bluuebunny/crossref_metadata_2025_split huggingface dataset:
High‐pressure vapor‐liquid equilibria in the propane‐1‐propanol system
Authors: Mühlbauer Andre L. , Raal J. David 
Published: June 2004

AbstractHigh‐pressure isothermal vapor liquid equilibrium data were measured for the propane‐1‐propanol system at 81.6, 105.2, and 120.1° C in a static equilibrium cell with liquid‐phase sampling by a piston‐driven sampling rod and homogenizing the sample with a static jet mixer. The vapor phase was sampled by releasing it into an evacuated manifold, and the gas chromatograph was calibrated with a new variable volumetric device. Satisfactory modeling was achieved with the combined method (Wichterle, 1978b) using the UNIQUAC equation with equations of state: the group contribution EOS (Skjold‐Jorgenson, 1986), Peng‐Robinson EOS (Peng Robinson, 1976) or the two‐parameter Virial EOS. Differences between the measured and calculated vapor‐phase mole fractions, however, were signficant for the lower pressure regions of the 81.6 and 120.1° C isotherms.UNIQUAC parameters aij, hitherto unavailable, with fairly strong temperature dependence in the 81.6 to 120.1° C range are proposed for the system. The covariance matrix indicated a significant correlation among the parameters. The classical mixing rule interaction parameters, σij, required for the original Peng‐Robinson EOS in the combined method were obtained using the direct method (Wichterle, 1978a) and were temperature‐independent for the isotherms for which the propane was supercritical. The possibility of propane/1‐propanol immiscibility was theoretically examined according to the criteria of Baker et al. (1982). The plots of Gibbs energy of mixing vs. phase mole fractions did not indicate liquid‐phase splitting, but the inferences are EOS‐dependent and must await visual confirmation. Our earlier vaporphase thermodynamic consistency test (1991a) indicated the data for all three data sets not to be inconsistent.
Effectiveness of calcium magnesium acetate as an SOX sorbent in coal combustion
Authors: Levendis Yiannis A. , Zhu Wenqi , Wise Donald L. , Simons Girard A. 
Published: June 2004

AbstractA fundamental study was conducted on the effectiveness of the chemical calcium magnesium acetate (CMA) as a sulfur capture agent during combustion of pulverized coal. It was based on high‐temperature laboratory‐bench experiments with the scope of exploring the use of CMA as a “dry scrubbing” medium for in‐boiler injection. Two methods of CMA introduction in the furnace were considered: dry‐spraying fine powders of the chemical and wet‐spraying aqueous solutions to generate fine aerosols. It considered conditions pertinent to post‐flame in‐boiler injection of CMA to identify optimum temperatures and residence times. In addition to the versatility of the water‐soluble CMA to enable spray drying injection and therefore eliminate grinding costs, there are other attractive features. Mainly, its ability to form highly cenospheric, “popcorn” ‐like, oxide particles on heating to high temperatures. These cenospheres possess thin, porous walls with blowholes that enable penetration of the SO2 in the interior of the particle which promotes high sorbent utilization. SO2 captures in the order of 90% were achieved with dry‐injection of the chemical at furnace gas temperatures of about 1,000° C, a Ca/S ratio of 2, and particle size of ≈ 50 μm. Moreover, CMA was superior(by over 40%) to either CaCO3 or Ca(OH)2 in sulfur capture effectiveness per unit mass of calcium. This commercially obtained CMA was even superior to reagent‐grade calcium acetate (by as much as 30%), again per unit mass of calcium. The utilization of CMA and calcium acetate depended on the cenosphere wall thickness, rather than the particle size and, thus, outperformed other sorbents regardless of the size of the resulting oxide particles.
Simplification of network theory for polymer melts in nonlinear oscillatory shear
Authors: Jeyaseelan Ranjit S. , Giacomin A. Jeffrey , Oakley Jason G. 
Published: June 2004

