viscosity of three different paper coating colors. The apparent extensional viscosity is compared to the shear viscosity in terms of the Trouton ratio. The Trouton ratio for one coating color is shown to exceed considerably the theoretical value of 3 expected for Newtonian fluids.
Solid State Rheological Properties of Ultra‐High Molecular Weight Polyethylene Foams
Authors: Rodrigue Denis , Zhang Zhijie , Aït‐Kadi Abdellatif
Published: July 2010

The rheological properties of ultra‐high‐molecular‐weight polyethylene (UHMWPE) foams were studied using solid state rheometry. Frequency and temperature sweeps were performed in the linear viscoelastic regime. For comparison purposes, low‐density polyethylene (LDPE) and high density polyethylene (HDPE) foams were also studied. For the range of densities under consideration (200‐700 kg/m3), several models for prediction of elastic moduli were compared. It was found that none of the models succeeded in representing completely the mechanical behavior of foams. Further refinements must be made in order to take into account parameters relating the morphology of the foam to its mechanical properties.
How to Make Inherent Safety Practice a Reality
Authors: Khan Faisal I. , Amyotte Paul R.
Published: July 2010

In recent years there has been an increased effort to develop inherently safer chemical processes, focusing on changing the process to eliminate hazards, rather than accepting the hazards and developing add‐on features to control them. This paper discusses design approaches to inherently safer processing, including examples of inherent safety principles. The paper also presents a state‐of‐the‐art review of the initiatives taken by various groups and agencies worldwide to promote inherent safety, and the tools developed to measure inherent safety for chemical processes. The discussion concludes with thoughts on why inherent safety is not yet a routine practice for accomplishing risk reduction, and suggestions for ways to make it routine (with reference to a brief case study).
Studies on Liquid—Gas and Three‐Phase Fluidized Beds with Pulsating Air Flows
Authors: Baker Christopher G. J. , Al‐Rashidi Thari S. T. , Khan Abdul R.
Published: July 2010

The effects of air‐flow pulsation and water and air flowrates on the hydrodynamics of liquid—gas and three‐phase fluidized beds containing 3‐mm glass beads have been studied in a 90‐mm i.d. column. Under steady‐flow conditions, both types of bed contained a relatively large number of small bubbles. With a pulsing air flow, however, a smaller number of much larger bubbles or slugs were formed. This was attributed to different mechanisms of bubble formation at the distributor. Variations in phase holdup were explained in terms of the effects of the operating parameters on the bubble characteristics.
Numerical Investigation of Turbulent Flow around a Rotating Stepped Cylinder for Corrosion Study
Authors: Yang Kyung‐Soo , Hwang Jong‐Yeon , Bremhorst Klaus , Nesic Srdjan
Published: July 2010

Direct numerical simulation has been carried out for turbulent flow set up by a rotating cylinder with two backward‐facing steps axisymmetrically mounted in the circumferential direction. This flow geometry creates a qualitatively similar flow pattern as observed near a sudden pipe expansion or a plane backward‐facing step, characterized by flow separation and reattachment. A region of intense turbulence intensity and high wall‐shear‐stress fluctuations is formed in the recirculating region downstream of the step, where high mass‐transfer capacity was also experimentally observed. Since corrosion is frequently mass‐transfer controlled, our findings put forward this apparatus as a useful tool for future corrosion research.
Oxidative Coupling of Methane in a Negative DC Corona Reactor at Low Temperature
Authors: Bagheri‐Tar Faezeh , Khodadadi Abbasali , Malekzadeh Azim , Mohajerzadeh S Shamsoddin
Published: July 2010

Oxidative coupling of methane (OCM) in the presence of DC corona is reported in a narrow glass tube reactor at atmospheric pressure and at temperatures below 200°C. The corona is created by applying 2200V between a tip and a plate electrode 1.5 mm apart. The C2 selectivity as well as the methane conversion are functions of methane‐to‐oxygen ratio, gas residence time, and electric current. At CH4/O2 ratio of 5 and the residence time of about 30 ms, a C2 yield of 23.1% has been achieved. The main products of this process are ethane, ethylene, acetylene as well as CO and CO2 with CO/CO2 ratios as high as 25. It is proposed that methane is activated by electrophilic oxygen species to form methyl radicals and C2 products are produced by a consecutive mechanism, whereas COx is formed during parallel reactions.
Breakthrough and Sulfate Conversion Analysis during Removal of Sulfur Dioxide by Calcium Oxide Sorbents
Authors: Dasgupta Kushal , Rai Kailash , Verma Nishith
Published: July 2010

