bluuebunny/crossref_metadata_2025_split huggingface dataset:
Liquid holdup in rotating packed beds: Examination of the film flow assumption
Authors: Bašić Andjelko , Duduković Milorad P. 
Published: June 2004

AbstractPossibilities of predicting liquid holdup in rotating packed beds are examined using the film flow theory. A hydrodynamic model based on film flow on the particle scale accommodates both laminar and turbulent films in the entry and developed regime. Conductance measurement was used for experimental determination of liquid holdup and estimation of the degree of anisotropy of liquid distribution. Experimental results represent the first data for liquid holdup in the rotating packed bed as a function of operating conditions and liquid properties. They indicate an anisotropic liquid distribution dependent on the operating variables. While the film model can be fitted to the experimental data, such a fit lacks a theoretical basis and the classical theory of film flow on the particle scale cannot explain the liquid flow in rotating packed beds. An empirical expression correlates well the holdup data with the operating parameters.
Continous‐mixture kinetics of coke formation from olefinic oligomers
Authors: McCoy Benjamin J. , Subramaniam Bala 
Published: June 2004

AbstractA model for interpreting the molecular‐weight distributions is presented for the olefinic oligomers and aromatic coke compounds that are experimentally observed in a catalyzed hexene isomerization process (the primary reaction). Reaction rate expressions for the secondary generation of hexene dimers, trimers and tetramers by irreversible reaction are represented in mass balances for a stirred‐tank reactor. Dehydrogenation of the oligomers to form coke aromatics and their subsequent adsorption and desorption are included. A molecular‐weight moment method allows solution of the model and computation of time dependence of molecular‐weight distributions for all components. The model is consistent with observations of decreased catalyst deactivation rates when coke desorption rates approach coke production rates. Catalyst activity maintenance, which can occur under supercritical conditions, is also predicted by the model.
Molecular dynamics simulation of diffusion in pillared clays
Authors: Yi Xiaohua , Shing Katherine S. , Sahimi Muhammad 
Published: June 2004

AbstractThe thermodynamics and transport properties of Lennard‐Jones particles in pillared catalytic clays are studied by molecular dynamics simulation. The clays are represented by parallel sheets separated by a given distance and connected by pillars of a given size. Two different spatial distributions of the pillars are studied to determine their effect on the properties of the system. Calculations did not indicate a strong dependence of the diffusivity on the spatial distribution of the pillars, except at low porosities. The solvation force increases monotonically with decreasing porosity of the clays and increasing density of the molecules. The percolation threshold φc of the system is estimated from the diffusivity measurements in the limit of infinitely low sorbate densities. Near φc the diffusivity D vanishes according to the power law, D ˜ (φ − φc)n, where φ is the porosity of the system, and n is a universal constant. The simulations yield n ⋍ 1.7. Since 2‐ percolation systems require n ⋍ 1.3 and 3‐D systems n ⋍ 2.0, pillared clays behave as a system with an effective dimensionality between 2 and 3.
Residence time distribution in three‐phase monolith reactor
Authors: Patrick Robert H. , Klindera Theresa , Crynes Lawrence L. , Cerro Ramon L. , Abraham Martin A. 
Published: June 2004

AbstractThe residence time distribution of the liquid phase within a three‐phase monlith reactor is determined using tracer studies. The actual liquid residence time in the monolith, relevant for reactor design purposes, is calculated from overall residence time measurements using deconvolution by Fourier transform. The liquid‐phase residence time decreases as liquid or gas flow rates increase, but the reactor Peclet number remains approximately constant. The residence time distribution and calculated values of the Peclet number reveal that the liquid phase is substantially well‐mixed. Comparison with results from experiments in a single glass capillary reveals that the monolith channels become predominantly liquid‐filled, particularly as the liquid flow rate becomes a significant fraction of the total flow rate.
Convective diffusion from a dissolving polymeric particle
Authors: Ranade Vivek V. , Mashelkar Ramesh A. 
Published: June 2004

