bluuebunny/crossref_metadata_2025_split huggingface dataset:
Subspace approach to multidimensional fault identification and reconstruction
Authors: Dunia Ricardo , Joe Qin S. 
Published: April 2004

AbstractFault detection and process monitoring using principal‐component analysis (PCA) and partial least squares were studied intensively and applied to industrial processes. The fundamental issues of detectability, reconstructability, and isolatability for multidimensional faults are studied. PCA is used to define an orthogonal partition of the measurement space into two orthogonal subspaces, a principal‐component subspace, and a residual subspace. Each multidimensional fault is also described by a subspace on which the fault displacement occurs. Fault reconstruction leads to fault identification and consists of finding a new vector in the fault subspace with minimum distance to the principal‐component subspace. The unreconstructed variance is proposed to measure the reliability of the reconstruction procedure and determine the PCA model for best reconstruction. Based on the fault subspace, fault magnitude, and the squared prediction error, necessary and sufficient conditions are provided to determine if the faults are detectable, reconstructable, and isolatable.
Structured approach to storage allocation for improved process controllability
Authors: Kelly J. D. , Forbes J. F. 
Published: April 2004

AbstractAn optimization‐based approach is presented that determines how plant feedstocks should be allocated to storage when there are fewer storage vessels than feedstocks. It is assumed here that material from the storage vessels will be subsequently blended for processing in downstream processes. The objective of the feedstock allocation strategy is chosen to ensure maximum flexibility for downstream process operation. Given the stated objective for feedstock allocation and the physical constraints, the feedstock storage allocation problem is posed in optimization form. The solution of the resulting singular‐value optimization problem is discussed in terms of semidefinite programming techniques. The ideas presented are illustrated using a crude‐oil storage case study. Finally, a number of observations regarding useful extehsions to the proposed methods are presented.
Boiling‐slurry reactor: Feasible operation and stability
Authors: Khinast J. , Luss D. , Leib T. M. , Harold M. P. 
Published: April 2004

AbstractIn this study the feasible operation and stability of a special boiling‐slurry reactor (BSR), in which a single exothermic chemical reaction occurs, are determined. Its feed consists of a nonvolatile liquid reactant dissolved in an inert solvent and gaseous reactants, while the effluent consists only of gaseous components. The BSR attains a unique steady state within a bounded range of operating conditions, the boundaries of which are defined by simple algebraic expressions. While the unique steady states are usually locally stable, they are not always globally stable. For example, when the start‐up temperature is too low, the reactor may not reach the steady state and instead reach a “fill‐up” state. In that state the liquid volume continuously increases, while the concentrations and temperature remain essentially constant. For some sets of start‐up temperatures two distinct fill‐up states may exist. When the start‐up liquid volume and temperature are very high, a “dry‐up” state may exist so that the liquid continuously decreases, while the reactor temperature and concentration remain essentially constant. This state eventually will shift the reactor to the unique steady state. Dry‐up, fill‐up, and a steady state coexist in some parts of the feasible operation region, thus requiring a special start‐up procedure. The BSR may exhibit sustained oscillations for some parameter sets.
Fischer‐tropsch synthesis in near‐critical n‐hexane: Pressure‐tuning effects
Authors: Bochniak David J. , Subramaniam Bala 
Published: April 2004

