bluuebunny/crossref_metadata_2025_split huggingface dataset:
Voidage variation in packed beds at small column to particle diameter ratio
Authors: de Klerk Arno 
Published: April 2004

AbstractRandomly 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

AbstractIt 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

AbstractThis 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

AbstractTransient 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

AbstractSubspace 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

AbstractA 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

AbstractVapor–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

AbstractA 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractMaximum 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

AbstractKinetic 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

AbstractSimilarity 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 Re<ReC. The upper limit ReC for the reactor Reynolds number is shown to be constrained by the volumetric flow ratio of reactant feed‐to‐pumping capacity. Moreover, for larger reactor Reynolds number Re>ReC, 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

AbstractMixing 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

AbstractThe 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

AbstractAn 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

AbstractA 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

AbstractAn 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.