AbstractGiacomin and Oakley (1991) have shown that an upper convected Maxwell model with a structure‐dependent relaxation spectrum incorporating the three‐parameter kinetic rate equation proposed by Mewis and Denn (1983) works remarkably well for a molten LDPE in large‐amplitude oscillatory shear (LAOS). In a search for a simpler framework for interpreting LAOS based on network theory, four nonlinear, differential constitutive equations, each with less than three parameters, were evaluated. These models are compared with the Mewis‐Denn model, and a two‐parameter model has been found to work just as well for molten IUPAC LDPE X. The LAOS behavior of molten LLDPE is also adequately described by this model.
NMR imaging of multiphase flow in porous media
Authors: Chen Songhua , Qin Fangfang , Kim Kyung‐Hoe , Watson A. Ted 
Published: June 2004

AbstractNuclear magnetic resonance (NMR) imaging techniques are used to determine porosity and saturation distributions. Difficulties in quantitation which arise from the short transverse relaxation times exhibited by fluids in porous media are addressed. Procedures are presented whereby transverse relaxation during the signal acquisition process is modeled to obtain accurate estimates of intrinsic magnetization intensity, and thus porosity and saturation. Special consideration is given to saturation/position dependence and multiexponential behavior of transverse relaxation. These procedures are validated with results for longitudinal profile images. The use of thin‐slice cross‐sectional profile images are demonstrated by observing fluid displacement in a rock sample with structural heterogeneities.
Wavelength and depth of ribbing in roll coating and its elimination
Authors: Hasegawa Tomiichi , Sorimachi Kazunori 
Published: June 2004

AbstractExperiment has been made on ribbing induced on a film coated over a roll surface by a two‐roll system: one roll rotated with a speed and the other fixed or rotated with relatively different speeds. The two rolls have the same diameters and are placed parallel with each other by keeping a gap. Test fluids are Newtonian (glycerin/water) and viscoelastic [polyacrylamide (Separan AP30)/glycerin/water] solutions. Wavelength and depth of ribbing are measured by a newly developed technique utilizing an image of a straight bar placed above the roll and reflected on the ribbing film surface. Nondimensionalized wavelength is correlated with capillary number for Newtonian liquids, but higher for dilute Separan solutions and lower for nondilute Separan solutions than for Newtonian liquids. The depth of ribbing increases for dilute Separan solutions with nearly the same value for nondilute Separan solutions as those for Newtonian liquid. This behavior observed for the ribbing seems to have some relation to the existence of a line of vortices that occurs visibly for nondilute Separan solutions in the entrance region of the gap between the rolls. Increase in the ratio of the velocities of two rolls has an effect of increasing both the wavelength and depth of ribbing for glycerine and nondilute Separan solutions, but it has the effect of decreasing them for dilute Separan solutions. Addition of Separan in glycerine solution promotes the generation of ribbing.A string spanned near over the gap to touch the surface of the liquid pool between the gap has the effect of eliminating the ribbing. This is successful in various combinations between the speeds of the two rolls and the diameters of the string.
Chromatographic study of alkanes in silicalite: Transport properties
Authors: Hufton Jeffrey R. , Danner Ronald P. 
Published: June 2004

AbstractMicropore diffusion coefficients for infinitely‐dilute methane, ethane, propane, n‐butane, and isobutane in silicalite were measured via concentration‐pulse chromatography. Two different samples of large laboratory‐synthesized crystals were investigated. Analysis of van Deemter plots clearly indicated the presence of a significant micropore mass‐transfer resistance for isobutane. Diffusion coefficients evaluated from these plots were consistent with results measured by the membrane technique. The linear alkane data differed completely in that the micropore masstransfer resistance for these adsorbates was very small, implying that the true diffusion coefficients were too large to be measured with this system. Thus, effective diffusion coefficients evaluated from these data represent a lower limit of the true values. Comparison of this limit with nuclear magnetic resonance data was favorable, since the latter are significantly larger in magnitude. Inconsistency was observed with diffusion coefficients obtained from other macroscopic techniques including the membrane method, zero‐length and tracer‐pulse chromatography, and some frequency response experiments.
Some complements in combinatorics of sharp separation systems synthesis
Authors: Floquet P. , Domenech S. , Pibouleau L. , Aly S. M. 
Published: June 2004

