bluuebunny/crossref_metadata_2025_split huggingface dataset:
High interaction regime Lockhart‐Martinelli model for pressure drop in trickle‐bed reactors
Authors: Pinna Dario , Tronconi Enrico , Tagliabue Lorenzo 
Published: April 2004

AbstractPressure drop and liquid saturation in a cold model representative of trickle‐bed reactors operating in the high interaction regime were measured using air and water at atmospheric pressure. Five different packing similar in shape and dimension to typica1 industrial catalysts (cylindrical pellets, raschig rings, extrudates) were tested, covering a wide range of geometric characteristics. The adequacy of the most recent literature correlations for pressure drop in trickle‐bed reactors was checked. The best predictions are provided by an empirical correlation based on the Lockhart‐Martinelli parameters. A new model of similar accuracy was derived, which provides a theoretical basis for the successful application of the Lockhart‐Martinelli approach.
Level‐by‐level flowsheet synthesis methodology for thermal system design
Authors: Manninen Jussi , Zhu X. X. 
Published: April 2004

AbstractA new level‐by‐level methodology for flowsheet synthesis presented. In the first level, an initial superstructure is constructed to form a master model. Optimization of the master gives an initial optimal flowsheet, which indicates major structural features. In the second level this initial flowsheet is analyzed using exergy analysis to identify relevent modification options. The Promising options are used to update the intial superstructure, which is optimized to obtain an improved design. The results from the above design process determine the flowsheet of overall system and provide targets for design of subsystems. Design of subsystems forms the third design level. The predetermined of subsystems. Design of subsystems froms the third design level due to use of simplistic models in the previous design levels. The master model is updated and then Optimized again. The overall design process terminates when designs for subsystems can meet the design targets determined by the master model.
Reliable computation of mixture critical points
Authors: Stradi Benito A. , Brennecke Joan F. , Kohn P. , Stadtherr Mark A. 
Published: April 2004

AbstractThe determination of critical points of mixtures is important for both practical and theoretical reasons in modeling phase behavior, especially at high pressure. This article presents the first completely reliable method for locating all the critical points of a given mixture. The method also verifies the nonexistence of a critical point if a mixture of a given composition does not have one. The methodology used is based on interval analysis, in particular an interval Newton/generalized bisection algorithm providing a mathematical and computational guarantee that all mixture critical points are located. The procedure is initialization‐independent and thus requires no a priori knowledge of the number of mixture critical points or their approximate locations. The technique is illustrated using several example problems involving cubic equation‐of‐state models; however, the technique is for general purpose and can be applied in connection with other thermodynamic models.
New method for conversion of gas sonic velocities to density second virial coefficients
Authors: Mossaad Ehab , Eubank Philip T. 
Published: April 2004

AbstractA new, numerical method was developed to calculate density second virial coefficients B(T) from sonic velocity measurements in gases at low pressures. Unlike existing methods, this procedure requires no model assumption as to the form of the temperature variation of B(T). Rather, it differences the measured accoustic second virial coefficient according to a new mathematical identity. While two higher‐ordered terms in the identity must be ignored to initiate the numerical calculations, the magnitude of these terms can later be found from the initial determination of B(T). This article describes new equations developed, numerical procedures, calculations with Redlich‐Kwong and Peng‐Robinson gases and, with a Lennard‐Jones model gas, to show the accuracy of the method and the magnitude of the two error terms, and the method applied to existing sets of sonic velocity data.
Preparation of enzyme‐in‐polymer composites with high activity and stability
Authors: Kim Jungbae , Kosto Timothy J. , Manimala Joseph C. , Nauman E. Bruce , Dordick Jonathan S. 
Published: April 2004

