bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling of batchwise xanthan production
Authors: Peters H.‐U. , Suh I.‐S. , Schumpe A. , Deckwer W.‐D. 
Published: July 2010

AbstractAn empirical model for the production of xanthan polysaccharide by batchwise cultivation of Xanthomonas campestris was developed. The effects of oxygen depletion in the liquid and bacterial growth rate on the xanthan production rate and the time‐course of the xanthan molar mass were taken into account. When the oxygen transfer was rate limiting in the non‐growth phase, the molar mass of the final xanthan product was lower than that observed in the absence of oxygen limitation. A constant feed of medium, containing citric acid, increased the xanthan productivity and allowed a polysaccharide concentration of 50 kg/m3 to be reached within 57 h. Low productivity observed in a 3 m3 reactor with small‐diameter Rushton turbines was attributed to stagnant zones in the wall region.
Spectral measurement of the complex refractive index of fly ashes of canadian lignite and sub‐bituminous coals
Authors: Lohi A. , Wynnyckyj J. R. , Rhodes E. 
Published: July 2010

AbstractThe complex spectral refractive index (absorption index) of fly ash from two generating stations burning Canadian lignite and sub‐bituminous coals have been examined by two different techniques. Ash samples collected at different combustion conditions were analyzed. It is shown that the absorption index of both ashes is in the range of 0.004 to 0.018 in the wavelength range of 0.7‐2.5 μm. The effects of presence of carbonaceous material in ashes, iron content and different operating (combustion) conditions are reported.
Heat transfer to newtonian and non‐newtonian liquids in a screw agitator and draft coil system
Authors: Carreau P. J. , Paris J. , Guérin P. 
Published: July 2010

AbstractHeat transfer has been investigated for several Newtonian and non‐Newtonian liquids mixed in a flat bottomed vessel equipped with a screw agitator and a coil acting simultaneously as draft tube and heat exchanger. Heat transfer rates from coil to liquid were determined for different coil designs, rheological properties and operating conditions in the heating and cooling modes. A circulation Reynolds number is defined, the characteristic length being the effective height of the heat exchanger (the coil) and the characteristic velocity being the circulation velocity of the fluid which was determined experimentally. Using this Reynolds number, it was possible to establish a single correlation for the Nusselt number as a function of Reynolds and Prandtl numbers. Geometric ratios do not appear in this correlation which could adequately represent more than 200 experimental data. A similar single correlation could not be obtained when using the conventional mixing Reynolds number. This novel system is shown to be very efficient for handling rheologically complex fluids.
Model based control of a high purity distillation column
Authors: Douglas P. L. , Fountain P. S. , Sullivan G. R. , Zhou W. 
Published: July 2010

AbstractIn this paper, the problem of dual product composition control of an industrial high purity distillation column, a deisohexanizer (DIH), is addressed using a Generic Model Control framework. A dynamic simulation of the DIH was performed for preliminary studies of the performance of different controller strategies/algorithms. The performance of Generic Model Control incorporating different process models was studied. Process models are presented ranging from simple first order approximations to mechanistic short cut distillation models where a tradeoff between model complexity and model adaptivity is investigated. The different controllers were implemented and compared using a dynamic simulation of an industrial deisohexanizer (DIH) to select the best condidate controller. A controller using a nonlinear process model emerged as the best controller and was implemented on the actual process, resulting in improved performance over the original controller. Simulation results and industrial plant data are presented.
Flow Generated by an Aerated Rushton Impeller: Two‐phase PIV Experiments and Numerical Simulations
Authors: Deen Niels G. , Solberg Tron , Hjertager Bjørn H. 
Published: July 2010

AbstractA two‐camera PIV technique was used to obtain angle resolved velocity and turbulence data of the flow in a lab‐scale stirred tank, equipped with a Rushton turbine. Two cases were investigated: a single‐phase flow and a gas‐liquid flow. In the former case, the classical radial jet flow pattern accompanied by two trailing vortices was observed. In the latter case, the velocity of the radial jet was reduced, and the vortices were diminished by the presence of the gas. Gas cavities clinging to the back of the impeller blades were observed. Both cases were also investigated with the use of three‐dimensional transient CFD simulations. For the single‐phase flow the simulations in the impeller region correspond very well with the experimental data. For the gas‐liquid flow both the mean and fluctuating liquid velocities in the impeller region are well predicted. This is also the case for the mean radial gas velocities.
Operational Characteristics of a New Energy‐saving Impeller for Gas‐Liquid Mixing
Authors: Vlaev Serafim D. , Mavros Paul , Seichter Pavel , Mann Reg 
Published: July 2010

