bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of CO2 capture by aqueous monoethanolamine
Authors: Freguia Stefano , Rochelle Gary T.
Published: April 2004

The process for CO2 removal from flue gases was modeled with RateFrac. It consists of an absorber, a stripper, and a cross heat exchanger. The solvent used in the model contains about 30 wt % monoethanolamine (MEA) in water. MEA reacts with CO2 in the packed absorber. The finite reaction rate requires a kinetic characterization. The RateFrac absorber model was integrated with a FORTRAN user kinetic subroutine to make the model consistent with the interface pseudo‐first‐order model and with a regressed Electrolyte‐NRTL equilibrium model. It was adjusted with laboratory wetted wall column data and field data from a commercial plant. Sensitivity analyses were performed on process variables to find operating conditions at low steam requirement. Many variables strongly affect the process performance, but an overall optimization shows that there are no economical ways to reduce the steam requirements by more than 10%. The reboiler duty can be reduced from that of a base case representing current industrial operating conditions, by 5% if acids are added to the solvent, by 10% if the absorber height is increased by 20%, and by 4% if the absorber is intercooled with a duty of one‐third of the reboiler duty. The power plant lost work is affected by varying stripper pressure, but not significantly, so any convenient pressure can be chosen to operate the stripper.
CO2 Plasticization of polyethersulfone/polyimide gas‐separation membranes
Authors: Kapantaidakis G. C. , Koops G. H. , Wessling M. , Kaldis S. P. , Sakellaropoulos G. P.
Published: April 2004

This work reports the CO2 plasticization of gas‐separation hollow‐fiber membranes based on polyimide and polyethersulfone blends. The feed pressure effect on the permeance of pure gases (CO2, N2) and the separation performance of a gaseous mixture (CO2/N2, 55/45%) is examined. Contrary to dense membranes, the permeance of CO2 through ultrathin asymmetric fibers increases immediately with pressure resulting in pronounced apparent plasticization and reduction of the ideal CO2/N2 selectivity. However, no evidence of plasticization was observed when a CO2/N2, 55/45% mixture was fed to the hollow‐fiber membranes. In all cases, CO2 permeance decreased with pressure, while that of N2 remained constant. Experimental results were validated by means of mathematical modeling. Membrane‐separation performance was overestimated when pressure‐independent permeabilities were used in the model, while pressure‐dependent permeabilities, due to the overall effect of plasticization and competition phenomena, explained excellently, the obtained stage‐cut and permeate purity.
Automated retrofit design of cooling‐water systems
Authors: Kim Jin‐Kuk , Smith Robin
Published: April 2004

An automated approach from the systematic investigation of interactions between cooling‐tower performance and the cooling‐water network design was developed for retrofit design of cooling‐water systems. Introducing reuse of cooling water between different cooling duties enables cooling systems to be debottlenecked. The series arrangement of heat exchangers, however, results in a pressure drop increase because of the cooling water reuse. An optimization model for cooling‐water networks developed considers pressure‐drop constraints, complexity of networks, and efficient use of the cooling tower. A new node‐superstructure model is suggested to consider the intensive property of pressure and the sequence of connections simultaneously. Physical insights are used to provide a good initialization for the resulting optimization problem. Issues of retrofit analysis are also addressed to give design guidelines for debottlenecking of cooling‐water systems.
Design of separation schemes for fractional crystallization of metathetical salts
Authors: Cisternas Luis A. , Torres Mauricio A. , Godoy María J. , Swaney Ross E.
Published: April 2004

The synthesis method of fractional crystallization processes for the separation of salts belonging to reciprocal salt pairs is presented based on a flow network model constructed between thermodynamic states. The state nodes represented in the model include feeds, products, intermediate products, and solid–liquid equilibrium states. Flows between the states are represented by arcs within the flow model. A systematic procedure is given for identification of the solid–liquid equilibrium states that could potentially serve as operating points. This identification is essential to the construction of the flow network and reduces the problem to a simple mathematical form. The advantages of the method lie in its capability to consider general process flow pattern, handle systems forming double salt, deal with several temperatures as potential operation conditions, and handle several feeds and products. Examples are given to illustrate the procedure.
Tracking control of general nonlinear differential‐algebraic equation systems
Authors: Liu X. P. , Rohani S. , Jutan A.
Published: April 2004

The problem of output tracking control is considered for a general class of nonlinear differential‐algebraic systems. Regularization algorithm proposed here provides sufficient conditions for the existence of a regularizing feedback controller that renders the closed‐loop system to have an index one. Based on the regularization algorithm, another algorithm is developed for constructing a tracking controller, which guarantees that the outputs of the closed‐loop system track the desired signals asymptotically. Simulation results on a typical chemical process show that the developed design method gives a satisfactory control performance.
Robust nonlinear model predictive control of batch processes
Authors: Nagy Zoltan K. , Braatz Richard D.
Published: April 2004

