bluuebunny/crossref_metadata_2025 huggingface dataset:
Cognitive Function Is Disrupted by Both Hypo- and Hyperglycemia in School-AgedChildren With Type 1 Diabetes: A Field Study
Authors: Gonder-Frederick Linda A. , Zrebiec John F. , Bauchowitz Andrea U. , Ritterband LeeM. , Magee Joshua C. , Cox Daniel J. , Clarke William L.
Published: March 2009

OBJECTIVE

We developed a field procedure using personal digital assistant (PDA) technology to test the hypothesis that naturally occurring episodes of hypo- and hyperglycemia are associated with deterioration in cognitive function in children with type 1 diabetes.

RESEARCH DESIGN AND METHODS

A total of 61 children aged 6–11 years with type 1 diabetes received a PDA programmed with two brief cognitive tests (mental math and choice reaction time), which they completed just before home glucose readings. The computer recorded time to complete each test and number of correct responses. Children completed several trials per day over 4–6 weeks for a total of 70 trials. Performance variables were compared across glucose ranges. Individual impairment scores (IISs) were also computed for each child by calculating the SD between performance during euglycemia and that during glucose extremes.

RESULTS

Time to complete both mental math and reaction time was significantly longer during hypoglycemia. During hyperglycemia, time to complete math was significantly longer and reaction time was marginally significant (P = 0.053). There were no differences on task accuracy. Decline in mental math performance was equivalent at glucose levels <3.0 and >22.2 mmol/l. IISs varied greatly across children, with no age or sex differences.

CONCLUSIONS

A decrease in mental efficiency occurs with naturally occurring hypo- and hyperglycemic glucose fluctuations in children with type 1 diabetes, and this effect can be detected with a field procedure using PDA technology. With blood glucose levels >22.2 mmol/l, cognitive deterioration equals that associated with significant hypoglycemia.
Produkteigenschaften und Verfahrenstechnik am Beispiel der Aromen
Authors: Uhlemann J. , Reiß I.
Published: March 2009

Formulierungsverfahren gewinnen in den letzten Jahren eine immer größere Bedeutung für den Produktdesign von Aromen. War klassischerweise der Fokus des Flavoristen und der ihn unterstützenden chemischen Fachabteilungen auf der chemischen Zusammensetzung der meist flüssigen Aromen, so haben heute trockene Formulierungen und technologisch beeinflussbare Produkteigenschaften wie Haltbarkeit und kontrollierte Freisetzung ein ähnlich großes Gewicht. Für die gezielte technologische Beeinflussung von Produkteigenschaften ist die genaue Kenntnis der physiko‐chemischen Eigenschaften von Aroma‐ und Trägerstoffen von Bedeutung. Nach einer einleitenden Darstellung und Eingrenzung des Fachgebietes wird insbesondere auf neuere Fortschritte in der Verfahrenstechnik der Mikroverkapselung von Aromen und vertieft auf eigene Arbeiten zu den Verfahren Sprühtrocknung, Sprühgranulation, Extrusion, Mehrstoff‐Düsenverfahren eingegangen.
Correlation of mist‐to‐annular transition during condensation
Authors: Soliman H. M.
Published: March 2009

A theory is proposed for correlating the mist‐annular transition during condensation based on a balance between destructive and stabilizing forces acting on the liquid film. The resulting correlation is shown to be capable of good agreement with a data base corresponding to a wide range of fluid properties and tube diameters. A fair deal of generality is demonstrated by testing the correlation outside the range from which it was developed.
Hydrodynamic characteristics of jet‐spouted beds
Authors: Markowski A. , Kaminski W.
Published: March 2009

Jet‐spouted beds characterised by high velocity gas jets (above 1.7 Umsl), and shallow bed depths H0 of around 2 D1 were investigated on laboratory scale beds and industrial scale beds and the results obtained thereof are correlated and presented in this work. Compared with the classical spouted beds, important differences in bed structure, solid movements and basic hydrodynamic characteristics were observed. The minimum spouting velocity, bed voidage and pressure drop during stabilized spouting are described in terms of dimensionless equations. Bed expansion was used as the basis for the classification of different jet‐spouting regimes (incoherent spouting, fast spouting, pneumatic conveying) and changes in the slope of the bed expansion curve are correlated with regime changes. This classification could be useful in the optimization of industrial scale jet‐spouted beds. A typically applicable regime of fast spouting was identified.
Drying characteristics of a draft tube spouted bed
Authors: Khoe G. K. , Van Brakel J.
Published: March 2009

Using the results of earlier work on the flow pattern of gas and solids in a draft‐tube spouted bed, the drying characteristics of such a spouted bed are discussed. Paddy (unpeeled rice) was dried in a 30 cm bed with a 5.5 cm draft tube and temperatures and moisture content of solid and gas phase were measured as a function of drying time at various points in the system. It appears that the (constant) drying rate is determined by the heat transfer in the recirculation zone (just above the air inlet) and in the draft tube. After the short and rapid heating in the tube, the temperature and moisture gradients in the particle equilibrate in the annulus. It is concluded that a draft‐tube spouted bed is a promising dryer design for heat‐sensitive particles with slow intra‐particle mass transfer coefficients.
Laminar natural convection heat transfer from a slender vertical cone to a power‐law fluid
Authors: Shenoy A. V.
Published: March 2009