AbstractThe fluid dynamic and mixing characteristics of a new hydrofoil impeller (termed Narcissus) for gas‐liquid mixing are reported. This impeller provides significant energy‐savings in bioreactor applications. Dye‐tracer visualization and CFD simulation have been used to uncover the prevailing flow patterns and the impeller liquid flow map is identified. Flow regime boundaries are shifted from those for disc‐style turbines. A mixing time corresponding to the turbulent mixing regime (i.e., Re > 104) is determined. The power characteristics are measured and compared with experimental data obtained for other impellers. The power number for the turbulent mixing regime for both cylindrical and square vessels was as low as 1. The aeration power at moderate Froude numbers (i.e., Fr < 1) decreased typically by only between 10 and 30%, confirming good gas‐handling capabilities for the new geometry. The gas hold‐up at a given power input was greater than for flat‐blade disc‐style turbines.
On the Comparison between Probability Density Function Models for CFD Applications
Authors: Fissore Davide , Marchisio Daniele L. , Barresi Antonello A. 
Published: July 2010

AbstractComputational fluid dynamics (CFD) for modelling turbulent reacting flows is based on the Reynolds‐average approach and requires a micro‐mixing model for the chemical source that appears in an unclosed form. Three different approaches are presented in this work: full PDF, finite‐mode PDF and beta PDF. The comparison was carried out in an ideal perfectly mixed batch reactor, that corresponds to the cell considered by CFD codes; competitive‐consecutive and competitive‐parallel reaction schemes were used to test model performances. The comparison showed that the disagreements between the approaches in a certain range of operative conditions are acceptable. The prediction obtained by using the Finite‐Mode PDF model and the Beta PDF model are comparable. Nevertheless the Finite‐Mode PDF model presents the main advantage of being simpler and faster.
On the Applicability of the Grace Curve in Practical Mixing Operations
Authors: Stegeman Yvonne W. , Van De Vosse Frans N. , Meijer Han E. H. 
Published: July 2010

AbstractAthough the Grace curve is often used to select the material components and optimal flow rates in blending operations, its validity for industrial mixing practice remains to be seen. Among other reasons, the flow field in industrial mixers is not homogeneous. This causes the actual shear/ elongation rate imposed upon a (moving) droplet to be time‐dependent. To investigate the importance thereof, analytical models are used which describe the droplet stretching rate as a function of the droplet shape, viscosity ratio and time‐varying capillary number. Both experiments and model predictions show that droplet breakup can be caused by inhomogeneous flow fields, even if the average capillary number is sub‐critical. Moreover, the model predicts how the critical capillary number is influenced by a non‐spherical initial shape. At higher aspect ratios the critical capillary number can be reduced significantly, especially for higher viscosity ratio droplets.
Dynamic Process Modelling using a PCA‐based Output Integrated Recurrent Neural Network
Authors: Qian Yu , Cheng Huanong , Li Xiuxi , Jiang Yanbin 
Published: July 2010

AbstractA new methodology for modelling of dynamic process systems, the output integrated recurrent neural network (OIRNN), is presented in this paper. OIRNN can be regarded as a modified Jordan recurrent neural network, in which the past values for certain steps of the output variables are integrated with the input variables, and the original input variables are pre‐processed using principal component analysis (PCA) for the purpose of dimension reduction. The main advantage of the PCA‐based OIRNN is that the input dimension is reduced, so that the network can be used to model the dynamic behavior of multiple input multiple output (MIMO) systems effectively. The new method is illustrated with reference to the Tennessee‐Eastman process and compared with principal component regression and feedforward neural networks.
Using a New Interfacial Area Transport Equation to Predict Interfacial Area in Co‐current Jet Mixers
Authors: Yarbro Stephen L. , Long Richard L. 
Published: July 2010

