bluuebunny/crossref_metadata_2025_split huggingface dataset:
Separation of a helium‐methane mixture in permeators with two types of polymer membranes
Authors: Perrin J. E. , Stern S. A. 
Published: June 2004

AbstractThe separation of a HeCH4 mixture containing 9.95 mol% He in permeator modules that incorporate two different types of polymer membranes was studied theoretically and experimentally. The membranes were symmetric dense capillaries of silicone rubber and asymmetric hollow fibers of cellulose triacetate. These membranes exhibit reverse selectivities for He and CH4, silicone rubber being more permeable to CH4, and cellulose triacetate more permeable to He. The simultaneous use of these two types of membranes in a permeator enhances the enrichment and recovery of He compared to the levels obtained with a single‐membrane permeator utilizing either membrane alone. The experimental results were found to confirm the theoretical predictions, the agreement being better at the lower stage cuts.
Measuring diffusion coefficients by Taylor's method of hydrodynamic stability
Authors: Quinn J. A. , Lin C. H. , Anderson J. L. 
Published: June 2004

AbstractDiffusion coefficients for liquid solutions can be measured using a hydrodynamic stability criterion first derived by G. I. Taylor. This method is used in the present work to determine diffusion coefficients for a range of solutes from small molecules to colloidal particles, at infinite dilution and at finite concentrations. The method is simple and accurate and seems to have wide applicability. Taylor's stability criterion can also be used to establish known, linear concentration gradients of several different solutes in one column of fluid, and one solute can be used to create a desired gradient of a second solute.
Dynamic studies of catalyst poisoning: Effect on adsorption and surface reaction rates for hydrogenation of α‐methyl styrene by Pd/Al2O3
Authors: Chen Song‐Ying , McCoy B. J. , Smith J. M. 
Published: June 2004

AbstractPulse‐response data for the hydrogenation of α‐methyl styrene were obtained as a function of poisoning of the Pd/Al2O3 catalyst. The reaction is a first‐order, reversible adsorption of hydrogen followed by a first‐order, irreversible surface reaction. The experiments, at 298 to 323 K and atmospheric pressure, were carried out in a three‐phase slurry reactor for which mass transport effects could be accurately accounted.Independent adsorption equilibrium data in cumene slurries showed that adsorption occurred to the same extent on both poisoned and unpoisoned sites with a heat of adsorption, ΔHc = −16.3 kJ/mol. Converted to styrene as the slurry liquid, ΔHs = −20.9 kJ/mol.The zero and first moments of the response curves indicated that the rate constant for the surface reaction was independent of the extent of poisoning. The analysis required developing a new theory for interpreting dynamic data where reactant adsorption occurred on both poisoned and unpoisoned sites. The rate constant (per unit mass of catalyst) for adsorption decreased continuously to zero as the extent of poisoning increased.The results are consistent with the concept that poisoning reduced the number of sites active for reaction, but that the activity per site for the surface reaction was constant. However, the activity per site for adsorption, while constant at poison levels up to 40%, appeared to decrease sharply at higher levels.
Unsteady heat convection over circular cylinders
Authors: Kim B. K. , Vandenbrink D. J. , Cramer M. S. , Telionis D. P. 
Published: June 2004

AbstractNumerical calculations of the velocity and temperature fields were conducted for unsteady flows over a single circular cylinder and a bundle of cylinders. Periodic disturbances, natural or externally imposed, were considered. Periodic and averaged heat transfer rates were examined. Results compare favorably with experimental data. Calculations were carried out to predict heat transfer rates in regimes of unsteady flows that have not been tested experimentally.
Modeling and analysis of biospecific adsorption in a finite bath
Authors: Arve B. H. , Liapis A. I. 
Published: June 2004

