bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrate phase equilibria of a near critical fluid: Effect of inhibition and separation
Authors: Østergaard Kasper K. , Tohidi Bahman , Burgass Rod W. , Danesh Ali , Todd Adrian C. 
Published: April 2004

AbstractThe hydrate phase boundary of a near critical fluid (NCF) was measured at 275–289 K in the presence of distilled water, synthetic formation water, and synthetic formation water with 10.41 wt. % methanol. The results agreed well with the predictions of an in‐house model, based on a cubic equation of state and statistical thermodynamics. To simulate a typical oil/gas production scenario, the NCF was flashed at 298.1 K and 17.189 MPa, and the resulting liquid was subsequently flashed at 298.0 K and 4.089 MPa. Hydrate free zones of the resulting liquid fractions were measured to investigate the physical separation effect on the hydrate phase boundary. The in‐house thermodynamic model was used to simulate the separators conditions and to predict the hydrate free zone of the resulting liquid and the vapor fractions. The predictions agreed closely with the experimental data, demonstrating reliability of the thermodynamic model. The results also showed that the hydrate phase boundaries of the vapor and liquid phases, which resulted from physical separation, are similar to that of the NCF.
Suspension polymerization of acrylamide in an oscillatory baffled reactor: From drops to particles
Authors: Ni X. , Johnstone J. C. , Symes K. C. , Grey B. D. , Bennett D. C. 
Published: April 2004

AbstractDroplet and particle‐size distribution of inverse phase suspension polymerization of acrylamide was studied in an oscillatory baffled reactor (OBR). A discretized population balance model developed estimates the coalescence droplet rate and the type of droplet interactions contributing to the coalescence process in the system. In an OBR, fluid mixing is achieved by eddies generated when a set of prespecified orifice baffles moves periodically through liquid. These vortices can be controlled by a combination of geometrical and operational parameters, such as orifice diameter, baffle spacing, oscillation frequency, and oscillation amplitude. This type of mixing, combining with a close‐to‐constant level of turbulence intensity in the reactor, has led to a high degree of controllability and repeatability for both droplet and particle size, and a fine particle level significantly lower than a conventional stirred‐tank reactor. Generic correlation is established linking the final bead size and Sauter mean droplet size with power dissipation.
Design for model parameter uncertainty using nonlinear confidence regions
Authors: Rooney William C. , Biegler Lorenz T. 
Published: April 2004

AbstractAn accurate method presented accounts for uncertain model parameters in nonlinear process optimization problems. The model representation is considered in terms of algebraic equations. Uncertain quantity parameters are often discretized into a number of finite values that are then used in multiperiod optimization problems. These discrete values usually range between some lower and upper bound that can be derived from individual confidence intervals. Frequently, more than one uncertain parameter is estimated at a time from a single set of experiments. Thus, using simple lower and upper bounds to describe these parameters may not be accurate, since it assumes the parameters are uncorrelated. In 1999 Rooney and Biegler showed the importance of including parameter correlation in design problems by using elliptical joint confidence regions to describe the correlation among the uncertain model parameters. In chemical engineering systems, however, the parameter estimation problem is often highly nonlinear, and the elliptical confidence regions derived from these problems may not be accurate enough to capture the actual model parameter uncertainty. In this work, the description of model parameter uncertainty is improved by using confidence regions derived from the likelihood ratio test. It captures the nonlinearities efficiently and accurately in the parameter estimation problem. Several examples solved show the importance of accurately capturing the actual model parameter uncertainty at the design stage.
Experimental study of gas‐induced liquid‐flow structures in bubble columns
Authors: Degaleesan S. , Dudukovic M. , Pan Y. 
Published: April 2004