AbstractFlash devolatilization was applied to incorporate an enzyme into a polymer matrix, which created a novel and highly active biocatalytic composite suitable for use in both aqueous and organic media. Enzymes were codissolved in toluene with commercial, high‐molecular‐weight polymers, and the solvent was then rapidly removed by injecting the mixture into a vacuum chamber. Subsequent cross‐linking of the enzyme with glutaraldehyde resulted in stable entrapped enzyme within the polymeric matrices. For example, a composite of α‐chymotrypsin and low‐density polyethylene showed no significant loss of enzymatic activity in aqueous buffer over a period of one month. The normalized activity of this biocatalytic material in organic solvents was 3–13 times higher than that of native α‐chymotrypsin lyophilized from aqueous buffer. Washing the composite material with aqueous buffer increased the activity in isooctane an additional ten fold. The composites of α‐chymotrypsin and polyethylene demonstrated the feasibility of obtaining active and stable biocatalytic materials via the application of compositional quenching to a biological system.
Scale effect on porosity and permeability: Kinetics, model, and correlation
Authors: Civan Faruk 
Published: April 2004

AbstractVariation of porosity and permeability by scale dissolution and precipitation in porous media is described based on fractal attributes of the pores, realization of flow channels as a bundle of uniformly distributed mean‐size cylindrical and tortuous hydraulic flow tubes, a permeability‐porosity relationship conforming to Civan's power law flow units equation, and the pore surface scale precipitation and dissolution kinetics. Practical analytical solutions, considering the conditions of typical laboratory core tests and relating the lumped and phenomenological parameters, were derived and verified by experimental data. Deviations of the empirically determined exponents of the pore‐to‐matrix volume ratio compared to the Kozeny‐Carman equation were due to the relative fractal dimensions of pore attributes of random porous media. The formulations provide useful insights into the mechanism of porosity and permeability variation by surface processes and accurate representation of the effect of scale on porosity and permeability by simpler lumped‐parameter models.
Viscous‐Gravity spreading of oil on water
Authors: Chebbi Rachid 
Published: April 2004

AbstractSpreading of oil on calm water is analyzed for the second stage of spread, which is controlled by a balance between gravity and viscous forces. The analysis, using the integral boundary‐layer method, agreed well with a numerical solution for the case of unidirectional spread. The analysis is extended to include axisymmetric spread for which there is no sound theoretical treatment presented in the literature. The approximations made in the model are discussed based on the lubrication approximation and order‐of‐magnitude arguments.
Free drainage in aqueous foams: Model and experimental study
Authors: Magrabi S. A. , Dlugogorski B. Z. , Jameson G. J. 
Published: April 2004

AbstractFree drainage in compressed‐air foams were studied experimentally and theoretically. The time evolution of liquid holdup profiles in a 0.2‐m‐high by 0.29‐m‐diameter foam column was determined at various heights by measuring sonic velocity. A new experimental technique was devised to measure the true drainage rate of surfactant solution leaving the foam column. A drainage model was outlined to predict the discharge rate and evolution of the liquid‐fraction profile in aqueous foams. The model led to the formulation of a nonlinear partial differential equation in which the liquid fraction was used explicitly as a dependent variable. The model was applied with one adjustable parameter to simulate drainage in foams made from fluorocarbon surfactants containing mobile plateau border and film walls. The liquid‐fraction profiles, drainage rates, and final equilibrium liquid profiles depended strongly on the surface mobility of plateau border and film walls; the bubble size; and therefore on the coarsening histoy in the foam under study. Over longer time periods this model needs to be coupled with interbubble gas diffusion to account for coarsening‐induced drainage.
Integrated membrane process for gold recovery from hydrometallurgical solutions
Authors: Kumar Anil , Haddad R. , Sastre A. M. 
Published: April 2004