Sorption of sulfur dioxide (SO2) was carried out on calcium‐based sorbents under dynamic conditions in a fixed bed. The experimental conditions were reaction temperature (700 to 1000°C), SO2 concentration (1000‐10 000 ppm), sorbent particles size (1 to 2 mm) and the types of sorbents (hydroxide or carbonate). The sorption process was found to be effective at low concentration levels (less than 10 000 ppm) as the breakthrough time significantly decreased with increase in concentration. The maximum removal of SO2 was observed at a reaction temperature of 950°C. The hydroxide‐based sorbents of relatively smaller particle size were found to exhibit superior sorption performance in terms of longer breakthrough time and higher sulfate conversion. A mathematical model developed, assuming a porous structure of the sorbent materials, attributed the low sulfation conversion during SO2 sorption due to a pore diffusion mechanism.
Effect of Frothers on Bubble Size and Foam Stability in Potash Ore Flotation Systems
Authors: Laskowski Janusz S. , Cho Yoon Seong , Ding Kejian
Published: July 2010

The objective of this project was to compare the effect of a selective flotation frother (MIBC) and powerful frothers (DEMPH and DF‐1012) on bubble size and foamability in water and in brine. In water, the bubble size is clearly reduced by flotation frothers which prevent bubbles from coalescing. The present study shows that the bubbles do not coalesce in brine and, therefore, frothers do not affect the size of bubbles in brine. The dynamic foamabality index measured in brine is much lower than that in water for weak frothers (e.g. MIBC); for both tested strong frothers the foamability measurements in brine reveal formation of meta‐stable foams.
Analysis of Steady‐State Temperature Profiles from a Laboratory Reactor by Means of a Process Simulator
Authors: Hudgins Robert R. , Posarac Dusko , Jaree Attasak
Published: July 2010

A process simulator was used for the analysis of steady‐state results from a laboratory‐scale tubular reactor for the oxidation of carbon monoxide over a platinum catalyst. From a set of 14 steady‐state experiments, temperature profiles were simulated with two adjustable parameters recovered by optimizing the fit: k°, the pre‐exponential portion of the rate constant, and hout, the outer wall heat transfer coefficient for the reactor tube. Simulation showed that despite elaborate insulation the reactor did not behave adiabatically. Simulation also predicted fairly well the magnitude of phenomena such as ignition, extinction, and rate hysteresis (caused by changes in feed temperatures or concentrations) but at temperatures below the experimental values.
Dynamic Analysis of Thermal Behaviour of a Laboratory Reactor Using a Process Simulator
Authors: Hudgins Robert R. , Posarac Dusko , Jaree Attasak
Published: July 2010

A process simulator was used to study dynamic results from a laboratory‐scale tubular reactor for the oxidation of carbon monoxide (CO) with oxygen over Pt/alumina catalyst. Passive response experiments were used to obtain lumped values of the heat capacity and the overall heat transfer coefficient. Temperature profile experiments were used to obtain the only adjustable kinetic parameter: k°, the pre‐exponential portion of the rate constant. Integral reactor phenomena were studied: step‐decreases in the feed temperature, step‐changes in feed concentration, and ignition of the reactor by pressure. Simulated results provided good agreement with experiments.
Residence Time Distribution of Solids in a Fluidized Bed
Authors: Babu M Prasad , Setty Y Pydi
Published: July 2010

Experimental investigation on RTD of solids is carried out in a single‐stage fluidized bed provided with an internal, using uniformly sized particles and a binary solid mixture, varying gas flow rate, solids rate, bed height, dilution and the bed geometry. The effect of these variables on first and second moments as well as on F‐curves has been determined. Using a binary solid mixture or an internal inside the bed is found to reduce backmixing of solids. The data is fitted to FTEM and the values of N obtained were compared for different variables.
Fick's First Law of Diffusion and Binary Gas Separation by Hollow‐Fiber Asymmetric Membrane
Authors: Gornshteyn B. J.
Published: July 2010

For calculating mass transfer through a hollow‐fiber asymmetric membrane, a fundamentally new theoretical method based on Fick's first law of diffusion is proposed. The main features of this method, and the ones currently used for the same purpose, have been compared. The current methods, also based on Fick's first law of diffusion, are shown to be theoretically less than adequate. Recommendations are given for the practical implementation of the new method.
Modeling of Groundwater Contamination by Phenol Released from Spilled Bitumen
Authors: Tang Joseph S.
Published: July 2010