AbstractFor Fe‐catalyzed FischerTropsch (FT) synthesis with near‐critical n‐hexane (Pc, = 29.7 bar; Tc, = 233.7°C) as the reaction medium, isothermal pressure tuning from 1.2–2.4 Pc, (for n‐hexane) at the reaction temperature (240°C) significantly changes syngas conversion and product selectivity. For fixed feed rates of syngas (H2/C0 = 0.5; 50 std. cm3/g catalyst) and n‐hexane (1 mL/min), syngas conversion attains a steady state at all pressures, increasing roughly threefold in this pressure range. Effective rate constants, estimated assuming a first‐order dependence of syngas conversion on hydrogen, reveal that the catalyst effectiveness increases with pressure implying the alleviation of pore‐diffusion limitations. Pore accessibilities increase at higher pressures because the extraction of heavier hydrocarbons from the catalyst pores is enhanced by the liquid‐like densities, yet better‐than‐liquid transport properties, of n‐hexane. This explanation is consistent with the single α ( =0.78) Anderson‐Schulz‐Flory product distribution, the constant chain termination probability, and the higher primary product (1 ‐olefin) selectivities ( ∼ 80%) observed at the higher pressures. Our results indicate that the pressure tunability of the density and transport properties of near‐critical reaction media offers a powerful tool to optimize catalyst activity and product selectivity during FT reactions on supported catalysts.
Synthesis and characterization of oriented MFI membranes prepared by secondary growth
Authors: Lovallo Mark C. , Gouzinis Anastasios , Tsapatsis Michael 
Published: April 2004

AbstractMFI membranes were prepared as free‐standing and supported films on porous alumina disks and nonporous substrates. They were synthesized using secondary growth of precursor layers. For self‐supported films the first step was to prepare an alumina–silicalite composite film, while for supported films the substrate was first coated with layers of the nanocrystalline silicalite particles. During the following hydrothermal treatment, silicalite particles acting as seed crystals form a dense film, which consists of 0.5–100‐μm‐thick columnar, intergrown, preferentially oriented grains. The crystal orientation of the MFI films was examined using X‐ray diffraction pole‐figure texture analysis. The crystals were preferentially oriented with both sinusoidal and straight channel networks along directions nearly parallel to the membrane surface. The degree of orientation increased with increasing membrane thickness. Single gas permeances through thin, oriented membranes were measured. Apparent actiuation energies for permeation were 16, 24, 30, 22 and 26 kj/mol for H2, N2, O2, CH4, and CO2, respectively. Ideal selectivities for H2/N2, CO2/CH4, and O2/N2 were as high as 30, 10, and 3.5, respectively. Binary permeation measurements for the gas pairs CO2/CH4, O2/N2, and CO2/N2 revealed trends similar to those of single gas permeation and the properties are attributed to the membrane microstructure.
Theory of batchwise centrifugal casting
Authors: Maarten Biesheuvel P. , Nijmeijer Arian , Verweij Henk 
Published: April 2004

AbstractIn batchwise centrifugal casting a cylindrical mold is filled with suspension and rotated rapidly around its axis. This results in the movement of the particulate phase toward the cylinder wall and the formation of a tubular cast. Theory is presented for particle transport in the suspension phase and subsequent cast growth using concepts from the related fields of centrifugal sedimentation and centrifugal separation. Most attention is given to the situation of complete mold filling, which allows for several distinct simplifications. Analytical expressions for suspension concentration and cast growth are presented for the case of unhindered settling. Numerical simulations are made for hindered settling. The outcome shows a good agreement with experiments in which homogeneous porous ceramic membrane supports are made from a submicronsized α‐alumina powder.
Random motility of swimming bacteria in restricted geometries
Authors: Biondi Sherri A. , Quinn John A. , Goldfine Howard 
Published: April 2004

AbstractThe effects of restricted geometries on the swimming behavior of Escherichia coli were examined. Videomicroscopy and image analysis techniques were used to measure single‐cell motility parameters (cell velocity, tumbling probability, and turn angle) in microfabricated 2‐D channels ranging from 2 to 20 μm in height. Macroscopic motility coefficients were calculated from the single‐cell data and compared to literature values. These observations indicate that single‐cell parameters remain nearly constant in confined spaces in which channel heights approach the size of the bacterium. The nearly constant swimming behavior of individual cells in confined geometries indicates that the macroscopic motility coefficient describing population behavior will be greater than the unrestricted value by a factor proportional to the dimensionality of the system.
Influence of transport and reaction on wormhole formation in porous media
Authors: Fredd Christopher N. , Fogler H. Scott 
Published: April 2004