NMPC explicitly addresses constraints and nonlinearities during the feedback control of batch processes. This NMPC algorithm also explicitly takes parameter uncertainty into account in the state estimation and state feedback controller designs. An extended Kalman filter estimates the process noise covariance matrix from the parameter uncertainty description and employs a sequential integration and correction strategy to reduce biases in the state estimates due to parameter uncertainty. The shrinking horizon NMPC algorithm minimizes a weighted sum of the nominal performance objective, an estimate of the variance of the performance objective, and an integral of the deviation of the control trajectory from the nominal optimal control trajectory. The robust performance is quantified by estimates of the distribution of the performance index along the batch run obtained by a series expansion about the control trajectory. The control and analysis approaches are applied to a simulated batch crystallization process with a realistic uncertainty description. The proposed robust NMPC algorithm improves the robust performance by a factor of six compared to open loop optimal control, and a factor of two compared to nominal NMPC. Monte Carlo simulations support the results obtained by the distributional robustness analysis technique.
Two‐section reactor model for autothermal reforming of methane to synthesis gas
Authors: Biesheuvel P. Maarten , Kramer Gert Jan
Published: April 2004

A 1‐D stationary reactor model describes the catalytic conversion of a gaseous hydrocarbon fuel with air and steam to synthesis gas by autothermal reforming and catalytic partial oxidation. The model defines two subsequent sections in the reactor: an upstream oxidation section and a downstream reforming section. In the oxidation section, all of the oxygen is converted, with partial conversion of the fuel. An empirical fuel utilization ratio is used to quantify which part of the fuel is converted in the oxidation section as a function of the relative flows of air and steam. In the oxidation section, the gas temperature rapidly increases toward the top temperature at the intersection with the reforming section. In this section the temperature decreases while the fuel is further converted with water and CO2 as oxidant. For methane as fuel, simulation results are compared with experiments. For multicomponent fuels such as natural gas and naphtha, application of the two‐section model is described.
Effect of fluid properties on dispersion in flow through packed beds
Authors: de Carvalho J. R. F. Guedes , Delgado J. M. P. Q.
Published: April 2004

An experimental study is described on the effect of liquid properties on axial dispersion in packed beds. Working with water between 278 and 373 K, the range 57<Sc<1,930 was covered, and this represents a significant fraction of the domain located between what is traditionally considered “gas behavior” (that is, Sc≅1) and “liquid behavior” (typically, Sc>600). A representation of PeL vs. Pem reveals the existence of a very flat minimum (typically 102<Pem<104) for each value of Sc. The value of the minimum is almost insensitive to variations in Sc, for Sc>700, but it increases significantly with a decrease in Sc, for Sc<700. The experimental data used to test available correlations for predicting DL show that they are inaccurate over considerable ranges of the variables.
Perturbation viscometer to measure the viscosity gradients of gas mixtures
Authors: Russell P. A. , Buffham B. A. , Mason G. , Heslop M. J.
Published: April 2004

Perturbation viscometry measures the logarithmic viscosity gradient of the viscosity–composition curve for gas mixtures. The flow and composition of a gas mixture flowing through a capillary are perturbed by adding a small flow of gas, normally one of the pure components of the gas mixture. Two pressure changes are seen at the capillary, the first due to the change in flow rate and the second, a short time later, due to the change in viscosity. The logarithmic viscosity gradient can be calculated from the ratio of these two pressure changes. Integration of logarithmic viscosity gradients measured over the full composition range gives the mixture viscosity relative to the viscosity of one of the pure components of the gas mixture. This method is attractive because, for measurements of equal precision, integration of the gradients is potentially an order of magnitude more precise than conventional methods that measure viscosities directly. It can also work at high and low temperatures and perhaps high pressures. The potential of this technique was previously demonstrated with a rudimentary apparatus, but its advantages and potential flaws need to be more closely examined. Here a fully thermostatted apparatus is detailed, including all modifications incorporated from experience operating the original apparatus. Experimental data for the helium–nitrogen mixture at 360°C, the practical upper operating limit of the apparatus, are presented. Integral consistency checks performed on the measured data show that high‐quality data produced compare well (less than 1% deviation) with the best literature data available.
Axial liquid mixing in high‐pressure bubble columns
Authors: Yang G. Q. , Fan L. S.
Published: April 2004

Axial dispersion coefficients of the liquid phase in bubble columns at high pressure are investigated using the thermal dispersion technique. Water and hydrocarbon liquids are used as the liquid phase. The system pressure varies up to 10.3 MPa and the superficial gas velocity varies up to 0.4 cm/s, which covers both the homogeneous bubbling and churn‐turbulent flow regimes. Experimental results show that flow regime, system pressure, liquid properties, liquid‐phase motion, and column size are the main factors affecting liquid mixing. The axial dispersion coefficient of the liquid phase increases with an increase in gas velocity and decreases with increasing pressure. The effects of gas velocity and pressure on liquid mixing can be explained based on the combined mechanism of global liquid internal circulation and local turbulent fluctuations. The axial liquid dispersion coefficient also increases with increasing liquid velocity due to enhanced liquid‐phase turbulence. The scale‐up effect on liquid mixing reduces as the pressure increases.
Voidage variation in packed beds at small column to particle diameter ratio
Authors: de Klerk Arno
Published: April 2004