AbstractThis work reports the nondispersive solvent extraction (NDSX) of gold cyanide from aqueous alkaline cyanide media with LIX79 and stripping of gold from the organic complex simultaneousty using two microporous hydrophobic polypropylene hollow‐fiber contactors for extraction and stripping, respectively. Extraction was studied under different hydrodynamic conditions and mass‐transfer correlations for shell and tube sides. The mass‐transfer process was compared with experimental results. The HFNDSX was operated with 12–18% LIX 79 in n‐heptane by contacting alkaline cyanide feed containing gold through the tube side and organic extractant through the shell side, which was recirculated between extraction and stripping hollow‐fiber modules through the shell side countercurrently. In the second HF contactor, the stripping solution, 1M NaOH flowed through the tube side countercurrently. Modeling of the system identified rate‐controlling steps under different experimental conditions. The interfacial chemical reaction rate at the dominant surface, and mass‐transfer resistance caused by this reaction controlled the entire extraction process. Several experiments with synthetic solutions of different compositions of gold hydrometallurgical solutions established optimum conditions to achieve a clean separation of Au(I). It was possible to separate Au(I) in the presence of other metal cyanide salts, such us Fe(II), Cu(II), Ni(II), Ag(I), and Zn(II) (NaCN = 1,000–5,000 ppm), which was concentrated in the stripping phase containing NaOH.
Propylene/propane separation by vacuum swing adsorption using 13X zeolite
Authors: Silva Francisco A. Da , Rodrigues Alírio E. 
Published: April 2004

AbstractA vacuum swing adsorption process using 13X zeolite pellets with five steps was designed to split an equimolar mixture of propylene/propane: pressurization with feed; high‐pressure feed; high‐pressure purge with product; cocurrent blowdown; and counter‐current vacuum blowdown, where the enriched propylene product is withdrawn. In the process, the partial pressure of the C3‐mixture is controlled with nitrogen, which is used as inert gas. With an equimolar feed of C3 diluted to 50% with nitrogen, the column is fed at 5 bar and 423 K, and the product is obtained when the total pressure is lowered to 0.1 bar. After 15–20 cycles, the cyclic steady‐state condition is achieved, a propylene‐enriched stream of 98% mol relative to propylene/propane mixture, with 3.2% of nitrogen, a recovery of 19% (molar basis), and a productivity of 0.785 mol/kg·h is obtained. The experimental work was complemented with numerical simulations, and the effect of different operating parameters on the performance of the VSA was considered.
Three‐dimensional flow patterns in cracking furnaces with long‐flame burners
Authors: Heynderickx Geraldine J. , Oprins Arno J. M. , Marin Guy B. , Dick Erik 
Published: April 2004

AbstractA 3‐D computational fluid‐dynamics model containing equations for mass, heat and momentum transfer and using a k‐ϵ closure model, was used to calculate the 3‐D flue‐gas flow pattern and the corresponding 3‐D temperature field for a pyrolysis furnace. The computational fluid dynamics model is combined with a reactor model for the cracking tubes and a radiation model for the radiative heat transfer in the furnace box. Detailed reaction kinetics for the naphtha cracking reactions in the tubes nnd a five‐step reaction mechanism for the combustion qf methane in the flames were used. This complete model reveals asymmetric flow patterns in a naphtha‐cracking furnace with 4/2/1 split‐coil reactors and fired with long‐flame burners.
Antisolvent crystallization of anhydrous sodium carbonate at atmospherical conditions
Authors: Oosterhof Harald , Witkamp Geert‐Jan , van Rosmalen Gerda M. 
Published: April 2004

AbstractWhen antisolvents are applied to crystallize sodium carbonate from aqueous solutions, the transition temperature at which the hydrates are in equilibrium is decreased. Two models proposed can predict the influence of the amount and type of antisolvent on the transition temperature. Only binary data of the water/sodium carbonate system and measured vapor pressures over ternary soda‐saturated mixtures of water and antisolvent are needed. To validate the two models, continuous crystallization experiments were carried out at various temperatures using ethylene glycol (EG) and diethylene glycol (DEG) as antisolvent, in varying concentrations. Both models predict the influence of the antisolvent on the transition temperature with good accuracy. Anhydrous soda with bulk densities of up to 950 kg/m3 was crystallized at temperatures as low as 80°C.
Thermodynamic activity‐based enzyme kinetics: Efficient tool for nonaqueous enzymology
Authors: Sandoval Georgina C. , Marty Alain , Condoret Jean‐Stéphane 
Published: April 2004

