bluuebunny/crossref_metadata_2025 huggingface dataset:
An experimental and modeling study of softening coal pyrolysis
Authors: Oh Myongsook S. , Peters William A. , Howard Jack B.
Published: June 2004

A quantitative model of softening coal pryolysis is developed and tested against observed behavior. The model treats intraparticle transport of gases and metaplast throughout the softening stage of pyrolysis via growth of bubbles uniformly dispersed in the molten coal. The model quantitatively describes the transient softening behavior including the initiation, duration, and magnitude of plasticity and swelling of the particle. The model kinetic parameters are derived from experiments, in which a highly softening Pittsburgh No. 8 bituminous coal was pyrolyzed, and total weight loss, and yields and molecular weight distributions of tars and pyridine extractables of cooled chars were measured. Model predictions of effects of pressure, particle diameter and temperature on tar yields and weight losses, of effects of pressure on swelling ratio, and of effects of heating rate on plasticity are presented. The model provides good fits to the laboratory data and predicts trends in pyrolysis behavior in good qualitative accord with expectations based on published data.
Thermodynamics of aqueous systems containing hydrophilic polymers or gels
Authors: Prange Monika M. , Hooper Herbert H. , Prausnitz John M.
Published: June 2004

A quasichemical partition function is applied to represent the thermodynamic properties of aqueous solutions of nonelectrolytes, including linear polymers and crosslinked polymers (gels). The partition function extends conventional lattice theory; to take into account strong specific interactions (hydrogen bonds) as encountered in aqueous solutions, each molecule (polymer segment) may possess three energetically different types of contact sites. We distinguish between sites that interact through dispersion forces and sites that can participate in a hydrogen bond; hydrogen‐bonding sites are divided into electron‐pair donating sites and electron‐pair accepting sites. The Helmholtz energy of the mixture is obtained using an oriented quasichemical approximation. The final equation contains three independent adjustable binary parameters; these are the exchange energies for different types of contact paris. To represent quantitatively upper or lower critical solution phenomena, we include the semitheoretical fluctuation correction recently proposed by de Pablo. Comparison with experimental data indicates that the proposed molecular‐thermodynamic model may be useful for representing phase equilibria for a variety of aqueous systems including swelling equilibria for hydrophilic gels.
Periodic separating reactors: Experiments and theory
Authors: Vaporciyan Garo G. , Kadlec Robert H.
Published: June 2004

The novel combination of a pressure swing adsorber (PSA) with a periodic flow‐forced packed‐bed reactor is explored. The device provides integral component separation and reaction. Feed sequences studied for the periodic separating reactor (PSR) were those of rapid, single‐bed pressure swing adsorption (RPSA). The experimental investigation employed CO oxidation over a packed bed of supported platinum catalyst and molecular sieve adsorbent. A reaction rate limited model is formulated and solved for a variety of irreversible and reversible reactions.

The presence of irreversible chemical reaction is shown to greatly enhance the separation achievable by RPSA alone. For a wide range of inlet CO/O2 ratios, CO2 production could be increased up to two times over steady‐state plug‐flow reactor operation, while providing a recycle stream without phase change or extractive procedures. Selectivity and conversion improvements were predicted for multiple reaction systems. Other unusual features of operation, such as separation reversals, were also predicted and observed.
Causality‐based failure‐driven learning in diagnostic expert systems
Authors: Rich Steven H. , Venkatasubramanian Venkat
Published: June 2004

It has been recognized that a diagnostic expert system's ability to learn from past experience will improve its diagnostic efficiency as well as make it acquire new heuristics. In this paper, we propose a failure‐driven learning scheme by which the expert system automatically updates its compiled knowledge by acquiring new heuristics or refining existing heuristics. A heuristic is refined if it hypothesizes the wrong causal origin during a diagnosis. Using its deep‐level knowledge of the process, the expert system draws inductive inferences from causal models to determine why the hypothesis proposed by the heuristic is inconsistent with the current state of the process. The refinement limits the applicability of the heuristic and prevents it from firing if a similar situation were to subsequently arise.
Diffusion and solid dissolution/precipitation in permeable media
Authors: Novak Craig F. , Schechter Robert S. , Lake Larry W.
Published: June 2004

We have developed an analytical solution which describes mineral zonation caused by diffusion in permeable media. For a semiinfinite domain, the species conservation equations transform into ordinary differential equations that yield a closed‐form solution. The solution exhibits shock dissolution/precipitation fronts and gradual (nonshock) precipitation fronts. The solution can exhibit regions (gaps) containing no reactive solids which separate moving dissolution and precipitation fronts. The analysis is, in principle, extendable to include intraaqueous reactions, although the mathematics quickly becomes intractable.

