bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of sorbents and isotherm models for NH3‐gas separation by adsorption
Authors: Helminen Jarkko , Helenius Joni , Paatero Erkki , Turunen Ilkka 
Published: April 2004

AbstractAdsorption equilibrium isotherms of ammonia gas were measured at temperatures between 298 and 393 K on 13X zeolite, 4A zeolite, alumina, silica gel, and activated carbon. The applicability of these sorbents to ammonia gas separation was compared based on equilibrium data. In the pressure range of 1 to 100 kPa activated carbon has its highest working capacity (5.5 mmol·g−1) at 298 K, and the working capacity drops rapidly with temperature, reaching its lowest point at 393 K. The two zeolites provide almost the same working capacity, 3.0–3.5 mmol·g−1, over the entire temperature range. Silica gel and alumina showed low working capacities. The experimental equilibrium data were fitted to 16 different isotherm models, with accuracy and reliability statistically evaluated. The Langmuir–Freundlich model with the van't Hoff equation for the equilibrium constant and with a thermal expansion equation for the saturation sorbate concentration provided the most accurate fit for the 13X and 4A zeolites. This model was also very accurate for the alumina and silica gel data, even though the Dubinin–Astakhov model gave slightly higher predictions. The Henry and vacancy solution models provided the best fit for activated carbon.
Dynamic data rectification using the expectation maximization algorithm
Authors: Singhal Ashish , Seborg Dale E. 
Published: April 2004

AbstractAlthough on‐line measurements play a vital role in process control and monitoring process performance, they are corrupted by noise and occasional outliers (such as noise spikes). Thus, there is a need to rectify the data by removing outliers and reducing noise effects. Well‐known techniques such as Kalman Filtering have been used effectively to filter noise measurements, but it is not designed to automatically remove outliers. A new methodology based on the Kalman filter rectifies noise as well as outliers in measurements. Filter equations were formulated in the form of probability distributions. Then the Expectation‐Maximization algorithm was used to find the maximum‐likelihood estimates of the true measurement values based on a state‐space model, past data, and current observations. This approach was evaluated when the assumption of normally distributed outliers is not valid. The method can be used with any dynamic process model, as shown by integrating it with an extended Kalman Filter and by an augmented linear state‐space model to account for unmeasured disturbances. It also can be used to provide diagnostic information about changes to the process or sensor failures.
Design sensor trajectory for control: Application to sheet‐forming processes
Authors: Chang Der‐Ming , Yu Cheng‐Ching , Chien I‐Lung 
Published: April 2004

AbstractThe conventional scanning sensor generates a zig‐zag pattern for the sheet‐forming process, immediately leading to the problem of unequal measurement update intervals in state estimation. Instead of reconstructing the profile given a zig‐zag pattern, the sensor trajectory was redesigned to better estimation and control. In this work, the characteristics of the conventional scanning sensor were explored as well as the implications in estimation and control. The concept of elliptic sensor contour is presented, deriving analytical expressions for the sensor trajectories. Alternatively, the improved sensor trajectory can be obtained using a variable‐speed scanning sensor under linear sweep. That implies that control performance can be improved by reprogramming the motor of the existing sensor. Moreover, several alternatives for sensor arrangement are also explored. The results for estimation and control can be used as guidelines for the development of future sensor technology.
Passive control design for distributed process systems: Theory and applications
Authors: Alonso Antonio A. , Banga Julio R. , Sanchez Isidro 
Published: April 2004

AbstractA recently developed theory linking passivity with the second law of thermodynamics was used to develop a robust control design methodology for process systems with states distributed in time and space. Asymptotic stabilization of the infinite dimensional state thus can be accomplished for convection–diffusion processes with nonlinear production terms. Two examples representative of these phenomena were considered: chemical reactors and thermal treatments induced by electromagnetic fields. The first case shows how mixing and reactor size are critical control design parameters. If mixing is complete, at least in some direction, exponential stabilization can be achieved by high gain control. If not, stabilization is still possible for reaction domains smaller than a critical volume. In the second case, the electromagnetic field power supplied can always be manipulated to preserve passivity for any domain size. Two important consequences are that the infinite dimensional state can be reconstructed at arbitrary precision by robust observers and that control of the energy inventory will suffice to provide asymptotic stabilization. Theoretical justification of these findings is given on a general framework and illustrated through simulation experiments.
Spatiotemporal patterns in thermokinetic models of cross‐flow reactors
Authors: Nekhamkina Olga , Rubinstein Boris Y. , Sheintuch Moshe 
Published: April 2004