AbstractIn multiphase operations, such as liquid‐liquid or gas‐liquid systems, the interfacial area affects the interfluid heat, mass and momentum transfer and ultimately, the overall equipment performance. To better understand the mixing process, we developed a multi‐fluid model that predicts interfacial area for kerosene‐water mixtures in co‐current jet mixers. The model has ensemble‐averaged conservation equations for each fluid and includes a transport equation, derived from an overall energy balance, for the interfacial area concentration. In the model, the mechanical energy of the continuous phase creates interfacial area. Comparing the final, one‐dimensional model to experimental data proved the model is accurate. Over 93% of the calculated and experimental data obtained from 0.027 inch and 0.041 inch diameter co‐current jet mixers compared within 15%.
Laminar Mixing in Eccentric Stirred Tank Systems
Authors: Alvarez Mario M. , Arratia Paulo E. , Muzzio Fernando J. 
Published: July 2010

AbstractLaminar flow structure and mixing patterns in stirred tanks with eccentrically located impellers is examined using tracer visualization techniques and laser induced fluorescence (LIF). The displacement of the shaft from the centerline of the tank has a remarkable effect on the manifold structure of the flow: segregated regions of regular motion observed in concentric systems are destroyed, impeller mid‐plane separatrices are eliminated, and the axial circulation is greatly improved even in systems agitated even by radial impellers.
Unconventional Configuration Studies to Improve Mixing Times in Stirred Tanks
Authors: Ascanio Gabriel , Brito‐Bazán Magdalena , Brito‐De La Fuente Edmundo , Carreau Pierre J. , Tanguy Philippe A. 
Published: July 2010

AbstractDynamic perturbations and off‐centered single and dual mixing impeller configurations have been investigated to reduce mixing time with viscous fluids. Mixing times, measured with a color‐discoloration technique based on a fast acid‐base reaction, reveal the presence of both segregated and dead zones. A statistical design approach has been used to evaluate the effect of the impeller position as well as the dynamic conditions. Homogenization is significantly enhanced when a radial flow impeller is used under both off‐centered and dynamic perturbation conditions. In the case of an axial flow impeller, a combination of long clockwise times and short counter‐clockwise times give better mixing times. An enhanced homogenization is also observed when a dual impeller configuration is used.
Investigation of Flow Patterns in Continuous‐flow Stirred Vessels by Laser Doppler Velocimetry
Authors: Mavros Paul , Xuereb Catherine , Fořt Ivan , Bertrand Joël 
Published: July 2010

AbstractThe flow structure of a continuous‐flow reactor stirred by a Rushton turbine was investigated by laser Doppler velocimetry for two different mean residence time‐mixing time ratios. Velocity measurements were obtained for two inlet locations, corresponding to the incoming liquid stream being fed co‐currently or counter‐currently to the flow discharged by the turbine. In all investigated configurations and for all operating conditions, it was found that the flow disruption caused by the incoming liquid stream was observable mainly in the first vessel quarter, which followed the feed‐tube plane. From comparison of the velocities encountered in the various planes in the continuous‐flow reactor to the velocities of the batch reactor, it was also concluded that it may be possible to intensify the usage of the turbine‐stirred vessel by decreasing the characteristic times ratio, without considerable flow by‐pass and/or short‐circuiting problems.
The Influence of Viscosity Ratio on Mixing Effectiveness in a Two‐fluid Laminar Motionless Mixer
Authors: Ventresca Amy L. , Cao Qing , Prasad Ajay K. 
Published: July 2010

AbstractAn investigation of dependence of laminar mixing efficiency of a motionless mixer upon viscosity ratio at low Reynolds number (⩽3) was performed. Viscosity ratios up to 340 were investigated. The liquids were aqueous solutions of carboxymethylcellulose (CMC). Two transparent liquid streams, one marked with a fluorescing dye, were injected into a pipe housing five elements of an SMX mixer. The degree of mixing was evaluated by imaging a downstream cross‐section of pipe using laser induced fluorescence (LIF). Highly resolved spatial variations of fluorescence intensity were recorded using a CCD camera. Mathematical evaluations using correlograms, scale of segregation, COV, and intensity histograms are presented.
An Aqueous Phase Equilibrium Calculation Algorithm
Authors: Makkuni Ajay , Phoenix Aaron V. , Rohani Sohrab 
Published: July 2010