A theoretical analysis of laminar natural convection heat transfer from a slender vertical cone to a power‐law fluid has been done by the approximate integral method. Assuming unequal thermal and momentum boundary layer thicknesses, and using the appropriate boundary and compatibility conditions, a “similar” solution of the boundary layer equations has been obtained for high Prandtl numbers. Due to lack of experimental data for power‐law fluids, a comparison of the predictions of the present analysis has been done with the experimental data available for Newtonian fluids and good agreement has been found.
The production of the antibiotic patulin in a three phase fluidized bed reactor: II. Longevity of the biocatalyst
Authors: Berk Dimitrios , Behie Leo A. , Jones Alan , Lesser Barry H. , Maurice Gaucher G.
Published: March 2009

The longevity of the enzyme system for the production of the antibiotic patulin by immobilized Penicillium urticae cells was studied in a three phase fluidized bed reactor. Calculation of the global rate of patulin production indicated that, if the cells were not allowed to grow, the production of patulin gradually declined and stopped at 320 h. Intermittent pulse additions of nutrients stimulated the slow growth of the cells and resulted in an extended production time of 525 h. This long term production was the result of the formation of new cells rather than the maintenance of the original ones.
Model discrimination: Posterior probabilities
Authors: Dunne Adrian , Lacey Laurence
Published: March 2009

Expressions were derived for the computation of regression model posterior probabilities under a number of assumptions regarding the form of the uniform parameter prior probability density function. It was demonstrated that some of these forms may lead to a bias in the model posterior probabilities. The variance known and unknown situations were considered under both homoscedastic and heteroscedastic conditions. Bias of the model posterior probabilities may partly explain the unstable behaviour reported by previous workers.
Visualization of flow patterns in axial flow between horizontal coaxial rotating cylinders
Authors: Gu Z. H. , Fahidy T. Z.
Published: March 2009

The structure of Taylor vortices in the annulus of coaxial horizontal rotating cylinders with and without axial flow was studied by a flow visualization technique based on the colour change of analytical indicators. Flow interaction effects can be characterized by three parameters whose numerical values are obtained from photographs and super 8 mm film strips.
Influence of forced cycling on the fischer‐tropsch synthesis part III. A model for forced concentration cycling over promoted iron catalyst
Authors: Feimer J. L. , Hudgins R. R. , Silveston P. L.
Published: March 2009

A model has been developed for the forced feed concentration cycling of a Fischer‐Tropsch synthesis reactor containing an iron catalyst promoted with potassium and copper. It was based on an initiation sequence proposed by Vannice (1975) for methanation, a propagation sequence using the CO‐insertion mechanism, and termination step based on the desorption of each n‐mer, including CH4. Only surface adsorption, surface reaction and desorption steps were considered; no storage in the catalyst bulk was assumed.

Agreement of the model and experimental results permits interpretation of steady‐state, as well as the cycling and step‐change rate measurements. The model shows that hydrogen is involved in the rate determining step, and further that, except for methane, the results of hydrocarbon production from steady‐state, step‐change, and periodic experiments could all be reconciled for the results from C2 to C9. Failure of the model properly to predict rates of methane formation during cycling operation is attributed to changing carbidization of the catalyst.
A new analysis of the turbulent flow of non‐newtonian fluids
Authors: Wilson Kenneth C. , Thomas Allan D.
Published: March 2009

A new analysis has been developed for the turbulent flow of non‐Newtonian fluids. Based on enhanced viscosity effects at the small time and length scales of the dissipative micro‐eddies, the analysis predicts a thickening of the viscous sub‐layer tending to increase throughput velocity and thus promoting drag reduction. The required flow parameters can be determined directly from rheograms, without employing correlations based on pipe‐flow data. The results give good descriptions of flows of fluids with both power‐law and Bingham behaviour and explain a number of peculiarities of such flows.
Gas composition and temperature profiles in a spouted bed coal gasifier
Authors: Haji‐Sulaiman Z. , Lim C. J. , Watkinson A. P.
Published: March 2009

Verification of scale‐up models of the spouted bed gasifier requires experimental gas composition and temperature profiles within the reactor. Radial and axial profiles are presented for key gaseous species in a 0.30‐m. dia, atmospheric pressure gasifier fed at about 30 kg coal/h. Low calorific value gases were generated at air/coal mass ratios of 2.87‐4.08, while medium calorific value gases were produced at an oxygen/coal mass ratio of 0.84 and steam/coal ratios of 2.23‐2.84. The combustion zone within the gasifier is delineated and the effects of operating conditions on gas composition and temperature profiles are illustrated for typical sub‐bituminous and bituminous coals. Recycle of char to the bed from the primary cyclone and bed depth show little effect on profile shape.
Modelling of culture kinetics and physiology for c. acetobutylicum
Authors: Yerushalmi L. , Volesky B. , Votruba J.
Published: March 2009