AbstractThe behavior of stationary and moving spatially‐periodic patterns in a simple cross‐flow reactor was simulated and analyzed for a situation in which reactant is supplied continuously along the reactor and a first‐order exothermic reactor occurs. The Danckwerts boundary conditions for realistic Le and Pe values. While the unbounded (infinitely long) reactor is an asymptotic case used to study the stability of the homogeneous solution, the moving waves that emerge in the convectively unstable unbounded system may be arrested at the boundaries of a bounded system and stationary waves are established above some amplification threshold. Sustained periodic and aperiodic behavior may emerge under certain conditions. The spatial behavior in the bounded system with Pe→∞ is analogous to the temporal behavior of the simple thermokinetic CSTR problem and the behavior of the distributed system is classified according to that of the lumped one.
Ultrasound‐modulated two‐fluid atomization of dilute polymer solutions
Authors: Tsai Shirley C. , Luu Patrick 
Published: April 2004

AbstractNew findings presented can further our understanding of the atomization of dilute polymer solutions. First, contrary to the conventional view that viscoelastic liquids are more difficult to atomize than Newtonian liquids, it was found that aerodynamic conditions required to form uniform drops are less severe for some viscoelastic liquids than for Newtonian liquids. Under similar aerodynamic conditions, using ultrasound‐modulated two‐fluid atomization at 54 kHz, 40‐μm‐dia. uniform drops determined by the third harmonic frequency were obtained for gel‐forming xantham gum solutions, but not for Newtonian liquids. Second, ultrasonic atomization yielded 350–400‐μm‐dia. drops for aqueous solutions of rodlike polyethylene oxides (PEO) with molecular weights of 1‐2×105at 54 kHz, supporting previous predictions that PEO relaxation times may be as short as 10−4s. Third, at smaller molecular weights (up to 2×104), aqueous solutions of PEO behave like Newtonian liquids in accordance with modified Taylor's dispersion relation.
Sorbate/sorbent phase transition during adsorption of p‐xylene in silicalite
Authors: Mohanty S. , Davis H. T. , McCormick A. V. 
Published: April 2004

AbstractAn analytically solvable lattice model was used to study the difference in the physics of p‐xylene adsorption in ORTHO and PARA phases of silicalite. The model predicts that a phase transition of p‐xylene in the pore space does not necessarily require a silicalite‐phase transition. Conditions for the sorbate‐phase transition are identified. The sign of the sorbate‐sorbate interactions is critical to sorbate‐phase transition. It is suggested that although the sorbate‐ and sorbent‐phase transitions can be distinct events, there is strong coupling between the two. It is reasonable to suppose that the fluid‐phase change may drive the zeolite phase change. Finally, this equilibrium study suggests the possibility of hysteresis at higher coverages depending on the kinetics of adsorption.
Progress in the thermal sciences: AIChE Institute Lecture
Authors: Churchill Stuart W. 
Published: April 2004

AbstractRather than merely surveying progress in the prediction of heat transfer over the past half century, attention is focused on the factors that have led to significant advances in understanding and practice. An almost one‐to‐one correspondence is demonstrated between advances in heat transfer and those in computer hardware and software. However, the development of specialized algorithms for flow and heat transfer by individual investigators appears in most cases to be an essential ingredient. Direct contributions of experimentation are relatively minor, but the synergy of combined experimentation and numerical analysis is most often the key to discovery and innovation. A quiet revolution has occurred in the form of correlative equations, and the primary and almost sole contribution of closed‐form analysis has been the derivation of asymptotes for that purpose. Finally, progress in heat transfer has occurred primarily in discrete steps, and most often as a consequence of exploratory research and/or the observation and pursuit of the explanation for an anomaly.
Motion in a particle bed agitated by a single blade
Authors: Laurent B. F. C. , Bridgwater J. , Parker D. J. 
Published: April 2004