Leaching of phenol from spilled bitumen into flowing aquifer poses an environmental threat to groundwater contamination. A two‐dimensional model with de‐coupled transfer was built to model phenol propagation in the flowing stream. The model predicted that the produced phenol concentration monitored at an observation well would rise sharply and then decline gradually as the phenol flux emerging from the bitumen surface was depleted with time. The model is useful in estimating the size of the spill, produced phenol concentration, phenol spatial distribution and the time required for the phenol concentration to decline to an environmentally acceptable level. It is well suited to other water pollution problems with chemical spills.
La génération de solides divisés par fluides supercritiques
Authors: Fages Jacques , Lochard Hubert , Rodier Elisabeth , Letourneau Jean‐Jacques , Sauceau Martial
Published: July 2010

Les procédés de cristallisation utilisant les fluides supercritiques (FSC) constituent une nouvelle voie pour obtenir des solides finement divisés. En utilisant principalement la pression comme paramètre opératoire, ces procédés permettent l'obtention de poudres fines et monodisperses. On distingue deux familles de procédés selon que le fluide supercritique — généralement le CO2— est utilisé comme solvant (RESS) ou comme anti‐solvant (SAS). Pour le procédé RESS, la chute de densité liée à une détente brutale est le moteur de la nucléation. Pour les procédés de type SAS c'est la dissolution réciproque d'un solvant organique et du FSC qui provoque la précipitation. Des applications industrielles se dessinent dans de nombreux secteurs, même si c'est l'industrie pharmaceutique qui semble la mieux placée pour rassembler une majorité de ses développements.
Fluidized Bed Air Drying: Experimental Study and Model Development
Authors: Henneberg Markus , Heinrich Stefan , Ihlow Matthias , Mörl Lothar
Published: July 2010

The presented study describes the processes and mechanisms of batch fluidized bed drying. The influencing factors of hot air drying are theoretically and experimentally examined, in order to present the relations between temperature and humidity profiles and all other drying parameters. A physical model is presented to facilitate the calculation of the drying processes under defined conditions. Three succeeding drying stages are therefore modeled. Mass and energy balances including all components taking part in the process are formulated. The model clarities the drying process under the assumption of pure heat transfer mechanisms. It does not contain adaptive parameters and takes into account an inactive bypass fraction of the fluidization and drying medium. The evaluation of the model was successful for two fluidized bed plants with nominal widths of 100 mm and 400 mm. The experiments showed sufficient accuracy and transferability of the model to equipment of application‐oriented dimensions.
Modélisation de l'efficacité de filtration d'un échangeur cyclone
Authors: Caetano Richard , Donnot André , Rigo Marie‐Odile
Published: July 2010

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.
Selective Production of C4 Hydrocarbons from Syngas Using Fe‐Co/ZrO2 and SO42—/ZrO2 Catalysts
Authors: Bi Yonghong , Dalai Ajay K.
Published: July 2010

Modified Fischer‐Tropsch (MFT) syntheses were carried out to convert synthesis gas to C4 hydrocarbons over Fe‐Co/ZrO2 (FT) and SO42—/ZrO2 (SZ) catalysts in a dual reactor system, keeping the FT to SZ catalysts ratio at 1:1.5. Five Fe‐Co/ZrO2 catalysts with different Fe and Co loading, and SZ with 15 wt% SO42— were prepared and extensively characterized using various physico‐chemical methods. The FT synthesis process was initially performed using a Fe‐Co/ZrO2 catalyst in a single reactor and the effects of Fe and Co mass ratio, reaction temperature, space velocity on the production of C4 hydrocarbons and C2‐C4 olefins were investigated. Results indicated that a 3.71% Fe—8.76% Co/ZrO2 mixed oxide catalyst alone at 260°C and 5 h—1 gave high selectivities of C2‐C4 olefins (∼26.1 wt%) and total C4 hydrocarbon product (∼16.2 wt%). The MFT process 150°C gave higher C4 (∼31.6 wt%), isobutane (∼22.9 wt%) and C2‐C4 (31.1 wt%) selectivities.
Phase Diagram for Liquid Crystalline Polymer/ Polycarbonate Blends
Authors: Huang G , Chan P. K. , Kamal M. R.
Published: July 2010

