bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of increased gas density on hydrodynamics of bubble‐column reactors
Authors: Krishna Rajamani , De Swart Jeroen W. A. , Hennephof Daniëlle E. , Ellenberger Jürg , Hoefsloot Hubertus C. J. 
Published: June 2004

AbstractA mechanistic background to the understanding of the hydrodynamics of high‐pressure bubble column reactors in both the homogeneous and heterogeneous flow regimes is discussed. An important parameter determining the stability of homogeneous bubbly flow in a bubble column is shown to be the Richardson‐Zaki exponent in the bubble swarm velocity relationship Vswarm = v∞(1‐ϵ)n‐1. Experimental data for the bubble swarm velocity were obtained in 0.05‐ and 0.1‐m‐dia. bubble columns with various gases (helium, air, argon, sulfur hexafluoride) using water as the liquid phase. Bubble swarm velocity data show that with increasing gas density the Richardson‐Zaki exponent value decreases; physically this means that increasing gas density reduces interaction between neighboring bubbles and, consequently, reduces chance of propagation of instabilities. This rationalizes the experimental observation that the influence of increased gas density ρG is to delay the transition from homogeneous bubbly flow to churn‐turbulent flow: increasing ρG increases the regime transition velocity. A stability analysis rationalizes the observations. The hydrodynamics of bubble columns in the churn‐turbulent regime is considered to be analogous to that of a bubbling gas‐solid fluidized bed, and the two‐phase theory of gas‐solid fluid beds is extended to describing bubble columns by identifying the “dilute” phase as the fast‐rising large bubbles and the “dense” phase as the liquid phase with entrained small bubbles. A simple coalescence rationalizes experimental large‐bubble holdup data.
Continuous‐Mixture kinetics of thermolytic extraction of coal in supercritical fluid
Authors: Wang Ming , Zhang Chunjie , Smith J. M. , McCoy Ben J. 
Published: June 2004

AbstractThermolysis of coal yields a complex mixture of many extract products whose molecular‐weight distribution (MWD) varies with time for continuous‐flow, semi‐batch experiments. A laboratory flow reactor with a differential fixed bed of coal particles contacted by supercritical tert‐butanol was used to provide dynamic MWD data by means of HPLC gel permeation chromatography of the extract. The experimental results, multipeaked, time‐dependent MWDs of extract molecules, are interpreted by a novel mathematical model based on continuous‐mixture kinetics for thermal cleavage of chemical bonds in the coal network. The parameters for the MWDs of extractable groups in the coal and the rate constants are determined from the experimental data. The effect of temperature on the kinetics of the extraction is explained in terms of one‐ and two‐fragment reactions of the extractable groups in the coal. At lower temperatures (613 and 633 K) single‐fragment reactions dominate, but at higher temperatures (653 and 673 K) more bonds in the coal are broken and the two‐fragment reactions become significant. Also, the detailed MWDs are related to conventional lumped data for the thermolytic extraction process. The results yield information about the structure of coal, as well as the kinetics and mechanism of supercritical thermolytic reactions.
Falling film evaporation of binary mixtures
Authors: Palen J. W. , Wang Qi , Chen J. C. 
Published: June 2004

AbstractThe interactive effects of heat and mass transfer in evaporation of binary mixtures flowing as falling films on vertical surfaces was investigated. Evaporative heat‐transfer coefficients were measured for aqueous mixtures of ethylene and propylene glycol, with boiling ranges up to 55°C. Tests were carried out at atmospheric pressure with heat fluxes ranging from 3,000 to 25,000 W/m2, and film Reynolds numbers ranging from 300 to 3,000. Results indicated that the heat‐transfer coefficient for mixtures depends weakly on wall superheat and film Reynolds number, but strongly depends on mixture composition. Analysis of the results indicates that mass‐transfer resistance in the liquid film causes significant elevation of the interface temperature, causing a reduction of the effective temperature driving force. A semiempirical model for correlation of the interactive heat‐and mass‐transfer phenomena is proposed.
Model‐predictive pH control using real‐time NARX approach
Authors: Pröll Thomas , Nazmul Karim M. 
Published: June 2004