AbstractA multiphase chemical equilibrium algorithm is developed which can be used with aqueous systems. The algorithm uses an average chemical potential for each species as a reference chemical potential. Incipient phases can be identified and their proximity to appearance can be determined through their tangent plane distance. Illustrative examples include the calculation of CaSO4 solubility and the calculation of vapour pressures above an SO2‐NaCl‐H2O system, including the prediction of a three‐phase equilibrium. The algorithm proved robust and versatile. The appearance of incipient phases was easily tracked. Future work needs to be done to optimize damping/acceleration coefficients in the calculations.
Gas Hold‐Up in Stirred Tank Reactors in the Presence of Inorganic Electrolytes
Authors: Yawalkar Archis A. , Heesink Albertus B. M. , Versteeg Geert F. , Pangarkar Vishwas G. 
Published: July 2010

AbstractGas hold‐up (ϵG) in air‐aqueous electrolyte solutions in stirred tank reactors (STR) is correlated using a relative gas dispersion parameter, N/Ncd and a surface tension factor (STF), (c/z)(dδ/dc)2. For electrolyte concentration below transition concentration (ct) a single correlation in the form of ϵG = f(N/Ncd, vvm, STF) shows good agreement with gas hold‐up data over a wide range of system and operating conditions. Above ct no effect of STF on gas hold‐up is observed and the correlation obtained is of the form ϵG = f(N/Ncd, vvm). Data available in the literature on large STR show good fit with the proposed correlation.
Solids Circulation Flux and Gas Bypassing in a Pressurized Spout‐fluid Bed with a Draft Tube
Authors: Xiao Rui , Zhang Mingyao , Jin Baosheng , Liu Xiangdong 
Published: July 2010

AbstractAn experimental study on solids circulation flux and gas bypassing of a spout‐fluid bed with a draft tube at elevated pressures up to 600 kPa was performed in a 200 mm diameter cylindrical steel column with a 608 conical distributor. Glass beads with mean diameter 2.067 mm were used as bed materials to investigate the effect of operating conditions and geometric configuration on the solids circulation flux and the gas distribution between the annulus and the draft tube. A novel technique has been developed to measure the solids fluxes under pressure, and gas (CO2) traces have been employed to investigate gas bypassing characteristics. The solids circulation flux is greatly enhanced when operating pressure and auxiliary gas flowrate are increased, and it is also strongly influenced by geometric configuration. Two experimental relations are proposed for predicting solids circulation flux enhancement factors.
Flow of a FENE Fluid in Packed Beds or Porous Media
Authors: Kozicki William 
Published: July 2010

AbstractAn analysis describing viscoelastic flow of a FENE fluid in packed beds or porous media is presented based on the capillary hybrid model of the flow. A close similarity is revealed between the functional relationship of the reduced elongational viscosity to and that relating the reduced mean elongational viscosity λH ϵ to the Deborah number which is utilized in the flow expressions. The agreement obtained between the predicted and experimentally determined evaluations of the resistance factor, including the effects of variation of polymer concentration, molecular weight and solvent quality was found to be satisfactory. Onset Reynolds numbers for enhanced flow resistance are also predicted successfully.
Prediction of the Crevice Corrosion Incubation Period of Passive Metals at Elevated Temperatures: Part II — Model Verification and Simulation
Authors: Heppner Kevin L. , Evitts Richard W. , Postlethwaite John 
Published: July 2010

AbstractA flexible computational model for the initiation of crevice corrosion has been developed. Based upon a mechanistic theory, empiricisms do not limit the scope of this work. The model is formulated in a previous paper and this sequel publication showcases the performance of the algorithm. Designed for widespread applicability, passive crevice corrosion of metals may be modelled in suitable electrolytes. The initiation of crevice corrosion has been simulated for several passive metals. Reaffirming past observations, higher temperatures are predicted detrimental to the passivity of metals. The predictions are compared with the experimental work of others and excellent agreement is seen between the simulated chemical composition of the crevice solution and experimental reality.
An Extensive Analysis on the Start‐up of a Simple Distillation Column with Multiple Steady States
Authors: Benz Sonia J. , Scenna Nicolas J. 
Published: July 2010