AbstractA comprehensive mathematical model for describing the process of dissolution of a spherical polymeric particle in a convective field is developed. It includes the process of glass transition, reptation of macromolecules, disengagement of these molecules from the gel‐liquid interface, and diffusion in the boundary layer surrounding the gel‐liquid interface. Different controlling regimes for the dissolution process are identified and quantitatively delineated in this moving boundary problem. Analytical solutions for the estimation of dissolution time for various limiting cases are presented. Key predictions from the model are verified by comparison with preliminary experimental data. A novel feature of a particle‐size‐independent dissolution of polymeric particles below a critical size brought out by the model is verified experimentally. The findings have pragmatic implications in diverse areas, such as polymerization, drag reduction, and microlithography.
Reformulation of Wong‐Sandler mixing rule for cubic equations of state
Authors: Orbey Hasan , Sandler Stanley I. 
Published: June 2004

AbstractThe cubic equation of state mixing rule of Wong and Sandler is reformulated in a way that eliminates one of its parameters and so that it can go smoothly from activity coefficient‐like behavior to the classical van der Waals one‐fluid mixing rule merely by variation of its parameters. The parameters in the reformulated mixing rule can be obtained from correlation of vapor–liquid equilibrium data or from the two infinite dilution activity coefficients for each binary pair in the mixture. When these activity coefficients are estimated from the UNIFAC group contribution model, the mixing rule becomes completely predictive. The correlative and completely predictive forms of this mixing rule are tested here and shown to be accurate for five difficult binary systems and one ternary mixture over large ranges of temperature and pressure.
Experimental measurement of diffusion in aqueous polyvinylpyrrolidone solutions
Authors: Metaxiotou Zoe A. , Nychas Stavros G. 
Published: June 2004

AbstractDiffusivities of aqueous dilute and semidilute polyvinylpyrrolidone solutions Mw = 50,500 and Mw = 867,000 were measured at 25°C. The measurements were performed by Taylor's hydrodynamic stability method and the dynamic light scattering (DLS) method. Taylor's method was compared to DLS and evaluated as an experimental technique to determine the molecular diffusivity in polymer solutions. The agreement between the two methods was very good with Taylor's method proving to be a reliable, simple, and inexpensive technique that provided diffusivity data with a maximum error of 5%.
Continuum random walk simulations of diffusion and reaction in catalyst particles
Authors: Drewry H. P. G. , Seaton N. A. 
Published: June 2004

AbstractTo predict the effect of pore structure on the performance of heterogeneous catalysts, a realistic model of the catalyst particle is required. Lattice‐based models in which the diffusion and reaction phenomena are restricted to sites and bonds within a regular or irregular lattice are widely used. However, for the realistic simulation of diffusion and reaction in amorphous catalyst supports, such as alumina or silica, a continuum model, which does not artificially restrict the domain in which the reactants are allowed to diffuse, is required.An efficient method based on a “first passage time” approach is developed for the simulation of diffusion and reaction in a supported catalyst. The model catalyst is composed of spheres representing the support and active sites. By varying the algorithm used to generate the model catalyst, a range of structures can be created. The effect of the structure, and the size and distribution of active sites on the reaction rate is studied.
Binary activity coefficients from microdroplet evaporation
Authors: Ray Asit K. , Venkatraman Sankar 
Published: June 2004

AbstractA method‐based on evaporation of a constant‐composition droplet containing two components that differ markedly in volatility accurately estimates activity coefficients of both components. This new technique is developed to simultaneously determine the evaporation rate and composition of a droplet from intensity peaks observed in the light scattered by the droplet. It has no upper or lower limits on the relative volatility of the system and is particularly suitable for systems containing one relatively nonvolatile component. The data on the glycerol‐ethanol system, obtained from evaporation of glycerol droplets in ethanol vapor and correlated with Margules and Wilson equations, are thermodynamically consistent. The results of this study agree with ethanol activity coefficients calculated from the total pressure vs. solution composition data previously reported.
Molecular thermodynamic properties of protein solutions from partial specific volumes
Authors: Pjura P. E. , Paulaitis M. E. , Lenhoff A. M. 
Published: June 2004