AbstractThe transport and reaction of fluids in porous media results in unique pore growth and channel evolution as the media are dissolved. This often leads to the formation of highly conductive flow channels, commonly referred to as wormholes. The objective of this work is to predict the influence of transport and reaction on the structure of the wormhole channels. An experimental and theoretical investigation of a variety of fluid systems, including strong acids, weak acids, and chelating agents, provides a wide range of conditions for studying wormhole formation. A generalized description of the dissolution phenomenon is introduced, and a common dependence on the Damköhler number is demonstrated. The Damköhler number is shown to dictate the type of wormhole structure formed by systems with various degrees of transport and reaction limitations. An optimum Damköhler number for channel formation is observed at a value of approximately 0.29 for all of the fluid systems investigated. The stochastic nature of the dissolution phenomenon is described using network models. Results from a 2‐D network model and a 3‐D physically representative network model agree qualitatively with experimental results and substantiate the existence of an optimum Damköhler number.
Mechanisms by which pulsatile flow affects cross‐flow microfiltration
Authors: Li Hong‐yu , Bertram Christopher D. , Wiley Dianne E. 
Published: April 2004

AbstractThe effect of pulsatile flow on particle deposition during cross‐flow microfiltration was studied to establish the degree to which backflushing and shear‐rate changes induced during pulsation alter cake formation. The minimum transmembrane pressure and maximum absolute cross‐flow velocity derivative were chosen to quantify the backflushing and shear effects, respectively. Experiments were conducted for pulsatile flows with four distinct types of transmembrane pressure and flow‐rate waveforms. In the absence of backflushing the cake resistance was reduced at high values of shear rate, but not significantly affected at low values compared with steady flow. Tests at constant shear rate demonstrated that the cake resistance was reduced when backflushing was imposed on the system. In tests with two transmembrane pressure waveforms, cake deposition was almost completely eliminated by instantaneous backflushing. Although both backflushing and shear‐rate changes reduce cake deposition in microfiltration, backflushing achieved the greatest reductions.
Hydrogen purification from refinery fuel gas by pressure swing adsorption
Authors: Malek A. , Farooq S. 
Published: April 2004

AbstractHydrogen purification and recovery from various process streams constitutes the largest commercial use of pressure swing adsorption (PSA) technology. This study investigates the performance of a six‐bed, dual‐sorbent PSA operation for hydrogen purification from the refinery fuel gas. Major impurities are methane, ethane, propane and butane, and comprise 30–40% of the feed. The dual‐sorbent PSA bed consists of an initial layer of silica gel adsorbent for trapping heavier hydrocarbons and a subsequent layer of activated carbon for removing lighter hydrocarbons. A numerical simulation model of the H2‐PSA process developed with all the essential features of the actual operation shows that butane is more strongly adsorbed on activated carbon than silica gel, and, hence, is less easily desorbed from the former using simple pressure reduction in the PSA cycle. Therefore, the initial layer serves to prevent butane from degrading the adsorptive capacity provided by activated carbon for other lighter hydrocarbons. The simulation model agrees well with the experimental results from a laboratory unit as well as with available H2 ‐PSA plant data from a refinery. The results also indicate the importance of heat effects in this process. Extensive parametric studies, which show effects of feed velocity and cycle time on the variation of product recovery and purity obtainable from the industrial unit, provide a valuable guide for its proper operation.
Robust optimization framework for process parameter and tolerance design
Authors: Bernardo Fernando P. , Saraiva Pedro M. 
Published: April 2004

AbstractThis article introduces a framework for including different uncertainties at the chemical plant design stage. Through an integrated robust optimization approach and problem formulation, equipment, operating, control, and quality costs are simultaneously taken into account, leading to system, parameter, and tolerance design. Rather than using single pointwise solutions in the decision space, operating windows leading to overall best performance are identified and defined. Such windows and their width allow us to point out control needs and goals at a very early stage of plant design. Two small‐scale case studies (for a CSTR and a batch distillation column) provide enough evidence to support the practicality of the optimization framework: the robust solutions found are different and much better than the corresponding solutions obtained with the fully deterministic optimization paradigms.
Numerical analysis of kinetic rate constants derived from stochastic computer simulation
Authors: Wu Peiru , McGuffin Victoria L. 
Published: April 2004