Numerical simulation exhibits all of the features of the more restricted analytical solution and is in good agreement with the data on hydroxyapatite dissolution taken by Kim and Cussler (1987).
Laser capillary spectrophotometry for drop‐size concentration measurements
Authors: Bae J. H. , Tavlarides L. L.
Published: June 2004

A laser capillary spectrophotometric technique (LCS), based on the method of Verhoff et al. (1969, 1977), is developed for the rapid and accurate determination of the bivariate drop size‐concentration distribution for reactive liquid‐liquid dispersions. The method employs a precision bore capillary, through which a sample is drawn from the mixing vessel by a vacuum pump. An appropriate light source is used to distinguish between the slugs of dispersed phase and continuous phase as the sample passes by two detection points in the capillary. The optical device is designed to measure drop size by the difference of light refraction between the two phases and drop concentration by the light absorbance of the organic phase in the drop. The new technique can automatically measure drop‐size and drop‐concentration distributions of thousands of drops within a few minutes. This technique can provide important information on the state of a reactive dispersion in situ and can provide information on the influence of dispersed‐phase mixing effects on mass transfer and/or reactions in liquid‐liquid dispersions. Further, the LCS technique provides the capability for on‐line monitoring and control of units processing liquid dispersions.
Adaptive extremum control using approximate process models
Authors: Golden Melinda P. , Ydstie B. Erik
Published: June 2004

The proposed on‐line adaptive optimization technique incorporates a priori knowledge in the form of approximate steady‐state models. The steady‐state geometric characteristics of the model are periodically recalculated using a Hammerstein system and recursive least squares. The algorithm is self‐tuning in the sense that it converges to the optimal performance provided that a matching condition is satisfied and that the data are persistently exited. Simulation and experimental studies performed on a continuous fermentation system have been conducted to illustrate the performance of the optimization algorithm and demonstrate the viability of adaptive extremum control.
Competition among flow, dissolution, and precipitation in porous media
Authors: Rege Sunil D. , Fogler H. Scott
Published: June 2004

A theoretical and experimental study has been carried out on flow, dissolution, and precipitation in porous media. Flow experiments were performed on linear carbonate cores using acidic ferric chloride solutions. Dissolution of the carbonate by the acid causes an increase in the solution pH, thereby precipitating ferric hydroxide. This precipitate plugs up the pore throats in the medium and increases the resistance to fluid flow. Fluctuations in the permeability ratio were observed during core flood experiments, confirming the competition between channel formation due to dissolution and pore plugging due to precipitation. The evolution of the pore structure was characterized by Wood's metal castings.

A network model has also been developed to describe flow and reaction in porous media. The model was used to simulate the ferric chloride system, and pressure oscillations predicted by the model show identical trends to those observed experimentally. Additionally, the evolution of pores in the network were graphically represented.
High‐temperature adsorption of alkali vapors on solid sorbents
Authors: Punjak W. A. , Uberoi M. , Shadman F.
Published: June 2004

Vapors of alkali metal compounds can be removed from coal combustion and gasification flue gases using high‐temperature aluminosilicate sorbents. The fundamentals of alkali adsorption on kaolinite, bauxite, and emathlite are compared and analyzed both experimentally and through theoretical modeling. The results show that the process is not a simple physical condensation, but a complex combination of diffusion and reaction. The kinetics of adsorption on these sorbents have similarities: the process is diffusion‐influenced, the rate decreases with time, and there is a final saturation limit. There are, however, differences in reaction mechanisms leading to potentially different applications for each sorbent. In adsorbing alkali chloride vapors, kaolinite and emathlite release all the chlorine back to the gas phase while bauxite retains some of the chlorine. Moreover, the products of reaction with emathlite have a melting point significantly lower than those for kaolinite and bauxite. Therefore, emathlite is more suitable for lower‐temperature sorption systems downstream of the combustors/gasifiers, while kaolinite and bauxite are suitable as in‐situ additives.
Synthesis of mass exchange networks
Authors: El‐Halwagi Mahmoud M. , Manousiouthakis Vasilios
Published: June 2004

The purpose of this work is to introduce the notion of synthesizing mass‐exchange networks (MEN's). A systematic, two‐stage, procedure is proposed for the synthesis of cost‐effective MEN's. In the first stage, a thermodynamically‐oriented procedure is used to identify the thermodynamic bottlenecks (pinch points) that limit the extent of mass exchange between the rich and the lean process streams. Preliminary networks, that feature maximum mass exchange, are generated at this stage. The objective of the second stage is to improve the design of these preliminary networks so as to develop a final configuration of the MEN that satisfies the assigned exchange duty at minimum venture cost. This approach is applied to the synthesis of MEN's with single‐component targets as well as multicomponent, compatible targets. An illustrative example on the sweetening of coke‐oven gas is presented to demonstrate the applicability of the proposed synthesis procedure.
Porosity effects in hydrogen reduction of iron oxides
Authors: Fortini Arthur J. , Perlmutter Daniel D.
Published: June 2004