AbstractPartial specific volumes at 25°C are reported for α‐chymotrypsinogen in aqueous solutions containing NaCl, citrate, and/or polyethylene gycol (PEG) over a range of protein concentrations. The concentration dependence of the partial specific volume can be either positive or negative, depending on the solvent. For example, the partial specific volume increases with increasing protein concentration in NaCl/citrate solutions at high salt concentrations, and decreases with increasing protein concentration in solutions containing PEG. Kirkwood‐Buff solution theory has been applied to interpret these results, and it was found that the concentration dependence is determined by two factors: (1) the effective or solvent‐averaged interactions between protein molecules in solution, and (2) three‐body protein – protein – solvent and protein – solvent ‐ solvent interactions. An approach is proposed for the experimental determination of both contributions that involves measuring osmotic pressures and volumetric properties of dilute to concentrated protein solutions.
Numerical simulation of flow in helical ducts
Authors: Wang Jing‐Wu , Andrews J. R. G. 
Published: June 2004

AbstractHelical pipes and ducts are used widely in industry. There is a huge literature on flow in curved pipes and bends, but comparatively little has been published on flow in helical pipes. To simplify the problem, most theoretical work on flow in helical pipes has assumed zero pitch: a toroidal pipe following the work of Dean in 1927. Recent theoretical studies on helical pipes have used helical coordinate systems. These systems, however, are not appropriate when studying helical ducts. The following results are reported: a coordinate system appropriate for helical ducts; the detailed equations of continuity and motion in this coordinate system; the numerical method used to find the fully developed laminar flow of a Newtonian liquid in helical ducts; the simulations vs. published experimental data; and effects of the pitch ratio, curvature ratio and pressure gradient on secondary flow in a helical duct.
Influence of adsorbate size and adsorbent heterogeneity of IAST
Authors: Sircar Shivaji 
Published: June 2004

AbstractThe ideal adsorbed solution theory (IAST) can introduce serious errors in the calculation of multicomponent gas adsorption equilibria from the corresponding pure gas adsorption isotherms when the adsorbate sizes and the degree of adsorbent heterogeneity for adsorption of the components differ substantially. The multisite Langmuir and heterogeneous Langmuir models were used to evaluate the extent of these errors. It is shown that large diferences in adsorbate sizes and degrees of heterogeneity of adsorption of the components of a mixture can cause the formation of an adsorption azeotrope that cannot be described by IAST.
Balanced realization for state‐space identification and optimal output regulation
Authors: Ramirez W. Fred , Maciejowski Jan M. 
Published: June 2004

AbstractA new input ‐ output approach is presented for optimal regulatory control of systems based on balanced state realization. State‐space identification is achieved using input–output data and a balanced realization algorithm. Based on the realized model, an optimal controller design is presented to regXSulate the system outputs at desired levels. The optimal control algorithm is model‐predictive in that predictions are made based on measured disturbances. It also compensates for unmeasured disturbances through integral state feedback. This control concept is tested using a continuous stirred‐tank chemical reactor model.
Analysis of fiber formation during air‐gap wet spinning
Authors: Simon Volker 
Published: June 2004

AbstractThe steady formation of fibers in the air‐gap wet‐spinning process is analyzed, in which solidification of the fiber material is brought about by the diffusional exchange of solvent and nonsolvent in a coagulation bath. The concentration profile within the fiber is determined, and a simple model is given for the change of the material behavior with changing concentration. The material behavior of the uncoagulated spinning solution is described by a constitutive model for viscoelastic liquids that allows the incorporation of a relaxation‐time spectrum. The behavior of the solidified fiber is described by a model for rubberlike elastic solids. The effects of variable fiber temperature and skin friction on the fiber motion are also taken into account. The computed velocity profiles are compared to experimental data. These data were obtained by spinning three samples of nominally identical spinning solutions. Even though the theoretically predicted profiles agree well with those obtained with the first two samples, they completely fail to do so for the third. This failure is attributed to the unexpected extreme sensitivity of the model predictions to the width of the dynamic spectrum that is used to infer the relaxation‐time spectrum. It is also found that the velocity profile depends rather strongly on the initial conditions for the stress.
Ternary microemulsions as model disordered media
Authors: Knackstedt Mark A. , Ninham Barry W. 
Published: June 2004