A novel mechanism to form binary polymer blends is through phase separation by spinodal decomposition in the unstable region of the phase diagram. The present work investigates the effects of thermally‐induced phase separation by spinodal decomposition on the morphology development of liquid crystalline polymer/polycarbonate blends. Moreover, a thermodynamic binary phase diagram is obtained using a twin‐screw extruder at various processing melt temperatures. Differential scanning calorimetry and scanning electron microscopy were used to study the miscibility of the blends and the resulting morphology. A thermodynamic binary phase diagram exhibiting a lower critical solution temperature was obtained. The droplet size distribution of the blend was also obtained and discussed in light of the Cahn‐Hilliard theory.
Scale‐up and Spouting of Two‐Dimensional Beds
Authors: Costa Márcio De A. , Taranto Osvaldir P.
Published: July 2010

The objective of this paper is to present an analysis on the scale‐up procedure of two‐dimensional spouted beds. The task was carried out with three different beds measuring 0.15, 0.30 and 0.80 in width. The conditions of scale‐up were studied through geometrical similitude analysis. Some parameters of scale were adimensionalised, tested and validated in order to propose relationships capable of predicting values of dependent properties. Those relationships should be followed in a prototype of an equipment of industrial scale. The study permitted the development of correlations to predict values of maximum pressure drop, minimum spout velocity and maximum height of spouting.
Dynamic Gauging in Duct Flows
Authors: Tuladhar Tri R. , Paterson William R. , Wilson D Ian
Published: July 2010

Dynamic gauging is demonstrated experimentally to work well in duct flows, thereby being suitable for monitoring the development of soft films in flowing systems, as illustrated using the growth of a freezing fouling layer viz. an ice film. For low duct velocities (440 < ReD < ca. 2000) we identify an undesirable multiple steady state phenomenon and show how to eliminate it. Dynamic gauging then proves useful up to ReD = ca. 10 000. Above that, we infer that the throat of the gauge nozzle would no longer be within the viscous sublayer and recommend further investigation of this regime.
Structural Disruption of Toothpastes Under Deformation — An Easy Release of Active Ingredients
Authors: Doytcheva Boyka K.
Published: July 2010

The author suggests a technological approach relevant to the optimization of toothpaste compositions with regard to the easy release of the therapeutic ingredients under shear deformation. It is based on the comparative assessment of the steady‐state viscous behaviour of placebo samples (mixtures containing all the components except the therapeutic ingredients) and the final products. It is presumed that the maximum beneficial effect of the toothpastes, as therapeutic agents, is achieved if the final products and the placebo blends display similar shear‐thinning characteristics.
Transfert de matière liquide‐disque dans l'écoulement radial divergent entre disques — étude portant sur différentes échelles du système
Authors: Fahidy Thomas Z. , Cœuret François
Published: July 2010

Le travail étudie expérimentalement le transport de matière stationnaire liquide‐disque dans le cas de l'écoulement radial divergent entre disques circulaires parallèles faiblement distants. Les résultats sont analysés en prenant en compte l'influence de l'effet d'échelle, et au travers d'une corrélation empirique générale entre groupes adimensionnels (Sh, Re, Sc) et facteurs géométriques adimensionnels. La corrélation empirique obtenue est comparée à une solution théorique approchée pour le régime laminaire.
Airlift Bioreactors: Review of Recent Advances
Authors: Merchuk José C.
Published: July 2010

Airlift reactors are popular in the modern bioprocess research and development, over a broad spectrum of processes. Those range from the production of very expensive biochemicals to wastewater treatment. In both extremes the reason behind the selection of the airlift reactor is related to fluid dynamic characteristics. During the last few years, a large number of research papers dealing with the dependence of reactor performance on liquid flow have been published. In some of them, descriptions of devices that have been developed in order to improve, or to gain further control of the fluid patterns in the reactor are reported.
Fluid Dynamic Studies in Support of an Industrial Three‐Phase Fluidized Bed Hydroprocessor
Authors: McKnight Craig A. , Hackman Larry P. , Grace John R. , Macchi Arturo , Kiel Darwin , Tyler Jonathan
Published: July 2010

Reducing gas hold‐up has been identified as a key objective to improve the performance of Syncrude's LC‐FinerSMunit. Redesign of the liquid recycle pan in the freeboard region, aided by multiphase CFD simulation and tests in a kerosene cold model experimental system, led to reduced gas hold‐ups. The addition of an anti‐foam agent did not provide any improvement. Cold‐flow dimensional similitude tests demonstrated the importance of gas density, distributor geometry, and interfacial phenomena. Grid redesign was undertaken to diminish swirl and provide improved radial distribution of gas. Dispersion tests indicate favourable catalyst mixing in the reactors.
Suspension of Particles from the Bottom of Pipes and Stirred Tanks by Gassed and Ungassed Flows
Authors: Thorpe Rex B. , Stevenson Paul
Published: July 2010

