bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical study of laminar condensation of downward flowing vapour on a single horizontal cylinder or a bank of tubes
Authors: Asbik Mohamed , Daif Abdallah , Panday Prabodh Kumar , Khmou Ahmed 
Published: March 2009

AbstractThe results of numerical calculations for the downward flow of pure vapour condensing on horizontal tubes are presented. An implicit finite difference method is used. The equality of shear stress at the liquid—vapour interface is used as the coupling condition between the two phases. The inertia and convection terms are retained in the analysis. The vapour phase velocity is obtained from potential flow. The method of source density distribution on the body surface is used for the determination of the vapour flow in tube banks. The effect of flooding produced by condensation on upper tubes is taken into account by assuming that the vapour velocity field is not affected by the condensate flow from one tube to another. The results presented show that the vapour boundary layer separation depends on the Froude number. The heat transfer in the intertube space is analyzed and compared with the theoretical and experimental results of other authors. Good agreement is shown.
Laminar flow in certain ducts of symmetric cross section
Authors: Wang C. Y. 
Published: March 2009

AbstractViscous flow in certain symmetrical ducts can be solved by a modified Levy's method with internal matching. The method is simple, efficient and accurate. Approximate analytic formulas are also derived for the extreme cases. It is found that cutting convex corners has little effect on the flow rate, but a centered core, however slender, decreases flow dramatically. The graphs for flow rates are useful for the design of ell, cross and nested square ducts and also for the prediction of the permeability of parallel‐structured porous media.
Kinetics of leaching of tunisian phosphate ore particles in dilute phosphoric acid solutions
Authors: Brahim Faouzi Ben , Mgaidi Arbi , Elmaaoui Mohamed 
Published: March 2009

AbstractVan der Sluis et al.'s model was used to determine the rate of the partial dissolution of a Tunisian phosphate rock with dilute phosphoric acid (1.5 mass% P2O5). When the temperature rises from 25 to 90°C, for a given particle size, the mass‐transfer coefficients, kL°, vary from 3 × 10−3 to 8 × 10−3 m ·s−1. The corresponding diffusion coefficients, D, lies between 6 × 10−7 and 27 × 10−7 m2·s−1. Activation energy is equal to 14 kJ·mol−1 and values of kL°, at 25°C, are in the range of 0.28 × 10−3 and 4 × 10−3 m·s−1 when the agitation speed goes from 220 to 1030 rpm, showing that the leaching process is controlled by diffusion rather than by chemical reaction.
Chromic acid removal by anion exchange
Authors: Tan Henry K. S. 
Published: March 2009

AbstractThe kinetics of dilute chromic acid removal by anion exchange was studied using a batch system. Rate model formulated for total Cr(VI) removal based on film diffusion control was applied. This rate model was shown to adequately fit the experimental rate data. In addition, column experimental runs were performed by using 20‐50 mesh anion resin with feed solution containing 0.2 g/L CrO3. The bed heights of 15, 25 and 35 cm and flow rates ranging from 1.02 cm/s to 2.38 cm/s were employed in the experiments. Linear driving force rate expression based on film diffusion rate control was incorporated in the model equations for simulation of column performance. The kinetic parameter and equilibrium relation in the rate equation were obtained independently either by separate experiments or from data available in the literature. Satisfactory agreements between experimental and calculated breakthrough curves were obtained.
Catalytic conversion of palm oil to fuels and chemicals
Authors: Leng Tan Yee , Mohamed Abdul Rahman , Bhatia Subhash 
Published: March 2009

AbstractThe conversion of palm oil to hydrocarbons using a shape selective zeolite catalyst is reported in this work. Palm oil was passed over HZSM‐5 catalyst in a fixed bed micro‐reactor and the reactor was operated at atmospheric pressure, a temperature range of 360 to 420°C and weight hourly space velocity (WHSV) of 2 to 4 h−1. The main objective was to study the effect of reaction temperature and oil space velocity on the conversion and selectivity of gasoline range hydrocarbons. The results show that 40 to 70wt% of the palm oil can be converted to aromatics and hydrocarbons in the gasoline, diesel and kerosene range, light gases, coke and water. The maximum gasoline range hydrocarbons yield of 40wt% of total product formed was obtained at 400°C and 2 h−1 space velocity.
A new direct‐synthesis tuning method for pi‐controllers
Authors: Jung Chan Sul , Song Hyung Keun , Hyun Jae Chun 
Published: March 2009