AbstractThe analysis of combinatorics of sequences of sharp separation systems is a problem extensively studied in chemical engineering. Thompson and King (1972) first presented a closed‐form expression for determining a number of possible sequences for separating an n‐component mixture into pure products by using simple (one input and two outputs) sharp separators. Then, Shoaei and Sommerfeld (1986) showed that this determination could be interpreted in term of Catalan numbers; recently Wahl and Lien (1990) derived this formula from a generating function. This article presents a closed‐form expression for a number of different possible separation sequences when complex (one input and three or more outputs) separators are used.
Numerical simulation of Case II transport
Authors: Fu Thomas Z. , Durning Christopher J. 
Published: June 2004

AbstractA nonlinear conservation equation for the fluid concentration field during onedimensional viscoelastic diffusion is derived by retaining the concentration dependencies of physical properties in the fluid flux expression from the nonequilibrium thermodynamic treatment of Durning and Tabor (1986). The result is specialized to the limit of small, but finite, diffusion Deborah numbers to give a model essentially the same as that by Thomas and Windle (1982) for Case II transport (TW model). Orthogonal collocation on Hermite cubic trial functions together with a stiff ordinary differential equations integrator were used to solve the TW model for integral sorption in a dry film. The solutions show good agreement with previous analyses and confirm that strong nonlinearities in both the fluid diffusivity and the mixture viscosity are essential for prediction from the model of wave‐like concentration profiles associated with the Case II process. Also, the numerical results partially confirm the analytical asymptotic analysis of Hui et al. (1987b) for the Case II wave‐front velocity, v. They show that Hui et al.'s formula for the dependence of v on characteristic physical properties does not depend on the details of how the diffusivity and viscosity change with fluid content, as long as both are strongly nonlinear.
A dew point technique for limiting activity coefficients in nonionic solutions
Authors: Trampe Diane B. , Eckert Charles A. 
Published: June 2004

AbstractA new measurement technique for activity coefficients at infinite dilution has been developed involving the construction of a very dilute vapor phase and the accurate determination of its dew point. This method is especially applicable to systems of low solute relative volatility, precisely where other methods such as differential ebulliometry and headspace gas chromatography become less precise. Data are reported for γ∞ for N, N‐dimethylformamide, dimethylsulfoxide, and N‐methyl pyrrolidone in water over a range of temperatures.
Quasicritical behavior of dense‐gas solventsolute clusters at near‐infinite dilution
Authors: O'Brien James A. , Randolph Theodore W. , Carlier Claude , Ganapathy Shankar 
Published: June 2004

AbstractWe Compare molecular dynamics and electron paramagnetic resonance spectroscopic experiments on very dilute solutions of nitroxide free radicals in nearcritical and supercritical ethane. The measurement of the effective local density of solvent in the cybotactic region of the probe solute shows that maxima in local density enhancements occur in both computer and spectroscopic experiments at about half of the critical density, well removed from the maximum in the solvent's isothermal compressibility.Remarkably, at the bulk density where the maximum enhancement occurs, we observed long‐lived clusters in the vicinity of the solute molecule. Geometrically defined clusters persist for at least 100 picoseconds of simulated time. The persistence of these clusters is corroborated by the behavior of the solute diffusion coefficient, which shows fluctuating values over simulated time periods as long as 1.3 nanoseconds. We argue that fluctuations in the local solvent density about a solute molecule are not a long‐ranged solvent critical effect. Rather, they represent a localized, short‐ranged quasicritical phenomenon induced by the solute, which may be described in terms of a transition between weakly attractive and attractive behavior. We discuss the implications of time‐varying microstructure for reactions in supercritical fluid media.
A simple design strategy for fault monitoring systems
Authors: Chang Chuei‐Tin , Mah Kai‐Nan , Tsai Chii‐Shiang 
Published: June 2004