Widely accepted correlations and theoretical predictions for hydraulic conveying of solids in pipelines are compared with the literature on the suspension of particles in stirred tanks. Good agreement is found between the correlations and the theoretical predictions both within and between the two fields of study. The effect on the suspension velocity of introducing gas into the pipe and the stirred tank is remarkably similar. In both cases, the shear stress remains broadly unchanged when gas is added. Since the effect of the addition of gas on shear stress is quite well understood in both cases, this is a helpful result.
Liquid Dispersion in Large Diameter Bubble Columns, with and without Internals
Authors: Forret Ann , Schweitzer Jean‐Marc , Gauthier Thierry , Krishna Rajamani , Schweich Daniel
Published: July 2010

Liquid mixing has been studied in a 1 m diameter bubble column, with and without internals (vertical cooling tubes). The presence of internals significantly affects both large scale recirculation and local dispersion. The most common approach to model liquid mixing is the one‐dimensional axial dispersion model, validated many times in small bubble columns without internals. This paper shows that this model is still appropriate to large columns, but without internals. A two‐dimensional model, taking into account a radially dependent axial velocity profile, and both axial and radial dispersion, is required to account for the internals on liquid mixing.
Identification of Flow Regimes in a Flat Gas‐liquid Bubble Column via Wavelet Transform
Authors: Olmos Eric , Gentric Caroline , Midoux Noël
Published: July 2010

A flat bubble column reactor is studied experimentally to increase the understanding of flow regimes and their transitions. To perform this, qualitative observations and global gas hold‐up measurements are used to detect flow regime transitions. Liquid velocities are measured with Laser Doppler Anemometry (LDA). However, as these signals contain a huge amount of information, it is necessary to use signal treatment techniques to analyse them. Wavelet transform was employed in the present paper. The results show that this technique is a powerful tool to (i) describe liquid flow macrostructures, (ii) study gas distributor effects and consequently, (iii) identify flow regimes.
Experimental Determination of Bubble Coalescence and Break‐up Rates in a Bubble Column Reactor
Authors: Laari Arto , Turunen Ilkka
Published: July 2010

The accuracy of CFD calculations of bubble column reactors is often limited by a lack of knowledge regarding bubble coalescence and break‐up rates. The models describing coalescence and break‐up rates have parameters, which cannot be estimated from the available physical properties. The main objective of this work was to test different coalescence and break‐up models and to develop experimental methods for estimating the model parameters. In the experiments bubble size distributions were measured photographically at several reactor heights. A population balance model describing the evolution of the bubble size distribution with respect to reactor height was developed and solved numerically.
Fluid Dynamic Behaviour of Two‐ and Three‐Phase Airlift Reactors
Authors: Di Felice Renzo , Eroles Carmen Monfort
Published: July 2010

This work deals with two‐ and three‐phase airlift systems, employing ambient air, tap water and plastic spheres. The dependency of the main parameters (gas and liquid hold‐ups, liquid circulation rate) on the only external factor, the gas flow rate was investigated. Liquid circulation rate was correlated by a pressure balance which lead to the experimental determination of an overall friction coefficient. A digital camera was used was used, in the second part of the investigation, to determine bubble hold‐up and bubble size distribution. Gas flow rate in the downcomer could be inferred and a tentative correlation with the flow condition prevailing in the riser was suggested.
Vertical Cylinder‐to‐Slurry Heat Transfer in a Gas‐Slurry Transport Bed
Authors: Muroyama Katsuhiko , Kato Takafumi , Masuda Takesi , Kinoshita Susumu
Published: July 2010

In the present study we measured the immersed vertical cylinder surface‐to‐slurry heat transfer coefficient in the liquid‐solid and gas‐slurry (three‐phase) transport beds at controlled solid concentrations. The slurry contained 0.1 mm inert glass beads and the solid fraction in the slurry was varied from 0% to 10% by volume. The liquid viscosity was widely varied by using water and a 1.0wt% aqueous CMC solution. A unified dimensionless equation for the heat transfer coefficient with a coefficient of variation of 14.9% was successfully formulated in terms of the Nusselt number, the Prandtl number and the specific power group including the energy dissipation rate per unit mass of slurry in both transport bed systems. The presence of a good analogy was ascertained between the heat transfer and mass transfer on the vertical cylinder.
Hydrodynamics of a Three‐phase Airlift Reactor with an Enlarged Separator — Application to High Cell Density Systems
Authors: Klein Jaroslav , Vicente António A. , Teixeira José A.
Published: July 2010