Randomly packed beds of equal spheres exhibit damped oscillatory voidage variation in the near wall region. Models reported in literature were found to be lacking in their ability to relate this variation to average bed porosity. The changing mean of the voidage oscillations and deviations from sinusoidal behavior were not described well either. Experimental data and a new radial bed porosity model are presented. Improved radial bed voidage and average bed voidage predictions were demonstrated. It has further been shown that multiple stable packing configurations exist within the same packing mode, which complicates modeling at a small column to particle diameter ratio.
Asymptotic models for gas–liquid crystallization in two‐film systems
Authors: Cournil Michel , Herri Jean‐Michel
Published: April 2004

It is proposed to revisit the problem of gas–liquid crystallization in the framework of a two‐film model and with the help of experimental data from two experimental systems. Preliminary quantitative discussion of the order of magnitude of different effects makes possible realistic simplifications in the theoretical models. In particular, the role of the interfacial film in the whole process is clearly defined. As previous researchers have done, a formulation in terms of moments of the crystal size distribution is used; however, instead of the numerical solution to the corresponding differential system, a general procedure to express analytically the asymptotic behavior of the physical system is proposed. With this formulation, the influence of different parameters can be easily identified and validated on the available data from two experimental systems.
Residence time distribution in a size‐exclusion SMB for insulin purification
Authors: Mun Sungyong , Xie Yi , Wang Nien‐Hwa Linda
Published: April 2004

This study analyzes for the first time the residence time distribution in a size‐exclusion simulated moving bed (SMB) process. In an SMB, the raffinate port is located downstream from the feed port, whereas the extract port is located upstream from the feed port. The location of the product ports and periodic port movement results in a residence time distribution that strongly depends on solute injection time. The earlier a fast‐moving solute is injected during the switching period, the earlier it exits the raffinate port. In contrast, the earlier a slow‐moving solute is injected during the switching period, the later it exits the extract port. Furthermore, only a fraction of the stream is drawn as the raffinate product or the extract product. The rest is recycled. The recycle results in the splitting of a differential pulse into a pulse train with diminishing magnitude. The shape of the pulse train depends on the pulse injection time. A large recycle ratio, which results from a low selectivity, causes a long decay of the pulse train and increases tailing of the residence time distribution curve. Mass‐transfer effects broaden the pulse train and the residence time distribution. To shorten the residence time of a fast‐moving solute, one can increase the flow rate of zone II, decrease the length of zone III, or feed during the first half of the switching period. To shorten the residence time of a slow‐moving solute, one can decrease the flow rate of zone III, decrease the length of zone II, or feed during the second half of the switching period. Rate model simulations show that these strategies can significantly reduce the residence time of insulin in SMB.
MaximumA posterioriestimation of transient enhanced diffusion energetics
Authors: Gunawan R. , Jung M. Y. L. , Seebauer E. G. , Braatz R. D.
Published: April 2004

Transient enhanced diffusion (TED) of boron limits the formation of ultrashallow junctions needed in next‐generation microelectronic devices. A comprehensive TED model needs many parameters governing the physical and chemical processes. Prior estimates of the most likely values for the parameters as well as their accuracies are determined from maximum likelihood estimation applied to estimates from focused individual experiments and density functional theory calculations. Here a systematic approach to model‐parameter identification using maximum a posteriori estimation is employed combining the maximum likelihood parameter estimates and their uncertainties in conjunction with after‐anneal boron SIMS profiles to obtain accurate TED energetics. Guidance on future experimental and ab initio efforts are given based on the agreement (and disagreement) between the prior and posterior distributions.
Input design for model order determination in subspace identification
Authors: Misra Pratik , Nikolaou Michael
Published: April 2004

Subspace identification methods require that the inputs to the process being identified be persistently exciting. This may be inadequate for subspace identification of ill‐conditioned multivariable processes, because the process model order may be underestimated, leading to subsequent identification of poor models. To remedy the problem, it is proposed that inputs must be used that excite a process to be identified in a way that produces as uncorrelated process outputs as possible. This can be accomplished either in open or in closed‐loop fashion. Simulations on a high‐purity distillation column and on a heat exchanger illustrate the merit of the proposed approach.
Design concept to reduce fuel NOX in catalytic combustion of gasified biomass
Authors: Andrae Johan C. G. , Björnbom Pehr H. , Glarborg Peter
Published: April 2004

A reactor concept was studied to reduce the fuel NOx at conditions relevant to catalytic combustion of gasified biomass containing ammonia. A hybrid reactor is modeled with passive and active channels, where only part of the fuel is combusted catalytically in the active channels. The completion of the reactions is carried out in the subsequent homogeneous zone. The air–fuel ratio is found to be the most important parameter for the NOx emission level. When the primary zone is operated fuel‐lean, no favorable conditions are established for selective noncatalytic reduction reactions in the homogeneous zone, and the fuel nitrogen is largely oxidized to NO. However, if the air supply to the monolith is staged rich‐lean, a 95% reduction in NO is possible. The NO reduction is facilitated by the remaining fuel components, CO and H2.
Vapor–liquid equilibria of mixtures containing nitrogen, oxygen, carbon dioxide, and ethane
Authors: Stoll Jürgen , Vrabec Jadran , Hasse Hans
Published: April 2004