AbstractStudies on the agitation of granular materials were conducted in a horizontal cylindrical shell stirred by a single long flat blade located on radial arms fixed to a rotor shaft. Positron emission particle tracking, a noninvasive method of investigating opaque systems, permitted the motion of a single particle to be followed. Axial flow patterns showed two loops of circulation inside each compartment defined by the radial arms of the rotating blades. Results revealed the presence at 20% of fill of a circulation zone in the cross‐sectional plane directly beneath the rotating shaft where little agitation occurred. This zone decreased in size and moved toward the agitator shaft as fill increased from 20% to 60%. Velocity profiles and Fourier analysis of particle displacement showed that particle movement was controlled by the number of blade passes. Torque measurements on the agitator shaft were correlated with distribution of material in the cross section of the mixer and distribution of tangential velocity. This opens the prospect of relating torque to powder flow patterns. The information can now be incorporated into models for heat transfer, chemical reaction, or agglomeration.
Predicting adsorption equilibrium using molecular simulation
Authors: Davies Graham M. , Seaton Nigel A. 
Published: April 2004

AbstractThe capability of molecular simulation, combined with pore‐size distribution (PSD) analysis, to predict adsorption equilibrium in microporous carbon adsorbents, using as a case study the adsorption of methane and ethane, was investigated. The calculations indicate that a wide range of data for the adsorption of pure components and binary mixtures can be predicted successfully. Significantly, only a limited set of experimental data comprising three or four adsorption measurements is required to calculate the PSD. This predictive ability is relevant to both the design of adsorptive separation processes and the design of new adsorbents.
CFD modeling of heat transfer in turbulent pipe flows
Authors: Thakre S. S. , Joshi J. B. 
Published: April 2004

AbstractTwelve versions of low Reynolds number k‐ϵ and two low Reynolds number Reynolds stress turbulence models for heat transfer were analyzed comparatively. Predictions of the mean axial temperature, the radial and axial turbulent heat fluxes, and the effect of Prandtl number on Nusselt number were compared with the experimental data. The model by Lai and So from the k‐ϵ group and Lai and So from the Reynolds stress group had the best overall predictive ability for heat transfer in turbulent pipe flow. The Lai and So model was attributed to its success in the predictions of flow parameters such as mean axial velocity, turbulent kinetic energy, eddy diffusivity, and the overall energy dissipation rate. The k‐ϵ models performed relatively better than the Reynolds stress models for predicting the mean axial temperature and the Nusselt number. This qualitative and quantitative study found the need for more sophisticated near‐wall experimental measurements and the accuracy of the dissipation (of turbulent energy) and the pressure‐scrambling models.
Statistical and causal model‐based approaches to fault detection and isolation
Authors: Yoon Seongkyu , MacGregor John F. 
Published: April 2004

AbstractBoth fundamental and practical differences between two common approaches to fault detection and isolation are examined. One approach is based on causal state‐variable or parity‐relation models developed from theory or identified from plant test data. The faults are then detected and isolated using structured or directional residuals from these models. The multivariate statistical process control approaches are based on noncausal models built from historical process data using multivariate latent variable methods such as PCA and PLS. The faults are then detected by referencing future data against these covariance models, and isolation is attempted through examining contributions to the breakdown of the covariance structure. There are major differences between these approaches arising mainly from the different types of models and data utilized to build them. Each of them has clear, but complementary, strengths and weaknesses. These are discussed using simulated data from a CSTR process.
Ethylene compressor monitoring using model‐based PCA
Authors: Rotem Y. , Wachs A. , Lewin D. R. 
Published: April 2004

