bluuebunny/crossref_metadata_2025_split huggingface dataset:
Onset of solutal marangoni convection in a suddenly desorbing liquid layer
Authors: Kang Kyoung H. , Choi Chang K. , Hwang In G. 
Published: April 2004

AbstractThe onset of surface‐tension‐driven convection in an initially quiescent liquid layer experiencing sudden desorption from a free surface is analyzed using the linear stability theory. The propagation theory was developed for the basic time‐dependent concentration profile, which is strongly nonlinear. Based on this theory, a new set of stability equations is derived in considering the effect of Gibbs adsorption and by neglecting the surface diffusion. It is found that the liquid layer becomes more stable by decreasing the Schmidt and Biot numbers. It is interesting that, during an initial period, the system is stable, depending on the Gibbs effect. The predictions agree favorably with the existing experimental results of triethylamine desorption in water in a wetted‐wall and a liquid‐jet column.
Dynamic behavior of freely rising buoyant solid spheres in non‐Newtonian liquids
Authors: Dewsbury K. H. , Karamanev D. G. , Margaritis A. 
Published: April 2004

AbstractThe results of the hydrodynamic study of rising solid spheres in non‐Newtonian (pseudoplastic) fluids are reported. The hydrodynamic parameters including drag coefficient, trajectory of rise, and terminal velocity were determined. The behavior of free‐rising spheres was compared to that of falling spheres in the same type of fluids to see if any differences exist. It was observed that rising solid spheres behave differently from falling solid spheres at higher Reynolds numbers in non‐Newtonian (pseudoplastic) fluids. At high Reynolds numbers rising solid spheres display a spiraling motion, while falling spheres display a linear trajectory. The angle between the velocity vector and horizontal plane of the spiraling trajectory was 60°. The spiraling trajectory led to a drag coefficient that was more than two times higher for rising solid spheres than that established for falling spheres in the Newton's law range in a non‐Newtonian (pseudoplastic) liquid. The first ever correlation is proposed to calculate the drag coefficient of freely rising light solid spheres in non‐Newtonian (pseudoplastic) fluids.
Riser hydrodynamics: Simulation using kinetic theory
Authors: Neri Augusto , Gidaspow Dimitri 
Published: April 2004

AbstractComputational fluid dynamics (CFD) for fluidization is reaching maturity (Roco, 1998). It has become common practice to compare time‐averaged solid velocities and concentrations to measurements of fluxes and densities. The dynamic behavior of the riser, however, has not been previously compared to experiments. This article shows that the dynamics of solids flow in the riser is in the form of clusters, but the time‐averaged particle concentrations and fluxes give us the core‐annular flow regime in agreement with measurements. The computed clusters, which are essentially compressible gravity waves, produce major frequencies of density oscillations in agreement with measurements. The model and the CFD code compute granular temperature distributions, agreeing qualitatively with data. For volume fraction around 3–4%, which is the average particle concentration in the riser, the computed viscosity agrees with our experimental measurements.
Effects of microstructure on the compressive yield stress
Authors: Channell Glenn M. , Miller Kelly T. , Zukoski Charles F. 
Published: April 2004

AbstractThe effects of microstructure on the compressive properties of aggregated alumina suspensions are determined by intentionally introducing heterogeneities into the suspension. Suspensions are prepared at a high volume fraction and diluted with low shear hand mixing to a series of initial concentrations. As the initial concentration is increased, larger heterogeneities are introduced, and the suspension becomes more compressible relative to the compressive yield stress of the uniform suspension. A simple model is proposed in which the heterogeneous suspensions compress by rearrangement of the dense aggregates until a critical concentration (ϕc, which coincides with the volume fraction prior to dilution) is reached. Above ϕc, the suspensions consolidate identically to the uniform suspension. With a single fitting parameter (the size of the heterogeneities), the model shows semiquantitative agreement with the experimental data.
Filtration of highly compactible filter cake: Variable internal flow rate
Authors: Lee D. J. , Ju S. P. , Kwon J. H. , Tiller F. M. 
Published: April 2004