AbstractA general model is presented and used to predict the dynamic behavior of the adsorption and wash stages of biospecific adsorption (affinity chromatography) in a finite bath. The model accounts for film and diffusional mass transfer resistances as well as for the rates of interaction between adsorbates and ligands. The model is applicable to single and multicomponent biospecific as well as nonspecific adsorption, and the adsorbates may be monovalent or multivalent. The predictions of the model are compared with the experimental data of the adsorption of β‐galactosidase onto immobilized anti‐β‐galactosidase.The results of biospecific adsorption of bivalent adsorbates indicate that a competition for ligands occurs between molecules forming one‐site interaction and two‐site interaction complexes. This competition can lead to the displacement of the adsorbate from the adsorbate‐ligand complex whose formation is least favored.
Hydrodynamics of gas‐liquid‐solid annular fluidization
Authors: Fan Liang‐Shih , Kitano Kunihiro , Kreischer B. E. 
Published: June 2004

AbstractIn a strict sense, operation of the three‐phase ebullated bed reactor used in the H‐Oil process is not characterized by conventional three‐phase fluidization, but by annular three‐phase fluidization. In annular three‐phase fluidized beds differences in the hydrodynamic behavior over that found in conventional beds occur through changes in the bubble behavior. The addition of a concentrically located inner column in a gas‐liquid‐solid fluidized bed promotes bubble coalescence. This increase in coalescence can be observed either through changes in the liquid velocity of transition from the coalesced bubble regime to the dispersed bubble flow regime or through changes in holdup behavior. A hydraulic diameter defined for the annulus region proves suitable when comparing different annular systems having the same outside column diameter, but unsuitable when comparing systems having different outside column diameters.
Measurement of critical temperatures of thermally unstable n‐Alkanes
Authors: Smith R. L. , Teja A. S. , Kay W. B. 
Published: June 2004

AbstractA modified sealed‐tube apparatus has been developed for the measurement of the critical temperatures of thermally unstable fluids. The apparatus has been used to measure the critical temperatures of the normal alkanes from n‐octane to n‐hexadecane. Since the higher alkanes (with more than 10 carbon atoms) decompose at temperatures well below their critical temperatures, a new method of analysis of the apparent critical temperature vs. time data has been developed. This method employs reaction kinetics based on an irreversible first‐order reaction and is used to linearize the data and to perform an unambiguous extrapolation to the critical temperature of the undecomposed substance. The method is successful because the temperature history of the substance is recorded by computer, and ampoule contents are analyzed at the completion of the experiment. The critical temperatures of the n‐alkanes reported in this paper have been compared with values found in previous studies.
A scaling procedure for the structural and interaction analysis of dynamic models
Authors: Bonvin Dominique , Mellichamp D. A. 
Published: June 2004

AbstractMany techniques that are used for analyzing the structure of large‐scale, interactive systems (including the structural dominance analysis and singular‐value decomposition methods) require a careful scaling of input and output variables to yield useful results. A suitable scaling procedure motivated by physical arguments and aimed at expressing input and output variables in common terms is presented and illustrated through several examples, including nonlinear lumped‐parameter and distributed‐parameter models.
Alkali‐alumina sorbents for high‐temperature removal of SO2
Authors: Gavalas G. R. , Edelstein Sergio , Flytzani‐Stephanopoulos M. , Weston T. A. 
Published: June 2004

AbstractThe high‐temperature removal of SO2 by sorbents consisting of sodium and lithium salts supported on α‐Al2O3 has been investigated with emphasis on the chemistry of regeneration. The sulfated sorbents were regenerated by reduction with CO at 700–800°C in a thermogravimetric analyzer and a packed‐bed microreactor. Sulfur removal from the sorbent and distribution of gaseous products were measured at different alkali loadings, temperatures, and CO concentrations. The results are interpreted in terms of a network of reactions wherein alumina is important as a catalyst and as a reactant. During regeneration sulfate is converted to aluminate and sulfide, the fraction of aluminate defining the extent of regeneration. The rate and extent of sulfur removal increase with the ratio of alumina to alkali and are higher in the presence of lithium. The product gas consists of SO2, COS, and elemental sulfur, the latter compound constituting up to 35% of the sulfur removed.
A cautious self‐tuning controller for chemical processes
Authors: Papadoulis A. V. , Tsiligiannis C. A. , Svoronos S. A. 
Published: June 2004

