bluuebunny/crossref_metadata_2025_split huggingface dataset:
Performance assessment of constrained model predictive control systems
Authors: Ko Byung‐Su , Edgar Thomas F. 
Published: April 2004

AbstractA constrained minimum variance controller is derived based on a moving horizon approach that explicitly accounts for hard constraints on process variables. A procedure for the performance assessment of constrained model predictive control systems is then developed based on the constrained minimum variance controller. The performance bound computed using the proposed moving horizon approach converges to the unconstrained minimum variance performance bound when the constraints on process variables become inactive. The utility of the proposed method in the performance assessment of constrained model predictive control systems is demonstrated through a simulated example.
Distributed models in plantwide dynamic simulators
Authors: Martinson W. S. , Barton P. I. 
Published: April 2004

AbstractModeling support for dynamic simulation of chemical‐process flowsheets, which is of significant value for plantwide dynamic simulation using differential–algebraic model formulations, is to date very limited when one or more unit models include partial differential equations. Several new techniques that provide modeling support for such simulations are presented. These techniques are based on a generalized characteristic analysis and a differentiation index analysis of partial differential–algebraic models. They can be used to uncover systems that cannot be solved as part of a dynamic simulation, and to determine whether or not the initial and boundary conditions supplied by the modeler form a well‐posed problem. In a network flow context, they can further be used to select, enforce, and adapt the boundary conditions as required to maintain automatically a mathematically well‐posed problem. Each of these provides time‐saving support to the system modeler.
Design of fuel additives using neural networks and evolutionary algorithms
Authors: Sundaram Anantha , Ghosh Prasenjeet , Caruthers James M. , Venkatasubramanian Venkat 
Published: April 2004

AbstractIt is difficult and challenging to design high‐performance fuel additives in an industrial‐design setting where data are sparse and noisy, and fundamental knowledge is often limited. An automated framework is presented for the design of such fuel‐additive molecules that minimize the intake‐valve deposit in the automobile. A hybrid model that combined functional descriptors from a first‐principles degradation model with a statistical/neural‐network model was developed to predict additive performance, given the additive structure. The results of the predictive model are discussed for different real industrial case studies. An evolutionary method using specialized representation and constrained operators to enforce formulation constraints was used to generate optimal additive molecules that meet desired performance criteria. The evolutionary design strategy in combination with the hybrid prediction model was successful in identifying novel additive molecules that also possess good synthesis potential.
Verification of scaling laws for degrading PLA‐b‐PEG‐b‐PLA hydrogels
Authors: Metters Andrew T. , Bowman Christopher N. , Anseth Kristi S. 
Published: April 2004

AbstractSeveral macroscopic properties of degrading poly(lactic acid)‐b‐poly(ethylene glycol)‐b‐poly(lactic acid) (PLA‐b‐PEG‐b‐PLA) hydrogels were compared to one another as functions of degradation time. The specific hydrogel properties measured were the compressive modulus (K), the volumetric swelling ratio (Q), and the normalized compressive modulus (KNORM = KQ1/3). Their comparisons were used to evaluate the applicability of fundamental thermodynamic theories developed for nondegradable hydrogels on a degradable system. The equations predict scaling factors of −2, −5/3, and 6/5 for the dependence of K on Q, KNORM on Q, and K on KNORM, respectively. These important experimental data for a degrading hydrogel system initially show good agreement with the scaling predictions. Further examination, however, reveals the scaling factors to change over the course of the degradation process. These changes are attributed, at least in part, to the changing chemical, mechanical, and ionic properties of the degrading copolymer networks.
Application of sieve‐tray air strippers to the treatment of surfactant‐containing wastewaters
Authors: Kibbey Tohren C. G. , Pennell Kurt D. , Hayes Kim F. 
Published: April 2004