A mathematical model of the batch acetone‐butanol fermentation has been proposed which reflects the process kinetics and biochemistry. The degree of importance of the key kinetic parameters has been established by a parametric sensitivity analysis. The basic model was further extended by incorporating additional culture physiological parameters such as the number of active mass transport sites and the permeability of the cellular membrane as well as the intracellular and extracellular conditions. The model assisted in studying the role of the cellular membrane in the control of the culture performance and solvent biosynthesis. The theoretical predictions were confirmed by experimental results.
Experimental study of the inverse fluidized bed biofilm reactor
Authors: Nikolov L. , Karamanev D.
Published: March 2009

A new apparatus, the inverse fluidized bed biofilm reactor, is described. Introduction of the so called inverse fluidized bed, in which low density particles covered by a biofilm are fluidized by downflow of the liquid, allows control of the biofilm thickness and provides a high oxygen concentration in the reacting liquid. Characteristics of the reactor were studied by carrying out two important biotechnological processes: aerobic wastewater treatment by a mixed bacterial culture, and ferrous iron oxidation by the bacteria Thiobacillus ferrooxidans. The bioreaction rates per unit volume of the reactor were up to 14 times higher than those in the equivalent airlift bioreactor. The structure of the liquid flow was determined by a tracer method.
Predicting thermal conductivity of binary liquid mixtures on basis of coordination number
Authors: Tobitani Atsumi , Tanaka Tatsuo
Published: March 2009

By applying a model of a randomly mixed packing of spheres of two sizes to binary liquid mixtures, the thermal conductivity of the mixture is related to the physical properties of each component through the number of contact points. Further, two parameters are introduced to account for the effect of the hydrogen bond and are correlated with the Lennard‐Jones (6‐12) parameters σ and ϵ, or the boiling temperature. In comparing the calculated values with the experimental data for 13 aqueous liquids and 21 non‐aqueous liquid systems, the present equation turns out to be more accurate than previous ones.
Study of an air‐lift system. Part I: Hydrodynamics of the atara piston bubble cannon mixer
Authors: Grandjean B. P. A. , Ajersch F. , Carreau P. J. , Patterson I.
Published: March 2009

Hydrodynamic studies of the two‐phase flow of air‐water mixtures were carried out in an innovative air‐lift system called the “Atara Piston Bubble Cannon Mixer”. Slug and churn flows were observed in the discharge tube. The bubble velocity in the slug flow regime and the pressure drop were measured. Bubble entrance effects, found to affect the pressure drop particular to this configuration, are explained The air‐lift pump performance is analysed and a hydrodynamic model is developed to predict the pumping capacity as a function of the gas flow rate.
Design of vertical air classifiers for municipal solid waste
Authors: Biddulph Michael W.
Published: March 2009

A previously published diffusion‐based mathematical model is used to simulate data from two vertical air classifiers operating on shredded municipal solid waste streams. Good agreement with the model is achieved at high values of the air/solids ratio, that is, the region where interaction between solid particles would be expected to be insignificant. At lower values of the air/solids ratio the concept of a recovery efficiency is introduced to take account of interaction effects. This efficiency appears to show the expected dependence on air/solids ratio. A design method is proposed, based on feed particle size distribution and relationships between recoveries and product qualities.
Statistical assessment of a fluidized bed wood gasifier model
Authors: Wong L. A. , Bacon D. W. , Hsu C. C.
Published: March 2009

Sensitivity analyses were carried out to assess the behaviour of a fluidized bed wood gasifier simulation model in response to changes in the values of design variables, operating variables, and model coefficients. The model was originally developed using the modified Bubble Assemblage Model. Physical design specifications of the fluidized bed were found to have little influence on the quality of the product gas; in fact the composition of the gas was found to depend almost exclusively on the degree of approach to equilibrium. Overall thermal efficiency could be improved only by increasing the dry wood to oxygen ratio and reducing the moisture content in the wood feed. Because wood gasifiers produce volatiles that greatly enhance the chance of slugging, the influences of the design and operating variables on the occurrence of slugging were also investigated. The onset of slugging was found to be related most strongly to the dynamic bed height.
Control of a continuous polybutadiene polymerization reactor train
Authors: Kelly S. J. , Macgregor J. F. , Hoffman T. W.
Published: March 2009

An approach to controlling a continuous industrial polymerization reactor train for the production of stereoregular butadiene rubber based on the use of quality control laboratory data is presented. Empirical transfer function and disturbance models are identified directly from data collected from a designed experimental program carried out while the plant remained under operator control. The models are used to design minimum variance type control strategies for the monomer conversion and the Mooney viscosity of the final product. These controllers manipulate the flowrates of the Ziegler‐Natta catalyst components and a chemical transfer agent. The plant testing program, the development of the control strategy, and results from testing the control strategy in the plant are all described.
Effect of water on the solubilities and mass transfer coefficients of gases in a heavy fraction of fischer‐tropsch products
Authors: Karandikar B. M. , Morsi B. I. , Shah Y. T. , Carr N. L.
Published: March 2009

The effects of water on the solubilities, C*, and volumetric mass transfer coefficients, kLa, for CO, H2, CH4 and CO2 in a heavy fraction of Fischer‐Tropsch liquid were examined at elevated pressures and temperatures at different mixing power inputs. For these gases, higher solubilities were measured in the hydrocarbon mixture saturated with water than those obtained in the hydrocarbon free of water. The kLa values for the four gases were slightly affected by the presence of dissolved water in the hydrocarbon mixture; and they were strongly dependent on the power input per unit liquid volume. Two empirical correlations for kLa as a function of turbine speed and pressure are proposed.
Optimal design on an economic basis for continuous stirred tank reactors in series using michaelis‐menten kinetics for ping‐pong reactions
Authors: Xavier Malcata F.
Published: March 2009