AbstractA new comprehensive real‐time identification/control methodology based on the concept of nonlinear autoregressive exogenous input (NARX) models and adaptive, nonlinear, model‐predictive control (ANMPC) is applied to a pH neutralization process. The existing NARX model theory has been extended by incorporating measured disturbances. NARX models have shown superior predictive characteristics in comparison to linear models. The proposed real‐time methodology uses a pointer vector being created during an initial identification and model structure selection procedure. Using this pointer vector, which allocates the chosen elements from the pool of all possible linear and nonlinear combinations, one needs no explicit information about the model structure for the closed‐loop control. The nonlinear programming problem encountered in ANMPC is solved by a gradient‐based modified Marquardt and finite difference methods. The design procedure and explicit algorithms are discussed for the multiinput/multioutput case. A pH wastewater neutralization process used illustrates and verifies the procedure by computer simulations and a real‐time laboratory‐scale experiments.
Estimating interfacial tension via relaxation of drop shapes and filament breakup
Authors: Tjahjadi Mahari , Ottino Julio M. , Stone Howard A. 
Published: June 2004

AbstractTwo methods are presented for calculating the interfacial tension between two immiscible Newtonian fluids. The procedures require only two measurements of the approximate interface shape during the low‐Reynold‐number interfacial‐tension‐driven transient motion of (i) the relaxation of a modestly elongated drop back to a spherical shape or (ii) the growth of capillary wave instabilities along the surface of a thread. The interfacial tension can be estimated by comparing the time differences between the two experimental measurements with tabulated and numerically generated results for the approximate shape evolution. The numerical results are generated using boundary integral method for similar model free‐boundary problems at low Reynolds numbers. The tabulated results are presented for drop to suspending fluid viscosity ratios 0.01 to 10.
Breakage and coalescence models for drops in turbulent dispersions
Authors: Tsouris C. , Tavlarides L. L. 
Published: June 2004

AbstractA substantial effort has been made by numerous investigators to describe droplet breakage and coalescence in turbulent dispersions. An attempt is made here to improve these models based on existing frameworks and recent advances described in the literature. Two‐step mechanisms are considered for both the breakage and coalescence models. The drop breakage function is structured as the product of the drop‐eddy collision frequency and breakage efficiency which reflect the energetics of turbulent liquid‐liquid dispersions. The coalescence function retains the former structure of the product of drop‐drop collision frequency and coalescence efficiency. The coalescence efficiency model has been modified to account for the effects of film drainage for drops with partially mobile interfaces. These models overcome several inconsistencies observed in previous efforts and are applicable for dense dispersions (about ϕ[0.10–0.30]). For the daughter drops produced by breakage, a probability density is proposed based on the energy requirements for the formation of daughter drops.
On‐line molecular weight distribution estimation and control in batch polymerization
Authors: Ellis Mark F. , Taylor Tad W. , Jensen Klavs F. 
Published: June 2004

AbstractA molecular weight distribution (MWD) estimator for batch methyl methacrylate solution polymerization is implemented experimentally for on‐line control and estimation of the MWD. The estimator is based on an extended Kalman filter and provides current estimates of the entire MWD, reaction temperature, monomer conversion, and initiator conversion. It uses a detailed polymerization model, on‐line monomer conversion measurements, temperature measurements, and periodic, time‐delayed measurements of the MWD from an on‐line size‐exclusion chromatograph. The estimator is shown to perform well with several on‐line MWD estimation experiments. Real‐time feedback control of the molecular weight is presented by utilizing the on‐line MWD information. Temperature, monomer‐addition, and simultaneous temperature and monomer‐addition control are investigated experimentally to achieve a specific constant weight‐average molecular weight. The on‐line feedback control is effective in rejecting realistic disturbances which deteriorate molecular weight control.
Synthesis of reactive mass‐exchange networks with general nonlinear equilibrium functions
Authors: Srinivas B. K. , El‐halwagi M. M. 
Published: June 2004