The hydrodynamic study of a three‐phase airlift reactor with an enlarged head zone was carried out. Effects of gas‐solid‐liquid separator design and riser to downcomer cross‐sectional area using different lengths and diameters of the draft tube were investigated. Ca‐alginate beads with entrapped yeast biomass at different loadings up to 21 % (v/v) were used in order to mimic the solid phase of conventional high cell density systems. The main hydrodynamic parameters — liquid circulation velocity, gas and solids holdups in all reactor sections have been measured and experimental values were satisfactorily predicted using an appropriate three‐phase model. The results of this study may be applied to suggest the optimal design (in terms of hydrodynamic behaviour) of a batch/continuous three‐phase ALR for high cell density fermentations.
Bubble Emission Frequency and Weeping Rate at a Submerged Orifice with Bulk Liquid Flow
Authors: Zhang Wenxing , Tan R. B. H.
Published: July 2010

Bubble emission frequency and weeping rate has been quantitatively compared in the case of induced and forced liquid flow. A stabilizing baffle was designed to eliminate induced liquid circulation and surface waves due to continuous gas emission. The effects of presence or absence of stabilizing baffle on bubble frequency and weeping rate were shown. Forced liquid cross‐flow was produced and the effect on reducing weeping rate was presented. The results show that liquid weeping is significantly reduced in unbaffled, swirling flow and also with liquid cross‐flow. This is due to a combination of an increase in bubble frequency and a decrease in driving force for liquid weeping. The practical implications of our findings are discussed.
Bubble Distribution in Shear Flow of Highly Viscous Liquids
Authors: Terasaka Koichi , Murata Sayako , Tsutsumino Kaori
Published: July 2010

The size of bubbles distributed from a horizontal nozzle into shear field generated by a Couette flow between concentric cylinders was investigated using dual high‐speed video cameras as parameters, i.e., shear rate, gas flow rate, nozzle diameter, gas chamber volume and liquid viscosity. When the bubble was lifted up by buoyancy and stretched horizontally by shear flow, the cut of the bubble neck was caused by the greater deformation. When the inclined bubble angle by shear flow was greater than the elevation angle by buoyancy, the bubble's detachment was governed not by viscosity but by shear flow. To estimate the bubble size, a correlation equation was proposed in this study.
Stationary State Model in Reforming HCFC22 (CHClF2) to Difluoromethylether (CH3OCHF2)
Authors: Kato Ryo , Nishiumi Hideo
Published: July 2010

To prevent the ozone layer depletion, we proposed a new dechlorination process at room temperature and atmospheric pressure. We have a strong interest in reforming reaction of chlorodifluoromethane (CHClF2, HCFC22) to difluoromethylether (CH3OCHF2), because fluoroethers are expected to be the third generation refrigerants. In a previous paper, we reported that the model that NaCl precipitation, which disturbed mixing of a solution, decreased the reaction rate as the reaction proceeded. In this work, we found that the concentration of HCFC22 was kept constant and smaller than the solubility. The Reaction rate constant k1 was estimated from NaCl production rate and volumetric coefficient KLa was estimated from material balance of HCFC22 in a solution at stationary state. Calculation results gave excellent agreement with experimental data.
Important Factors in Bubble Coalescence Modeling in Stirred Tank Reactors
Authors: Sudiyo Rahman , Virdung Torbjörn , Andersson Bengt
Published: July 2010

Bubble coalescence has been studied in a 2.6 L stirred tank. Instantaneous velocity fields were measured using PIV and corresponding turbulent kinetic energy, dissipation rate, various length and timescales were estimated. All of these data, combined with data of local gas hold‐up, bubble size and coalescence rate obtained with shadowgraph were used to assess bubble coalescence at different positions. Results show that bubble coalescence takes place mostly near the tank wall, especially on the leeward side of baffles. The most important factors affecting coalescence are gas hold‐up, fluctuation of liquid velocity, different rise velocities of bubbles, and trapping of bubbles in stationary and turbulent eddies.
Parametric Study of a Novel Basket Impeller Column
Authors: Safinski Tomasz , Adesina Adesoji A. , Young Brent R.
Published: July 2010