AbstractPrincipal component analysis (PCA), which is widely used in process monitoring, performs best when the system variables are linearly correlated. In practice, however the variables are often nonlinearly related and may be subject to periodic forcing, both of which compromise the performance of conventional PCA. In model‐based PCA (MBPCA), multivariate statistics are used to analyze the portion of the observed variance that cannot be predicted using a model of the process and thus significantly enhances the attainable diagnostic resolution. Here, MBPCA is used for fault‐detection monitoring of an ethylene compressor, which operates under a significant periodic disturbance caused by the ambient temperature. An analytical expression is derived to predict the limits of identifiable faults given bounds on the parametric model uncertainty.
Residual activity of sorbent particles with a long residence time in a CFBC
Authors: Abanades Juan Carlos , de Diego Luis Francisco , García‐Labiano Francisco , Adánez Juan 
Published: April 2004

AbstractTo characterize the sulfation capacity of limestone as a sorbent of SO2 in a circulating fluidized‐bed combustor (CFBC), long‐term sulfation tests were carried out in a thermobalance. In order to cover the range of residence times expected in a large‐scale combustor, the experiments lasted 24 h. The residual activity of the sorbent after the first hours of reaction indicated a conversion of ∼0.1, depending on the particle's size and sulfation conditions. The shrinking core model described well these residual activities. An effective gas‐phase diffusion coefficient was derived from plots of the measured conversion vs. time between 3 and 24 h. These diffusivities ranged between 1.7 and 4.1×10−9 m2/s at 850°C and depended only on the limestone. It is argued that this simple description could be incorporated into more complex sulfation models of the first few hours of reaction and also account for the subsequent increases in conversion over longer time scales. It is also stressed that, to predict a sorbent's performance in a boiler, characterization techniques should be expanded to experimental time scales similar to those expected in large‐scale CFBCs.
Low‐flow limit in slot coating: Theory and experiments
Authors: Carvalho Marcio S. , Kheshgi Haroon S. 
Published: April 2004

AbstractThe region of acceptable quality in the space of operating parameters of a coating process is called coating window. Their limits are set by coating defects. For the slot‐coating process the low‐flow limit is important. It corresponds to the maximum web speed at a given film thickness, or the minimum film thickness at a given web speed, at which the coating bead remains stable. The available viscocapillary model is based on the Landau‐Levich equation, which is limited to small Capillary and Reynolds numbers. Under these conditions, the minimum film thickness that can be coated decreases with decreasing coating speed, but many coating processes do not occur at low Capillary numbers. It is important to determine the range of validity of the viscocapillary model and find the low‐flow limit outside this range. The low‐flow limit was determined here theoretically and experimentally. The 2‐D Navier‐Stokes equations with free surfaces describe liquid flow in the coating bead. Theoretical approaches solve the Navier‐Stokes system by either using Galerkin's method with finite‐element basis functions or applying a long‐wave expansion. The minimum layer thickness at a set of parameters was determined by the turning point on the solution path as the thickness was diminished. The minimum film thickness was measured experimentally by determining the flow rate at which the coating bead breaks, leading to stripes of coated and uncoated web. Results show that the low‐flow limit of the coating bead at large Capillary and Reynolds numbers fundamentally differs from that at their low numbers. At large Capillary and Reynolds numbers, the minimum film thickness that can be coated decreases with increasing coating speed. The coating window of the process is much larger than that in the literature, broadening the applicability of this coating method.
Development of volume‐average theory for deep‐bed filtration
Authors: Stephan E. A. , Chase G. G. 
Published: April 2004

AbstractOver the past 20 years, researchers have attempted, with limited success, to develop a general correlation for permeability loss within a deep‐bed filter. The research presented here yields a unique result by rigorously developing a filtration model that focuses on the effective surface area as the dominant factor causing permeability loss. Both a constitutive relation and a geometric interpretation are developed to represent the effective surface area. The resulting macroscale equations accurately model the permeability reduction by incorporating the lower scale mechanisms. The model was tested using the specific process of water injection into a sandstone formation with experimental variables of salt concentration, pH, and concentration of influent fines. Postulated forms of the constitutive relations were verified through these experiments. By accounting for the changes in effective surface area, the model uniquely and accurately describes the permeability loss within a deep‐bed filter.
Convection‐enhanced mass transfer in aggregated beads for gel chromatography
Authors: Li Qiangliang , Grandmaison Edward W. , Goosen Mattheus F. A. , Taylor David 
Published: April 2004