AbstractA new efficient tuning method for proportional‐integral (PI) controllers is proposed using overdamped closed‐loop dynamics of the system. In line with other direct‐synthesis and IMC methods, this new approach uses the desired closed‐loop response to satisfy usual control and tuning objectives, but unlike the most other tuning methods hitherto‐reported for PID controllers, it does not require that a process model be identified. Yet this new direct‐synthesis (NDS) method is capable of making the controller perform the dual control functions of both good set‐point tracking and disturbance rejection. Furthermore, it turns out that the new tuning method works equally well for difficult cases like large time delay and nonminimum phase processes. Finally, it can be said that this NDS method can be easily implemented and understood by the plant operating personnel because it has been developed emphasizing its on‐site utility.
Bed‐to‐wall heat transfer in a downer reactor
Authors: Kim Yong Jeon , Bang Jin Hwan , Kim Sang Done 
Published: March 2009

AbstractThe effects of superficial gas velocity (0.5 to 4.5 m/s), solid circulating rate (0 to 40 kg/m2·s), suspension density (0 to 19 kg/m3) and particle sizes (83, 103, 163, 236 μm) on the bed‐to‐wall heat transfer coefficient have been determined in a downer reactor (0.1 m I. D. × 3.5 m high). Bed‐to‐wall heat transfer coefficient increases with increasing suspension density. The heat transfer coefficient by gas convection played a significant role, especially at lower solid circulation rates or suspension densities and larger particle sizes. At a given particle suspension density in the downer reactor, the heat transfer coefficient increases with decreasing particle size. A model is proposed to predict the bed‐to‐wall heat transfer coefficient in a downer reactor.
Mass transfer and influence of the local catalyst activity on the conversion in a riser reactor
Authors: Venderbosch Rob H. , Prins Wolter , Van Swaaij Wim P. M. 
Published: March 2009

AbstractGas–solids contacting in risers has been studied based on measurements of mass transfer controlled CO oxidation over a Pt/γ‐alumina catalyst, and on experimental results published by Ouyang et al. (1995) for the kinetically controlled ozone decomposition. In the present experiments, the catalyst activity was varied by mixing the active catalyst particles with similar, but inert γ‐alumina particles (in ratios from 150 to 2500 m3inert/m3cat), whereas Ouyang and co‐workers varied the operating temperature ( de 300 à to 500 K). Mass transfer controlled CO oxidation occurs at temperatures above 750 K. A negative square root dependency has been observed for the relationship between the Sherwood number and the solid hold‐up. Increasing the gas velocity always improves the gas–solids contacting. The local catalyst activity appears to be an important parameter. As an important conclusion of the present work, it can be stated that at a high local activity, the conversion rate per unit volume of catalyst decreases significantly due to local depletion of reactant.
Novel technologies of VOC decontamination in fixed, moving and fluidized catalyst‐adsorbent beds
Authors: Dolidovich Alexandre F. , Akhremkova Galina S. , Efremtsev Vyacheslav S. 
Published: March 2009

AbstractSome findings are reported on theoretical and experimental research studies of mechanical, structural, physical and chemical properties, micro‐and macrokinetic adsorptive, catalytic and regenerative characteristics of heterogeneous alumina catalyst‐adsorbents used for decontamination of individual volatile organic compounds (VOC) and their multicomponent mixtures. Data on fluid dynamics, heat and mass transfer in fixed, gravity‐moving and fluidized beds in novel energy‐saving (i) adsorptive, (ii) adsorptive‐catalytic, (iii) thermocatalytic with a quasistationary fluidized and (iiii) with a fixed catalyst beds and deep intercyclic heat recovery of purification systems are obtained and discussed. Correlations are suggested to calculate a number of investigated parameters, and the schematics and operating principles of these technologies are described.
On the measurements of regime transition in high‐pressure bubble columns
Authors: Lin T.‐J. , Tsuchiya K. , Fan Liang‐Shih 
Published: March 2009