The Basket Impeller Column combines the mass transfer advantages of a spinning basket reactor with the practicality of a dual flow tray column to achieve controllable liquid holdup, as well as a potential solution to many of the problems plaguing current catalytic distillation internals. Sieve plate design, impeller size and speed, along with water and air, flow rates were explored in order to establish a feasible design. An optimal set of specifications was determined via statistical evaluation. Additional experiments were then conducted to obtain correlations for liquid holdup, gas holdup, froth height, pressure drop and power in terms of the significant hydraulic variables.
On the Numerical Modeling of Gas Absorption into Reactive Liquids in a Laminar Jet Absorber
Authors: Aboudheir Ahmed , Tontiwachwuthikul Paitoon , Chakma Amit , Idem Raphael
Published: July 2010

A comprehensive numerically solved absorption‐rate/ kinetics model that takes into account the coupling between chemical equilibrium, mass transfer, and the chemical kinetics of all the possible chemical reactions involved was developed for the absorption of a gas into a reactive liquid. Also, absorption rate measurements to determine the kinetics of the process were obtained in a laminar jet absorber and used to validate this new model. The results show that the model used in conjunction with our numerical method is capable of predicting the gas absorption rates, enhancement factors, and the kinetics of the reaction. Also the model predicted kinetic data for the absorption of CO2 into monoethanolamine (MEA) solutions that were found to be in accordance with published kinetic data. These results show that the developed numerically solved absorption‐rate/kinetics model is both accurate and efficient.
Mass Transfer Characteristics in Gas‐liquid‐liquid System
Authors: Kundu Arunabha , Dumont Eric , Duquenne Anne‐Marie , Delmas Henri
Published: July 2010

Experimental results of mass transfer in air‐water system with a dispersed immiscible organic liquid in a bubble column 0.076 m in diameter for seven different organic liquids at various hold‐up are presented. Experiments are carried out at gas superficial velocity in the range 0.0052‐0.026 m/s at 293 K. The volumetric mass transfer coefficient, kLa is determined by dynamic gas absorption technique. Overall gas hold‐up is also measured. Slight addition of n‐decane, dodecane and n‐heptane in air‐water medium significantly enhances mass transfer from the gas phase, to the continuous aqueous phase whereas toluene, anisole and 2‐ethyl‐1‐hexanol retard mass transfer.
Dynamics of Interfacial Mass Transfer in a Gas‐Dispersed System
Authors: Tsuchiya Katsumi , Ishida Toshiki , Saito Takayuki , Kajishima Takeo
Published: July 2010

Dynamics of mass transfer across gas—liquid interface in a gas‐dispersed system are examined via high‐sensitivity, high‐speed imaging. The dispersive dynamics of the dissolved component, CO2, into the liquid phase are visualized using laser‐induced fluorescence (LIF) with pH‐sensitive pyrene (HPTS) for both a single‐ and multi‐bubble systems. The fluctuating dynamics of the bubble surface are characterized by capillary waves associated with the bubble motion. Enhancement of the mass transfer is found to be associated with the (nonlinear) wave formation, influence of which could be included in modeling the mass‐transfer coefficient, apart from an physical account of the near‐surface concentration gradient.
CFD Simulation of Gas Chamber for Gas Distributor Design
Authors: Dhotre Mahesh T. , Joshi Jyeshtharaj B.
Published: July 2010

The gas chamber is an integral part of various gas‐liquid equipment such as packed columns, plate columns, bubble columns, etc. CFD simulation of the flow pattern was carried out in a gas chamber of square cross‐section and provided with sieve‐plate distributor. Velocities through all the holes were estimated for assessing the uniformity of the gas chamber distribution. The aspect ratio and superficial gas velocity were varied in the range of 0.5 to 4 and 0.02 to 0.2 m/s respectively. The effects of free area and hole diameter were investigated in the range of 0.6 to 6% and 3 to 9 mm respectively. The role of nozzle size and its location with respect to the distributor was analyzed on the uniformity of gas distribution.
Influence of Operating Conditions and Column Configuration on the Performance of Reactive Distillation Columns with Liquid—Liquid Separators
Authors: Klöker Markus , Kenig Eugeny Y. , Schmitt Markus , Althaus Klaus , Schoenmakers Hartmut , Markusse A Peter , Kwant Gerard
Published: July 2010