A theoretical analysis of the reactant concentration profile along a given number of CSTR's in series for ping‐pong type reactions following Michaelis‐Menten kinetics (with equal initial concentrations for both substrates) has been developed. Minimising the total holding time was taken as the intermediate objective function whereas minimising the total capital investment was assumed to be the main objective function.
Characteristics of a countercurrent reciprocating plate bubble column. I. Holdup, pressure drop and bubble diameter
Authors: Rama Rao N. V. , Baird M. H. I.
Published: March 2009

The hydrodynamics of countercurrent air/water flow in a 5 cm diameter reciprocating plate bubble column have been studied; the plates contained 14 mm diameter perforations and had a fractional open area of 0.57. The ranges of superficial velocities of air and water were respectively 0‐0.99 cm/s and 0‐3.95 cm/s. The stroke was in most cases 4.5 cm and the reciprocation frequency was in the range 0–5 Hz.

The pressure drops were measured in the absence of reciprocation for single phase and two phase flow conditions. Pressure fluctuations and time‐averaged pressure drops were measured with plate reciprocation under single and two‐phase conditions. The results were described in terms of the simple quasi‐steady state model; the effective orifice coefficients of the perforations were within the range 0.4 to 0.97 depending on the reciprocation conditions.

The Sauter mean diameters of the bubbles decreased with agitation; they were about twice the values predicted from an earlier correlation developed for liquid‐liquid systems. The gas holdups were also substantially greater than predicted from correlations based on liquid‐liquid systems. Both these effects were explained as due to the tendency for bubbles to cluster in the plate region.
Characteristics of a countercurrent reciprocating plate bubble column. II. Axial mixing and mass transfer
Authors: Baird M. H. I. , Rama Rao N. V.
Published: March 2009

Oxygen absorption from air into water and axial dispersion in the aqueous phase have been measured in a 5 cm diameter reciprocating plate bubble column. The volumetric mass transfer coefficients in semi‐batch conditions were found to increase with agitation and were correlated with the specific power input and air flow rate. Under countercurrent conditions, it was found that axial mixing had little effect and conditions approached plug flow. The volumetric mass transfer coefficients were correlated with specific power input, air and water flow rates. Mass transfer coefficients were estimated using holdup and bubble diameter results. Comparison of the coefficients with the literature values indicated that the bubble surfaces were partially mobile.
Strategies for solving the chemical equilibrium problem and an efficient microcomputer‐based algorithm
Authors: Smith William R. , Missen R. W.
Published: March 2009

General strategies for solving the problem of computing the equilibrium composition of a multiphase, multispecies, chemically reacting system are discussed. An efficient new algorithm is presented based on these strategies, together with a microcomputer‐based implementation. Numerical examples show the algorithm's utility, and its advantages over other recently proposed methods in terns of a number of criteria, including speed and certainty of convergence. The range of problem types within the capability of the new algorithm, and its limitations are discussed.
Dispersive‐force modelling of turbulent suspension in heterogeneous slurry flow
Authors: Wilson K. C. , Pugh F. J.
Published: March 2009

The force‐balance model, originally developed for coarse‐particle slurries, has now been extended to slurries of finer particles susceptible to turbulent suspension. The analysis involves a turbulent dispersive force — an equivalent body force between the fluid and solid phases. The use of this force, together with the intergranular stresses for contact‐load particles, allows the calculation of concentration and velocity profiles which vary continuously with height. The calculated profiles are found to be in generally good agreement with experimental data from the Saskatchewan Research Council.
The inverse gaussian density function as applied to the ziegler‐natta catalysis in the oligomerization of ethylene to linear alpha‐olefins
Authors: Favis D. V.
Published: March 2009

Product distributions taken as a function of the number of ethylene molecules per olefin fraction fit adequately a mostly two parameter inverse Gaussian distribution with a χ2goodness of fit, statistical values ranging from 0.016 to 0.037 and levels of significance α, when applicable, ranging from 0 to 0.002. The examples included typical and modified Ziegler‐Natta catalytic systems. Limited data indicate a good applicability for non Ziegler‐Natta homogeneous or heterogeneous systems. Biased reactions showed poor, if any, applicability. A typical Ziegler ethylene growth to linear alpha‐olefins mole data gave a good fit on a three parameter inverse Gaussian distribution. On a speculative basis, the results indicate a common element of underlying mechanism of most of the examined syntheses, possibly associated with a first passage time process such as that found in Brownian motion.
Kinetic modelling of the pyrolysis of biomass and biomass components
Authors: Koufopanos C. A. , Lucchesi A. , Maschio G.
Published: March 2009