The rates of reduction of hematite to magnetite and of magnetite to iron in hydrogen / nitrogen / water vapor atmospheres were each studied with respect to variation in temperature, gas composition, and solid pore structure. It is shown that at temperatures below 350°C, the reactions are under chemical kinetic control, and diffusional limitations are negligible. The activation energies for the reduction of hematite to magnetite and of magnetite to iron were found to be 185 kJ / mol and 76.6 k J / mol, respectively. Both reactions exhibit first‐order behavior for hydrogen partial pressures less than 76 kPa. The conversion and rate data for each reaction were interpreted in terms of the random pore model of Bhatia and Perlmutter (1980), which takes into account the detailed pore structure of the starting material as well as the changes that occur as the reaction proceeds. The model predictions of conversion with time agree with the measured data to within 2%, and the rate vs. conversion predictions agree to within 5%.
An investigation of CaO sulfation mechanisms in boiler sorbent injection
Authors: Stouffer Mark R. , Yoon Heeyoung
Published: June 2004

A laboratory differential reactor study was conducted at temperatures of 975–1,275 K to investigate CaO sulfation mechanisms with calcine (CaO) samples derived from pulverized limestones and dolomites, and hydrated limes. The limestones had 8–115 μm mean particle sizes, a range applicable for boiler sorbent injection for SO2 control. Under conditions applicable for boiler sorbent injection, the sorbent performance, in terms of initial reaction rate and saturation utilization, was limited by the SO2 pore diffusion rate and by premature pore mouth plugging by CaSO4 product and, thus, depended on CaO particle size and pore size. Hydrated lime and Na2CO3‐promoted limestones showed performance superior to that of limestones, because they produced calcines with larger pores. Intrinsic reaction rate as reported by Borgwardt and Bruce (1986) was observed at temperatures below 1, 100 K.
A macroscopic model for countercurrent gas‐liquid flow in packed columns
Authors: Dankworth David C. , Sundaresan S.
Published: June 2004

A macroscopic model based on the volume‐averaged equations of motion is presented for countercurrent gas‐liquid flow in a packed bed. The model yields a column‐limited flooding point as the loss of existence of uniform states. It correctly predicts the existence of two uniform states below the flooding point. The lower branch corresponds to the trends commonly observed experimentally. It is shown that the upper branch is made unattainable by the gas distributor/support plate at the bottom of the column. The occurrence of premature flooding induced by the support plate is also explained. It is suggested that the occurrence of spontaneous liquid segregation, necessitating frequent liquid redistribution in columns with large dumped packings and porosities, is a consequence of the loss of stability of the uniform state in the lower branch.
Dissolution equilibria and kinetics of fluorite and calcite mixtures
Authors: Qi Jian , Knaebel Kent S.
Published: June 2004

Minerals commonly contain impurities, and their dissolution involves complicated ionic equilibria and multicomponent mass transfer. This paper describes the experiments that were carried out and proposes a mechanism for dissolution behavior of fluorspar containing calcite as a major impurity in both batchwise and continuous packed‐bed systems.

The mechanism is based on analysis of coupled equilibria among the soluble species. Of more than eight potentially relevant species, only three (viz., F−, HCO3−, and Ca2+) are significant. The coupled flux equations for F− and HCO3− are written in terms of “main” and “cross” mass transfer coefficients, with the concentration of ca2+ being accounted for by electroneutrality. Only one main mass transfer coefficient needs to be determined experimentally; and other coefficients can be evaluated from it by means of simple diffusion coefficient ratios, which are determined independently. The Stanton number based on the main mass transfer coefficient is correlated with Reynolds number and the Schmidt number for packed bed dissolution.
Solid flow in the annular region of a spouted bed
Authors: Benkrid Abdelhakim , Caram Hugo S.
Published: June 2004

The solid circulation in the annular region of a 0.146 and a 0.292 m ID semicylindrical and cylindrical air spouted beds was investigated for different spouting conditions. Stroboscopic photography, stopwatch and fiber optic methods were used to measure the vertical particle velocities in the annular region. The optical fiber probe enabled the measurement of particle velocities inside the dense annular phase and was validated at the walls. Velocity profiles in half beds were very different from those found in full beds. The work was then limited to full beds. Experimental results show that the solids flow is characterized by a point sink at the nozzle entrance with the solids moving almost in plug flow higher in the bed. There is negligible entrainment of solids along the spout wall and slow, thin wall layers are observed near the walls and spout. The velocity profiles are independent of the total height of the bed. A kinematic model successfully describes the observed velocity field.
Melt transesterification of dimethyl terephthalate with ethylene glycol
Authors: Besnoin J.‐M. , Lei G. D. , Choi K. Y.
Published: June 2004

The kinetics of a semibatch melt transesterification of dimethyl terephthalate (DMT) with ethylene glycol (EG) is studied with zinc acetate as a catalyst. This paper quantifies the effect of various reactor operating conditions on the transesterification rate and the product composition distribution. Our experiments support the assumption that the methylesters in DMT and growing oligomer chains have the same reactivities for transesterification with EG and that the reactivity of hydroxyl groups in pure EG for esterification with DMT is twice that of the hydroxyl group in oligomers. With a molecular species model in which various oligomers are identified by the type of functional end groups, the progress of the transesterification and the oligomer concentration distribution were estimated and the agreement between the model predictions and the experimental data were excellent. It has also been shown that 30 wt. % of oligomers are produced for [EG]/[DMT] molar ratio of three, and up to 70 wt. % oligomers are produced at the [EG]/[DMT] molar ratio of one.
Observation of a dynamic wetting process using Laser‐Doppler velocimetry
Authors: Mues W. , Hens J. , Boiy L.
Published: June 2004

The purpose of this study is to observe the dynamic wetting process of a slide coater flow (Ca = 0.16; Re = 14.4; St = 0.0142; ΔeP = 2.5), using a specially‐developed Laser‐Doppler measuring technique.

