bluuebunny/crossref_metadata_2025_split huggingface dataset:
Distribution of volatile species in a refluxing polymer colloid
Authors: Zollars Richard L. , Chen Chein‐Tai , Jones D. Adrian 
Published: June 2004

AbstractMonomer partitioning between the aqueous and polymer phases in a latex determines many properties of an emulsion polymerization, such as the reaction rate, molecular weight development and, if operated under refluxing conditions, the reaction temperature. A unique two‐chamber vapor‐liquid equilibrium cell was used during this investigation to obtain an in situ separation of the aqueous phase from the latex, thus permitting a direct determination of the compositions of the aqueous, polymer, and vapor phases in a latex, even under refluxing conditions. Thermodynamic analysis of the vapor‐liquid equilibrium problem allows the prediction of the composition of all phases from measured values of the temperature and pressure only. These predictions agreed well with data from other investigations under nonrefluxing conditions and with the aqueous and vapor phase compositions from this investigation. The polymer phase composition data for vinyl acetate polymers with average molecular weights in excess of 106 showed consistently higher polymer volume fractions than predicted. This latter result may be due to crosslinking or strong entanglements resulting from increased chain branching at these high molecular weights.
Augmented back equation of state for polar fluids
Authors: Lee M. J. , Chao K. C. 
Published: June 2004

AbstractThe pressure of water is decoupled into a polar pressure and a nonpolar pressure, the latter being obtained from the BACK equation based on the size and nonpolar energy of the water molecule determined by Jorgensen and coworkers. The polar pressure is obtained upon subtracting the nonpolar pressure from the total pressure given by the steam table equation of Keenan et al. The polar pressure function thus obtained for water is generalized to augment the BACK equation for the general description of polar fluids.Equation constants are reported for 26 substances. Calculated vapor pressure, liquid molal volume, and pressure‐volume‐temperature (PVT) behavior are compared with data. Mixing rules are introduced to express poles interacting with poles and dispersion modes interacting with dispersion modes, but not poles interacting with dispersion modes. PVT relationship, vapor‐liquid equilibrium, and liquid‐liquid equilibrium in mixtures of water and nonpolar substances are calculated.
Theory of transport processes in single crystal growth from the melt
Authors: Brown Robert A. 
Published: June 2004

AbstractThe quality of large semiconductor crystals grown from the melt for use in electronic and optoelectronic devices is strongly influenced by the intricate coupling of heat and mass transfer and melt flow in growth systems. This paper reviews the present state of understanding of these processes starting from the simplest descriptions of solidification processes to detailed numerical calculations needed for quantitative modeling of processing with solidification. Descriptions of models for the vertical Bridgman‐Stockbarger and Czochralski crystal growth techniques are included as examples of the level of understanding of industrially important methods.
Manufacture of optical waveguide preforms by modified chemical vapor deposition
Authors: Kim Kyo‐Seon , Pratsinis Sotiris E. 
Published: June 2004

AbstractManufacture of optical waveguide preforms by modified chemical vapor deposition (MCVD) is theoretically investigated. For the first time, a model accounting for the concurrent heat transfer, chemical kinetics, and silica aerosol dynamics during lightguide preform fabrication by MCVD is presented. Silica particles are formed by high‐temperature oxidation of SiCl4, grow by coagulation, and deposit to the preform walls by thermophoresis and Brownian diffusion. Assuming first‐order SiCl4 oxidation and approximating the aerosol size distribution by a log normal function throughout the process, five partial differential equations describe this process. The emphasis of this study is on the achievement of high process yield (deposition efficiency of MCVD).Process conditions for operation in the particle transport‐limited and reaction‐limited regimes are quantitatively identified. Operation in the former regime results in complete oxidation of the inlet SiCl4 but only about half of the product SiO2 particles deposit to the tube wall. Operation in the latter regime results in limited oxidation of inlet SiCl4 (about 40%) but almost all product SiO2 particles deposit to the tube wall. This study shows that high process yields and deposition rate can be achieved in lightguide preform manufacture by MCVD by combining operation in the reaction‐limited regime with recycling of the exit gases from the preform tube.
Carbon dioxide absorption into promoted carbonate solutions
Authors: Tseng P. C. , Ho W. S. , Savage D. W. 
Published: June 2004

AbstractCO2 absorption rates into diethanolamine (DEA)‐promoted carbonate solutions were measured over a wide range of carbonate conversions and temperatures. Analysis of the data showed that the CO2‐DEA reaction rate was controlled by the rate of formation of zwitterion intermediate for carbonate conversions below 30%, and was controlled by the rate of abstraction of proton from the zwitterion intermediate for carbonate conversions greater than 30%. Hydroxyl ion, free amine, and carbonate ion were identified to act as bases to abstract the proton from the zwitterion. The modeling of the CO2 absorption rates and the effects of carbonate conversion and amine concentration on the CO2‐DEA reaction kinetics were investigated.
Parallel algorithms for multicomponent separation calculations
Authors: Wait R. , Landauro J. 
Published: June 2004