The kinetics of the pyrolysis of lignocellulosic materials was studied with a view of providing simple kinetic models for engineering purposes. Experimental data obtained by means of thermal analysis techniques suggest that the pyrolysis of fine particles (below 1 mm) can be considered to be controlled by pyrolysis kinetics. The rate of pyrolysis of one biomass type can be represented by the sum of the corresponding rates of the main biomass components (cellulose, lignin, hemicellulose). The kinetics of each of these components was simulated by a kinetic scheme capable of predicting the pyrolysis rate and the final weight‐loss for a wide range of pyrolysis parameters including various heating conditions.
Reactor development for the ultrapyrolysis process
Authors: Berg D. A. , Briens C. L. , Bergougnou M. A.
Published: March 2009

A new impinging‐jet reactor system has been developed for the fast pyrolysis (ultrapyrolysis) of particulate carbonaceous materials. The reactor system serves to promote rapid uniform mixing between a fine particulate heat carrier and a particulate feedstock in order to achieve the high heat transfer rates necessary for fast pyrolysis. Flow visualization experiments in a cold model testing unit indicated that the system performed effectively over a wide range of conditions. A sampling system utilizing isokinetic sampling probes was developed to investigate the small scale solids mixing. The effects of reactor geometry and operating conditions upon the solids mixing are reviewed.
Experimental laminar falling film heat transfer coefficients on a large diameter horizontal tube
Authors: Rogers J. T. , Goindi S. S.
Published: March 2009

A test rig was designed and fabricated to measure local heat transfer coefficients from a large‐diameter, steam‐heated horizontal tube to thin falling films of water. The results of the experiments generally support the theory developed by Rogers for laminar film conditions, which were found to persist up to film Reynolds numbers of about 2000. Agreement between theoretical predictions of heat transfer coefficients and the measured values is reasonable for the thermal boundary layer development region, but measured values are about 20% lower than predicted values in the developed region. The lower values in the developed region are attributed mainly to measured film thicknesses being greater than predicted values.
Laminar start‐up flow in short pipe lengths
Authors: Patience Gregory S. , Mehrotra Anil K.
Published: March 2009

A solution method is described for the start‐up flow of an incompressible Newtonian fluid in a short pipe. The complete Navier‐Stokes equations are solved numerically using a fragmented control volume method. The solution procedure involves a novel approach for accommodating the time‐dependent condition for pressure at the pipe inlet. It is shown that the start‐up time for short pipes is less than that for long pipes, due to kinetic head development and entrance region effects. Correlations are presented for estimating the start‐up time.
A study of bitumen recovery by gravity drainage using low temperature soluble gas injection
Authors: Dunn S. G. , Nenniger E. H. , Rajan V. S. V.
Published: March 2009

A gravity drainage concept has been proposed and tested for in‐situ recovery of bitumen by mobilization with soluble gases at ambient reservoir temperature conditions. Experiments were done using carbon dioxide and ethane gases at ∼ 20°C to recover Athabasca bitumen from a scaled reservoir model. Thermal gravity drainage theory has been modified for the mass transfer case. The measured drainage rates were higher than those predicted by the model using molecular diffusivity data but fit the model better using an increased effective diffusivity. Lateral dispersion theory does not predict the high measured effective diffusivities. A preliminary economic evaluation of field production indicates potential application to recovery of Lloydminster heavy oil.
A study of a simulated moving bed adsorber based on the axial dispersion model
Authors: Kubota Katsuyuki , Hata Chito , Hayashi Shinya
Published: March 2009

On the basis of the axial dispersion model, the concentration profiles for a simulated moving bed adsorber were theoretically predicted. Experimentally, an apparatus consisting of four sections was employed. Glucose and sorbitol were separated from the liquid dissolved with these components both co‐currently and counter‐currently. The experimental results seemed to support the predicted curves.
Rheology of oil in water emulsions with added solids
Authors: Pal Rajinder , Masliyah Jacob
Published: March 2009

The effect of added solids on the rheology of oil in water emulsions was investigated. The range of the oil concentration, solids free basis, was (0‐70%) and the solids volume fraction was (0‐0.16). The solids mean diameter was 45 μm and it was about four times larger than the oil droplets. In the absence of added solids, non‐Newtonian behaviour was observed for oil concentrations above 40%. The added solids increased the emulsion viscosity in a manner similar to the addition of solids to a homogeneous fluid.

The rheological data of all the emulsion‐solids mixtures investigated were correlated as relative viscosity versus solids volume fraction, where the relative viscosity is defined as the ratio of the emulsion‐solids mixture viscosity to the solids‐free emulsion viscosity. In the case of non‐Newtonian systems, the emulsion‐solids mixture viscosity and the solids‐free emulsion viscosity were calculated at the same shear stress. The Barnea and Mizrahi viscosity correlation was found to fit the data well.
Bubble size distribution in bubble columns
Authors: Saxena A. C. , Rao N. S. , Saxena S. C.
Published: March 2009

The bubble size distributions are measured for the air‐water system as a function of air velocity at room temperature in two bubble columns. High speed cinephotography and fiber optic probe techniques are used to measure the bubble size. Our limited measurements suggest that the bubble size may be independent of gas velocity in the range 3.6 to 9.2 cm/s and may be dependent on column diameter with smaller bubbles for narrower columns. The bubble size appears to be smaller at the column wall than at distances away from the wall.
Reaction kinetics over iron catalysts used for the fischer‐tropsch synthesis
Authors: Zimmerman William H. , Bukur Dragomir B.
Published: March 2009