AbstractThe ternary microemulsion systems alkane/water/DDAB (didodecyldimethylammonium bromide) form ideal model‐disordered media. The static microstructure is described by a simple parameter‐free model that can be predetermined and agrees with SAXS and SANS scattering experiments. The component volume fraction can be varied to exhibit bicontinuous random structures with a predicted percolation transition to disconnected water‐in‐oil droplets. Structural transitions are analyzed in the context of theories of percolative phenomena. Experimental transport properties agree well with model predictions based on an effective medium approximation. Critical exponents that describe the scaling of the transport properties near percolation are consistent with theoretical expectations near a static percolation transition. Through variation of component volume fractions a medium of known microstructure can be prescribed, so that independent measurement of transport and mechanical properties is possible.
Solvation effects on reactions of triplet benzophenone in supercritical fluids
Authors: Roberts Christopher B. , Brennecke Joan F. , Chateauneuf John E. 
Published: June 2004

AbstractLaser flash photolysis of the hydrogen abstraction reaction of triplet benzophenone (3BP) from 2‐propanol and 1,4‐cyclohexadiene in supercritical ethane and fluoroform was investigate. Bimolecular rate constants based on bulk concentrations decrease with an increase in pressure along both isotherms studied. These results corroborate our previous studies in CO2 that show increased reaction rates due to enhanced local compositions of cosolvent around the 3BP solute. Analysis of the results includes prediction of the thermodynamic pressure effect on the rate constant, which suggests an increase in the rate constant with pressure, as well as the effects of increased local cosolvent concentrations about 3BP. Spectroscopic measurements of the local composition of 2‐propanol about a solute in supercritical CO2 are used to explain the apparent discrepancy between experiment and prediction, providing reasonable evidence that the local environment can influence kinetically controlled reactions in supercritical fluids.
Newtonian drop impact with a solid surface
Authors: Scheller Brian L. , Bousfield Douglas W. 
Published: June 2004

AbstractThe spreading of Newtonian liquid drops after impact with a solid surface is reproted for a range of liquid and surface proeprties, drop diameters, and impact velocities. Results for liquid viscosities up to 300 mPa.s are given. For a given drop diameter and velocity, a range of liquid viscosities result in splashing even for smooth surfaces. The maximum spread radius, made dimensionless with the drop radius, is correlated as Rmax* = 0.61(Re2Oh)0.166, where Re and Oh are the Reynolds and Ohnesorge numbers. respectively. A model is proposed to account for inertial, viscous, and surface tension forces on the maximum spread radius. Good agreement is found between the model and experimental data from several sources.
Dilute turbulent gas‐solid flow in risers with particle‐particle interactions
Authors: Bolio Eduardo J. , Yasuna Jules A. , Sinclair Jennifer L. 
Published: June 2004

AbstractEarlier work of Sinclair and Jackson that treats the laminar flow of gas‐solid suspensions is extended to model dilute turbulent flow. The random particle motion, often exceeding the turbulent flucutations in the gas, is obtained using a model based on the kinetic theory of granular materials. A two‐equation low Reynolds number turbulence model is modified to account for the presence of the dilute particle phase. Comparisons of the model predictions with available experimental data for the mean and fluctuating velocity profiles for both phases indicate that the resulting theory captures many of the flow features observed in the pneumatic transport of large particles. THe model predictions did not manifest an exterme sensitivity to the degree of inelasticity in the particle‐particle collisions for the range of solid loading ratios investigated.
Efficiency estimation of liquid‐liquid Hydrocyclones using trajectory analysis
Authors: Wolbert D. , Ma B.‐F. , Aurelle Y. , Seureau J. 
Published: June 2004