AbstractAn adaptive controller is presented that is able to perform effectively in the presence of nonlinearities and of model uncertainty typical of industrial processes. The controller incorporates a minimum variance part and a caution part. The latter is independent of the estimated model and becomes dominant in the case of a large mismatch between plant and estimated model. Application to a simulated nonlinear continuous stirred‐tank reactor demonstrates its effectiveness, even when other adaptive controllers give unsatisfactory performance.
Design of enzyme‐pH electrodes
Authors: Varanasi Sasidhar , Stevens R. L. , Ruckenstein E. 
Published: June 2004

AbstractA theoretical framework useful for predicting the steady state response of enzyme‐pH electrodes is developed. The model takes into account that the catalytic activity of the enzymes as well as the degree of dissociation of the product acids and bases is strongly dependent upon the local pH, and that buffering salts present in solution facilitate the transport of H+ ions. It is shown that the electrode should operate under substrate diffusion‐limited conditions and the concentration of H+ ions should not have steep variations within the enzymic membrane. This condition can be fulfilled by adjusting the buffer concentration in the bulk solution. In the latter conditions the electrode response does not depend on the actual kinetics of the enzymic reaction, and can be predicted by an algebraic equation. The predictions are in excellent agreement with the experiments on penicillinase‐pH and urease‐pH electrodes.
Feedback control of CSD in a KCL crystallizer with a fines dissolver
Authors: Randolph A. D. , Chen Li , Tavana Aria 
Published: June 2004

AbstractOn‐line crystal size distribution control in an 18 L KCl crystallizer, equipped with a fines dissolver, was experimentally studied using inferential control of nuclei density. The control algorithm used was proportional control of inferred nuclei density by manipulation of fines removal rate. A sudden 5–8°C drop in the temperature of the crystallizer was used as a standard upset, which produced a fairly reproducible burst of nuclei. Nuclei density was then estimated from the fine crystal distribution in the fines loop using a light‐scattering instrument. The control study was implemented by a computer program that used the current value of nuclei density to calculate updated set points of the fines removal rate. Simple proportional control of nuclei density in response to changes in fines removal rate was shown to be an effective way to minimize fluctuations in the product crystal size distribution that are caused by nucleation disturbances.
Singular optimal control strategy for a fed‐batch bioreactor: Numerical approach
Authors: Menawat Anil , Mutharasan R. , Coughanowr D. R. 
Published: June 2004

AbstractThe production of bakers' yeast in a fed‐batch bioreactor can be maximized by controlling the substrate feed rate. This leads to a singular optimal control problem. An exact solution initially based on a heuristic argument and later quantified by the generalized Legendre‐Clebsch convexity condition is obtained. A numerical technique, obtained by embedding the singular problem in a sequence of nonsingular problems that converge to the singular one in a limit as ϵ → ∞ is demonstrated.
Flow of a thin liquid layer due to ambient disturbances
Authors: Ruschak K. J. 
Published: June 2004

AbstractA closed‐form solution for the transient deformation of a thin liquid layer caused by ambient pressure disturbances predicts the level of disturbances that will produce significant flow in the time available. The effects of viscosity, gravity, surface tension, and a soluble surface‐active agent are included in the analysis. The major simplification is the use of the lubrication approximation to the equations of flow. Nearly stationary pressure disturbances are found to be more dangerous than moving disturbances. Surface tension gradients arising from convection of surfactant in the surface oppose flow and reduce the film deformation. The thermodynamic properties of the surfactant, as well as its diffusion coefficient, are important in determining whether significant surface tension gradients develop. However, the effectiveness of a surfactant at minimizing film deformation also depends upon flow parameters such as the natural time scale for flow.
Scanning electron microscopy studies of polymer melt devolatilization
Authors: Albalak R. J. , Tadmor Z. , Talmon Y. 
Published: June 2004