The kinetics of the Fischer‐Tropsch (FT) and water‐gas shift (WGS) reactions were studied in a stirred tank slurry reactor, using a 100 Fe/0.3 Cu/0.2 K catalyst and a commercial catalyst, Ruhrchemie LP 33/81. The 100 Fe/0.3 Cu/0.2 K catalyst was more active than the Ruhrchemie catalyst for both reactions. FT kinetics which accounted for water inhibition was the best of the rate forms considered for the 100 Fe/0.3 Cu/0.2 K catalyst. First order in H2 kinetics was sufficient for the Ruhrchemie catalyst, probably due to the low conversions obtained during the test of this catalyst. WGS kinetics, which included product inhibition, were also studied for each catalyst.
Effect on surface charges of bubbles and fine particles on air flotation process
Authors: Okada Kenji , Akagi Yasuharu , Kogure Masahiko , Yoshioka Naoya
Published: March 2009

The adhesion of fine particles onto bubbles in flotation was studied on the basis of surface charge measurements of the bubbles and particles.

The surface charges of the bubbles were measured by the use of a micro‐electropheresis apparatus devised in our previous study and the mechanism of the bubble charging was studied under various experimental conditions. In distilled water, the bubbles were negatively charged and the iso‐electric point appeared at pH = 2.5. The surface charges of the bubbles in the surfactant solution were determined by the surfactant molecules adsorbed at the surface and depend strongly on the values of pH.

The flotation efficiency of latex particles (0.923 μm) was found to be strongly influenced by the surface charges of both the particles and the bubbles. The force between the particle and the bubble was estimated from the observation of the particle attachment to the bubble surface, and a simple equation including the effects of the hydrodynamic and surface charge interactions was proposed to determine the floatability limit.
Drop behaviour in a kühni column for a low interfacial tension system
Authors: Haunold Christophe , Cabassud Michel , Gourdon Christophe , Casamatta Gilbert
Published: March 2009

In order to simulate the hydrodynamics in a liquid‐liquid extraction column, a drop population model has been developed (Casamatta, 1981), taking into account the fundamental mechanisms: drop breakage, transport, and coalescence. Results of a set of experiments devoted to the description of drop breakage and transport in a Kuhni column stage are presented. A comparison between simulation results and experimental mean hold‐up and Sauter mean diameter data collected in a Kuhni column is finally undertaken, which leads to a study of the sensitivity of the model according to the transport and breakage parameters.
An evaluation of multiple binary interaction parameters in cubic equations of state
Authors: Trebble M. A.
Published: March 2009

Three cubic equations of state are utilized in regressing a large vapour‐liquid equilibrium data bank using single and multiple binary interaction parameters. A second binary interaction parameter is shown to be both physically significant and useful in improving the match of experimental data, particularly in polar systems. The use of a third binary interaction parameter in the Trebble‐Bishnoi equation of state is found to be of value in systems with large molecular size differences.
Recursive least squares based estimation schemes for self‐tuning control
Authors: Shah Sirish L. , Cluett William R.
Published: March 2009

Recursive Least Squares (RLS) is the most popular parametric identification method used for on‐line process model estimation and self‐tuning control. The basic least squares scheme is outlined in this paper and its lack of ability to track changing process parameters is illustrated and explained. Several variants of the basic algorithm which have appeared elsewhere in the literature are discussed. Some of these algorithms contain different modifications to the basic scheme which are intended to prevent this loss of alertness to changing process parameters. Other variations of the least squares algorithm are presented which attempt to deal with parameter estimation in the presence of disturbances and unmodelled process dynamics.
A two‐fluid model for non‐equilibrium two‐phase critical discharge
Authors: Schwellnus C. F. , Shoukri M.
Published: March 2009

A general two‐fluid model is developed to predict critical (choked) flow of initially saturated or subcooled flow from pipes and nozzles. The model contains improvements in the basic formulation, constitutive relations and solution technique over previously published models. It consists of six conservation equations as well as a seventh equation representing bubble growth in bubbly flow. It allows for hydrodynamic as well as thermal non‐equilibrium. The model considers the development of three flow regimes, namely, bubbly, churn and annular flow regimes. The model predictions were compared with the limited available experimental data for which the axial pressure distributions were recorded. Excellent agreement was obtained.
Polymer alloys and blends: Recent advances
Authors: Favis Basil D.
Published: March 2009

Polymer alloys and blends represent one of the fastest growing sectors of the plastics industry. To a large degree, the emphasis has now shifted from developing blends in the reactor to their creation through melt mixing on processing equipment such as extruders. As a result, intense activity is now being directed at controlling two particularly important considerations during melt processing: interfacial interactions and dispersed phase morphology. In this review, recent developments and trends in these two areas will be examined.
State estimation for continuous emulsion polymerization
Authors: Gagnon Louise , Macgregor J. F.
Published: March 2009

Various aspects of the use of extended Kalman Filters for tracking the states of continuous emulsion polymerization reactors are investigated. The importance of introducing meaningful nonstationary stochastic states to account for unknown impurities, initiator efficiencies, modelling errors, etc. is illustrated. The robustness of these state estimators to unmodelled and unmeasured disturbances, to modelling errors, and to input errors is evaluated. A procedure for selecting an optimal set of on‐line sensors is presented. The emulsion polymerization of styrene‐butadiene rubber (SBR) is used as the example system.
Equilibrium conditions for methane hydrate formation in aqueous mixed electrolyte solutions
Authors: Dholabhai P. D. , Englezos P. , Kalogerakis N. , Bishnoi P. R.
Published: March 2009