AbstractUsing sieve‐tray air stripping as a means of removing contaminants from surfactant solutions was studied to determine if tray air stripping can be applied successfully to treating surfactant‐containing wastewaters and, if so, to develop a quantitative approach for designing tray air‐stripping systems for treating surfactant‐containing wastewaters. High‐concentration surfactant solutions were prepared and contaminated with five different volatile organic compounds. Removal of the organic compounds was evaluated using a commercial sieve‐tray air stripper. Overall, the air stripper was able to efficiently remove the contaminants from solution, and correction of Henry's Law constants for micellar solubilization‐induced volatility reduction allowed tray air‐stripper design equations to quantitatively predict air‐stripper removal for all contaminants. Foaming within the air stripper could be controlled with low concentrations of a silicone‐polymer antifoaming agent. Although adding antifoaming agents may be undesirable for some applications, other applications can benefit from the operational and performance advantages of sieve‐tray air strippers. Issues related to air‐stripper design for low‐volatility compounds are also discussed.
Validation of a new filtration technique for dewaterability characterization
Authors: Usher Shane P. , De Kretser Ross G. , Scales Peter J. 
Published: April 2004

AbstractCharacterization of the compressibility and permeability of flocculated suspensions is a time‐consuming experimental process that often takes days to perform. A new pressure filtration method developed characterizes a sample only in hours. Using stepped pressure filtration, the compressive yield stress Py (ϕ) and a hindered settling function R(ϕ) of flocculated suspensions are determined as a function of the solids volume fraction ϕ. Traditional pressure filtration experiments involve the pressure filtration of a particulate suspension in which the time of filtration t is monitored as a function of piston height from which the specific volume of filtrate V is determined. Py (ϕ) is determined from the equilibrium solids volume fraction. The gradient d(t/V)/dV is traditionally used to determine R(ϕ) using a suspension filtration theory developed by Landman and White. The new method uses only one stepped pressure compressibility filtration test and one stepped pressure permeability filtration test to determine Py (ϕ) and R(ϕ) for multiple solids volume fractions and substantially decreases the time required for sample characterization. To eliminate the influence of a stepped pressure on calculated permeabilities, the analysis of experimental results was modified using the gradient dt/dV2. Results are presented for a zirconia suspension comparing both single and stepped pressure filtration.
Detection and identification of faulty sensors in dynamic processes
Authors: Qin S. Joe , Li Weihua 
Published: April 2004

AbstractA novel method proposed detects and identifies faulty sensors in dynamic systems using a subspace identification model. A consistent estimate of this subspace model was obtained from noisy input and output measurements by using errors‐in‐variables subspace identification algorithms. A parity vector was generated, which was decoupled from the system state, leading to a model residual for fault detection. An exponentially weighted moving average (EWMA) filter was applied to the residual to reduce false alarms due to noise. To identify faulty sensors, a dynamic structured residual approach with maximized sensitivity is proposed which generates a set of structured residuals, each decoupled from one subset of faults but most sensitive to others. All the structured residuals are also subject to an EWMA filtering to reduce the noise effect. Confidence limits for filtered structured residuals were determined using statistical inferential techniques. Other indices like generalized likelihood ratio and cumulative variance were compared to identify different types of faulty sensors. The fault magnitude was then estimated based on the model and faulty data. Data from a simulated 4 × 4 process and an industrial waste‐water reactor were used to test the effectiveness of this method, where four types of sensor faults, including bias, precision degradation, drift, and complete failure, were tested.
Kinetics for hydrocracking based on structural classes: Model development and application
Authors: Martens G. G. , Marin G. B. 
Published: April 2004

AbstractA kinetic model for hydrocracking of an industrial feedstock, fully incorporating the carbenium ion chemistry, was developed. Individual hydrocarbons in the reaction network were relumped into 8 lumps per carbon number: n‐alkane, mono‐, di‐ and tribranched alkanes, mono‐, di‐, tri‐ and tetraring cycloalkanes. The rate coefficient of a reaction in the relumped network resulted from the product of the rate coefficients of the elementary reaction steps with lumping coefficients. The former were obtained from regressions on gas‐phase hydrocracking data of model components. Lumping coefficients were calculated based on the assignment of all (cyclo)alkanes and the corresponding carbenium ions to structural classes comprising species with identical thermodynamic properties. The simulation of an industrial reactor with vacuum gas‐oil feed revealed the relative unimportance of transfer limitations for hydrocracking of saturated hydrocarbons and the model's ability to detail the influence of process conditions on the product composition.
Microfabricated packed‐bed reactor for phosgene synthesis
Authors: Ajmera Sameer K. , Losey Matthew W. , Jensen Klavs F. , Schmidt Martin A. 
Published: April 2004