AbstractTwo approaches are adopted in this study to identify the flow transition in a bubble column from the homogeneous regime to the heterogeneous regime at pressures up to 15.2 MPa and temperatures up to 78°C. These approaches, which yield essentially identical results, include those based on the standard deviation of the pressure fluctuation and the drift flux model. The experimental results obtained indicate that the regime transition velocity is delayed when the system pressure and temperature increase. The correlation proposed for the transition velocity by Wilkinson et al. (1992) predicts the present results to a reasonable extent, provided that the experimentally measured values for the physical properties of the fluids are used in the correlation. It is clear, however, that an improved correlation or model is needed for a quantitative account of the transition velocity for high‐pressure bubble column systems with different gas distributing capability.
The onset of liquid entrainment during discharge from two branches on an inclined wall
Authors: Hassan Ibrahim G. , Sims Grant E. , Soliman Hassan M. , Kowalski Janusz E. 
Published: March 2009

AbstractA theoretical investigation has been conducted for predicting the critical liquid height at the onset of liquid entrainment during dual discharge from a stratified two‐phase region through branches mounted on an inclined flat wall. The centerlines of the two branches are parallel and they fall in a common vertical plane. Two models have been developed; a simplified point‐sink model and a more‐accurate finite‐branch model. Predictions from the two models are shown to be in good agreement for the condition of high flow rates from the branches, while the finite‐branch model is necessary for accurate predictions at low branch flow rates. This behaviour has been confirmed experimentally for the vertical‐wall configuration.
Determination expérimentale et prédiction des temps de circulation et de mélange pour un système d'agitation hélicoïdal
Authors: Delaplace Guillaume , Leuliet Jean‐Claude , Dieulot Jean‐Yves , Brienne Jean‐Paul 
Published: March 2009

AbstractThe homogenization efficiency of an atypicalhelical ribbon impeller was investigated. In a first part, circulation and mixting times for Newtonian fluidshave been determiend byuse of conductivity and thermal methods. A transferfunction model havebeen used to fit response curves obtained after tracer injections. The proposed model only depends on twoparametrs. Variations of these two parametrs have been correlated wtih the rotational impeller speed and the Reynolds numbervalue. This work allowsus to prdict, whatever flow regimes and process conditions (viscosity, rotatiional impeller speed), the mixing process performance.
Corrosion des aciers et superalliages inoxydables en eau tritiée ‐ influence du tritium et des espèces radiolytiques
Authors: Bellanger Gilbert 
Published: March 2009

AbstractTo better understand the phenomena in metl equipment corrosion in tritiated water, a study of the behavior of oxide layers on a cobalt‐based stainless superalloy was made in this highly radioactive medium. The oxide characteristics are modified from the corrosion potential, in passivity and up to teh passivity and transpassivity limits. The corrosion of oxide sublayers, as exfoliation of the oxide, was shown. This would appear to be due to diffusion of tritiated species in the oxide. These species accumulate at the oxide‐alloy interface, thus modifying the number of charge carriers in te oxide.
Hydrodynamics and particle collection in turbulent bed contactor
Authors: Gimenes Marcelino L. , Handley Douglas 
Published: March 2009

AbstractPerforated spheres with 10% and 25% free area, oblate spheroids and the conventional plain spheres were tested as packing medium in a Turbulent Bed Contactor (TBC). Hydrodynamics and particle collection experiments were carried out in a column having 0.264 m diameter, at 3 static bed heights and several gas and liquid flow rates. Alumina (1.5 to 5.5 μm) was used as test powder for particle collection experiments. The higher efficiency of particle collection, the lower bed expansions and the higher fluidization velocities of perforated spheres, indicates that this packing type is suitable as contacting medium for particle collection in TBCs.
Transient response of granular bed motion in rotary kiln
Authors: Sriram V. , Sai P. S. T. 
Published: March 2009

AbstractA non linear model proposed by Perron and Bui (1994), which focuses on the dynamics of slow mode to predict the transient response induced by step changes in operating variables in the motion of the granular bed in a rotary kiln, was validated for different experimental conditions. The variables include feed rate of solids, inclination and rotational speed of the kiln, and dam height. The validity of the model for step changes in two or more variables at a time was also verified.
Plasmid stability analysis in a non‐homogeneous bioreactor for a recombinant fed‐batch fermentation
Authors: Patnaik Pratap R. 
Published: March 2009