Equilibrium data on the formation of methane hydrate in six mixtures of NaCl and KCl, six mixtures of NaCl and CaCl2 and a mixture of eight electrolytes found in sea water were experimentally obtained. The ionic strength (in molality units) of the NaCl and KCl mixtures ranged from 0.97 to 4.72 and that of the NaCl and CaCl2 mixtures from 1.27 to 3.90. The experimental temperatures ranged from 264 to 284 K and the pressures from 2.5 to 9.7 MPa.

Equilibrium pressures predicted using a recently proposed method (Englezos and Bishnoi, 1988) have been compared with the data obtained and it was found that the predictions match the data very well. The standard errors for the mixtures of NaCl and KCl, NaCl and CaCl2 and the synthetic sea water were 5.54, 3.5 and 1.4%, respectively. The largest prediction error for an experimental data point was 10.1%.
Behaviour of absorption/stripping columns for the CO2‐MEA system; Modelling and experiments
Authors: Escobillana Germán P. , Saez Jorge A. , Pérez‐Correa José R. , Neuburg Heinz J. , Kershenbaum Lester S.
Published: March 2009

A model is presented for the steady‐state simulation of a CO2 recovery pilot plant with aqueous monoethanolamine (MEA) solutions. CO2 absorption is performed in a column packed with 2.54 cm ceramic Pall rings. CO2 recovery is achieved in a 20 sieve tray steam stripping column.

The packed column absorption model was fitted to the experimental data using the specific interfacial area of the irrigated packing as an adjustable parameter. The equivalent average bubble diameter was used as the adjusting parameter in the sieve tray stripping column.

Modelling of both towers reproduces within 3% average error concentrations measured in a pilot plant. Measured temperatures were also well correlated.
Homogeneous azeotropic distillation: Comparing entrainers
Authors: Laroche L. , Andersen H. W. , Morari M. , Bekiaris N.
Published: March 2009

In this article, we present practical solutions (in the case of entrainers which add no azeotropes) to two problems of industrial relevance: Given a binary azeotrope which we want to separate into pure components, and a set of candidate entrainers, how do we determine which one is the best? Also, for each of these entrainers, what is the flowsheet of the feasible separation sequence(s)? We obtain these solutions by analyzing in details the mechanisms by which heavy, intermediate and light entrainers make separation feasible, using the new notions of equivolatility curves, of isovolatility curves and of local volatility order. We show that the second question finds an easy solution from the volatility order diagram.

This analysis shows that a good entrainer is a component which “breaks” the azeotrope easily (i.e., even when its concentration is small) and yields high relative volatilities between the two azeotropic constituents. Because these attributes can be easily identified in an entrainer from the equivolatility curve diagram of the ternary mixture azeotropic component #1 — azeotropic component #2 — entrainer, we can easily compare entrainers by examining the corresponding equivolatility curve diagrams. Finally, we demonstrate the validity and limits of this method with examples.
Local drop size variation in an agitated vessel
Authors: Chriistodoulou Dimitrios , Stamatoudis Michael
Published: March 2009

The local droplet diameters were measured at two positions inside the circulation region of a stirred tank. The Sauter mean diameter near the top of the vessel was always 1.4 times greater than the one just outside the impeller region for rotational speeds of 250, 300, 350 and 400 rpm and for hold‐up fractions of 0.01, 0.025 and 0.05. The drop size distributions at a hold‐up fraction 0.01 had one mode for all impeller speeds studied and at both positions. At higher hold‐up fractions the distributions usually were bimodal.
Extraction of phenols: I. distribution of individual phenols between organic solvents and water or aqueous solvents
Authors: Bízek V. , Horáček J. , Procházka J.
Published: March 2009

The distribution of phenol and o‐cresol between water or aqueous solutions of sodium hydroxide and n‐heptane, toluene or methyl‐isobutyl‐ketone (MIBK) was investigated. A mathematical model of extraction was formulated and its parameters were estimated for each solute‐solvent pair.
The effect of pre‐wetting on dynamic contact angles
Authors: Ghannam M. T. , Esmail M. N.
Published: March 2009

A roll‐coating experimental system is used to study the effect of pre‐wetting on dynamic contact angles, the interfacial displacement depth, and the associated phenomenon of air entrainment. The system consists of a roll, which is horizontally rotating in a liquid pool. The dynamic contact angle is recorded by a macrophotography system. The test liquids are glycerol solutions with viscosities in the range 104 < μ < 748 mPa · s. The value of (μV/ρg)0.5 is taken as the characteristic length to be used in the dimensionless relationships which correlate experimental measurements. The effect of base layer entry angle into the liquid pool on the dynamic contact angles and other flow parameters is studied. Comparison is made with measurements in dry tape‐coating and other pre‐wet roll–coating systems.
Modelling of turbulent flow and mass transfer with wall function and low‐reynolds number closures
Authors: Neŝić S. , Adamopoulos G. , Postlethwaite J. , Bergstrom D. J.
Published: March 2009

A recent laser doppler anemometer study, by other researchers, of turbulent flow through a sudden expansion has been simulated using a kinetic energy of turbulence‐dissipation rate of turbulence (k ‐ ϵ) model. The near wall region was modelled in two different ways; using wall functions (WF), and a low‐Reynolds number (LRN) formulation.