AbstractLipase‐catalyzed synthesis reactions must be performed in nonaqueous media (organic solvents or solvent‐free systems). The choice of the optimal solvent is usually a fastidious task that necessitates the determination of kinetic parameters in each solvent. The approach used here, to overcome the lack of a model that can predict the kinetics whatever the solvent, consists in the use of thermodynamic activities instead of concentrations of components, and assumes that activity‐based kinetic parameters are the same in all solvents. This assumption is discussed, and a solution is proposed which takes into account some observed residual solvent effects. The reaction chosen to test this approach was the esterification of oleic acid with ethanol catalyzed by an immobilized lipase, Lipozyme. For this reaction, the kinetics predicted in various organic solvents and in solvent‐free systems is in agreement with the experimental data.
Evaluation of sol‐gel processed BaO·nAl2O3 materials as NOx traps
Authors: Narula Chaitanya K. , Nakouzi Sabine R. , Wu Ruowen , Goralski Christian T. , Allard Lawrence F. 
Published: April 2004

AbstractAmong various strategies to treat NOx, trapping is considered an economical, consumer transparent approach for gasoline engines. The conventional NOx traps are based on alkaline‐earth metal impregnated alumina. These traps work well, but cannot sustain their NOx trapping efficiency after repeated exposure to high temperatures during regeneration. In search of thermally stable materials, a series of sol‐gel processed BaO·nAl2O3 (n = 1, 4, 6) materials including BaO·6Al2O3 molecular sieves were synthesized and evaluated as NOx traps using simulated exhaust at a 25,000 h−1 space velocity. Changes in structure and surface properties occurring on thermal treatment of sol‐gel processed BaO·nAl2O3 materials significantly affect the NOx trapping efficiency of these materials. Among these materials, sol‐gel processed and precious metal impregnated BaO·6Al2O3 powder offers the optimum combination of thermal stability and NOx trapping efficiency. We deposited this powder on a honeycomb substrate, impregnated it with 2% Pt and 0.4% Rh, and reevaluated it. The NOx trapping efficiency of this catalyst is 95% (cf. 75% for the powder) at 310°C. Our data on Pt/BaO·6Al2O3 also suggest that the optimum lean cycle length for this class of NOx traps is 1 min. The efficiency of NOx traps decreases rapidly and falls in 10–20% range with an alternating 5 min lean cycle and 1 min rich cycle.
Numerical simulations of pool‐boiling heat transfer
Authors: Dhir Vijay K. 
Published: April 2004

AbstractBoiling has been studied extensively during the last half of the 20th century. Many correlations and semimechanistic models have also been developed for various modes of boiling. However, due to the complexity involved in modeling continuously evolving vapor–liquid interfaces, unrealistic assumptions are often made in developing various models. With the advances of recent years in the area of computational science and engineering, it is now possible to solve, completely, the conservation equations of mass, momentum, and energy for liquid and vapor phases simultaneously when an interface is continuously evolving at and near a heated surface. The solutions provide not only detailed physics of associated thermal and hydrodynamic processes, but also the shape of the evolving interface. In demonstrating the application of numerical simulations as an effective tool, both pool nucleate and film boiling at normal earth gravity, and nucleate boiling under microgravity conditions are considered. Although these simulations have been computationally intensive, in the future calculations of this type are expected to become routine.
Simulation of the dynamics of depth filtration of non‐Brownian particles
Authors: Burganos V. N. , Skouras E. D. , Paraskeva C. A. , Payatakes A. C. 
Published: April 2004

AbstractA new simulator for flow of aqueous suspensions and deposition of non‐Brownian particles in granular media can predict the pattern of deposition and concomitant reduction in permeability as functions of depth, time and system parameters. The porous structure of the granular medium represented as a 3‐D network of constricted pores considers the converging–diverging character of flow within pores. Using Lagrangian‐type simulation the particle deposition rate was calculated. Gravity and drag, as well as hydrodynamic and physicochemical interactions between suspended particles and pore walls, were considered in calculating 3‐D particle trajectories. Deposit configurations were computed, and the evolution of the pore structure was simulated at discrete time steps. Changes in the pore geometry and nature of the collector surface affect flow and trajectory computations directly. Clusters of deposited particles were allowed to become reentrained if exposed to shear stress higher than a critical value. Reentrained clusters, which moved through downstream pores, might redeposit downstream at suitable sites and cause clogging of sufficiently narrow pores. Particle clusters clogging pores have a finite permeability, which significantly affects the system's transient behavior. Clogged pores act as collectors of solitary particles and of reentrained clusters, and substantially affect the transient behavior of the filter. The loss of permeability was monitored by calculating pore and network hydraulic conductance at each time step. Numerical results for the loss of permeability, temporal evolution of filter efficiency, and specific deposit profiles are based on suspension flow simulations in a typical granular porous medium.
Qualitative/quantitative simulation of process temporal behavior using clustered fuzzy digraphs
Authors: Li R. F. , Wang X. Z. 
Published: April 2004