AbstractA numerical approach has been developed to determine the individual rate constants (kf − s and ks − f), as well as the equilibrium constant from the ratio of the rate constants (kf − s/ks − f), by using stochastic simulation. This approach is illustrated for simulations of the absorption (partition) process between homogeneous fluid and surface phases under diffusion‐limited conditions. A pair of regression methods is derived from the chemical system with the initial distribution of molecules entirely in either the fluid or surface phase. These two methods are complementary in determining the rate constants for distribution coefficients that are lower or higher than unity, respectively. A standard exponential (two‐parameter) regression equation is compared with a biexponential (four‐parameter) equation, which provides for inherent correction of numerical error. The effects of the number of molecules, as well as the time increment and range, are examined in detail. This provides guidance to optimize the computational parameters of the simulation. The proposed approach has been successfully applied for distribution coefficients ranging from 0.01 to 100.0, yielding individual rate constants kf − s and ks − f with ± 0.84% and ± 0.57% average relative standard deviation, and the ratio of the rate constants with ± 1.04% average relative standard deviation and ± 1.14% average relative error.
Modeling and optimization of a model IV fluidized catalytic cracking unit
Authors: Ellis Robert C. , Li Xuan , Riggs James B. 
Published: April 2004

AbstractThe problem of on‐line optimization of a model IV fluidized catalytic cracking (FCC) unit is analyzed. The “process” was modeled by combining a model IV FCC unit dynamic simulator (McFarlane et al, 1993; Khandalekar, 1993) with a ten‐lump yield model (Jacob et al, 1976; Arbel et al., 1995) for the reactor section. The steady‐state optimization model consisted of macroscopic steady‐state models of the regenerator and reactor, a simplified reactor yield model, and models of the various process constraints. The steady‐state optimization problem was solved using successive quadratic programming software (NPSOL, Gill et al., 1986) and the optimum process set points were implemented on the process simulator using a nonlinear constraint controller (Kandalekar and Riggs, 1995). The relative performance of constraint control, off‐line optimization, and on‐line optimization is compared for different feed characteristics and product pricing structures.
Tuning alkylation reactions with temperature in near‐critical water
Authors: Chandler Karen , Liotta Charles L. , Eckert Charles A. , Schiraldi David 
Published: April 2004

AbstractQuantitative kinetics for the alkylation reactions of phenol and p‐cresol with tert‐butyl alcohol in near‐critical water as a function of temperature are reported. The reaction products of the alkylation reactions were ortho‐ and para‐substituted phenols, which are used extensively as antioxidants in numerous polymer systems. A new experimental reaction apparatus was designed, constructed, and successfully operated to allow pressure control and sampling of the reaction systems, which provided rate constants in the temperature range 250–300°C. Additionally, activation energies and heats of formation were calculated from the temperature dependence of the rate constants, and ortho‐substitution was found to be exothermic whereas para‐substitution was found to be endothermic. These results demonstrate that product distribution of the alkylation reactions could be tuned with temperature to produce specific products.
Horizontal drying fronts during solvent evaporation from latex films
Authors: Routh Alexander F. , Russel William B. 
Published: April 2004

AbstractLatex films cast on a substrate often dry nonuniformly, with a drying front separating fluid domains from solidified regions passing across the film. For initial film thicknesses that are smaller than the characteristic horizontal distance, the analysis predicts surface‐tension‐driven horizontal flow. In a limit that ensures vertical homogeneity it is shown how a front of close‐packed particles forms and propagates. Imposing a maximum for the capillary pressure causes a solvent front to recede into the film. This recession is minimal, but can markedly affect the propagation of the particle front. An overall mass balance offers a solution for infinite capillary pressure, thereby illustrating the mechanism for propagation of the front. The positions of the fronts are predicted for both infinite and finite domains as a function of the maximum capillary pressure. Selective or nonuniform evaporation produces final film profiles, while the evaporating regions are still visible. After predictions over different size areas are made, the smallest area is compared with experiment.
Optimal design and operation of heat exchangers under milk fouling
Authors: Georgiadis Michael C. , Rotstein Guillermo E. , Macchietto Sandro 
Published: April 2004