AbstractThe impact of start‐up procedures on the behaviour of simple distillation columns with multiple steady states is analyzed. A well‐known system with hysteresis is studied in this paper and transient responses for a binary distillation column yielding different steady states during the start‐up operation are shown. Several dynamic simulation results showing an interesting behaviour are presented. Through the examination of the profile evolutions corresponding to given start‐up policies, it can be seen how the column arrives to different steady states. It is shown that it is possible to identify a set of critical values for the start‐up supervision. Also, guidelines of general validity are achieved with the aim of finding the appropriate start‐up policy to obtain the desired solution.
NiMo Supported on Faujasite‐modified Al2O3 as Catalysts for the Hydrotreatment of a Light Cycle Oil/Straight Run Gas Oil Mixture
Authors: Marín Celia , Escobar José , Galván Ernesto , Murrieta Florentino , Zárate René , Cortés Víctor 
Published: July 2010

AbstractA study on the hydrotreating performance of sulfided NiMo supported in NH4+Y‐ and H+Y‐modified Al2O3 is reported. The effect of the addition of the corresponding NiMo‐exchanged zeolites was also investigated. The materials were characterized (by N2 physisorption and surface acidity measurements) and evaluated in the upgrading of a middle distillates (LCO‐SRGO) mixture under industrial conditions. The main effects of the integration of the NiMo‐exchanged zeolite (from the NH4+‐faujasite) were an improvement of textural properties and the creation of strong surface Lewis sites. The corresponding sulfided formulations showed higher hydrodesulfurization and hydrodearomatization activities than the catalyst prepared from the protonic zeolite.
A Trend to the Production of Calcium Hydroxide and Precipitated Calcium Carbonate with Defined Properties
Authors: Lõhmus Hilja , Räni Ahto , Kallavus Urve , Reiska Rein 
Published: July 2010

AbstractIn this paper, production of precipitated calcium carbonate (PCC) with required particle size and morphological structure, along with its dependence on technological parameters and the properties of Ca(OH)2, is discussed. The effect of the reaction environment on the kinetics of CaO hydration and the formation of crystals in water suspension was established. A remarkable difference in the system's restoration ability after stirring was observed. The hydration process is initially controlled by a kinetic mechanism, followed by a diffusion‐controlled process. The dissolution speed of lime hydrated to suspension is eight times higher than that of lime hydrated to powder. Particles of hydrated lime appeared in various forms.
Neural Optimization of Fed‐batch Streptokinase Fermentation in a Non‐ideal Bioreactor
Authors: Patnaik Pratap R. 
Published: July 2010

AbstractMicrobial fermentations involving two or more kinds of competing cells and operating under realistic conditions are difficult to monitor, model and optimize by model‐based methods. They deviate from ideal behavior in two significant aspects: incomplete dispersion in the broth and the influx of disturbances. The approach here has been to optimize the filtered noise and dispersion on‐line through neural networks. This method has been applied to the fed‐batch production of streptokinase (SK). The culture has two kinds of cells — active (or productive) and inactive — and their growth is inhibited by the substrate and the primary metabolite (lactic acid). Using simulated data, the fermentation was optimized by a system of three neural networks, updated continually during successive time intervals. Such sequential optimization with dynamic filtering of inflow noise generated better cell growth and SK activity than static optimization and even an ideal fermentation.
Thermal Sensor to Monitor Mechanical Properties in Polymer/Fiber Composite Molding
Authors: Rouison David , Varejka Milena , Picot Jules 
Published: July 2010

AbstractMulti‐layered samples of 1) continuous fiber axially aligned and 2) random oriented mat glass fiber composites were manually prepared for a fiber content ranging from zero to 20% (vol.). The uniaxially aligned samples displayed linear relations between both normalized elastic modulus and normalized thermal conductivity, and fiber content, for axially applied load and heat flux. For the random mat composite samples, similar results were obtained, with symmetry displayed in the plane of the mat. In both cases, measured axial thermal conductivity permits an evaluation of the axial elastic modulus. The Mathis surface probe used (US patent #5,795,064) is demonstrated as a non‐intrusive indirect method of obtaining thermal conductivity for heat flux parallel (i.e. axial or transverse) to the plane of a sample. The method shows potential for use as an in‐line monitoring device for the mechanical properties of molded composites.