AbstractConventional analyses used to interpret filtration data assume a constant internal liquid flow rate (qL) and a negligible solid velocity (the constant‐qL approximation). To interpret such data, the upper bounds of errors to estimate αav and kav were analytically derived by the constant‐qL approximation. The solution of the filtration model that incorporates a nonzero solid velocity was then analytically derived. When filtering a highly compactible filter cake, the cake was first compacted toward the filter medium that forms a skin layer and, in doing so, rapidly reaches the steady‐state distribution predicted by the constant‐qL approximation. Except at the first stage of the filtration, the approach of Tiller et al. (1999) is valid for interpreting filtration data of a highly compactible filter cake. Furthermore, the constant‐qL approximation provides the upper limit of errors in terms of estimating cake characteristics regardless of the solid velocity effect.
Adsorption behavior of surfactants and mass transfer in single‐drop extraction
Authors: Chen Liang‐Huei , Lee Yuh‐Lang 
Published: April 2004

AbstractThree surfactants—SDS, Triton X‐100, and DTMAC—were used to study effects of surfactants on the mass transfer in liquid–liquid extraction. Single‐drop extraction apparatus was used to obtain the mass‐transfer coefficient of acetic acid from dispersed CCl4 droplets to the continuous water phase. The excess mass‐transfer resistance was related to the adsorption behavior of surfactants on the interface. All of these surfactants significantly reduced the mass‐transfer rate. Mass‐transfer coefficient, KR, decreases rapidly with increasing surfactant concentration and reaches a minimum at concentrations less than 0.04 mM. The effectiveness of the surfactants in decreasing the mass‐transfer rate increases in the order: DTMAC<SDS = Triton X‐100. This effectiveness has no direct relation with the ionic types of surfactants, but is affected by the adsorption rate and adsorbed surface concentration on the interface. A slight increase in the mass‐transfer coefficient was found at higher concentrations of Triton X‐100 due to its higher adsorption kinetics. The excess mass‐transfer resistance exerted by the surfactant mainly resulted from the obstruction of the adsorbed barrier layer. The contribution of the inhibition of interfacial flow to the mass‐transfer resistance was considered to be minor.
Crystal growth rates and dispersion for D‐fructose from aqueous ethanol
Authors: Flood Adrian E. , Johns Michael R. , White Edward T. 
Published: April 2004

AbstractThe growth of fructose crystals from aqueous ethanolic solutions was studied using a 1‐L seeded batch crystallizer. The growth kinetics were found to linearly depend on the relative supersaturation of the crystallizing tautomer (β‐D‐fructopyranose). The growth‐rate constant increased slightly with increasing temperature and increasing solvent ethanol content. The growth rates are lower than those for aqueous solutions of comparable supersaturations. Fructose displays significant growth‐rate dispersion (q = 0.35) when crystallized from aqueous ethanolic solutions. The growth‐rate dispersion is independent of solvent composition and temperature within the range studied, although it is slightly higher than is seen in crystallization from aqueous solutions.
SMB enantioseparation: Process development, modeling, and operating conditions
Authors: Lehoucq Sylvie , Verhève Didier , Vande Wouwer Alain , Cavoy Emile 
Published: April 2004

AbstractThe design of a simulated moving bed (SMB) pilot used for chiral drug separation is presented. On‐line concentration measurements allow the observation of detailed concentration profiles along the SMB columns. Based on an extensive set of experimental data, an equivalent countercurrent model was derived. In this model, mass‐transfer kinetics are described by linear driving‐force models, while the equilibrium concentrations are given by modified competitive Langmuir isotherms. The isotherm parameters are estimated using a peak fitting procedure, which starts with initial values given by a simple retention‐time method. The dispersion phenomena are estimated through the variation of the HETP with the fluid‐phase velocity. The good agreement between the model and the real system is demonstrated by several cross‐validation results corresponding to the separation of given racemic mixtures under various operating conditions. The model defines a zone of complete separation and allows optimal operating conditions to be selected.
Flexibility analysis and design of linear systems by parametric programming
Authors: Bansal Vikrant , Perkins John D. , Pistikopoulos Efstratios N. 
Published: April 2004