AbstractA simple strategy is developed for the design of model‐based fault‐monitoring systems. Several new features allow this approach suitable for practical applications. The core of the suggested monitoring system is a parallel parameter estimation method designed to reduce the chance of bias. Two important criteria, diagnostic observability and diagnostic resolution, are adopted to evaluate the performances of alternative designs. By following a systematic procedure, it is possible to determine the best sensor locations in a complex chemical process based only on the structural informations of the system model. After selecting the most appropriate measurement variables, diagnostic resolution can be enhanced further by exploiting additional insights gained from analysis of the physical meanings of the model parameters and by comparing the fault patterns in diagnosis. Several effective on‐line implementation techniques are also proposed to minimize computation for the estimation algorithm. The correctness and efficiency of the suggested design strategy are demonstrated by the simulation results in examples.
Steps in CH4 oxidation on Pt and Rh surfaces: High‐temperature reactor simulations
Authors: Hickman D. A. , Schmidt L. D. 
Published: June 2004

AbstractThe direct oxidation of CH4 to H2 and CO in O2 and in air at high temperatures over alumina foam monoliths coated with high loadings of Pt and Rh has been simulated using a 19‐elementary‐step model of adsorption, desorption and surface reaction steps with reaction parameters from the literature or from fits to previous experiments. The surface reaction model for Pt is in good agreement with previously reported low‐pressure(0.1 to 1 torr) reactor measurements of CH4 oxidation rates at temperatures from 600 to 1,500 K and of OH radical desorption during CH4 oxidation at 1,300 to 1,600 K over polycrystalline Pt foils. The model predictions for both catalysts are also consistent with product selectivities observed over monolithic catalysts in an atmospheric‐pressure laboratory‐scale reactor, and the differences between Pt and Rh can be explained by comparing individual reaction steps on these surfaces. Because of the good agreement between the model and both low‐and atmospheric‐pressure reactor simulations, a complete energy diagram for methane oxidation at low coverages is proposed. The model results show that under CH4rich conditions at high temperatures, H2 and CO are primary products of the direct oxidation of methane via a pyrolysis mechanism.
Simulation of carbon gasification kinetics using an edge recession model
Authors: Kyotani Takashi , Leon Y Leon Carlos A. , Radovic Ljubisa R. 
Published: June 2004

AbstractAn edge recession modeling method is proposed as a new approach to the prediction of carbon gasification kinetics. Using this method, the variations in reactive surface area (RSA) and specific reactivity (R) with conversion were simulated for several polynuclear aromatic molecules adopted as models of carbon crystallites. The effects of crystallite size and shape, edge site reactivity and vacancies on the changes in RSA and R with conversion were investigated. As a result, RSA and R were found to be essentially independent of crystallite shape, but to depend on crystallite size and the presence of vacancies. Good agreement was obtained between model predictions and experimental data for several kinds of model carbon crystallites. In the case of structurally disordered carbons (such as chars), simultaneous gasification of model crystallites of two different sizes gave better predictions than that of single‐size crystallites. The edge recession model is proposed as an alternative, or at least complementary, approach to the more conventional (and, arguably, less physically meaningful) pore structure development models.
Heat transfer and cure in pultrusion: Model and experimental verification
Authors: Batch Gibson L. , Macosko Christopher W. 
Published: June 2004

AbstractThough pultrusion has existed for nearly 40 years, factors affecting temperature and resin reactivity are not completely understood. A model is tested to help explain the effects of die temperature, line speed and initiator concentration on curing inside a pultrusion die. The model includes radio frequency preheating, heat conduction, heat of cure, changing thermal properties with temperature and degree of cure, and hindered heat transfer due to shrinkage of the profile away from the die. The analysis is compared to experimental temperature measurements for a 1‐in. (25‐mm) round die, where die temperature, line speed, and initiator concentration were varied. Temperature predictions by the model are in good agreement with the data for many of the conditions tested. Considerable disagreement still persists, however, under processing conditions with faster line speeds and lower die temperatures.
Polydisperse mixture adsorption kinetics
Authors: Muralidhar Ramachandran , Talbot Julian 
Published: June 2004