Vapor–liquid equilibria of binary and ternary mixtures containing nitrogen (N2), oxygen (O2), carbon dioxide (CO2) and ethane (C2H6) are studied by molecular simulation using two‐center Lennard‐Jones plus point quadrupole models. Pure‐component models are taken from recent work. Mixtures are described using the Lorentz‐Berthelot combining rules. Predictions of vapor–liquid equilibria from pure‐component data alone agree well with experimental data, for example, the azeotropic behavior of the carbon dioxide + ethane system is predicted correctly. Further improvements are achieved by adjusting one parameter in the energetic term of the combining rule to binary data. For this purpose, a simple and efficient procedure is proposed. Excellent agreement between the molecular models and experimental data for vapor‐liquid equilibria, saturated densities, and enthalpies of vaporization is observed for the five binary systems studied in the present work (N2+O2, CO2+C2H6, O2+CO2, N2+CO2, N2+C2H6). Vapor–liquid equilibria of two ternary mixtures (N2+O2+CO2, N2+CO2+C2H6) are predicted well without any further adjustment of model parameters. Results from molecular simulation are compared to those from the Peng‐Robinson equation of state, the PC‐SAFT equation of state, and the BACKONE equation of state using the same data to determine model parameters. The quality of correlations with system‐specific binary interaction parameters from molecular simulation and equations of state is similar, and the predictive power of molecular simulation is clearly superior.
Catalyst wetting characteristics in trickle‐bed reactors
Authors: Kundu Arunabha , Nigam K. D. P. , Verma R. P.
Published: April 2004

A model for external wetting efficiency of the catalyst in trickle‐bed reactors was developed based on 1‐D force‐balance equations incorporating drag forces in a three‐phase system. The gas–liquid interfacial drag was considered, as well as the tortuosity effect. The overall model was tested with major experimental data of a 15.2‐cm‐dia. trickle‐bed reactor using a radioisotope tracer technique. Five catalyst packings, different in shape and size, were used in the experiment. External wetting efficiency was calculated from the square root of the ratio of the effective diffusivities in two‐phase and liquid‐filled operation. The model was also compared with other experimental data available in the literature. The predictions were within an average confidence limit of ±15%.
Pressure profiles along an abrupt 4:1 planar contraction
Authors: Doerpinghaus Phillip J. , Baird Donald G.
Published: April 2004

The ability to accurately predict the pressure profile along an abrupt 4:1 planar contraction is investigated. Predicted pressure profiles obtained using the Phan Thien and Tanner (PTT) and generalized Newtonian fluid (GNF) models are compared to experimental measurements for low‐density polyethylene (LDPE) and linear low‐density polyethylene (LLDPE) polymer melts. The results obtained for the extensional strain hardening, LDPE resin show that numerical predictions are consistently less than the experimental values by 10–15%. Furthermore, no significant difference between the PTT and GNF predictions were observed over the range of convergent solutions. On the other hand, the numerical predictions for the LLDPE melt were within 1.5–7% of the experimental values over the entire range of stable flow rates investigated. Again, the differences in accuracy of the PTT and GNF models were small. In fact, the GNF model was generally more accurate than the PTT model for the case of LLDPE. Closer investigation of the predicted streamlines patterns near the contraction clearly shows larger, more intense vortices for the extensional strain hardening LDPE than for the LLDPE melt, which is in agreement with experimental observations. However, analysis of the plane of symmetry shows that the magnitude of the planar extensional stress is mitigated by the fluid relaxation behavior as the melt briefly passes through the contraction region. Although it appears that a viscoelastic constitutive equation is not necessary for predicting the pressure profile along an abrupt 4:1 planar contraction, this is a fortuitous result of the small extensional deformations observed in the contraction region over the limited range of convergent solutions.
Polydisperse model for the hydrodynamics of expanded‐bed adsorption systems
Authors: Xue Bo , Tong Xiaodong , Sun Yan
Published: April 2004

A polydisperse model is established to describe the hydrodynamic behaviors of solid particles within an expanded‐bed adsorption column. This model has been used to simulate bed expansions conducted by different researchers under various operating conditions, and good agreements are found between the experimental and simulated results. The model is effective in simulating not only the change of bed height with fluid velocity, but also the size distributions of solid particles at different axial positions. Due to nonuniform flow in the column and density distribution of the particles, the calculated bed voidage is somewhat different from the measured one for the bottom and top regions of the column.
Batch heteroazeotropic rectification of a low α mixture under continuous entrainer feeding
Authors: Modla G. , Lang P. , Kotai B. , Molnar K.
Published: April 2004