AbstractA silicon micropacked‐bed reactor for phosgene synthesis is demonstrated as an example of the potential for safe on‐site/on‐demand production of a hazardous compound. Complete conversion of chlorine is observed for both a 2:1 CO/Cl2 feed at 4.5 std. cm3/min and a 1:1 feed at 8 std. cm3/min. The latter gives a projected productivity of ∼100 kg/yr from a 10‐channel microreactor, with the opportunity to produce significant quantities through operating many reactors in parallel. The versatility of silicon microfabrication technology for producing reactors for corrosive gases is demonstrated by a protective oxide coating formed during reactor fabrication. The increased heat and mass transfer inherent at the submillimeter reactor length scale provides a larger degree of safety, control, and suppression of gradients than is available in macroscale systems. These advantages are also explored in the extraction of chemical kinetics from microreactor experiments. The preexponential factor and apparent activation energy for phosgene formation are determined demonstrating the utility of micropacked‐bed reactors as laboratory research tools.
Theoretical calculation of polymer deposition thickness on a cylindrical substrate
Authors: Shiflett Mark B. , Foley Henry C. , Yokozeki Akimichi 
Published: April 2004

AbstractA theoretical model developed predicts the thickness of a polymer film, coated on a rotating and translating cylindrical support. A model for the deposition process can be used to determine optimal operating conditions. It was validated experimentally and shows that the film‐thickness morphology is quite sensitive to certain operating parameters. For example, particular sets of operating parameter values can produce highly nonuniform film thicknesses. Selected examples of the model calculations are discussed, as well as their implications.
Vapor–liquid equilibria of mixtures containing alkanes, carbon dioxide, and nitrogen
Authors: Potoff Jeffrey J. , Siepmann J. Ilja 
Published: April 2004

AbstractNew force fields for carbon dioxide and nitrogen are introduced that quantitatively reproduce the vapor–liquid equilibria (VLE) of the neat systems and their mixtures with alkanes. In addition to the usual VLE calculations for pure CO2 and N2, calculations of the binary mixtures with propane were used in the force‐field development to achieve a good balance between dispersive and electrostatic (quadrupole–quadrupole) interactions. The transferability of the force fields was then assessed from calculations of the VLE for the binary mixtures with n‐hexane, the binary mixture of CO2/N2, and the ternary mixture of CO2 /N2/propane. The VLE calculations were carried out using configurational‐bias Monte Carlo simulations in either the grand canonical ensemble with histogram–reweighting or in the Gibbs ensemble.
Simultaneous breakup of multiple viscous threads surrounded by viscous liquid
Authors: Knops Yolanda M. M. , Slot Johan J. M. , Elemans Pierre H. M. , Bulters Markus J. H. 
Published: April 2004

AbstractA scenario is proposed for the simultaneous breakup process of an arrangement of parallel viscous threads. At very close distances, threads will break up via an “in‐phase” mode, that is, droplets will be formed at the same axial positions along the threads. In the case of threads that are further apart, breakup will occur via an “out‐of‐phase” mode, that is, on neighboring threads droplets will be formed at axial positions that are shifted by one‐half of a wavelength. The smaller the viscosity ratio between the thread phase and the continuous phase, the closer the threads must be to break up via this in‐phase mode. This scenario agrees with recent experimental results.
Rapid filtration measurement of dewatering design and optimization parameters
Authors: de Kretser Ross G. , Usher Shane P. , Scales Peter J. , Boger David V. , Landman Kerry A. 
Published: April 2004