The synthesis of two different esters, ethyl acetate and hexyl acetate, by heterogeneously catalysed reactive distillation has been studied. The investigated column set‐ups were equipped with liquid—liquid separators for the distillate to separate water from the organic components. Experimental and theoretical investigations of operating conditions and different catalytic column internals, as well as different scales were performed. For the modelling and simulation of the reactive distillation columns, the rate‐based approach was applied. The simulation results are in satisfactory agreement with the experimental data. Performed simulation studies demonstrate the influence of both operating conditions and catalytic internals on the overall process performance.
Autocatalytic Cyclohexane Oxidation in a Bubble Column Reactor
Authors: Schäfer Rainer , Merten Clemens , Eigenberger Gerhart
Published: July 2010

The autocatalytic cyclohexane oxidation was investigated in a lab‐scale bubble column reactor with on‐line measurement of bubble sizes. Significant conversion was obtained at temperatures between 420 and 430 K. The main products were found to be cyclohexyl‐hydroperoxide, cyclohexanol and cyclohexanone. Rising oxygen concentrations favour the production of cyclohexanone. Temperature mainly affects the induction time. At conversion rates greater than 5 % bubble coalescence was inhibited, affecting bubble size distributions for gas hold‐ups above 1 %.
Measurements of Bubble Characteristics: Comparison Between Double Optical Probe and Imaging
Authors: Kiambi S. L. , Duquenne Anne‐Marie , Dupont J.‐B. , Colin C. , Risso F. , Delmas Henri
Published: July 2010

The objective of this study is to evaluate the accuracy of double optical probe technique in local two‐phase flow measurements. Able to provide both bubble velocity, chord length, and gas hold‐up, this technique involves nevertheless delicate signal treatment procedures and, being intrusive, depends on probe tips configurations and sizes. During probe‐bubble interactions, bubble surface is occasionally deformed and this can complicate measurements analysis. The current study is focussed on the rise of single bubbles of known sizes in still water (equivalent diameter of 2.15mm and 4.5mm). Bubble parameters obtained from digital image processing method and from a double optical probe are compared statistically.
A Novel Countercurrent Fixed Bed Reactor
Authors: Kundu Arunabha , Bej Shyamal K. , Nigam K. D. P.
Published: July 2010

A new three‐phase reactor configuration having countercurrent flow of gas and liquid is proposed. The reactor had an internal diameter of 0.04 m and a catalyst bed height of 1 m. A spiral coil made out of wire gauge was inserted inside the fixed bed of catalyst. The gas preferentially passed through the void spaces created due to the presence of the coil. Hydrodynamic studies were conducted using water as liquid and air as gas. The effect of various parameters such as the configuration of the spiral coil, flow rate of gas and liquid on the pressure drop and liquid hold up of the catalyst bed were studied and were also compared with that of a conventional trickle bed reactor.
Selectivity, Hydrodynamics and Solvent Effects in a Monolith Cocurrent Downflow Contactor (CDC) Reactor
Authors: Winterbottoma Mike , Marwan Husin , Natividad Reyna
Published: July 2010

The liquid phase hydrogenation of 2‐butyne‐1,4‐diol (B) to cis‐2‐butene‐1,4,‐diol (C) was studied in a Monolith (CDC) Reactor. The effect of temperature, pressure, different solvents and gas and liquid feed rates on reaction rate and selectivity was determined. RTD measurements were made under different hydrodynamic conditions. The liquid flow was largely laminar with evidence of a stagnant wall film. Selectivity to C was observed to increase with hydrogen pressure and approaches 1 at high superficial gas velocities and conversion of B (>95%) as plug flow is approached. The flow regime was of influence on selectivity and kinetics, which was described by a dual site Langmuir‐Hinshelwood mechanism.
Effect of Gas Density on the Hydrodynamics of Bubble Columns and Three‐Phase Fluidized Beds
Authors: Macchi Arturo , Bi Hsiaotao , Grace John R. , McKnight Craig A. , Hackman Larry
Published: July 2010

Experiments were performed at ambient temperature and pressure in a 127 mm inner diameter column with a 55% wt. aqueous glycerol solution, 6‐mm spherical borosilicate beads and four gases — helium, air, carbon dioxide and sulphur hexafluoride — giving a 35‐fold gas density range. The dispersed bubble flow regime was sustained to higher gas velocities and gas holdups for denser gases. This finding appears to be due to the reduction of the maximum stable bubble size (i.e. enhanced bubble break‐up), rather than to formation of smaller bubbles at the distributor with increasing gas density. The effect of gas density was significant both with and without the particles present, with gas holdup increasing, bed voidage increasing and liquid holdup decreasing with increasing gas density. The holdup correlations of Han et al. (1990) have been modified to incorporate the effect of gas density.