AbstractFed‐batch fermentation for tryptophan synthetase by a recombinant Escherichia coli strain has been analyzed through a model incorporating segregational loss of the plasmid pPLc23trpAl and imperfect macromixing of the broth. These features become significant in large fermentation vessels, where fluid circulation in the bioreactor influences the rates of cell growth and productivity. A simple model consisting of two interacting reactors describes the degree of macromixing, which is characterized by the respective (internal) dilution rates. Controlled imperfect macromixing is superior to other methods in arresting, and even reversing, the normal decline in the concentration of recombinant cells, thereby providing a method to exploit the non‐homogeneity of the broth in large bioreactors. Some physical implications are discussed.
Dispositif simple et performant pour disperser un gaz dans un liquide en vue d'effectuer des réactions chimiques ou biochimiques en présence ou non de particules solides
Authors: Botton Roger 
Published: March 2009

AbstractThe proposed system is a vertical liquid jet issuing from an orifice near the surface of a gas–liquid mixture. The jet sucks gas, then penetrates into a coaxial pipe until it hits a horizontal impact plate and disperses into the gas–liquid mixture. The coaxial tube has holes in its upper part to recycle the mixture. The performace of this gas–liquid contacting device are very good. Experimental relations are given and possible applications are examined. One example of reactor calculation is given.
Removal of acetic acid from water by catalytic distillation. Part 1: Experimental studies
Authors: Xu Zhanping , Afacan Artin , Chuang Karl T. 
Published: March 2009

AbstractCatalytic distillation experiments were carried out in a 100 mm diameter column for the removal of dilute acetic acid from water. The column was installed with a novel internal composed of alternating a dualflow tray and a catalyst basket. Amberlyst 15 was used as a catalyst to accelerate the esterification of acetic acid with methanol. The effects of various operating parameters on the acid removal were investigated. For the feed which contains 2.5 to 9.9 wt% of acetic acid in water, more than 50 wt% of acetic acid can be recovered as methyl acetate in the 1.5 meter high test column.
Catalytic combustion of methane in a monolith washcoat: Effect of water inhibition on the effectiveness factor
Authors: Hayes Robert E. , Awdry Serpil , Kolaczkowski Stan T. 
Published: March 2009

AbstractThis paper reports the results of a numerical investigation of the diffusion and reaction of methane in the washcoat of a catalytic monolith reactor. The kinetic rate expression used is an empirical equation determined experimentally for a palladium oxide catalyst. The effect of water inhibition on the reaction rate is included in the model. A multi‐species diffusion and reaction model is used to simulate the process. The model is solved in a 2‐D space using a finite element method. It is observed that the inhibiting effect of water tends to lower the observed reaction rate and that a higher surface water concentration results in an increase in the observed effectiveness factor. The effectiveness factor depends on three dimensionless parameters. Strong diffusion limitation can lead to high water concentrations at the interior of the catalytic washcoat.
Liquid holdup measurement techniques in laboratory high pressure trickle Bed Reactors
Authors: Al‐Dahhan Muthanna , Highfill Wes 
Published: March 2009

AbstractThree different techniques, which are tracer, drainage and weighing methods, are used to measure liquid holdup in a laboratory trickle‐bed reactor operated under high pressure. The holdup measurements are compared to determine the applicability of these methods at high pressure operation. It was found that tracer and drainage techniques give comparable values for the total liquid holdup. Although several investigators recommended the weighing method over the others based on their experiments performed at atmospheric conditions, it was found that the weighing method failed to measure liquid holdup properly at high pressure operation.
Model studies on the mechanism of endotoxin adsorption on flat‐sheet microfiltration membrane adsorbers
Authors: Anspach F. Birger , Petsch Dagmar , Deckwer Wolf‐Dieter 
Published: March 2009