AbstractTo characterize and optimize the compressive dewatering of suspensions, rapidly determinable material parameters are required. A mathematical framework exists for characterization of dewatering using three parameters: the compressive yield stress Py (ϕ), the hindered settling function r(ϕ), and a solids diffusivity D(ϕ). A new variation on traditional constant pressure, batch filtration tests is described along with a computer‐controlled filtration apparatus that enables complete characterization of a suspension with respect to dewatering in a matter of hours. The testing methods are validated experimentally on flocculated zirconia suspensions along with calculation of the material dewatering parameters. Application of the calculated parameters to modeling of a real filtration test shows excellent agreement. Practical implications of the modeling are also discussed.
Predicting liquid flow profile in randomly packed beds from computer simulation
Authors: Wen X. , Shu Y. , Nandakumar K. , Chuang K. T. 
Published: April 2004

AbstractOur previous work on the simulation of packing processes was extended to study the liquid trickle flow down randomly packed beds. An algorithmic procedure with detailed geometrical description of packing elements was developed for tracking the liquid flow and holdup distributions in packed beds. Unlike the conventional continuum‐based models such as the diffusion model, it goes into the subparticle scale to capture the geometrical characteristics of the packed bed. Three mechanisms of the trickle flow—film flow, dripping flow, and splash—were observed in packed beds, and the first two were captured in the model. At each point within a packed bed, liquid flow is simplified to two possible directions: vertically down and horizontally in the direction of the negative gradient of the packing surface. The 3‐D geometric model constructed with the packing process simulation was used to determine the direction of the horizontal flow and fraction of the flow rate in each direction. By assuming that the liquid flow is uniform free surface flow, the Manning formula was used to predict the liquid holdup with the width of the liquid rivulet on a packing surface calculated by the Shi and Mersmann correlation. Metal Pall rings and metal Raschig rings were simulated with water as the fluid. Results of liquid flow distributions and average liquid holdup were validated against experimental data and semiempirical correlation from Billet et al.
Model‐based synthesis of nonlinear PI and PID controllers
Authors: Wright Raymond A. , Kravaris Costas , Kazantzis Nikolaos 
Published: April 2004

AbstractPI and PID controllers continue to be popular methods in industrial applications. It is well known that linear PI and PID controllers result from the application of model‐based controller design methods to linear first‐ and second‐order systems. It is shown that nonlinear PI and PID controllers result from the application of nonlinear controller design methods to nonlinear first‐ and second‐order systems. As a result, the controllers resulting from nonlinear model‐based control theory are put in a convenient form, more amenable to industrial implementation. Additionally, the quantities used in the controller are useful for monitoring the process and quantifying modeling error. Chemical engineering examples are used to illustrate the resulting control laws. A simulation example further demonstrates the performance of the nonlinear controllers, as well as their useful process monitoring quantities.
Hamiltonian view on process systems
Authors: Hangos Katalin M. , Bokor József , Szederkényi Gábor 
Published: April 2004

AbstractThe thermodynamic approach of analyzing structural stability of process plants was extended to construct the simple Hamiltonian model of lumped process systems. This type of model enables us to design a nonlinear PD feedback controller for passivation and loop shaping. This approach is applicable for lumped process systems where Kirchhoff convective transport takes place together with the transfer and sources of various types, and the manipulable input variables are the flow rates. Systems with constant mass holdup and uniform pressure in every balance volume satisfy these conditions. General results are shown by simple examples of practical importance: on a bilinear heat exchanger cell and on an isotherm CSTR with nonlinear reaction.
Design of liquid‐liquid phase transfer catalytic processes
Authors: Samant Ketan D. , Singh Divya J. , Ng Ka M. 
Published: April 2004

AbstractIssues related to the conceptual design of liquid‐liquid phase transfer catalytic (LLPTC) processes are discussed. Based on a generic mathematical model, effects of reaction kinetics and mass transfer on the performance of LLPTC processes are captured in terms of Damköhler numbers. The effects of thermodynamic parameters on the process performance are also discussed. Elucidation of the basic mechanisms leads to the synthesis of two classes of flowsheets for LLPTC processes with recovery and recycle of the phase transfer catalyst. Salient features of operation are identified for both classes. The use of the model in making judicious choices of the reactor phase attributes, the catalyst recovery scheme, the catalyst, and the organic solvent is demonstrated.
Analysis and control of particulate processes with input constraints
Authors: El‐Farra Nael H. , Chiu Timothy Y. , Christofides Panagiotis D. 
Published: April 2004