AbstractThe computer‐automated radioactive‐particle tracking (CARPT) technique is used to investigate liquid recirculation and turbulence in bubble columns. Experiments are conducted in air–water bubble columns of different sizes, with various gas distributors, and operated over a range of superficial gas velocities. This study covers gas–liquid flows from the bubbly regime to the churn turbulent regime. The time‐averaged spatial flow structure, axial liquid velocity profiles, Reynolds shear stress, and turbulence intensities profiles are analyzed for different columns and flow conditions. Supplementary experiments, using the hot‐probe anemometry technique, are performed at selected flow conditions, and the results are compared with the corresponding ones from CARPT measurements. The Reynolds stress determined by CARPT was compared with that obtained by hot‐film anemometry in an independent investigation by Menzel et al. (1990).
Analysis of temperature and pressure fields in molten carbonate fuel cell stacks
Authors: Koh Joon‐Ho , Kang Byoung Sam , Lim Hee Chun 
Published: April 2004

AbstractA mathematical model based on fluid dynamics and heat‐transfer theories was applied to predict gas dynamic pressure and temperature distribution in a coflow molten carbonate fuel cell (MCFC) stack. The mass balance was simplified to obtain exact solutions with an assumption of uniform current density in the cell. The simulations were compared with data from a pilot‐scale MCFC stack. The effect of internal geometry of gas channels was simulated to accurately predict the gas‐pressure drop. A close prediction of pressure drop was possible from a partially blocked gas channel model that approximates the significant flow resistance. The effect of external boundary conditions on stack temperature profile was also analyzed. Temperatures were accurately predicted from a boundary heat conduction model with a reasonable assumption of wet seal temperatures. The 2‐D boundary conditions could be extended to 3‐D simulations to predict temperature distribution with the same accuracy. The model was applied to see the effect of scale‐up on the maximum temperature rise and average cell potential. The result verified a significant effect of cell size on the maximum stack temperature.
Tracer studies of high‐shear granulation: II. Population balance modeling
Authors: Hounslow M. J. , Pearson J. M. K. , Instone T. 
Published: April 2004

AbstractA population balance framework developed describes the tracer studies in Part I. A two internal coordinate population balance equation (PBE) links the evolution with time of granule‐size and tracer‐mass distributions to underlying rate processes. A new analytical PBE was developed for the tracer distribution and novel numerical techniques, including a new discretized population balance equation for breakage or grinding. Also developed is a general differential technique for extracting rate constants from measurements of particle‐size distributions. Granulation in a high‐shear mixer proceeds after nucleation, not studied here, with very high initial breakage rates but a relatively unchanging aggregation rate constant. The breakage function is bimodal on a mass basis and the selection rate decays exponentially over about 20 s. A heterogeneous strength hypothesis was used to account for this time dependence. Aggregation rates are the highest for interactions between small and large granules and may be quantitatively given by the Equipartition of kinetic energy kernel developed from the theory of collisions between gas molecules. The model can describe granule‐size and tracer‐mass distributions simultaneously with great accuracy. The need to replace time as a driving force variable in the kinetics for these systems is identified.
Local phase holdups in gas‐solids fluidization and transport
Authors: Bi Hsiaotao T. , Su Peng‐Cheng 
Published: April 2004

AbstractA two‐phase structural model consisting of a dense phase and a dilute phase with allowance for the dense‐phase expansion and the solids holdup in the dilute phase was developed and successfully applied to the analysis of local voidage fluctuation signals. Such a model can be used to derive local‐phase holdups and voidage in each phase in both bubbling/slugging/turbulent fluidized beds and circulating fluidized‐bed risers without ambiguity in defining criteria for dividing phases used by previous researchers. Such a model can also explain the existence of a maximum standard deviation at a local voidage around 0.7, and why a maximum peak is observed in the radial profiles of standard deviation of local voidage fluctuations in high‐velocity fluidized‐bed columns.
More fundamentals of dilute suspension collapse and choking for vertical conveying systems
Authors: Xu Guangwen , Nomura Kousuke , Gao Shiqiu , Kato Kunio 
Published: April 2004