The measurements, carried out with glycerol solutions, reveal that the observed contact line is apparent and that a thin air film is entrained between the web and the liquid surface. The liquid is accelerated along the lower free surface and attains approximately 50% of the web velocity at the apparent contact line. Downstream from the apparent contact line, the liquid is further accelerated along the air film to the web velocity at the real contact line.

The apparent contact angle increases with the capillary number Ca and air entrainment occurs at Ca = 0.25.
Improved oxygen mass transfer modeling for diffused/subsurface aeration systems
Authors: McWhirter John R. , Hutter Joseph C.
Published: June 2004

The mass transfer analysis of the oxygen transfer performance of diffused air or subsurface mechanical aeration systems has progressed very little over the past 20 years. The recently‐developed ASCE Standard method for determination of the oxygen mass transfer performance of diffused or subsurface aeration systems is based on a greatly over‐simplified mass transfer model. Although the ASCE Standard can be used to empirically evaluate point performance conditions, it does not provide a meaningful representation of the actual mass transfer process and is not capable of accurately assessing or predicting performance under changing operating or environmental conditions. A new oxygen mass transfer model has been developed which is a fundamentally more rigorous description of the actual mass transfer process in diffused aeration systems. This model can be confidently used to predict aerator performance under changing operating and environmental conditions. The model is easily adapted to numerical computer solution for routine aeration systems performance evaluation as well as process design.
Ultrapyrolysis of propane in a spouted‐bed reactor with a draft tube
Authors: Stocker Rudolf K. , Eng John H. , Svrcek William Y. , Behie Leo A.
Published: June 2004

Ultrapyrolysis or ultrarapid pyrolysis is a hydrocarbon thermal cracking process which offers the promise of greater product selectivity, higher yield and feedstock flexibility. In this paper, ultrapyrolysis of propane in a spouted bed with a draft tube was used as a test system to demonstrate these advantages. Experiments, carried out on a 20‐cm‐diameter pilot‐scale reactor, illustrate the spouted bed to be capable of achieving the extremely high reactant heating rates of up to 105 K/s and the short gas residence times of less than 500 ms necessary for this process. Moreover, reactant conversion and product yields can be enhanced by controlling the operating temperature of the bed. In addition, application of the propane pryolysis reaction scheme of Sundaram and Froment into a recently developed computer model indicates the ability to correctly simulate the spouted bed as an ultrapyrolysis reactor.
Hindered transport of spherical macromolecules in fibrous membranes and gels
Authors: Phillips R. J. , Deen W. M. , Brady J. F.
Published: June 2004

Methods are described for calculating the effects of hydrodynamic interactions on the hindered transport of solid spherical macromolecules in ordered or disordered fibrous media. These methods are applied to a medium made up of a square lattice of straight, bead‐and‐string‐type fibers. Hydraulic permeabilities and coefficients governing hindered diffusion and convection are obtained from a detailed hydrodynamic model, and the hindered transport coefficients are shown to be in very good agreement with an effective medium approach based on Brinkman's equation. The use of Brinkman's equation for the calculation of hindered transport rates in fibrous membranes and gels is validated further by comparing with experimental data from the literature.
The effect of pore structure on the char‐steam reaction
Authors: Chi Wei‐Kuang , Perlmutter Daniel D.
Published: June 2004

The kinetics of the char‐steam gasification reaction and the accompanying pore structure changes have been investigated experimentally and interpreted through the use of the random pore model of Bhatia and Perlmutter (1980) and its extensions developed in this study. To allow model evaluations, surface areas and pore‐size distributions were obtained for various partially‐reacted char samples. Surface areas follow the reaction rates as a function of conversion, supporting the interpretation that the reaction of porous char with steam is governed by the structural changes that occur as conversion proceeds. Reaction rate constants were obtained from the kinetic data.

A pyrolytic change of char mass was observed during the heatup period from room temperature to reaction temperature for each of the two char samples tested. This results in a significant increase in surface area and a decrease in pore structure parameter. It is shown that this pore structure parameter is very sensitive to changes in conversion when the initial parameter is large and the conversion is small.
Incipient fault diagnosis of chemical processes via artificial neural networks
Authors: Watanabe Kajiro , Matsuura Ichiro , Abe Masahiro , Kubota Makoto , Himmelblau D. M.
Published: June 2004

Artificial neural networks have capacity to learn and store information about process faults via associative memory, and thus have an associative diagnostic ability with respect to faults that occur in a process. Knowledge of the faults to be learned by the network evolves from sets of data, namely values of steady‐state process variables collected under normal operating condition and those collected under faulty conditions, together with information about the degree of the faults and their causes.