The separation of a low‐relative‐volatility, zeotropic mixture in a batch rectifier with a selective entrainer was studied by feasibility and rigorous simulation calculations. The entrainer is the high boiler in the system and forms a binary heteroazeotrope with the low‐boiler component. Beside the traditional batch addition, the continuous feeding of the entrainer was also investigated. The feasibility of the heteroazeotropic distillation in a batch rectifier was assessed by a new method, extending the methods published for the batch homoazeotropic distillation. The method is based on the analysis of the map of the possible overall liquid composition profiles, which also contains the heterogeneous liquid boiling envelope. The results obtained for batch addition and continuous feeding of the entrainer are compared. The influence of the most important operational parameters is also studied. The results are presented for the dichloromethane–acetone mixture by using water as a heterogeneous entrainer.
Simultaneous optimal design and operation of multivessel batch distillation
Authors: Low K. H. , Sørensen E.
Published: April 2004

The multivessel system is a novel batch distillation configuration that offers improved separation performance compared to the conventional single‐column batch rectifier. The optimal design of this system based on an economics performance index is solved for the first time here by adopting an evolutionary adaptive search technique. The utilization of an overall profitability index, and simultaneous consideration of key design and operation decision variables, allow the true optimum of the system to be obtained. The optimal system configuration is dependent on the separation duty and can contribute significantly to achieving a higher separation performance. The combined energy efficiency and production rate of the multivessel system is found to be greater than that of the regular column, and the benefit is more prominent when separating mixtures with more components. Further theoretical case studies are also presented to highlight the effect of feed composition, relative volatility, and product specification on the optimal column section configuration and feed distribution of the multivessel system.
Generalized least‐squares parameter estimation from multiequation implicit models
Authors: Marshall Simon L.
Published: April 2004

Maximum likelihood fit of nonlinear, implicit, multiple‐response models to data containing normally distributed random errors can be carried out by a combination of the Gauss‐Newton generalized nonlinear least‐square algorithm first described by Britt and Luecke in 1973, with a Fletcher‐Reeves conjugate gradient search for initial parameter estimates. The convergence of the algorithm is further improved by adding a step‐limiting procedure that ensures a reduction in the objective function for each iteration. Multiple‐equation regression methods appropriate to the solution of explicit fixed‐regressor models are derived from this general treatment as special cases. These include weighted nonlinear least squares (where the covariance matrix of the response is known), and uniformly weighted nonlinear least squares (where the responses are uncorrelated and characterized by a single common variance). Alternative methods for fixed‐regressor fits of explicit multiequation models with an unknown covariance matrix of the responses are also considered. The moment‐matrix determinant criterion appropriate in such situations is also efficiently minimized by use of the conjugate‐gradient algorithm, which is considerably less sensitive to the accuracy of the initial parameter estimate than the more usual Gauss‐Newton methods. The performance of the new algorithm for models defined by one, two, and three implicit functional constraints per point is illustrated by random‐regressor fits of isothermal p−X and p−X−Y vapor–liquid equilibrium data, and ternary liquid–liquid equilibrium data, respectively.
Adsorption of α‐amylase in a fixed bed: Operating efficiency and kinetic modeling
Authors: Bautista L. F. , Martínez M. , Aracil J.
Published: April 2004

Kinetic studies on the adsorption of α‐amylase from Aspergillus oryzae on the anion exchanger, Duolite A‐568, and the hydrophobic resin, Duolite XAD‐761, were carried out in a fixed bed. The efficiency with respect to the adsorbate and adsorbent was determined to estimate the performance of the process of adsorption. The effect of flow rate, α‐amylase inlet concentration, temperature, and particle size of the packing was analyzed. In addition, the transient response, in the form of experimental breakthrough curves, was fitted using a phenomenological mathematical model accounting for the external‐film and pore‐diffusion mass‐transfer mechanisms as well as axial dispersion along the column. Also, a Langmuir isotherm was included in the model to account for the extent of the equilibrium of adsorption. The model described satisfactorily the experimental breakthrough curves and it proved to predict successfully the behavior of a scaled‐up bed using the kinetic and equilibrium parameters estimated previously. Thus, the mathematical model can be considered a reliable tool for process design and scale‐up of similar systems.
Similitude in stirred‐tank reactors: Laminar feed
Authors: Forney L. J.
Published: April 2004

Similarity parameters are derived to correlate the selectivity of mixing controlled parallel reactions within stirred‐tank reactors. For the case of laminar reactant feed, the Kolmogoroff time is shown to correlate selectivity in turbulent, semibatch reactors, provided the reactor Reynolds number ReReC, the inertial time scale defined in terms of a reactor feed length is shown to correlate selectivity. Scaling laws are demonstrated from available tank data taken at up to three reactant feed points in both aqueous and viscous solutions, and for a range of vessel volumes, feed tube diameters, and feed times.
Fundamental approach to the design and optimization of static mixers
Authors: Szalai E. S. , Muzzio F. J.
Published: April 2004

Mixing in the Kenics static mixer is optimized using computational analysis and theoretical concepts. A total of 54 cases were examined to consider the effect of mixer geometry and inertia on flow and mixing performance. The effect of varying the standard geometry is discussed for a broad range of Reynolds numbers. While only the twist angle affects performance at low flow rates (Re≅1), both the element aspect ratio and the twist angle are shown to be important at high flow rates (Re⩽1,000). The energetic mixing efficiency decreases with increasing flow rate. Finally, a quality‐driven design method is developed based on stretching calculations, and is illustrated for the standard mixer design.
Three‐dimensional wave dynamics on a falling film and associated mass transfer
Authors: Park C. D. , Nosoko T.
Published: April 2004