AbstractThe devolatilization mechanism of polystyrene was studied by scanning electron microscopy. Strands of molten polystryene, containing 2,300 ppm styrene, and molten polystyrene containing 5% pentane, were extruded into a heated vacuum chamber. The strands were abruptly frozen, then fractured under liquid nitrogen and their morphology studied with scanning electron microscopy. A rich variety of morphological features in the core and on the surface of strands was discovered. These include micro‐ and miniblisters, fibrous structures, and crusty nodules on the inner surfaces of large macrobubbles. The source of these morphological features and their relevance to devolatilization is discussed.
Panel movement effects on solution flow in through‐holes of printed circuit panels
Authors: Galasco R. T. , David A. P. , Shaffer R. R. 
Published: June 2004

AbstractA hydrodynamic model is developed relating the movement of printed circuit panels to solution flow in through‐holes. Qualitative and quantitative model verification is experimentally established. Effects of external gas bubbling on hole solution transport are elucidated. Based on the hydrodynamic model, panel motion criteria for contamination‐free and fast chemical processing are introduced. Limits of mechanical panel movement as a method for processing holes of different geometry with typical wet chemical process baths are addressed.
A mechanistic model for two‐phase annular‐mist flow in vertical pipes
Authors: Yao S. C. , Sylvester N. D. 
Published: June 2004

AbstractThe physical phenomena associated with two‐phase annular‐mist flow in vertical pipes are considered. A new mechanistic model is developed to predict liquid entrainment, liquid film thickness, in situ velocities, and pressure drop. The model is compared to field data and found to be superior to the three commonly used empirical correlations.
Self‐tuning control with decoupling
Authors: Chien I‐Lung , Seborg D. E. , Mellichamp D. A. 
Published: June 2004

AbstractA new method to design adaptive, self‐tuning controllers is presented that incorporates decoupling for multivariable control problems. The algorithm is shown to result from two very different derivations. The first approach employs multiple single‐input/single‐output self‐tuning controllers but with a classical decoupling scheme incorporated; the second approach utilizes a novel selection of design parameters in an existing multivariable self‐tuning control method. The decoupling self‐tuning controller is capable of handling unknown or time‐varying time delays. Simulation studies utilizing two distillation column models show that the controller can provide excellent control even for highly nonlinear and highly interacting processes.
An experimental study of the effect of turbulent mixing on the selectivity of competing reactions
Authors: Mehta R. V. , Tarbell J. M. 
Published: June 2004

AbstractAn experimental study of the effect of turbulent mixing on the selectivity of a parallel‐consecutive reaction system (A + B → R; R + B → S) has been carried out in an unmixed feedstream (multijet) tubular reactor. Fluid mechanical characterization of the reactor by pulsed ultrasound Doppler velocimetry reveals that the mean and rms velocity fields are nearly constant over eight‐ninths of the reactor length. Axial profiles of mean product concentration (R and S) have been measured spectro‐photometrically with a fiber‐optic probe under constant hydrodynamic conditions but with variable feed concentration conditions. The concentration profiles (particularly the S profile) show very large deviations from the perfect mixing (classical plug flow reactor) limit. These data provide a good basis for discriminating among the many models of mixing and reaction available in the literature. This is demonstrated with two examples: the four‐environment model, which fits the data well, and the interaction by exchange with the mean model, which does not.
The kinematics of fountain flow in mold‐filling
Authors: Coyle D. J. , Blake J. W. , Macosko C. W. 
Published: June 2004

AbstractMoldability criteria and process optimization for both reactive and thermoplastic injection molding hinge on the mold‐filling step. The fluid mechanics of the filling step is typically described in terms of a one‐dimensional main flow and a complex two‐dimensional flow near the advancing front, often termed the “fountain flow.” A unique apparatus which permits direct observation of the fountain flow in a rectangular cavity is described. The motion of tracer lines as well as the pathlines have been photographed for both Newtonian and shear‐thinning liquids. The data show clearly the main flow, the transition to the front flow, and the deceleration and acceleration zones in the fountain flow, which lead to a “mushrooming” of the tracer line.In addition, Galerkin finite‐element analysis is used to predict the isothermal free‐surface flow of a Newtonian liquid near the advancing front between parallel plates. The most interesting visualization of the calculated flow is obtained by tracking lines of material, thus producing numerical tracer experiments. The calculations show the widely varying residence times and the complex shear and extensional deformation histories of fluid elements as they move through the fountain flow region. The calculations are in agreement with the experiments and clarify previous results, both theoretical and experimental, that did not capture the details of the entire flow field.
The role of porosity in filtration. Part XI: Filtration followed by expression
Authors: Tiller F. M. , Yeh C. S. 
Published: June 2004