Here, we describe how to apply artificial neural networks to fault diagnosis. A suitable two‐stage multilayer neural network is proposed as the network to be used for diagnosis. The first stage of the network discriminates between the causes of faults when fed the noisy process measurements. Once the fault is identified, the second stage of the network estimates the degree of the fault. Thus, the diagnosis of incipient faults becomes possible.
Axial dispersion in pulsed‐, perforated‐plate extraction columns
Authors: Prvcic Leanne M. , Pratt H. R. Clive , Stevens Geoffrey W.
Published: June 2004

Continuous‐phase backmixing coefficients have been determined by continuous tracer injection for pulsed‐plate extraction columns of 72‐, 152‐ and 300‐mm‐diameter. Both single‐phase water and two‐phase kerosene‐water were studied in all three columns, together with four other solvent‐water systems in the smallest column; in all cases, water was the continuous phase. Evidence of maldistribution of the phases was obtained in the largest column. The backmixing coefficient was found to increase with column diameter in single‐phase operation, but was diameter‐independent in the two‐phase case. Alternative correlations of the data were based on dimensional analysis and on a physical model, respectively. The influence of different systems was accounted for in the latter in terms of droplet size and terminal velocity, dispersed phase holdup, and density difference. Qualitative color tracer tests on the dispersed phase gave no evidence of backmixing of this phase, although strong forward dispersion was observed in the emulsion regime.
Robust isolable models for failure diagnosis
Authors: Gertler Janos , Luo Qiang
Published: June 2004

The paper presents a design procedure to generate parity equation models for analytical failure detection and isolation. The models are in “statistically‐isolable” structure that prevents incorrect isolation decisions under marginal failure size if the residuals are tested in parallel. Of the combinatorial multitude of structurally‐suitable models, a choice is made on the basis of sensitivities with respect to different failures and robustness relative to uncertainties in selected parameters of an underlying model. A complete set of parity equations fitting the isolable structure is first generated from a state‐space model. The equations unsuitable for sensitivity are eliminated, and a suboptimally‐robust diagnostic model is obtained in a constrained discrete search over the remaining set.
Partitioning of spherical solutes into sponge‐type materials
Authors: Fanti Lisa A. , Glandt Eduardo D.
Published: June 2004

Partition coefficients are computed for hard spherical solutes in equilibrium with sponge‐type matrices containing randomly‐placed spherical cavities or pores using grand canonical Monte Carlo simulation. The random pore model is representative of a variety of disordered porous solids including porous glasses and some polymeric materials. The algorithm used brings additional realism to the problem by rigorously distinguishing between accessible and inaccessible pore space. The simulation results display significant concentration effects which are often observed experimentally and are compared to data obtained by Brannon and Anderson (1982) for the partitioning of bovine serum albumin into controlled‐pore glass.
Turbulence‐producing eddies in the viscous wall region
Authors: Lyons S. L. , Hanratty T. J. , McLaughlin J. B.
Published: June 2004

A computer simulation of turbulent flow in a channel is used to detect flow patterns related to the production of Reynolds stress. It is found that quadrant 2 and quadrant 4 events possess a streaky structure in the viscous wall region and that these events can be best understood by examining the velocity field in the y‐z plane. Large turbulence production in the viscous wall region is found to occur in updrafts and downdrafts associated with closed eddies. These eddies, on average, have a spanwise dimension of 50 wall units and a streamwise dimension of 400–450 wall units. They are often seen to originate from small attached eddies at the wall.
A neural network methodology for process fault diagnosis
Authors: Venkatasubramanian Venkat , Chan King
Published: June 2004

The ability of knowledge‐based expert systems to facilitate the automation of difficult problems in process engineering that require symbolic reasoning and an efficient manipulation of diverse knowledge has generated considerable interest recently. Rapid deployment of these systems, however, has been difficult because of the tedious nature of knowledge acquisition, the inability of the system to learn or dynamically improve its performance, and the unpredictability of the system outside its domain of expertise.

This paper proposes a neural‐network‐based methodology for providing a potential solution to the preceding problems in the area of process fault diagnosis. The potential of this approach is demonstrated with the aid of an oil refinery case study of the fluidized catalytic cracking process. The neural‐network‐based system successfully diagnoses the faults it is trained upon. It is able to generalize its knowledge to successfully diagnose novel fault combinations it is not explicitly trained upon. Furthermore, the network can also handle incomplete and uncertain data. In addition, this approach is compared with the knowledge‐based approach.
Mass transfer with chemical reaction in a threehyphen;phase foam‐slurry reactor
Authors: Stangle Gregory C. , Mahalingam R.
Published: June 2004