AbstractTearing and simultaneous correction techniques coupled with an odd‐even cyclic reduction parallel algorithm are used to carry out calculations of multicomponent separation problems. The old‐even algorithm implements effectively on most parallel processors. No noticeable differences are found when numerical results are compared with those obtained using serial algorithms. The results for three example problems are presented to illustrate the method. Calculations were carried out using single precision arithmetic.
Analysis of multicomponent diffusion in pore networks
Authors: Sotirchos Stratis V. , Burganos Vasilis N. 
Published: June 2004

AbstractDiffusion flux models are developed for isobaric diffusion of a multicomponent gas mixture in pore networks of distributed pore size and length constructed by arranging pore segments around the bonds of a lattice of constant coordination number. Eigenvalue‐eigevector analysis is used to decompose the dusty‐gas model equations, written for each pore segment in the network, into a set of independent single‐species diffusion problems, each of which is then treated by combining the effective medium theory for resistor networks with the smooth field approximation (Burganos and Sotirchos, 1987). Results for a ternary mixture diffusing in a porous slab show that direct application of the smooth field approximation underestimates significantly the mass transport resistance.
A new liquid membrane technique for gas separation
Authors: Majumdar Sudipto , Guha Asim K. , Sirkar Kamalesh K. 
Published: June 2004

AbstractA new liquid membrane separation technique for gas mixtures has been developed: feed and sweep gases flow through the lumen of two different sets of hydrophobic microporous hollow fibers while a liquid on the shell side acts as the membrane. This membrane is identified as the contained liquid membrane (CLM). Major shortcomings of immobilized liquid membrane techniques are eliminated. The novel separation device is identified as the hollow fiber contained liquid membrane (HFCLM) permeator. Experimental studies are made with different CO2‐N2 feed mixtures and a pure helium sweep stream, with special emphasis on model landfill gas purification. Either pure water or an aqueous solution of K2CO3 is used as membrane. The effects of several variables on the performance of the HFCLM permeator have been studied. A three‐component permeation model, incorporating axial pressure drop, is developed for binary mixture separation in a HFCLM permeator having a sweep gas stream. The experimental data show good agreement with the theoretical predictions.
Minimum reflux behavior of complex distillation columns
Authors: Wachter John A. , Ko Terry K. T. , Andres Ronald P. 
Published: June 2004

AbstractA continuum model for multicomponent distillation in the minimum reflux limit, first proposed by Nandakumar and Andres, is refined for the special case of constant relative volatility (CRV) and constant molar overflow (CMO) and is extended to columns with multiple feeds and multiple products. A relaxation algorithm for calculating steady‐state conditins in any minimum reflux CRV, CMO column is established. This generalization of Underwood's classic treatment of single‐feed columns is used to explore the characteristics of several single‐feed and multiple‐feed distillation systems. Critical operating points at which the steady‐state composition profile in a minimum reflux column is indeterminate are identified and analytical expressions predicting the location of these points are established.
NMR study of mass transfer in granulated molecular sieves
Authors: Kärger Jörg , Pfeifer Harry , Richter Reinhard , Fürtig Helmut , Roscher Wolfgang , Seidel RÜDiger 
Published: June 2004

AbstractNuclear magnetic resonance (NMR) tracer desorption technique in combination with the traditional pulsed field gradient technique is applied to measure directly intracrystalline and long‐range molecular transport, as well as molecular exchange rates, between the individual crystallites in granulated molecular sieves. It is found that the granulation process leads to the formation of transport resistances on the external surface of the crystallites, which may be dramatically enhanced during their technical application. As an example, for granulated zeolite NaCaA the enhancement of such surface barriers under hydrothermal conditions and under the influence of a hydrocarbon atmosphere is studied. Since both intra‐ and intercrystalline transport are found to remain practically unaffected by this treatment, changes in the overall transport behavior are caused by the enhanced transport resistance on the external surface of the zeolite crystallites.
Mass transfer in the absorption of nitrogen oxides in alkaline solutions
Authors: Newman Bernard L. , Carta Giorgio 
Published: June 2004

AbstractThe absorption of mixtures of nitrogen oxides into aqueous solutions of NaOH in the range of partial pressures of 0.004‐ to 0.05‐atm NO and 0.002‐ to 0.015‐atm NO2 was investigated. Absorption experiments were conducted in a gas‐liquid contactor that permitted independent variation of the gas and liquid mass transfer coefficients. The results were analyzed in terms of a model which accounted for diffusion, reaction, and formation of higher oxides and oxyacids in the gas and in the liquid phases. Absorption of both HNO2 and N2O3, formed in the bulk gas and within the gas diffusion film, were found to be significant. Using a rate coefficient of 8.8 × 10−3 mol/s · cm3 · atm3 for the formation of HNO2 in the gas phase (England and Corcoran, 1975), a value of the absorption factor, H √Dk, for N2O3 of 2.5 × 10−3 mol/s cm2 atm was determined at 25°C. This value was found to decrease with temperature and was 1.2 × 10−3 at 40°C. The use of concentrated base as an absorbent solution prevented the formation of nitric acid mist, a problem encountered in many previous studies of NOx absorption.
A condition number scaling policy for stability robustness analysis
Authors: Chanh Nguyen T. , Barton Geoffrey W. , Perkins John D. , Johnston Richard D. 
Published: June 2004