AbstractThis paper addresses the question of the relative amounts of liquid removed during filtration and expression as a function of cake compressibility. As liq
uid flows through a porous cake, the accumulative drag collapses the particulate structure, thereby increasing the solid content and displacing the liquid. The use of pump pressure in filtration represents the simplest hydraulic deliquoring process. In expression operations, pistons, membranes, rollers or belts are employed to squeeze the particulate cake after filtration is complete.Filtration followed by expression at constant pressures ranging from 0.6 to 24.7 MPa (6.1‐243.6 atm) was investigated theoretically and experimentally. During filtration and the early stages of expression, the flow rate and average liquid content of highly compressible attapulgite were virtually unaffected by increasing pressure in the range investigated.
Averting extinction in autothermal catalytic reactor operations
Authors: Metchis S. G. , Foss A. S. 
Published: June 2004

AbstractA multiloop control system and an on‐line reactor operability analysis were developed for the purpose of detecting and averting extinction of the autothermal state of a laboratory catalytic reactor. The reactor system consisted of a feed‐effluent heat exchanger and two packed beds in which the exothermic reaction between hydrogen and oxygen occurred.The strategy of control was based on the preservation of the relative stability of the autothermal steady state when the reactor experienced large changes in feed concentration and flow rate. Such a strategy involved a model‐based prediction of reactor conditions that so preserved stability, and a procedure to guide the process rapidly and smoothly to those new conditions. Experiments demonstrated the successful avoidance of extinction and the orderly attainment of new operating conditions in about three reactor‐system time constants. The procedures developed could serve as a component of an on‐line expert system for safe reactor operations.
Phase holdups in three‐phase fluidized beds
Authors: Lee S. L. P. , de Lasa H. I. 
Published: June 2004

AbstractThe local bubble frequency, the local phase holdups and the local bed porosity in three‐phase fluidized beds were measured. Air, water, and 250 μm glass beads were used as the gas, liquid, and solid phases. The effects of gas and liquid velocities on phase holdups were studied. Time‐averaged local gas holdup and bubble frequency were measured by an optical fiber probe. Mass balances were performed at various axial positions along the fluidized beds to check the accuracy of the measurements.
Hindered transport of large molecules in liquid‐filled pores
Authors: Deen W. M. 
Published: June 2004

AbstractTransport in liquid‐filled pores of molecular dimensions plays an important role in membrane separations, in various forms of chromatography, and in catalysis, to name a few examples. A frequent observation is that if the pore dimensions are of the same order as those of a solute molecule, the apparent diffusion coefficient of that solute is much lower than in bulk solution. Likewise, rates of convective transport of such solutes are generally lower than the product of bulk concentration and volume flow rate. Thus, solute transport is typically “hindered” or restricted. A key objective of research on hindered transport is to be able to predict the applicable transport coefficients from such fundamental information as the size, shape, and electrical charge of the solutes and pores. The present status of this research is reviewed.
Trickle‐bed reactors: Liquid diffusional effects in a gas‐limited reaction
Authors: Beaudry E. G. , Duduković M. P. , Mills P. L. 
Published: June 2004

AbstractA model is developed for predicting the performance of a partially wetted trickle‐bed reactor for a gas‐limiting reaction of order less than or equal to one. The model indicates that under certain conditions the liquid reactant may affect the reaction rate due to its inability to rapidly diffuse to catalyst areas that are in direct contact with the gas. This model is the first to explain and predict on a rational basis the experimental results for the hydrogenation of diluted ć‐methylstyrene and aqueous maleic acid reported in the literature. A criterion that determines when liquid reactant effects can be expected is developed and reported.