The evolution of solitary waves into three‐dimensional (3‐D) waves was experimentally observed on a vertically falling water film at mainly Re = 10–100. At Re greater than 40, 2‐D solitary waves are very unstable in the face of spanwise perturbations of approximately 2‐cm wavelengths and disintegrate into isolated horseshoe‐shaped solitary waves and clusters of dimples between the horseshoes, whereas wavefront modulations are limited to low levels at Re below 40. Horseshoes of larger velocities have larger curvature heads, and extend longer oblique legs upward. Curving capillary ripples preceding each horseshoe widen their wavelengths with an increase in the wavefront inclination, showing that the ripples possess the characteristics of the shallow‐water capillary waves. The horseshoes may hold vortices inside, and they have similarities in shape and size to hairpin vortices observed in laminar–turbulent transition regions of boundary layers on walls. The disintegration of waves into dimples is caused by a capillary instability similar to the one for breakup of a cylindrical soap film. This transition of wave dynamics at Re≈40 is associated with a drastic change in the mass transfer from the surface into the film.
Transient method for the liquid laminar flow friction factor in microtubes
Authors: Brutin D. , Topin F. , Tadrist L.
Published: April 2004

An original method is highlighted to determine precisely the friction factor of laminar flows in capillaries. The experiments were performed at Reynolds numbers ranging from 10 to 1,000 using a transient method and a steady‐state method. The results deduced from all the implemented methods are in good agreement. Nevertheless, uncertainties differ from one method to another. A set of experiments were carried out and specific processing methods were developed. Among these methods, it was found that the integral method is the most accurate one. The friction factor obtained for capillary diameters of 320 and 530 μm are slightly higher (5.5 and 4.2%) compared to the Poiseuille law.
Design of SMB for a nonlinear amino acid system with mass‐transfer effects
Authors: Xie Yi , Farrenburg Chad A. , Chin Chim Y. , Mun Sungyong , Wang Nien‐Hwa L.
Published: April 2004

A standing wave design (SWD) method and an experimental shortcut design method are developed in this study for SMB systems with nonlinear isotherms and mass‐transfer effects (nonideal systems). In the SWD, the mass‐transfer correction terms derived in a previous study for linear, nonideal systems are incorporated into the design equations for nonlinear, nonideal systems. The SWD requires accurate isotherm and mass‐transfer parameters to ensure high product purity and high yield. If these parameters are unknown, the experimental shortcut design can be applied. Frontal experiments with a binary mixture at a fixed feed concentration and three or more different flow rates are needed to formulate a series of empirical correlations for the SMB design. The two methods were tested for the binary separation of phenylalanine and tryptophan. Both rated model simulations and experimental data showed that high product purity (99.1%–100%) and high yield (96.3%–100%) were achieved in both methods. The experimental shortcut design method is simpler than the SWD, but is limited to a fixed feed concentration. A dimensionless number is derived to quantify the deviation of an actual nonideal system from a system without mass‐transfer effects (ideal system). If the dimensionless number has a value greater than 0.005 for the binary amino acid separation, the system deviates from its corresponding ideal system and the design considering mass‐transfer effects gives significantly higher purity and yield than the ideal design.
Mixed‐logic dynamic optimization applied to batch distillation process design
Authors: Oldenburg Jan , Marquardt Wolfgang , Heinz Dieter , Leineweber Daniel B.
Published: April 2004

An approach for the optimal configuration and sequencing of complex batch‐distillation processes is presented. The proposed method is based on formulating a mixed‐logic dynamic optimization problem in which a performance index is minimized subject to a disjunctive dynamic model and constraints. The disjunctive model comprises a given set of equipment modules, such as stacks of trays of different size or feed and product vessels, available for the distillation process under consideration along with logical relationships provided by the design context. The optimization based on this model may yield unconventional design and operational strategies, and thus improve the economic efficiency to a significant extent. The logic‐based solution technique proposed in this work offers some favorable properties when compared to established mixed‐integer dynamic optimization problem solution techniques reported in the literature. The design of a multistage batch‐distillation process serves as an example to illustrate the proposed modeling and solution method.
Multilamellar vesicles in a commercial surfactant system
Authors: Liaw M. S. , Mackley M. R. , Bridgwater J. , Moggridge G. D. , Bayly A. E.
Published: April 2004