AbstractUsing gas‐solid flows in circulating fluidized‐bed risers to analogize vertical pneumatic conveying systems, the collapse of dilute suspension, that is, the choking of accumulative type, was studied in three different risers with respect to different particles. The collapse of dilute suspension was dominated by an identical differential pressure drop over the measuring section. This differential pressure drop was independent of gas velocity and riser diameter, but varied with particle properties. The saturation carrying capacity, the solid flow rate at the dilute suspension collapse, was closely related to particle characteristics and riser diameter. With an increase in the riser diameter, it increased for lighter and smaller particles, but decreased for heavier and larger particles. Based on these experimental measurements, as well as the related literature reports, a correlation was developed for the saturation carrying capacity by analyzing its dependencies on gas velocity and riser diameter. More than 150 experimental data of the saturation carrying capacity available in the literature were compiled to evaluate the accuracy of the proposed correlation by comparing with 13 other literature correlations, demonstrating that this new method has the highest accuracy.
Disjunctive optimization design models for complex liquid–liquid multistage extractors
Authors: Reyes‐Labarta Juan A. , Grossmann Ignacio E. 
Published: April 2004

AbstractA new method for the optimal design of multicomponent liquid–liquid extraction processes using multistage countercurrent extractor systems is proposed. The method determines the optimum number of equilibrium stages and flow rates needed to obtain a specified product separation and recovery, and accounts for the possibility of side feed streams and product extractions. A superstructure is proposed that has embedded all potential configurations and interconnections. Based on this superstructure representation, the problem is formulated as an optimization problem using generalized disjunctive programming (GDP) to minimize the total cost of the process, subject to design specifications. The robustness and computational efficiency of the model is illustrated with different cases involving single and complex countercurrent cascades in a quaternary liquid–liquid system.
A new approach in the modeling of the critical heat flux and enhancement techniques
Authors: Sefiane Khellil 
Published: April 2004

AbstractUnderstanding of the boiling crisis mechanism is still incomplete; starting from experimental observations of the dry spots during boiling crisis, a new approach to bridge this gap is proposed. The thermal instabilities occurring at the triple contact lines where evaporation is intense are focused on. The “dry‐out” phenomenon is local; it depends on the local conditions at a very tiny evaporating meniscus adjacent to the heating surface. The enhancing role of EHD for CHF is studied through a stability analysis of the meniscus subjected to an electrical‐field. The equations describing the evaporating system are modified to account for the effect of electrical forces. We have found that the electrical‐field delays thermocapillary instability. Our analysis revealed that the onset of instability is very sensitive to the interface deformation.
Crystallization of para‐xylene in scraped‐surface crystallizers
Authors: Patience Daniel B. , Rawlings James B. , Mohameed Hazim A. 
Published: April 2004

AbstractCrystallization kinetics of para‐xylene in batch pilot‐scale scraped‐surface crystallizers were determined for commercial crystallization of a xylene mixture currently produced in Amoco plants. Dynamic mass and energy balances, coupled with the dynamic population balance, were used to model the scraped‐surface crystallizer. The model assumes that crystal nucleation occurs at the walls of the crystallizer and crystal growth occurs in the bulk. The parameters in the kinetic models were estimated from online measurements of bulk temperature and slurry transmittance. Concentration measurements show that the xylene mixture is always saturated (supersaturation is essentially zero) during all crystallization runs. Therefore, a reduced, two‐parameter, high growth rate model was developed to describe these crystallizers. The kinetic parameters were correlated highly for the reduced model. A new batch experiment with an alternative temperature profile was determined that removes the correlation and allows both parameters to be determined uniquely.
Design of integrated crystallization systems
Authors: Wibowo Christianto , Chang Wen‐Chi , Ng Ka M. 
Published: April 2004