AbstractThis article presents a procedure for the simultaneous optimization of the design and operation of heat exchangers under milk fouling. This scheme is based on a highly accurate dynamic model described by integral, partial differential, and algebraic equations. Design and operating parameters determined by the dynamic optimization include the length and diameter of the exchanger, the control policy, and the timing of the key operating steps. An economic objective function is used to account for the important factors related to milk heat treatment, and many operating constraints are imposed. Three heat exchanger configurations are considered to study the effect of fouling on the optimal plant design. Optimization indicates that the cost factor due to the interruption of production is dominant, while an increase in energy consumption due to fouling is not very important. The constant wall temperature configuration proved to be the most economical. The economic impact of different control structures was also explored.
Microbial enhancement of TCE and 1,2‐DCA solute flux in UF‐membrane bioreactors
Authors: Inguva Subbalaxmi , Boensch Melissa , Shreve Gina S. 
Published: April 2004

AbstractAn ultrafiltration membrane process was used to remove and biograde chlorinated aliphatic hydrocarbons trichloroethylene (TCE) and 1,2‐dichloroethane (1,2‐DCA) from dilute aqueous streams. The effect of microbial biodegradative activity on TCE and 1,2‐DCA solute flux in a polypropylene membrane was examined using microbial strains Pseudomonas cepacia PR131 for the biodegradation of TCE and Xanthobacter autotrophicus GJ10 for the biodegradation of 1,2‐DCA. Initial experiments were conducted in diaphragm cells in the absence of microorganisms to determine the diffusion coefficient of 1,2‐DCA and TCE in the polypropylene ultrafiltration (UF) membranes. The diffusivities were 4.7 × 10−8 cm2/s for 1,2‐DCA and 1.41 × 10−7 cm2/s for TCE. Subsequent experiments were conducted with microorganisms on the permeate side to examine the effect of microbial degradation of 1,2‐DCA and TCE on the solute flux across the UF membrane. Experiments were conducted sequentially in batch and flow diaphragm cells and then in a hollow‐fiber UF module to systematically examine the effect of microbial activity on the solute flux in each configuration and the ability of mathematical models to predict the microbial enhancement of solute flux. Microbial biodegradation of TCE and 1,2‐DCA significantly enhanced the solute flux, and experimental results were correlated with steady‐ and nonsteady‐state solute component balance models for the flow and batch diaphragm cells, respectively. Model and experimental results agree well. Implications for using membrane bioreactors to treat CAH contaminated groundwater and industrial effluents are discussed, as well as a method for examining the effect of biological reaction on membrane transport processes.
Computational analysis of slot coating on a tensioned web
Authors: Feng James Q. 
Published: April 2004

AbstractWhen a web (thin substrate with considerable flexibility) travels through a coating applicator in free span between the two supporting rollers, the gap between web and coating applicator is determined primarily by the hydrodynamic stresses in the coating flow and externally applied tension on the web. The elastohydrodynamic interaction between the tensioned‐web deformation and the viscous liquid flow in the coating bead has not been extensively studied, in spite of its practical importance. A tensioned‐web wrapped around a slot coater was analyzed here by finite‐element computations. The externally applied tension on the web typically is much greater than the force due to hydrodynamic stresses. Hence, tension in the web is assumed to be constant in the process direction tangential to the web surface. By neglecting the bending and twisting moments as in the approximation of membrane theory, the shape of the flexible web is determined by a normal stress balance equation, quite similar to that of the free surface of coating flow with a constant surface tension. In this work, elastohydrodynamic effects in tensioned‐web slot coating are examined with respect to variations of the liquid feeding rate and externally applied web tension, web wrap angle, and other variables.