The manufacture of concentrated detergent granules in the detergent industry can be achieved by the incorporation of surfactant pastes, such as linear alkylbenzene sulfonate paste (LAS)—a lamellar liquid crystalline material (surfactant concentration of ca. 78 wt. %). LAS paste was processed at 25°C and 60°C, in both the absence and presence of sodium disilicate (Na2O:2SiO2) additive, and the effect on the formation of shear‐induced multilamellar vesicle (MLV) microstructures was studied. Our results suggest that LAS pastes of high hardness and stiffness are always associated with MLV microstructures and vice versa—these are known as “structured” pastes in industry, and also appear nonadhesive. MLVs are able to form from “pure” LAS at 25°C, although, at 60°C, sodium disilicate is necessary. With increased processing time, the size of the MLVs decreases and becomes more uniform—pastes are also increasingly hard and stiff. When stored, “structured” pastes eventually revert back to being soft and sticky, reflecting the metastable nature of the MLVs.
Gas turbulence modulation in a two‐fluid model for gas–solid flows
Authors: Zhang Yonghao , Reese Jason M.
Published: April 2004

Recent rapid progress in the theoretical and experimental study of turbulence modulation has led to greater understanding of the physics of particle–gas turbulence interactions. A new two‐fluid model incorporating these advances for relatively dilute gas–solid flows containing high‐inertia particles is established. The effect of aerodynamic forces upon the particulate stresses is considered in this kinetic theory‐based model, and the influence of the particles on the turbulent gas is addressed: the work associated with drag forces contributes to the gas turbulent energy, and the space occupied by particles restricts the turbulent length scale. The interparticle length scale, which is usually ignored, has been incorporated into a new model for determining the turbulent length scale. This model also considers the transport effect on the turbulent length scale. Simulation results for fully developed steady flows in vertical pipes are compared with a wide range of published experimental data and, generally, good agreement is shown. This comprehensive and validated model accounts for many of the interphase interactions that have been shown to be important.
Optimal design of batch‐storage network with recycle streams
Authors: Yi Gyeongbeom , Reklaitis Gintaras V.
Published: April 2004

An effective methodology is reported for determining the optimal capacity (lot size) of batch processing and storage networks which include material recycle or reprocessing streams. It is assumed that any given storage unit can store one material type which can be purchased from suppliers, internally produced, and internally consumed and/or sold to customers. It is further assumed that a storage unit is connected to all processing stages that use or produce the material to which that storage unit is dedicated. Each processing stage transforms a set of feedstock materials or intermediates into a set of products with constant conversion factors. The objective for optimization is to minimize the total cost composed of raw material procurement, setup, and inventory holding costs, as well as the capital costs of processing stages and storage units. A novel production and inventory analysis formulation, the PSW model, provides useful expressions for the upper/lower bounds and average level of the storage inventory holdup. The expressions for the Kuhn‐Tucker conditions of the optimization problem can be reduced to two subproblems. The first yields analytical solutions for determining batch sizes, while the second is a separable concave minimization network flow subproblem whose solution yields the average material flow rates through the networks. For the special case in which the number of storage units is equal to the number of process stages and raw materials storage units, a complete analytical solution for average flow rates can be derived.
Process variations and the transient behavior of extruders
Authors: Mudalamane Rajath , Bigio David I.
Published: April 2004

To explain output fluctuation problems in extrusion, a transient model of material flow through an extruder is developed and used to study the transmission of external disturbances through the extruder. This model can be implemented for any extrusion geometry for which a pressure‐throughput model exists. Simulation results show that every extrusion process has a characteristic critical frequency. All disturbance frequencies above this critical value are damped out and the lower frequency components are transmitted through the process with little amplitude attenuation. These low frequency disturbances are of most concern since they are not damped by the extrusion process. Extrusion screw configurations are designed to satisfy steady‐state performance requirements, and nonsteady‐state performance is rarely considered. The findings indicate that a two pronged approach would be required combining screw design (passive control) to handle higher frequencies and closed‐loop control (active control) to detect and remove lower frequency disturbances.
Diagnostic tool to detect electrode flooding in proton‐exchange‐membrane fuel cells
Authors: He Wensheng , Lin Guangyu , Van Nguyen Trung
Published: April 2004

An electrode flooding monitoring device designed for PEM fuel cells with interdigitated flow distributors was proposed and tested. The pressure drop between the inlet and outlet channels can be used as a diagnostic signal to monitor the liquid water content in the porous electrodes, because of the strong dependence of the gas permeability of the porous electrodes on liquid water content. It can be used with no modification to existing fuel‐cell assembly to give real‐time flooding information in the electrode backing layers during operation. The device has been employed to investigate the correlation between the fuel‐cell performance and the liquid water saturation level in the backing layers, the effects of various operating parameters, and the dynamics and hysteresis behavior of liquid water in the backing layers. The results provide, for the first time, direct evidence to show that inadequate water removal causes liquid water build up in the cathode, which in excessive amounts can severely reduce the performance of a PEM fuel cell. It was observed that more than 30 min. were needed for a PEM fuel cell to reach a new steady state when subjected to current‐density changes, and this was attributed to the slow liquid water transport process. The results confirmed that increasing air flow rate or cell temperature increased the liquid water removal rate from the backing layers. The hysteresis behavior of fuel‐cell performance was related to the water imbibition and drainage cycles in the electrode backing layers and was attributed to the difference in the water removal rate by capillary force and the difference in membrane conductivity.
Influence of n‐paraffin composition on the aging of wax‐oil gel deposits
Authors: Paso K. G. , Fogler H. Scott
Published: April 2004