AbstractA systematic procedure is developed for designing an integrated crystallization system by considering the interaction between crystallization and downstream processing. Potential problems related to unit operations such as filtration, washing, dewatering, recrystallization, and drying are anticipated and resolved by determining an operating policy and configuration for the crystallizer as well as the downstream units. The approach can be applied to both batch and continuous crystallizers. First, the possible impacts of particle‐size distribution (PSD) on the downstream processing units are identified. This forms the basis for determining a target PSD in the second step. Third, possible means by which the desired PSD can be achieved are selected. Fourth, the alternatives thus generated are evaluated and compared to identify the best design. Heuristics are provided along the way to guide the decision making. Shortcut equipment models are used to compare the performance of the alternatives. The procedure is illustrated with two industrial examples, including the production of adipic acid.
Model‐based control of batch chromatography
Authors: Dünnebier Guido , Engell Sebastian , Epping Achim , Hanisch Felix , Jupke Andreas , Klatt Karsten‐Ulrich , Schmidt‐Traub Henner 
Published: April 2004

AbstractIn the chemical industry, life science products are considered the most promising markets for the near future. Since pharmaceutical products, food, and fine chemicals are subject to increasingly more complex standards and stricter legal restrictions, efficient methods for the separation of thermally unstable products are needed. Chromatographic separations, for example, usually create the main costs of the overall production process. To realize the full potential of the chromatographic separation, the desired product quality has to be maintained, while operating the process at the economic optimum by reliable and efficient process monitoring and control. For control of batch chromatography, model parameters were estimated and operating parameters were optimized online. The concept has been tested on a laboratory‐scale column with an industrial process control system. Experimental results for a sugar separation are given.
Theoretical account of a dry sorption injection experiment
Authors: Allen R. W. K. , Archer E. D. , MacInnes J. M. 
Published: April 2004

AbstractA theoretical representation of adsorption by particles injected into a gas stream that was developed previously is used to assess results from a dry sorption injection experiment. The particle‐size distribution is required in the theoretical model, and this distribution is measured for the experimental particles. The pore‐size distribution is also measured and used to determine particle properties, including the effective diffusivity in the pore passages within the particles, which is required by the model. Comparison of the model and experiment establishes the crucial importance of accurate knowledge of the equilibrium relation for the actual adsorbate–adsorbent system considered and of a reliable representation of particle size and shape.
Coupled model of concentration polarization and pore transport in crossflow nanofiltration
Authors: Bhattacharjee Subir , Chen Jim C. , Elimelech Menachem 
Published: April 2004

AbstractA coupled model of concentration polarization and pore transport of multicomponent salt mixtures in crossflow nanofiltration rigorously predicts local variations of ionic concentrations, flux and individual ion rejections along a rectangular crossflow filtration channel by a coupled solution of the convective‐diffusion and extended Nernst‐Planck equations. Coupling the pore transport model with the multicomponent convective‐diffusion equation in the concentration polarization layer provides a comprehensive understanding of the interplay between concentration polarization and salt rejection. The coupled model is used to predict the local variations of ion rejection, permeate flux and mixture composition in a rectangular crossflow filtration channel for three‐component salt mixtures. The total membrane surface concentration of the ions and the ratio of different ions in the mixture (salt ratio) can change considerably along a crossflow filtration channel, and, consequently, cause remarkable variations in intrinsic ion rejections with axial position in the channel.
Effect of pore structure, randomness and size on effective mass diffusivity
Authors: Mezedur Minas M. , Kaviany Massoud , Moore Wayne 
Published: April 2004