AbstractWe present a theoretical study of the adsorption kinetics of particles with a continuous distribution of sizes. If the particles interact with short‐ranged forces, the diminishing rate of adsorption with increasing surface coverage can be attributed to a geometrical blocking effect of the preadsorbed particles. We exploit the fact that at low coverages the blocking effects result from isolated adsorbed particles to develop an analytic description of the adsorption kinetics using a moment expansion approach. We evaluate the time‐dependent surface coverage, density and the average size of the adsorbed particles and compare these quantities with those of the bulk phase. The effect of desorption is studied by introducing a size‐independent desorption constant, and the corresponding adsorption equilibria properties, which are valid at low coverages, are derived. Simulation results for irreversible adsorption are obtained and compared with the theoretical predictions.
Gross error detection when variance‐covariance matrices are unknown
Authors: Rollins D. K. , Davis J. F. 
Published: June 2004

AbstractEquations introduced here identify measurement biases and process leaks, when gross errors exist in measured process variables and the variance‐covariance matrix of the measurements, Σ, is unknown. Σ is estimated by the sample variance, S, using process data.For an unknown Σ, the global test statistic is the well‐known Hotelling T2 statistic. Its power function has a noncentral F‐distribution. For component tests used for specific identification of measurement biases and nodal leaks, two tests are presented with Σ unknown. The first test is independent of the number of component tests, k, and is given by a statistic with an F‐distribution. The second test depends on k and has a student t‐distribution. The power functions for both component tests are provided. Process examples and a Monte Carlo simulation study presented demonstrate the use and performance of these statistical equations in identifying biases and process leaks.
Mathematical modeling of wax deposition in oil pipeline systems
Authors: Svendsen John A. 
Published: June 2004

AbstractDeposition of wax on the wall of oil pipelines is often regarded as a problem since the tube diameter is reduced. Consequently, more power is needed to force the same amount of oil through the system. A mathematical model for quantitative prediction of wax deposition for each hydrocarbon component has been developed. Each component is characterized by weight fraction, heat of fusion, and melting point temperature. A model explains how a phase transition in the flow from liquid oil to waxy crystals may create a local density gradient and mass flux, which depends on the local temperature gradient. The model predicts that wax deposition can be considerably reduced even when the wall temperature is below the wax appearance point, provided the liquid/solid phase transition, expressed by the change in moles of liquid with temperature, is small at the wall temperature. Deposition as function of time has been obtained as a solution of differential equations derived from the principles of mass and energy conservation and the laws of diffusion.
Kinetics of hydrogen absorption and desorption in LaNi5‐xAlx slurries
Authors: Snijder E. D. , Versteeg G. F. , van Swaaij W. P. M. 
Published: June 2004

AbstractThe kinetics of hydrogen absorption and desorption in LaNi4.8Al0.2,LaNi4.9Al0.1 and LaNi5, suspended in cyclohexane and LaNi5 in ethanol have been investigated. The absorption process can be described in terms of mass transfer and reaction resistances in series. The rate‐limiting steps for this process are dissolution of hydrogen in the solvent and the reaction of hydrogen with the metal alloy. Over a broad range of hydrogen loadings, the reaction of hydrogen with the metal follows the rate equation:

This type of kinetic equation indicates that during hydride formation in a slurry a surface process is the rate‐determining step, which was confirmed by the observed influence of the solvent. Desorption of hydrogen can be described best with a shrinking core relation:

The phase transformation at the β/α boundary appears to be the rate‐determining step. Alloys with higher aluminum contents produce a lower reaction rate constant.
Residence time distribution in screw extruders
Authors: Chen Liqin , Pan Zaoqi , Hu Guo‐Hua 
Published: June 2004

AbstractA companion article (Chen and Hu, 1993a) discussed a statistical theory that for a system consisting of two closed subsystems, the residence time density (RTD) functions of the two subsystems will be statistically independent, if a two‐dimensional perfect mixing exists at the subsystem boundary. In this case, the overall RTD function is related to that for individual subsystems through the convolution integral. This theory has been validated experimentally using two die‐screw combinations.Based on this theory, a predictive RTD model for an intermeshing counterrotating twin‐screw extruder has been developed. The screw in the longitudincl direction has been treated as C‐chambers in series. The overall RTD of leakage flows has been calculated from the RTDs of these individual chambers and then converted into the RTD of the extruder. The predicted RTD has been tested against experimental results with success.