An excess Gibbs free energy model is applied to investigate the influence of n‐paraffin composition on the aging behavior of wax‐oil gel deposits known to form in subsea petroleum transport pipelines. The aging of wax‐oil gels occurs by a counterdiffusion process where wax molecules with carbon numbers greater than a critical carbon number (CCN) diffuse into the gel matrix, and vice versa. Model crude oils were formulated to exhibit varying decreasing exponential distributions of n‐paraffin components in the range n‐C9 to n‐C53. Deposition experiments were conducted using a laboratory cold finger apparatus simulating the cold wall of a subsea pipeline. Gas chromatography analysis of gel deposit compositions yielded experimental CCN values. A solid‐liquid‐phase equilibrium model, employing a modified version of UNIQUAC to compute solid‐phase component activity coefficients, was able to successfully predict the critical carbon number for a variety of model oil n‐paraffin compositions.
Thermodynamic isotope effect in partial oxidation of methane to syngas
Authors: Hu Yun Hang , Feeley Jennifer S.
Published: April 2004

Thermodynamic deuterium substitution effects on reactant conversion and product selectivity were investigated by computer simulation for the stoichiometric partial oxidation of methane. Methane conversion shows a normal deuterium isotope effect, whereas CO selectivity shows an inverse deuterium isotope effect. H2 selectivity exhibits a large normal deuterium effect. Moreover, deuterium isotope effects are dependent on reaction temperatures and pressures. When reaction pressure is very low, such as 0.001 MPa, all thermodynamic deuterium isotope effects are negligible at 650°C or above. Three criteria, based on the deuterium‐isotope effects, were proposed to determine whether a partial oxidation reaction of methane is kinetically controlled without accurately measured reaction temperatures.
Jenseits thermodynamischer Acidität: der Komplex‐induzierte Näherungseffekt (CIPE) bei Deprotonierungen
Authors: Whisler Marna C. , MacNeil Stephen , Snieckus Victor , Beak Peter
Published: April 2004

Das Konzept des Komplex‐induzierten Näherungseffekts (complex induced proximity effect, CIPE) bei Deprotonierungen ist hilfreich bei der Aufklärung von Mechanismen in der Carbanionenchemie und bei der Planung organischer Synthesen. Im vorliegenden Aufsatz werden die Konsequenzen der Komplexierung von Organolithiumbasen an funktionellen Gruppen der Substrate vor dem Protonenübertragungsschritt diskutiert. Dabei zeigt sich, dass die experimentellen Daten aus kinetischen Messungen und Isotopenmarkierungsexperimenten ebenso wie die Ergebnisse von Rechnungen in vielen Fällen auf einen Prälithiierungskomplex als Reaktionsintermediat hinweisen. Einige Beispiele aus der Naturstoffsynthese verdeutlichen, wie mithilfe dieses Konzepts Zwischenstufen gezielt regio‐ oder stereoselektiv erhalten werden können. Von besonderem Interesse sind dabei Funktionalisierungen an Positionen, die von der koordinierenden Gruppe vermeintlich weit entfernt sind.
Properties of thermoplastic composites based on wheat‐straw lignocellulosic fillers
Authors: Le Digabel F. , Boquillon N. , Dole P. , Monties B. , Averous L.
Published: April 2004

Lignocellulosic fractions from wheat straw were used as natural fillers in composites of a polyolefin (a copolymer of polyethylene and polypropylene) and a biodegradable polyester [poly(butylene adipate‐co‐terephthalate)]. The mechanical properties of these injected composites were investigated with tensile and impact testing. A reinforcing effect of wheat‐straw residues was found for both types of composites. Compared with the polyester‐based composites, the polyolefin composites were more brittle. The addition of compatibilizing agents (γ‐methacryloxypropyltrimethoxysilane, maleic anhydride modified polypropylene, and stearic acid) did not improve the properties of the polyolefin composites. The surface properties were studied with contact‐angle measurements, and poor interfacial adhesion was found between the hydrophilic lignocellulosic filler and the hydrophobic polyolefin matrix. Thermal characterization revealed the formation of low intermolecular bonds between the polyester matrix and the lignocellulosic filler, in agreement with the surface tensions results and scanning electron microscopy observations. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 428–436, 2004
New oligomer‐bound antioxidants in natural rubber/polybutadiene rubber and natural rubber/styrene–butadiene rubber blends
Authors: Sulekha P. B. , Joseph R. , Manjooran K. B.
Published: April 2004

New paraphenylene diamine antioxidants were prepared. The efficiency and permanence of these oligomer‐bound paraphenylene diamines were compared with those of conventional amine‐type antioxidants in elastomer blends such as natural rubber/styrene–butadiene rubber and natural rubber/polybutadiene rubber. These oligomer‐bound antioxidants showed improved aging resistance and ozone resistance in comparison with the blends containing conventional antioxidants. The liquid oligomer‐bound paraphenylene diamine could replace the plasticizer required for compounding. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 437–443, 2004