AbstractA methodology is presented for qualitative modeling and simulation of the temporal behavior of individual variables and the composite process. The temporal behavior of a variable in a windowed time scale is captured categorically using principal‐component analysis, while the process is modeled as a causal digraph with interacting and recycle nodes. Rigorous, rather than ad hoc, reasoning rules can be devised for the causal digraph using a learning mechanism. Quantitative information can also be incorporated into the method with the introduction of fuzzy c‐means clustering without compromising the cognitive level of information embedded in the nodes and the digraph.
Analyzing mixing in periodic flows by distribution matrices: Mapping method
Authors: Kruijt Peter G. M. , Galaktionov Oleksiy S. , Anderson Patrick D. , Peters Gerrit W. M. , Meijer Han E. H. 
Published: April 2004

AbstractA novel mapping method presented analyzes the long‐term efficiency of distributive mixing in Stokes flows. It uses the results of an accurate front tracking technique to calculate a distribution or mapping matrix. For the first time, it is possible to efficiently investigate the influence of geometric configurations and operating conditions on overall mixing quality. The technique was tested using the mixing dynamics of a model time periodic prototype flow; namely Stokes flow in a 2‐D, lid‐driven cavity. The method however, can also be extended to examine more realistic spatially periodic flows such as static mixers or twin screw extruders.
Comparative analysis of CFD models of dense gas–solid systems
Authors: van Wachem B. G. M. , Schouten J. C. , van den Bleek C. M. , Krishna R. , Sinclair J. L. 
Published: April 2004

AbstractMany gas–solid CFD models have been put forth by academic researchers, government laboratories, and commercial vendors. These models often differ in terms of both the form of the governing equations and the closure relations, resulting in much confusion in the literature. These various forms in the literature and in commercial codes are reviewed and the resulting hydrodynamics through CFD simulations of fluidized beds compared. Experimental data on fluidized beds of Hilligardt and Werther (1986), Kehoe and Davidson (1971), Darton et al.(1977), and Kuipers (1990) are used to quantitatively assess the various treatments. Predictions based on the commonly used governing equations of Ishii (1975) do not differ from those of Anderson and Jackson (1967) in terms of macroscopic flow behavior, but differ on a local scale. Flow predictions are not sensitive to the use of different solid stress models or radial distribution functions, as different approaches are very similar in dense flow regimes. The application of a different drag model, however, significantly impacts the flow of the solids phase. A simplified algebraic granular energy‐balance equation is proposed for determining the granular temperature, instead of solving the full granular energy balance. This simplification does not lead to significantly different results, but it does reduce the computational effort of the simulations by about 20%.
Heat conduction in granular materials
Authors: Vargas Watson L. , McCarthy J. J. 
Published: April 2004

AbstractHeat transfer in particulate systems is important to a vast array of industries, yet is poorly understood even in the simplest case—conduction through the solid phase. This is due in part to the stress and contact heterogeneities inherent to these systems. Heat conduction in a packet bed of cylinders is investigated both experimentally and computationally. A novel model is developed based on the Discrete Element Method, which not only sheds light on fundamental issues in heat conduction in particles, but also provides a valuable test bed for existing theories. By explicitly modeling individual particles within the bulk material, bed heterogeneities are directly included, and dynamic temperature distributions are obtained at the particle level. Comparison with experiments shows that this model yields a quantitatively accurate temperature field without the need for adjustable parameters or detailed microstructural information. This simple system may also provide insight into such phenomena as reactor hot spot formation and spontaneous combustion of bulk reactive materials.