Studies on mass transfer coupled with chemical reaction were conducted in a gas‐liquid‐solid foam bed contactor under a variety of operating conditions in order to establish the controlling parameters for such a contacting system. Analytical equations were derived in order to predict the influence of solids dissolution on the specific rate of absorption in the stable foam stage of a three‐phase foam‐slurry reactor. Experimental investigations on the absorption of carbon dioxide in the presence of an aqueous foam‐slurry containing calcium hydroxide particles were carried out in order to verify the theoretical model. Results indicate that the gas‐liquid interfacial area and gas flow rate strongly affected the rate of mass transfer, while solids holdup affected mass transfer rates only moderately over the range of solids holdup studied. A comparison with conventional chemical reactor configurations (e.g., bubble column, CSTR) was made to demonstrate the gas‐liquid‐solid system, for which this novel reactor might be employed. Foam stability enhancement, due to the presence of solid particles, was not observed.
Extensional flow of a two‐phase fiber
Authors: Park Chang‐Won
Published: June 2004

A steady, isothermal flow of a two‐phase fiber spinning has been studied. To investigate the spinline velocity profile affected by the interaction between two fluids with different rheological properties, a Newtonian and an upper‐convected Maxwell fluid were considered to be the core and skin layers, respectively. Unlike the one‐dimensional analysis, which has been the typical approach for spinning flows, radial dependency of the flow field was maintained in our analysis. Consequently, a set of partial differential equations were derived for the flow field in the draw‐down region where lubrication scalings are applicable. Asymptotic solutions were then obtained for two limiting cases, where the Deborah number of the skin layer is small and the applied axial tension is large. When the Deborah number of the skin layer is small, a velocity correction to the Newtonian profile indicates a strong effect of the flow rate ratio as well as the shear viscosity ratio of the two fluids. For the case of a large applied tension, which is more relevant to industrial practice, very interesting flow behaviors are predicted. In this limit, the viscoelasticity effect of the skin layer is shown to be dominant and dictates the mechanics of the flow even when both its flow rate and shear viscosity may be much smaller than those of the Newtonian core layer. The result also predicts that hoop stress has a negligible effect on the axial velocity profile.
A dynamic model for the interaction of caustic reagents with acidic oils
Authors: Chiwetelu Chris I. , Hornof Vladimir , Neale Graham H.
Published: June 2004

This paper describes the mechanisms and a quantative analysis of the interaction between a multicomponent acid mixture with a spectrum of caustic solutions. A physico‐chemical model of the acidic oil/caustic system has been proposed which demonstrates the effect on dynamic interfacial tension (IFT) of variations in caustic concentration as well as changes in the initial composition and ionization properties of the constituent acids of the oleic phase. The model relies on the Langmuirian theory of interfacial sorption kinetics in addition to the Nernstian theory of convective diffusion. Pertinent kinetic and mass transfer parameters for all contributing surface‐active species were determined from a recently proposed single‐component dynamic model (Chiwetelu et al., 1988a). The validity of this multicomponent dynamic model was confirmed by the close agreement between predicted IFT and experimental data for a binary carboxylic acid system in contact with a broad range of caustic concentrations.
Shear thickening (dilatancy) in concentrated dispersions
Authors: Boersma Willem H. , Laven Jozua , Stein Hans N.
Published: June 2004

A new criterion is introduced for the onset of shear thickening in a concentrated dispersion. The criterion follows from the assumption that shear thickening occurs when the shear forces overrule the interparticle forces. A force balance at small interparticle distances is used to predict the dependence of this critical shear rate on the volume fraction. It is deduced that the critical shear rate is proportional to the interparticle distance, has a linear dependence on the magnitude of the stabilizing force, an inverse linear dependence on the dispersion medium viscosity, and an inverse linear dependence on the particle radius. The model is confirmed experimentally with viscosity measurements on various electrostatically stabilized dispersions. The validity of the model is also checked with data obtained from the literature. Experiments indicate that polydisperse dispersions exhibit pronounced shear thickening but with a less dramatic increase in viscosity than monodisperse dispersions.
Solubility models for amino acids and antibiotics
Authors: Gupta Ram B. , Heidemann Robert A.
Published: June 2004

An approach is presented for modeling the effects of temperature and pH on the solubility of amino acids in water. The amino acids studied are alanine, amino‐butyric acid, glycine, hydroxy‐proline, proline, serine, threonine, and valine. The data employed are activity coefficients and solubilities of the amino acids in neutral water and the dissociation constants for the various amino‐acid ionization reactions. Activity coefficients are correlated with the modified UNIFAC group contribution model and with new glycine and proline groups being introduced.

A similar approach is presented for modeling the solubilities of certain antibiotics in mixed nonaqueous solvents. Fusion temperature data and solubilities of the antibiotics in pure organic solvents are used to deduce modified UNIFAC energy interaction parameters between new large antibiotic groups and the standard alkane (CH2), alcohol (OH), aromat (ACH), and ester (CCOO) groups.
Analysis of autocatalytic reactions in isothermal catalyst particles
Authors: Hu R. , Sapre A. V.
Published: June 2004