AbstractA new, unified theory and algorithms, based on multiparametric programming techniques, for the solution of flexibility analysis and design optimization problems in linear process systems are presented. They are used for the flexibility test and index problems in systems with deterministic parameters, and for the stochastic and expected stochastic flexibility evaluation problems in systems with stochastic parameters. They are computationally efficient and give the explicit dependence of various flexibility metrics on the values of the continuous design variables. The latter feature enables the easy and efficient comparison of design alternatives. It also allows for the compact formulation of design optimization problems that can be solved parametrically to yield the exact algebraic form of the trade‐off curve of economics against flexibility. Key features of the proposed approach are demonstrated through both mathematical and process examples.
Effective extraction of titanium from rutile by a low‐temperature chloride process
Authors: Yang Fenglin , Hlavacek Vladimir 
Published: April 2004

AbstractThe carbochlorination of rutile is carried out at high temperatures (800–1,500°C) in the commercial chloride processes of the pigment industry. Chlorination at high temperatures results in high energy consumption, rapid corrosion of the equipment, pipeline and control system, and agglomeration of solid reactants in the reactor. In a typical chloride process, rutile is used as a primary reactant, Cl2 as a chlorinating agent, and carbon as a reductant. The thermodynamic equilibrium simulation of the reaction system shows that a complete conversion of rutile is feasible at a temperature as low as 200°C. Kinetic and diffusion barriers, however, make the reaction practically impossible at low temperatures. In the study, these barriers were removed by intensifying the rutile‐carbon solid–solid contact. In the low‐temperature chloride process developed, reaction temperatures are reduced to 350–450°C. The conversion rate of the rutile at 385°C is 30% higher than that at 1,000°C. A fluidized‐bed reactor was used for the chlorination process. It was concluded that the formation of an activated TiO2CCl complex on the TiO2/C interface accounts for the gas–solid–solid reaction mechanism.
Thermodynamically consistent modeling of a liquid‐phase nonisothermal packed‐bed reactor
Authors: Syed Faisal H. , Datta Ravindra , Jensen Kyle L. 
Published: April 2004

AbstractThe equilibrium‐limited steady‐state nonisothermal behavior of an integral packed‐bed reactor is described for the liquid‐phase synthesis of ethyl tert‐butyl ether with a model that is inherently consistent with thermodynamics. It involves a coupled one‐dimensional mass‐ and enthalpy‐balance equation with temperature‐dependent thermochemical properties and reaction equilibria. The model accounts for the nonideal nature of the liquid‐phase reaction system by utilizing species activities in the rate expression for the reversible reaction, which is also consistent with thermodynamic equilibrium. Experiments agreed well with theory with all of the kinetic, thermodynamic and other physicochemical parameters being obtained from independent experiments, indicating that the theoretical approach is robust. Further, the results clearly endorse the use of species activities rather than concentration, or mole fractions, in the rate expression for the nonideal liquid‐phase reactions. There is a paucity of such studies in the literature, especially for liquid‐phase nonisothermal packed‐bed reactor analysis.
Newtonian radial entrance flow
Authors: Chatterjee Ajay 
Published: April 2004

AbstractThe laminar flow of a Newtonian fluid is considered through a prototype radial entrance geometry that consists of a circular pipe joined to the bottom plate of a pair of parallel circular plates, a configuration that mimics and idealizes important practical flows. The equations of motion are solved numerically to compute the velocity field as a function of the Reynolds number Re and the geometrical aspect ratio e. This work extends limited previous results on flow development in this entrance geometry. A range of e and Re are considered, and the Re–e parameter space corresponding to flow separation is delineated. The computed results are used to illustrate the role of the aspect ratio in influencing flow development for small e≲1 and are analyzed to quantify the large e asymptotic behavior of various quantities characterizing the developing flow field. The limiting value of aspect ratio beyond which the asymptotic behavior applies is relatively small e≳2. The dependence of these quantities on Re also is analyzed. The results are discussed in light of available experimental measurements and existing analytical results. An important implication of the results in the context of confined laminar impinging jet heat transfer is described. The entrance configuration is contrasted with a companion radial entrance flow (radial source flow); although flow separation occurs in both cases, some basic features are quite distinct. The influence of the elongational character of this radial flow field is highlighted by comparing certain aspects of flow development between this axisymmetric configuration and its 2‐D Cartesian analog.
Gas dispersion in downflowing high velocity fluidized beds
Authors: Cao Chunshe , Weinstein Herbert 
Published: April 2004