AbstractThe problem of synthesizing reactive mass‐exchange networks (REAMENs) is addressed for which the equilibrium relations governing the transfer of a certain species from rich streams to reactive mass‐separating agents are nonlinear (convex and/or nonconvex). Previously developed synthesis procedures for REAMENs are not applicable to such cases, since they were developed for cases of linear and/or convex equilibria. Two peculiar phenomena are associated with REAMENs with general nonlinear equilibria: the location of a mass‐exchangers may straddle the pinch point even for networks featuring the minimum cost of mass‐separating agents. To account for such intriguing characteristics, a systematic procedure is developed to synthesize cost‐effective REAMENs with general nonlinear equilibria. In addition, a robust solution procedure is devised to guarantee the identification of the global solution of the developed optimization programs. Applicability and usefulness of the proposed synthesis procedure are demonstrated via a case study on the desulfurization of gaseous wastes from a coal‐to‐methanol plant.
Dynamic modeling of product grade transitions for olefin polymerization processes
Authors: Debling J. A. , Han G. C. , Kuijpers F. , Verburg J. , Zacca J. , Ray W. H. 
Published: June 2004

AbstractMost olefin polymerization processes produce a wide range of resin grades to suit market demand. Determining the transition policy between these grades is an important consideration that can affect process economics and safety. In this article, we compare several grade transition strategies and the relative performance of solution, slurry, bulk and gas‐phase processes for the production of polypropylene, linear low‐density polyethylene, high‐density polyethylene and ethylene‐propylene rubber. It is shown that the most important parameters that determine the grade transition performance of a process are reactor design, residence time, runtime per grade and residence time distribution of the polymer, gas and/or solution phases. Slow hydrogen dynamics severely retard grade changes involving increases in product molecular weight. The simulation results are obtained by using the dynamic simulation package “POLYRED” developed at the University of Wisconsin‐Madison.
Effect of pressure on the oxidative coupling of methane in the absence of catalyst
Authors: Chen Q. , Couwenberg P. M. , Marin G. B. 
Published: June 2004

AbstractThe oxidative coupling of methane was carried out in the absence of catalyst in a continuous flow setup at total pressures up to 1,000 kPa, temperatures from 950 to 1,230 K, and inlet molar ratios of CH4/O2 down to 2.5. At constant temperature and residence time, the conversions of methane and oxygen increase drastically with increasing pressure. At oxygen conversions higher than 80%, product selectivities are comparable at different pressures. The space‐time yield of the C2 products reaches a level comparable to that required for industrial operations from 400 kPa on. A radical‐reaction network consisting of 38 elementary reactions allows to describe the experimental data. To describe adequately the effect of total pressure, the pressure fall‐off behavior of the rate coefficients for the unimolecular reactions in the network has to be taken into account explicitly.General features of the reaction mechanism do not depend on the total pressure. Methyl and hydrogen peroxy radicals are the most abundant radicals. The total pressure increase results in a drastic increase of the concentrations of the chain carriers, particularly the hydrogen peroxy radical. Higher pressure favor the oxidative route from ethane to ethylene compared to the pyrolytic route. Increasing the total pressure leads to an increase of the primary and a decrease of the consecutive CO formation relative to the coupling. The balance between these nonselective routes determines the effect of the total pressure on the integral selectivity to C2 products at different conversions. The major contribution to the integral CO selectivity comes from the oxidation of methyl radicals.
Solubilization in nonionic reverse micelles in carbon dioxide
Authors: McFann Gregory J. , Johnston Keith P. , Howdle Steven M. 
Published: June 2004

AbstractPhase behavior data and FTIR spectra along with solubilities and solvatochromic shifts of ionic indicator dyes are reported for binary, ternary and quaternary systems composed of pentaethylene glycol n‐octyl ether (C8E5), CO2, water, and n‐pentanol as a function of temperature, pressure and composition. With the addition of n‐pentanol as a cosurfactant, the water to surfactant ratio, W0, reaches values as high as 12. As water is added further, a surfactant‐rich phase precipitates due to micellemicelle interactions. Ionic dyes are soluble at levels of 0.03 mM, far in excess of the negligible solubility in pure CO2.
Reduction of ion‐exchange equilibria data using an error in variables approach
Authors: Vamos Richard J. , Haas Charles N. 
Published: June 2004