AbstractConvection‐enhanced mass transfer in aggregated κ‐carrageenan beads was assessed using experimental and mathematical modeling studies. Aggregated beads, prepared from subsidiary beads in a fluidized bed, were employed for gel chromatography of proteins. The efficiency of a chromatography column was measured by the plate height. The plate height of the aggregated beads was much lower than that of conventional carrageenan beads of the same size. This was attributed to intraparticle convection, which occurred even at relatively low flow rates due to the large intraparticle channels resulting from the low degree of aggregation. A general equation for predicting the reduced plate height was modified by using an apparent diffusivity in order to incorporate intraparticle convection. The modified equation was in good agreement with experimental data. The protein productivity of an aggregated bead column (mg/h/mL column) was estimated to be six times higher than that of a conventional column.
Numerical modeling of helical flow of viscoplastic fluids in eccentric annuli
Authors: Hussain Q. E. , Sharif M. A. R. 
Published: April 2004

AbstractHelical flow of viscoplastic Herschel‐Bulkley fluids in concentric and eccentric annuli with rotating inner cylinder was investigated numerically. Similar flows occur in drilling operations of oil and gas wells. A finite volume algorithm with a nonstaggered grid system and a nonorthogonal curvilinear coordinate system to handle irregular geometry of an eccentric annulus was used to analyze the problem. Papanastasiou's modification of the Herschel‐Bulkley (Yield‐Power‐Law) constitutive equation was used to model the shear rate‐dependent viscosity of a viscoplastic fluid. For a fixed axial pressure gradient, the axial flow rate increased with increasing rotational speed of the inner cylinder. The discharge, as well as torque required to rotate the inner pipe, increased with increasing eccentricity for a fixed axial pressure gradient and inner cylinder rotational speed. Discharge also increased with increasing axial pressure gradient at a fixed eccentricity and rotational speed of the inner pipe. The flow field in an eccentric annulus is complex because vigorous secondary flow is produced in addition to the primary axial helical flow. Blockage at the narrow part of the eccentric annulus, when present, intensifies this secondary flow, with the discharge decreasing initially, then increasing, and decreasing again with increasing height of the blockage.
Product transfer between plants using historical process data
Authors: Jaeckle Christiane M. , MacGregor John F. 
Published: April 2004

AbstractBased on the concepts laid out in an earlier article (Jaeckle and MacGregor, 1998), this paper defines the problem of moving the production of a particular product grade from a plant A to another plant B when both plants have already produced a similar range of grades. Since the two plants may differ in size, configurations, and so on, the process conditions required to produce any given product grade may be very different in the two plants. How historical process data on both plants may be utilized to assist in this problem is investigated. A multivariate latent variable method is proposed that uses data from both plants to predict process conditions for plant B for a grade previously produced only in plant A. The approach is illustrated by a simulation example.
Process control structure selection based on economics
Authors: Heath Jonathan A. , Kookos Ioannis K. , Perkins John D. 
Published: April 2004

AbstractIn process systems, selecting suitable sets of manipulated and controlled variables and the design of their interconnection, known as the control structure selection problem, is an important structural optimization problem. The operating performance of a plant depends on the control structure selected, as well as the characteristics of the disturbances acting on the plant. The economic penalty associated with the variability of main process variables close to active constraints was used in this work to develop a quantitative measure for the ranking of alternative control structures. The problem is formulated as a mixed integer nonlinear optimization problem of special structure, which was used for an algorithm to solve this problem to global optimality. The final formulation is a mixed integer linear problem for which effective solution methods are currently available. The validity and usefulness of the method are demonstrated through a number of case studies.