AbstractMeasurements are presented of gas mixing in a downflowing high‐velocity fluidized bed using helium tracer detected by an on‐line analyzer. It was found that gas backmixing is very limited in the downer, and the lateral mixing is comparable with that in the riser. A dispersion model is applied to characterize the behavior of the gas mixing in the two‐phase downflowing mixture.
Pricing interprocess streams using slack auctions
Authors: Jose Rinaldo A. , Ungar Lyle H. 
Published: April 2004

AbstractWhen plantwide optimization problems must be decomposed and solved in pieces due to numerical complexity or practical concerns, it is natural to view each plant division as a separate profit maximizer. For a division to maximize its profit, however, it must know the prices of interprocess streams. It is claimed that the correct way of finding these prices is to define slack resources over the process streams and price them using slack auctions. When slack auctions terminate properly, it can be shown that the plant divisions' solutions are globally optimal. How slack auctions are related to Lagrangean relaxation and how they can overcome some of the problems that standard decomposition and relaxation techniques have are discussed.
Phase‐equilibrium fractionation of continuous distributions
Authors: McCoy Benjamin J. , Sterling W. Jerome 
Published: April 2004

AbstractFractionation of continuously distributed homologous mixtures is described in terms of molecular distributions. The concepts apply to phase equilibrium in vapor–liquid hydrocarbon mixtures and sol–gel polymer mixtures. Models of both differential and finite phase‐equilibrium separations are presented when the partition coefficient for the equilibrium distributions is given. Analytical solutions for the distributions, including a similarity solution for a differential fractionation, can be formed. A differential fractionation solution compares satisfactorily with experimental data.
Separation of light gas mixtures using SAPO‐34 membranes
Authors: Poshusta Joseph C. , Tuan Vu A. , Pape Eric A. , Noble Richard D. , Falconer John L. 
Published: April 2004

AbstractContinuous SAPO‐34 membranes were prepared on porous alumina tubular supports, and shown to be useful for light gas separations at low and high temperatures. Single‐gas permeances of CO2, N2 and CH4 decreased with increasing kinetic diameter. For the best membrane at 300 K, the He and H2 permeances were less than that of CO2, because He, H2, and CO2 were small compared to the SAPO‐34 pore, and differences in the heat of adsorption determined the permeance order. The smaller component permeated the fastest in CO2/CH4, CO2/N2, N2/CH4, H2/CH4 and H2/N2 mixtures between 300 and 470 K. For H2/CO2 mixtures, which were separated by competitive adsorption at room temperature, the larger component permeated faster below 400 K. The CO2/CH4 selectivity at room temperature was 36 and decreased with temperature. The H2/CH4 mixture selectivity was 8 and constant with temperature up to 480 K. Calcination, slow temperature cycles, and exposure to water vapor had no permanent effect on membrane performance, but temperature changes of approximately 30 K/min decreased the membrane's effectiveness.
Molecular simulation of multicomponent reaction and phase equilibria in MTBE ternary system
Authors: Lísal Martin , Smith William R. , Nezbeda Ivo 
Published: April 2004