AbstractAn error in variables method (EVM) was used to reduce binary ion‐exchange equilibria data. Ion‐exchange equilibria data were collected via batch equilibrium experiments. Three binary ion‐exchange systems were studied: the Na+1‐Cd+2, Na+1‐Cu+2, and Cu+2‐Cd+2 systems with a strong acid synthetic ion‐exchange resin. The Wilson model and a three‐suffix, two‐parameter Margules equation were used to model the dependency of the resin phase activity coefficients with resin‐phase composition. The EVM was used to determine the best‐fit estimates of the Wilson and Margules equation binary resin‐phase activity coefficient parameters. Statistical analysis of the data fits indicates that although both equations were able to adequately model the resin phase nonidealities, the Wilson model provided the superior data fits based on the minimized objective functions.
Use of relay‐feedback test for automatic tuning of multivariable systems
Authors: Shen Shih‐Haur , Yu Cheng‐Ching 
Published: June 2004

AbstractThe Åström‐Hägglund autotuner is extended to multivariable systems. The proposed multivariable automatic tuning performs the identification‐design procedure in a sequential manner. Its advantages are discussed, as well as the process characteristics resulted from sequential design. One important feature is that the sequential design often leads to underdamped process characteristics. Given these characteristics, potential problems in the Ziegler‐Nichols tuning are discussed and a modification is made. The sequential identification and the modified Ziegler‐Nichols controller design method form the basic structure for the multivariable autotuner. The properties of convergence, the implications of tuning sequence, and the indications of undesirable pairing for the autotuner are explored. Consequently, a multivariable autotuning procedure is proposed. Two nonlinear distillation examples and a 3 × 3 linear system are used to illustrate the effectiveness of the autotuner. Simulation results show that good performance can be obtained with minimal engineering effort and the autotuner works well for very difficult processes in a very simple way.
Centrifugation assay of IgE‐mediated cell adhesion to antigen‐coated gels
Authors: Chu Lily , Tempelman Linda A. , Miller Cynthia , Hammer Daniel A. 
Published: June 2004

AbstractThe adhesion of biological cells to substrates is often mediated by binding between cellular receptors and substrate‐bound ligand. In this work, we used a centrifugation assay to measure the adhesion of rat basophilic leukemia (RBL) cells coated with immunoglobulin E (IgE) to substrates coated with the ligand dinitrophenol (DNP). Increasing force, decreasing DNP substrate density, and decreasing cell surface IgE density all led to decreasing adhesion. Experiments performed at low IgE cell surface densities, in which few tethers from between cell and substrate suggest individual tethers have a binding strength of 2 to 4 microdyne, in agreement with previous measurements of the force to uproot receptors from the plasma membrane. We use this system to show how subpopulations expressing different numbers of cell surface receptors may be separated by exploiting their differential adhesiveness to substrates.
Two methods of selecting smoothing splines applied to fermentation process data
Authors: Thornhill Nina F. , Manela Mauro , Campbell John A. , Stone Karl M. 
Published: June 2004

AbstractTwo methods for generating smoothing splines are compared and applied to data from a fed‐batch fermentation process. One method chose both the degree of the spline and its parameters by minimizing the generalized cross validation (GCV) function using a genetic algorithm (GA). The other method adjusted the smoothing spline to a specified chi‐square goodness‐of‐fit, requiring prior knowledge of the measurement variability. The GCV/GA method led to excellent results with all the fermentation data records. The goodness‐of‐fit method gave a family of spline fits; splines with a low percentage fit extracted trends from the data, while for general use a 50% fit appeared satisfactory. The goodness‐of‐fit method executed more quickly than the GCV/GA method, but the GCV/GA method was more generally applicable as it chose both the degree of the spline and the amount of smoothing automatically.
Process monitoring and diagnosis by multiblock PLS methods
Authors: MacGregor John F. , Jaeckle Christiane , Kiparissides Costas , Koutoudi M. 
Published: June 2004