The reattachment length under particular flow conditions was obtained. Radial profiles for the mean axial and radial velocity, turbulence kinetic energy and Reynolds shear stress were determined for six locations downstream of the sudden expansion. Both models performed reasonably well in predicting the flow with the LRN approach performing slightly better than the WF approach near to the wall.

The application of the LRN approach to the calculation of local mass transfer rates in wall bounded complex turbulent flows is demonstrated.
Slow non‐newtonian flow through packed beds: Effect of zero shear viscosity
Authors: Jaiswal A. K. , Sundararajan T. , Chhabra R. P.
Published: March 2009

The slow non‐Newtonian (inelastic) flow through packed beds of mono‐size spherical particles has been simulated by solving the equations of motion numerically. The inter‐particle interactions have been modelled by using a simple cell model. Theoretical estimates of pressure, friction and total drag coefficients as function of the pertinent physical (l≥n≥ 0.2; 0.3 ≤ e ≤ 0.5) and kinematic parameters (0.01 ≤ '≤ 100) for a fixed value of Reynolds number {Re = 0.001) have been obtained. The theoretical predictions reported herein have been validated using the suitable experimental results available in the literature, and the importance of including the zero shear viscosity in analyses for the creeping flow problems is convincingly demonstrated.
Coking threshold in hydroprocessing of asphaltenic oils
Authors: Kriz J. F.
Published: March 2009

The coking propensity of asphaltenic oils is quantitatively described using experimentally determined threshold values for temperature and hydrogen pressure. Results using this method are compared with more conventional information based on solubility properties. The threshold values are shown to be more pertinent for quantitative analyses. A model exponential function based on a simple mechanistic consideration is fitted through experimental points and used to explain curve patterns.
Global optimization of the bifunctional catalyst problem
Authors: Luus Rein , Bojkov Bojan
Published: March 2009

As shown by Luus et al. (1992), determination of the optimum catalyst blend along a tubular reactor to maximize the yield of a particular component is a difficult problem due to the large number of local optima. By using iterative dynamic programming, the effects of the region reduction factor and the choice of the initial region size are analyzed in detail for this problem. Even if a single grid‐point for the state is used, the likelihood of obtaining the global optimum is very high if the initial region size is chosen to be sufficiently large.
Modeling of the 3D hydrodynamics of 2‐blade impellers in stirred tanks filled with a highly viscous fluid
Authors: Abld Mohammed , Xuereb Catherine , Bertrand Joël
Published: March 2009

This paper deals with mixing in stirred tank reactors by paddle agitators and two‐blade impellers with different blade widths. Computational Fluid Dynamics (CFD) is used to solve the 3D hydrodynamics and to obtain at every point the flow patterns, the stress components and the viscous dissipation function. From the latter information, the power consumption is calculated. These results are compared with available experimental data: good agreement is observed. For example, for a paddle agitator, the flow is essentially plane far away from the horizontal walls. That means that, in order to create an axial circulation in the volume of the tank, the impeller height has to be decreased.

This work documents the ability of CFD to model changes in flow patterns for three dimensional flows in stirred tanks.
Thermal diffusion in inclined flat‐plate columns of the frazier scheme
Authors: Yeh Ho‐Ming
Published: March 2009

The separation theory of thermal diffusion in inclined flat‐plate columns of the Frazier scheme has been developed and investigated. The equations for the best angle of inclination and maximum separation have been derived. Considerable improvement in separation is obtained when thermal diffusion columns are operated at the best angle of inclination.
Viscosity: A critical review of practical predictive and correlative methods
Authors: Monnery Wayne D. , Svrcek William Y. , Mehrotra Anil K.
Published: March 2009

This paper reviews methods for the prediction and correlation of Newtonian viscosity for pure components and mixtures of dilute gases, dense gases and liquids, focussing on those which are suited for practical engineering use. The methods reviewed were chosen because they are well known and accepted or appear potentially promising. They are categorized as theoretical, semi‐theoretical or empirical and further distinguished as predictive or correlative.

Brief derivations with relevant equations and discussions on limitations and reliability of results are presented. In addition, the applicability and average deviations for each method are tabulated, with the recommended methods clearly stated. Furthermore, some gaps in viscosity prediction/correlation are identified and promising approaches are discussed.
Heat‐Transfer analysis for quenched impact test specimens of polymers
Authors: Bui V. T. , Liu T. M.
Published: March 2009

An approximate but simple method for the low temperature mechanical testing of polymers is frequently used. It consists of quenching the polymer sample into liquid nitrogen and then installing it on the testing apparatus. The required test temperature is determined by the time where the experiment is started. In this work, the time‐temperature patterns of two quenched impact test samples, in high density polyethylene and polyurethane, were first measured and then compared with the values obtained from a graphical method of unsteady‐state heat conduction. The agreement between experimental data and calculated values is better than 8% in terms of relative error.