AbstractReaction and phase equilibria in the isobutene + methanol + MTBE ternary system were studied using the reaction‐ensemble Monte Carlo (REMC) simulation method. The system was modeled at the molecular level by an OPLS force field. No adjustable binary cross‐interaction parameters or mixture data of any kind were used in the simulation model, and only vapor‐pressure data for the pure components was required as input. The REMC method also computes excess internal energies and molar volumes as a biproduct of the simulations. Both the nonreacting and reacting ternary systems were considered over the temperature range of practical interest at 5 bar. Results are compared with the calculations using two conventional thermodynamic approaches: the Wilson and UNIFAC free‐energy models for the liquid phase, together with a truncated virial equation of state for the gas phase in both cases. Computer simulation results were similar to those of the thermodynamic approaches, and they are arguably more accurate.
Multiple steady states in distillation: Effect of VL(L)E inaccuracies
Authors: Bekiaris Nikolaos , Güttinger Thomas E. , Morari Manfred 
Published: April 2004

AbstractOutput multiplicities in heterogeneous azeotropic distillation columns were studied. The accuracy of the thermodynamic description is a key factor that determines if multiplicities can be observed in numerical simulations. The descriptions used in the multiplicity‐related literature are analyzed. The ∞/∞ analysis of Bekiaris et al. (1996) was used to check implications of inaccuracies in the reported thermodynamics on the existence of multiplicities in azeotropic distillation. On this basis, guidelines are derived concerning what features of thermodynamic descriptions need special attention for use in multiplicity prediction and simulation. Secondly, numerical studies on output multiplicities in heterogeneous azeotropic distillation in the literature were compared to the ∞/∞ predictions wherever possible. The ∞/∞ analysis was used to derive the relations between the reported multiplicities and to identify the physical phenomena causing them.
Nonlinear inferential cascade control of exothermic fixed‐bed reactors
Authors: Hua Xiangming , Jutan Arthur 
Published: April 2004

AbstractA nonlinear inferential cascade control strategy for a tubular fixed‐bed reactor with highly exothermic reaction is presented. Tight control of exit conversion and stabilization of hot‐spot temperature was achieved over a wide range of operating conditions. A multiple cascade structure was developed by lumping the distributed‐parameter system and partitioning it into three subsystems. Practical issues of implementing the control system are addressed, as well as physical insight and assumptions used for model reduction of each subsystem. The direct synthesis approach for nonlinear control systems is used to design the controllers of the important subsystems separately. A lag was added in the primary subsystem, and fast stabilization of the secondary subsystem was implemented. Unknown temperature states and inlet concentration were estimated by a nonlinear observer from only a few temperature measurements. The control problem of the moving hot‐spot temperature was also addressed. Simulation on an industrial phthalic anhydride fixed‐bed reactor showed that the observer can give excellent dynamic tracking of the reactor. The resulting cascade control system can achieve good set‐point tracking and disturbance rejection performance, which is robust in the presence of measurement error and model mismatch, and superior to a single‐loop control system.
Robust steady‐state target calculation for model predictive control
Authors: Kassmann Dean E. , Badgwell Thomas A. , Hawkins Robert B. 
Published: April 2004

AbstractIn practice, model predictive control (MPC) algorithms are typically embedded within a multilevel hierarchy of control functions. The MPC algorithm itself is usually implemented in two pieces: a steady‐state target calculation followed by a dynamic optimization. A new formulation of the steady‐state target calculation is presented that explicitly accounts for model uncertainty. When model uncertainty is incorporated, the linear program associated with the steady‐state target calculation can be recast as a second‐order cone program. This article shows how primal‐dual interior‐point methods can take advantage of the resulting structure. Simulation examples illustrate the effect of uncertainty on the steady‐state target calculation and demonstrate the advantages of interior‐point methods.
Pyrolysis of sawdust in a conical spouted‐bed reactor with a HZSM‐5 catalyst
Authors: Olazar Martin , Aguado Roberto , Bilbao Javier , Barona Astrid 
Published: April 2004

AbstractThe effect was studied of using in‐situ catalyst based on a HZSM‐5 zeolite in flash pyrolysis with an inert gas (N2) of sawdust of pinus insignis in a conical spouted‐bed reactor in the 400–500°C range and for a gas residence time of 50 ms. The use of the catalyst increases the yield of gases and decreases the yields of liquid and char. Likewise, the yield of CO2 decreases, whereas the yield of C4− hydrocarbons increases (15.9 wt. % at 450°C). The catalyst is efficient for partial deoxygenation of the liquid product.