Multiplicity features of autocatalytic reactions in isothermal catalyst particles with diffusion interaction are presented. Discussed also are two types of autocatalytic reactions—A + B → 2B (quadratic) and A + 2B → 3B (cubic)—and a decay reaction for autocatalyst B, B → C, and a nonautocatalytic reaction, A → B, which generates the autocatalyst. For quadratic reactions, the bifurcation diagrams for a catalyst particle are similar to those for a CSTR. The location of the branch solution, however, is somewhat different. For cubic autocatalytic reactions, the exact parameter regions, where the isola, mushroom, reverse‐S, and reverse‐S‐plus‐isola patterns of bifurcation exist, are determined. Furthermore, the parameter space, where a unique solution exists for all Thiele moduli, is also given.
Particle generation in a chemical vapor deposition process with seed particles
Authors: Okuyama Kikuo , Ushio Ryuichi , Kousaka Yasuo , Flagan Richard C. , Seinfeld John H.
Published: June 2004

The formation of aerosol particles by gas‐phase chemical reaction in the presence of seed particles has been studied experimentally and theoretically. Titanium tetraisopropoxide (TTIP) vapor containing ultrafine TiO2 seed particles was introduced into a laminar flow aerosol reactor, and the properties of produced TiO2 aerosol were measured. By comparing the particle numbers and size distributions of the resulting aerosol with those of the seed particles and those of homogeneously nucleated particles in the absence of seed particles, the effects of initial concentrations of TTIP vapor, reaction temperatures, and properties of seed particles on the suppression of homogeneous nucleation were experimentally clarified. In the theoretical analysis, the population balance equation expressing simultaneous generation of TiO2 monomer, Brownian coagulation and diffusive deposition of TiO2 monomer and aerosols was solved. The observed suppression of homogeneous nucleation by the seed particles is explained qualitatively by the theoretical analysis.
Gas‐liquid mass transfer from a single bubble in liquid‐solid fluidized beds
Authors: Song Gyung‐Ho , Fan Liang‐Shih
Published: June 2004

Experiments were conducted to study the gas‐liquid mass transfer of a single bubble containing an ozone‐oxygen gas mixture in liquids and liquid‐solid fluidized beds. A spectrophotometric technique is developed for the measurement of the instantaneous mass transfer coefficient and the local concentration distribution around the bubble wake. The method employs an ultraviolet light source and optical fibers. Axial variations of the mass transfer rate are studied. An ozone and starchiodide complex reaction is employed to visualize the mass transfer phenomena.
Nondispersive membrane solvent back extraction of Phenol
Authors: Basu R. , Prasad R. , Sirkar K. K.
Published: June 2004

Nondispersive back extraction of phenol from methyl isobutyl ketone into caustic solutions has been studied using microporous polymeric membranes in flat as well as hollow‐fiber form. Dispersion‐free reactive back extraction was successfully achieved using the correct phase pressure difference. The predictive capabilities of the mathematical models developed for such a system have been investigated. This study indicates that the overall mass transfer can be controlled by boundary layer resistance and/or the membrane transfer resistance, depending on the flow configuration, the nature of the membrane, and the regime of caustic concentration. Individual film transfer coefficients on the shell side and the tube side have been isolated for different hollow‐fiber modules. A commercially available 15 cm long module containing hydrophobic microporous hollow fibers has provided very low values of height of transfer unit (HTU) and very high phenol recoveries. The experimentally obtained HTUs of this module have been predicted with significant accuracy.
Effect of mixing on the precipitation of barium sulfate in an MSMPR reactorssss
Authors: Fitchett David E. , Tarbell John M.
Published: June 2004

The effect of mixing intensity (power input) on the precipitation/crystallization of barium sulfate in a two‐feedstream (sodium sulfate, barium chloride) continuous stirred‐tank crystallizer with mixed product removal was investigated through experiments and companion mathematical models. Crystal growth rate and nucleation rate were very sensitive to mixing intensity, with growth rate increasing eightfold and nucleation rate decreasing 100‐fold as power input per unit mass was increased from 0.001 to 0.73 m2/s3 (0 to 1,200 rpm stirrer speed). Experimental results at high feed concentration were accurately described by a model accounting for homogeneous nucleation and kinetic growth of particles as well as turbulent mass transfer to particles and turbulent micromixing of feedstreams. The principal mixing effect was due to particle mass transfer, not micromixing. Experiments at low feed concentration were more difficult to model because of a more complex nucleation mechanism and altered particle morphology.
Rigorous dynamics and feedforward control design for distillation processes
Authors: Rovaglio Maurizio , Ranzi Eliseo , Biardi Giuseppe , Fontana Marco , Domenichini Rosa
Published: June 2004

Feedforward control has the theoretical potential for perfect control; therefore, research to simplify and improve the use of such a control strategy for possible industrial applications has potential value. A general model for simulation of controlled distillation columns is used to reproduce operating trends of some monitored variables for an industrial column. Comparisons between simulated and operating data show a general good agreement.