AbstractAs the use of hydrocyclones for liquid‐liquid separation becomes increasingly common, the need for a satisfactory method to assess their efficiency increases. Curerntly available efficiency theories were developed for liquid‐solid separations, based on the velocity distributions inside a hydrocyclone. These theories, however, appear less suitable for emulsions where the dispersed phase is slightly lighter than the continuous phase, such as oil/water emulsions. An efficiency computation based on the analysis of the trajectories of the droplets is presented. Trajectories are characterized through a differential equation combining models for the three bulk velocity distributions (axial, radial, and tangential) and the settling velocity defined by Stokes' law. From the critical trajectory and given operating conditions, a characteristic droplet diameter d100 can be deduced that corresponds to the smallest droplet with a 100% efficiency. Other efficiencies are obtained by changing the initial condition for the trajectory equation. The efficiency result of different hydrocyclone configurations are compared with experimental results, and residual emulsion distributions are estimated.
Experimental and theoretical investigation of the validity of asymptotic lumped kinetics
Authors: Ho T. C. , White B. S. 
Published: June 2004

AbstractContinuum approximation is often used to treat problems involving reaction mixtures of a vast number of species. Previous studies predicted that in many situations the lumped kinetics of a continuum of reactions, regardless of their kinetics, are of the power law form after a long time. In this article we present experimental support for such asymptotic power law kinetics. The system considered is catalytic deep desulfurization of a petroleum distillate. In addition, a theoretical analysis is made to establish the condition under which the continuum approximation is valid in the long‐time limit. The condition turns out not to be very stringent for practical purposes.
Continuous kinetics for thermal degradation of polymer in solution
Authors: Wang Ming , Smith J. M. , McCoy Ben J. 
Published: June 2004

AbstractContinuous kinetics of thermal degradation of poly (styrene‐allyl alcohol) (PSA) in solution are explored theoretically and experimentally. Thermal degradation experiments for PSA of number‐average molecular weight 1,640 in t‐butanol solution were conducted in a steady‐state flow reactor at 6.8 MPa and 403–473 K. The molecular‐weight distributions (MWDs) of the original polymer and its reaction products were measured as a function of residence time by gel permeation chromatography The MWD of the initial PSA is described by a gamma distribution function. Experimental data indicated that the polymer cracks to specific, low‐molecular‐weight (MW) products and degrades by random chain scission. Results are interpreted by a mathematical model based on the continuous kinetics for specific and random degradation processes. Rate coefficients are determined separately from the dynamic data of the MW moments for the specific products and the MWDs for the reacting polymer. Activation energies obtained are 5.9 – 7.4 kcal/mol for specific degradation processes and 35 kcal/mol for the random degradation process. The detailed MWDs are related to conventional lumped (numberaverage molecular‐weight) data.
Taylor dispersion in a polymer solution flowing in a capillary tube
Authors: Vartuli M. , Hulin J. P. , Daccord G. 
Published: June 2004

AbstractTracer dispersion in polysaccaride (scleroglucan) solution flowing through 0.56‐mm‐ID capillary tubes was studied experimentally. In contrast with experiments modeling enhanced recovery processes, the polymer concertration remains constant during a given experiment, while the tracer concerntration varies. A preparation procedure giving stable rheological characteristics is described, as well as their dependence on the polymer concentration Cp (100 mg/L ≤ Cp ≤ 2,000 mg/L). Dispersion measurements are performed with ionic tracers at Péclet numbers between, showing that the Taylor dispersion mechanism remains dominant. At a constant flow velocity, K decreases by about 75% when Cp increases from 0 to 2,000 mg/L. This variation is related to the flattening of the velocity profile and can be predicted both with a power‐law rheological model and Monte Carlo simulations. The extension of these measurements to heterogeneous porous media is discussed.