AbstractThe effective mass diffusivity 〈 Dm 〉 of large specific surface area catalytic porous coatings is analyzed using 2‐D network models of connecting arms and verified experimentally for a multiple pore length scale coating layer. The network model includes effects of variation in the lattice randomness (Voronoi tessellation in the form of Delaunay lattice triangulation), pore coordination number, pore size (Knudsen effect), and pore‐size distribution on the predicted 〈 Dm 〉. The effect of pore poisoning, resulting in a pore blockage, is analyzed. Correlations for the porosity and pore‐blockage dependency of 〈 Dm 〉, as well as relationships for the pore size (low‐dimensionality) and multiple pore length scale effects, are also discussed. An experiment performed on a catalytic converter washcoat segment (represented by three pore length scales) placed on an otherwise impermeable wall of an electrochemical sensor shows a good agreement with the predicted 〈 Dm 〉 based on a multiple pore length scale medium with parallel diffusion paths.
Steady‐state and decay dynamics for impellers of varying aspect ratio in unbaffled tanks
Authors: Maynes D. , Butcher M. 
Published: April 2004

AbstractHydrodynamic torque measurements on impellers of square cross section were conducted for 33 different impellers in 3 different cylindrical unbaffled tanks. The tanks differed in volume by two orders of magnitude, and the Reynolds number range of the data was 104–105. A wide range of impeller sizes and aspect ratios was investigated, focusing on the decay regime where the tank walls impacted the torque measurement, and the steady state where the torque is constant on average. The number of revolutions required for spin‐up to steady state is a function of the tank radius and height and the impeller radius and height, and an expression is presented that describes the spin‐up time in terms of these variables and is valid for all of the data. At steady state and for a Reynolds number of 105, the torque coefficient or power number depended primarily on the height of the impeller and tank, but not on the impeller radius. During the decay regime, the measured torque coefficient decreases with a power‐law relation and is proportional to the number of revolutions raised to the k power. The k value did not depend on the height of the tank, but only on the impeller radius, impeller height, and tank radius. Expressions relating the steady‐state torque coefficient and the decay exponent, k, to the geometric variables model all of the data quite well. With these relations, the effects of the varying impeller aspect ratios on the energy required for mixing of momentum, and on the time required for mixing to occur, can be quantified.
Dispersive granular flow in a horizontal drum stirred by a single blade
Authors: Laurent B. F. C. , Bridgwater J. 
Published: April 2004

AbstractTo understand the detailed processes occurring in stirred systems for particulate materials, experiments were conducted in a horizontal cylindrical mixer, 270 mm dia. and 650 mm long. It was stirred by a single long flat blade, varying the level of fill between 20 and 70% and the agitator speed between 20 and 45 rpm. The dispersion of blobs in three regions—in the transaxial plane near the wall, in the path of the blade, and in the bulk—suggested two classes of behavior. The dispersive behavior of particles was characterized by axial dispersion coefficients and root mean‐square radial displacements, parameters commonly useful for process design. Both parameters showed that powder flow was independent of blade speed and controlled by the number of blade passes. Agitation was nonuniform in the transaxial plane with two regions of enhanced axial and radial displacement. These occurred near the free surface and immediately beneath the region where the blade arm was horizontal so that material readily slides off the blade. The axial dispersion coefficient was a maximum at a fill level of 40%, contributing effects arising from the free surface area of the bed and the conveying capacity of the blade.
Constrained process monitoring: Moving‐horizon approach
Authors: Rao Christopher V. , Rawlings James B. 
Published: April 2004

AbstractMoving‐horizon estimation (MHE) is an optimization‐based strategy for process monitoring and state estimation. One may view MHE as an extension for Kalman filtering for constrained and nonlinear processes. MHE, therefore, subsumes both Kalman and extended Kalman filtering. In addition, MHE allows one to include constraints in the estimation problem. One can significantly improve the quality of state estimates for certain problems by incorporating prior knowledge in the form of inequality constraints. Inequality constraints provide a flexible tool for complementing process knowledge. One also may use inequality constraints as a strategy for model simplification. The ability to include constraints and nonlinear dynamics is what distinguishes MHE from other estimation strategies. Both the practical and theoretical issues related to MHE are discussed. Using a series of example monitoring problems, the practical advantages of MHE are illustrated by demonstrating how the addition of constraints can improve and simplify the process monitoring problem.