When a rigorous model is available and can be proved reliable for practical purposes, the design of feedforward control schemes becomes viable and can be incorporated in the more conventional approach. A specific industrial example shows the practical implementation problems and the real economic value of a feedforward control strategy to optimize the process behavior. In particular, the feedforward control action can reduce the inherent error from changes in feed composition when a basic feedback control structure is used to infer composition.
Growth and dissolution of succinic acid crystals in a batch stirred crystallizer
Authors: Qiu Yanfeng , Rasmuson Åke C.
Published: June 2004

Growth and dissolution of succinic acid crystals have been studied in an isothermal stirred tank crystallizer. Seeded desupersaturation and deundersaturation experiments have been performed. Parameters of a desired growth rate equation are estimated by fitting the supersaturation balance equation directly to the supersaturation measurements. The procedure is based on nonlinear optimization techniques. Thus, uncertainties in the traditional approximation of the concentration vs. time curve are circumvented. The growth process for succinic acid crystals in an aqueous solution is found to be controlled by a significant resistance in both the volume diffusion step and in the surface integration step. An implicit equation is given to accurately represent the crystal growth rate as a function of the supersaturation. When extrapolating outside the range of experiments, this equation is shown to predict growth rates that are significantly different from those predicted by a corresponding power law expression. The dissolution rate exhibits a nonlinear dependence on undersaturation which is interpreted as changes in the crystal shape. Initial dissolution rate coefficients are in good agreement with volume diffusion coefficients obtained from growth experiments.
Lumped kinetics of many parallel nth‐order reactions
Authors: Ho T. C. , White B. S. , Hu R.
Published: June 2004

The kinetics of lumped nth‐order reactions are examined both asymptotically and numerically. The lumped kinetics in most cases are Mth order at large times. There exist two critical values for n, denoted by n* and n*, which are expressed explicitly as functions of the feed properties. It is shown that (1) M = n when n > n*, (2) M is linear in n when n* < n < n*, and (3) M does not exist when n = n* or n ≤ n*. Whenever the feed contains some unconvertibles, M is independent of n for −∞ < n < n*. The overall effective rate constant is not continuous at n = n* nor at n = n*. Unexpectedly, when n > n* the lump's long‐time behavior is governed by all species, not just by the most refractory species. Although the asymptotic kinetics are developed for long times, they are useful for fitting the whole‐time behavior of the lump by an mth‐order model. This is true even when M does not exist in the asymptotic regime. Numerical experiments show that M and m behave similarly in many respects. For example, as n increases, they both become closer to n and less dependent on the feed properties. Some published data are rationalized in light of the present results.
Prediction of slug frequency in horizontal two‐phase slug flow
Authors: Tronconi Enrico
Published: June 2004

Available data on slug frequency in horizontal two‐phase intermittent flow are predicted with adequate accuracy by assuming that the slug frequency is one half of the frequency of the unstable waves precursors of slugs, as determined according to published analyses of finite amplitude waves in conduits. The experimental effects of gas and liquid flow rates, pipe diameter, gas density and liquid viscosity on slug frequency are explained by modifications of the wave properties due to changes in the liquid level of the stratified flow existing in the pipe inlet region prior to slug formation. Simple generalized equations are provided to estimate the slug frequency for engineering calculations.
Effect of adsorption on the optimal displacement of acidic crude oil by alkali
Authors: Ramakrishnan T. S. , Wasan D. T.
Published: June 2004

Recovery of acidic crude oil from porous media can be enhanced by injection of alkaline agents. For this process we have analyzed the detrimental effect of alkali adsorption on the mineral surface. The model, which is an extension of our earlier inert solid model, was formulated by conserving three independent species. The previous solution procedure is shown to fail and a new analysis of composition paths is necessary. By introducing the notion of critical point, a short‐cut procedure is developed.

The predicted profiles and effluent histories are discussed. A new result is that adsorption on the solid surface could change the ultimate recovery even for an infinite slug of alkali due to the reduced influence of the optimal region in displacing oil. Further, the influence of a favorable viscosity ratio in displacing oil is also shown to be reduced by adsorption.
Steady laminar round jets of a viscous liquid falling vertically in the atmosphere
Authors: Adachi K. , Tagashira K. , Banba Y. , Tatsumi H. , Machida H. , Yoshioka N.
Published: June 2004

The shape of a laminar, liquid jet emerging from a round vertical tube into the atmosphere and the total axial force exerted on the liquid filament at the tube exit were investigated experimentally over a wide range of flow conditions. An integral invariant of the exact solution was used to check consistency between the two kinds of data. A new equation to predict the jet shape agreed moderately well with the present experimental data as well as with various previous results. The key idea of the present work is that exact knowledge of the total axial force will be very useful to predict reasonably the jet shape at a given flow condition by means of a simplified approach or to check theoretical or empirical results on free falling jets.
Competitive hydrodesulfurization and hydrogenation in a monolithic reactor
Authors: Irandoust Said , Gahne Olof
Published: June 2004

Competitive liquid‐phase hydrodesulfurization of thiophene and hydrogenation of cyclohexene on a monolithic CoMo/γ‐Al2O3 catalyst were studied. The flow pattern in the monolithic catalyst reactor was segmented gas‐liquid flow (slug flow). The hydrogen pressure and the temperature were varied between 30–40 bar and 509–523 K, respectively. The experimental data are consistent with rate expressions of the Langmuir‐Hinshelwood type where the reactions proceed on two different types of active sites. This kinetic model is based on hydrogenation of the thiophene ring prior to sulfur elimination.