AbstractThe adsorption of endotoxin from E.coli O 111:B4 and bovine serum albumin on membrane adsorbers with the ligands polymyxin B, L‐histidine, deoxycholate, poly(L‐lysine), poly(ethyleneimine) and diethylaminoethyl was studied under equilibrium and dynamic conditions. Apparent association constants varied between 30 and 30 000 mL/mg for endotoxin, whereas with BSA only approximately 1 mL/mg was found on average. With all ligands a reduction of the removal efficiency was experienced in the presence of BSA, which was used as model protein. Detailed analysis of the influence of BSA on the association constants as well as the equilibrium and dynamic capacities of endotoxin adsorption demonstrated that endotoxin and BSA molecules recognize distinct binding centres on the membrane adsorbers. Competition for binding sites plays a less important role than assumed so far. It is concluded that interactions of endotoxin with protein molecules in solutions are limiting endotoxin clearance from protein solutions. With net‐positively charged proteins, electrostatic interactions yield protein‐endotoxin complexes. Net‐negatively charged proteins attract endotoxin by the mediation of calcium ions that are derived from endotoxin micelles and vesicles. In the latter case, endotoxin clearance can be significantly improved by the addition of EDTA.
Extractive distillation of 2‐methoxy‐2‐methylpropane + ethanol using 1‐butanol as entrainer: Equilibria and simulation
Authors: Arce Alberto , Rodil Eva , Soto Ana 
Published: March 2009

AbstractIsobaric (101.32 kPa) liquid‐vapour equilibrium data for the system 1‐butanol + ethanol + 2‐methoxy‐2‐methylpropane (MTBE) were determined and fitted with Wilson, NRTL and UNIQUAC equations, and their prediction by various group contribution methods (ASOG and modified and unmodified UNIFAC methods) was examined. The NRTL equation was used to calculate, by simulation, the influence of plate number and entrainer/feed flow ratio on the quantity and composition of the distillate afforded by extractive distillation of azeotropic MTBE + ethanol using 1‐butanol as the entrainer. The quantity of distillate and its MTBE content both increased with plate number, and the quantity of distillate also increased with entrainer/feed flow rate ratio.
Hypochlorite production on Ru‐Sn binary oxide electrode and its application in treatment of dye wastewater
Authors: Yang Chien‐Hsin 
Published: March 2009

AbstractRuthenium‐tin binary oxides [(Ru+Sn)O2] were coated on titanium substrates by thermal decomposition. The surface morphologies and elemental analyses of these electrodes were examined by means of scanning electron microscopy. The electrochemical behaviours were characterized by cyclic voltammetry and linear‐scan voltammetry (LSV) methods. The effects of electrolysis condition for the current efficiency (CE) of hypochlorite production on binary (Ru+Sn)O2 electrodes and the treatment of a high salt‐containing dye wastewater using this hypochlorite were also investigated. The highest CE for hypochlorite production exists on an RS3 (40 to 80 mol% Sn in coating solution) electrode. The major factors influencing CE for hypochlorite production are the electrolyte flow rate, current density, and chloride (Cl‐) concentration. Major factors affecting energy yield are current density, Cl‐ concentration, and electrode distance. For low current density (300 mA.cm−2), high Cl‐ concentration (1 mol.L−1), and 0.45 cm electrode separation, a high specific energy is obtained. The RS3 electrode exhibits the best removal of organics and chromophor groups in the dye wastewater. On this electrode, better removal of organics and chromophor groups is obtained at 300 mA.cm−2. The colour of black‐red dye wastewater becomes light yellow when a charge of 792 A·min was passed, while the chemical oxygen demand (COD) of this wastewater is decreased from 10500 mg.L−1 to 1250 mg.L−1.
Modeling the influence of mineral rocks, active in different hot gas conditioning systems and technologies, on the production of light α‐olefins
Authors: Taralas Georgios 
Published: March 2009

AbstractA mechanistic reaction model of the pyrolysis of vaporized n‐heptane in the presence of steam (P ≈︁ 18&–32 kPa) is developed based on overall first‐order decomposition kinetics, which satisfactorily describes the experimental data. The mechanistic model predicted that calcined, naturally occurring and readily available mineral rocks, Swedish quarried calcium oxide (quicklime) and Norwegian (Norsk Hydro) magnesium oxide (dolomitic magnesium oxide) applied as the catalytic materials increase the conversion of the vaporized feedstock (P = 2.9–4.7 kPa) without changing the distribution of light α‐olefins (i.e., C2H4, C3+, C4H8), compared to pyrolysis in an empty reactor viz. thermal steam‐cracking. The simulation calls attention to the fact that the endothermic pyrolysis reaction of the alkane n‐heptane is proceeding not only in the homogeneous gas‐phase but also on the mineral particles (catalytic cracking) with the same mechanism.