AbstractA general methodology is proposed for the analysis and control of spatially‐homogeneous particulate processes with input constraints modeled by population balance equations. A nonlinear model reduction procedure based on the method of weighted residuals is used for the construction of finite‐dimensional ordinary differential equation (ODE) systems that accurately reproduce the dominant dynamics of the particulate process. These ODE systems are used to analyze the limitations imposed by input constraints on the ability to modify the dynamics of the particulate process, leading to an explicit characterization of the set of admissible set points that can be achieved in the presence of constraints. This information, together with the derived ODE systems, is then used as the basis for the synthesis of practically‐implementable nonlinear bounded output feedback controllers with well‐characterized constraint‐handling capabilities. The designed controllers enforce exponential stability in the closed‐loop system and achieve particle‐size distributions with desired characteristics in the presence of active input constraints. Precise closed‐loop stability conditions are given and controller implementation issues are addressed. This method is successfully used to regulate a continuous crystallizer with constrained control action at an open‐loop, unstable equilibrium point.
Binary adsorption equilibrium of organics and water on activated carbon
Authors: Linders M. J. G. , van den Broeke L. J. P. , Kapteijn F. , Moulijn J. A. , van Bokhoven J. J. G. M. 
Published: April 2004

AbstractAdsorption isotherms of hexafluoropropylene (HFP), methanol and ethanol were measured under dry and humid conditions using Norit R1 carbon. The presence of water lowered the HFP capacity over the whole pressure range as compared to the single component isotherm, while increasing the methanol and ethanol capacity. The Dubinin‐Radushkevich equation was applicable for methanol, and ethanol, and the Dubinin‐Astakhov equation gave a satisfactory description for water. The ideal adsorbed solution (IAS) theory satisfactorily described the binary, miscible systems of methanol and ethanol with water. Because water and HFP are not miscible, the IAS theory cannot be used. This binary system was described well by the independent co‐adsorption of the two components, that is, HFP vapor is adsorbed in the micropore volume left free by water.
Banded liquid–liquid Taylor‐Couette‐Poiseuille flow
Authors: Zhu Xiaoyan , Vigil R. Dennis 
Published: April 2004

AbstractIt has been reported that several distinct flow patterns may result when two immiscible liquids undergo Taylor vortex flow in the annular gap between a fixed outer cylinder and a rotating concentric inner cylinder. One such flow pattern (banded flow) apparently arises when less dense disperse phase droplets migrate to Taylor vortex cores due to the centrifugal force associated with the rotation of the vortices. Using the hypothesis that centrifugally driven droplet migration to vortex cores competes with turbulent diffusion, a simple criterion for predicting when banded flow patterns arise shows consistency with numerical simulations and experiments.
Microdivers to study sedimentation in polydisperse, concentrated colloidal suspensions
Authors: Biesheuvel P. Maarten , Verweij Henk , Breedveld Victor 
Published: April 2004

AbstractA small amount of polymer particles with diameters in the 100 μm range can be used as an ensemble of “microdivers” to study sedimentation velocities of polydisperse submicron particles in concentrated opaque suspensions. This tracer technique, based on Berg's (1941) diver method, is simple, measures velocities directly, and does not require underlying theory beyond conservation of momentum. It confirms that the polymer tracers reside at the position in the suspension where the suspension density corresponds to their own density. Aqueous inorganic suspensions of 250–750 nm α‐alumina particles were studied, which is electrostatically stabilized with nitric acid in water, using ∼100 μm polymethylmetacrylate and polystyrene particles as tracers. Experiments were compared with predictions by state‐of‐the‐art continuum models for multicomponent sedimentation to underpin the validity of the tracer technique.