AbstractSchemes for monitoring the operating performance of large continuous processes using multivariate statistical projection methods such as principal component analysis (PCA) and projection to latent structures (PLS) are extended to situations where the processes can be naturally blocked into subsections. The multiblock projection methods allow one to establish monitoring charts for the individual process subsections as well as for the entire process. When a special event or fault occurs in a subsection of the process, these multiblock methods can generally detect the event earlier and reveal the subsection within which the event has occurred. More detailed diagnostic methods based on interrogating the underlying PCA/PLS models are also developed. These methods show those process variables which are the main contributors to any deviations that have occurred, thereby allowing one to diagnose the cause of the event more easily. These ideas are demonstrated using detailed simulation studies on a multisection tubular reactor for the production of low‐density polyethylene.
Diagnosis of multiple simultaneous fault via hierarchical artificial neural networks
Authors: Watanabe Kajiro , Hirota Seiichi , Hou Liya , Himmelblau D. M. 
Published: June 2004

AbstractWe discuss a new type of macroarchitecture of neural networks called a HANN and how to train it for fault diagnosis given appropriate data patterns. The HANN divides a large number of patterns into many smaller subsets so the classification can be carried out more efficiently via an artificial neural network. One of its advantages is that multiple faults can be detected in new data even if the network is trained with data representing single faults. The use of a HANN is illustrated in fault diagnosis of a chemical reactor.
Stability in optimal design: Synthesis of complex reactor networks
Authors: Kokossis A. C. , Floudas C. A. 
Published: June 2004

AbstractA systematic methodology applicable to the optimal design of stable process systems is presented. It is based on the formulation of a parametric problem that provides bounds on the optimal stable solution and an iterative algorithmic approach that attains convergence of the bounds in a finite number of iterations. The bounds on the optimal stable solution are based on analytical expressions of bounds on the eigenvalues of the Jacobian matrix using the concept of the measure of the matrix. When extended to the synthesis problem of reactor networks, the approach is able to couple the optimization problem with stability issues even in cases where the number of reactors is large and the reaction mechanism is described by a general complex reaction scheme. Furthermore, since at the synthesis level the reactor network represents an exhaustive superposition of the existing structural and operational alternatives, the approach fully exploits these alternatives and coordinates a weighted optimal search that improves the objective and accommodates a stable reactor network. This approach is not restricted to the synthesis of reactor networks and can be applied to the design of total process flowsheets.
Formulations for three‐phase flash calculations
Authors: Chien Henry Hung‐Yeh 
Published: June 2004

AbstractA study of flash equations associated with multicomponent systems that can form three phases at a given temperature and pressure indicated that different equations are needed at different boundaries of the solution space. This problem dictates that one‐ and two‐phase trial solutions be obtained first on the boundaries prior to a search in the three‐phase interior region. Two new formulations of the flash equations have been developed to avoid this problem. Solutions at boundaries as well as those in the three‐phase region can now be obtained with a single search procedure. The new formulations are made using functions that are monotonic in the selected coordinates. These properties facilitate the use of nested, single‐variable search methods. Interpolating with second‐order functions, when applicable, nested search methods are often faster than two‐dimensional simultaneous search methods. Tests of these formulations have demonstrated the advantages of these characteristics.
Modeling of combined discrete/continuous processes
Authors: Barton P. I. , Pantelides C. C. 
Published: June 2004

AbstractThe dynamic behavior of processing systems exhibits both continuous and significant discrete aspects. Process simulation is therefore a combined discrete/continuous simulation problem. In addition, there is a critical need for a declarative process modeling environment to encompass the entire range of processing system operation, from purely continuous to batch. These issues are addressed by this article.A new formal mathematical description of the combined discrete/continuous simulation problem is introduced to enhance the understanding of the fundamental discrete changes required to model processing systems. The modeling task is decomposed into two distinct activities: modeling fundamental physical behavior, and modeling the external actions imposed on this physical system. Both require significant discrete components. Important contributions include a powerful representation for discontinuities in physical behavior, and the first detailed consideration of how complex sequences of control actions may be modeled in a general manner.