AbstractThe condition number of the process transfer function G(s) has been proposed and used as an indicator of the inherent controllability of a process even though it is a scale‐dependent quantity. A rapid suboptimal scaling policy known as G‐balancing is developed for the case of the l2 norm where the condition number is the ratio of the largest to the smallest singular value of G(s). For 2 × 2 systems, G‐balancing gives the same optimal scaling as an available analytical solution. The higher order examples given compare the results of G‐balancing with the known analytic results for l2 norm optimal scaling.
Critical impeller speed for solid suspension in mechanically agitated contactors
Authors: Raghava Rao K. S. M. S. , Rewatkar V. B. , Joshi J. B. 
Published: June 2004

AbstractCritical impeller speed for the suspension of solid particles, Ncs, has been measured in 0.3, 0.4, 0.57, 1.0, and 1.5 m ID mechanically agitated contactors. Tap water and quartz particles (100, 340, 700, 850, 2,000 μm) were used as liquid and solid phase, respectively. The impeller speed was varied from 3.5 to 13.3 r/s and solid loading from 0 to 50 wt. %. Three types of impellers were employed: disk turbine, pitched turbine downflow, and pitched turbine upflow. The impeller diameter to vessel diameter ratio was varied in the range 0.175 to 0.58 and the impeller blade width to impeller diameter ratio was varied in the range 0.25 to 0.4. The impeller clearance from the tank bottom was varied from 0.5 to 0.167 of tank diameter. The effect of impeller blade thickness was also studied.The pitched‐blade impellers were found to be more efficient than a conventional disk turbine, and the pitched turbine downflow type was found to be more efficient than a pitched turbine upflow impeller. An attempt has been made to explain the mechanism of suspension on a rational basis and a correlation has been proposed for the estimation of Ncs that is expected to be useful in design.
Enzyme‐caytalyzed oxidation of cholesterol in supercritical carbon dioxide
Authors: Randolph T. W. , Blanch H. W. , Prausnitz J. M. 
Published: June 2004

AbstractSupercritical carbon dioxide was studied as a solvent for the enzymatic oxidation of cholesterol with molecular oxygen. Enzymes isolated from Streptomyces sp., Norcardia sp., Pseudomonas sp., and Gloeocysticum chrysocreas are active in supercritical carbon dioxide.For the oxidation of cholesterol to cholest‐4‐ene‐3‐one (via cholesterol oxidase) from Gloeocysticum chrysocreas, turnovers are almost two orders of magnitude higher than those found in aqueous solutions; initial rates of the reaction catalyzed by Streptomyces sp. in supercritical carbon dioxide are comparable to or greater than those found in aqueous solutions. Cholesterol oxidase from Gloeocysticum chrysocreas is stable in supercritical carbon dioxide at 100 bar and 35°C, while the enzyme from Streptomyces sp. is not. A trace amount of water is necessary for catalysis in carbon dioxide.The rate of oxidation is increased markedly by addition of small amounts of tert‐butanol and iso‐butanol, moderately by ethanol, slightly by acetone and n‐butanol, and not at all by addition of methanol. Solubility data cannot explain these observations.EPR spectroscopy reveals no large conformational changes in the enzyme from Gloeocysticum chrysocreas as a function of carbon dioxide pressure or cosolvent addition. However, EPR spectroscopy indicates that aggregation of cholesterol molecules in supercritical carbon dioxide is strongly affected by changes in pressure or cosolvent content. The degree of cholesterol aggregation correlates well with observed rate enhancements.
Qualitative simulation of chemical process systems: Steady‐state analysis
Authors: Oyeleye Olayiwola O. , Kramer Mark A. 
Published: June 2004

AbstractA method of qualitative simulation for continuous process systems that predicts the steady‐state measurement patterns generated as a result of process malfunctions is presented. The method is based on qualitative versions of the steady‐state process equations and requires no numerical information beyond the signs and relative values of certain groups of parameters. Previous methods of qualitative simulation (Umeda et al., 1980; de Kleer and Brown, 1984; Forbus, 1984; Kuipers, 1986) have tended to generate multiple solutions that do not coincide with any observable system behaviors. In the current method, spurious solutions are reduced using “latent” constraints associated with analytically redundant model equations, and “nonlatent” constraints based on causality, and derived from the extended signed directed graph (ESDG). The ESDG is similar to the signed directed graph (SDG) (Iri et al., 1979), but includes certain nonphysical branches that account for complex dynamics (inverse and compensatory response due to negative feedback). Necessary conditions based on the topology of the SDG for the occurrence of complex dynamics are developed. Based on these criteria, assumptions concerning disturbance propagation are introduced that minimize spurious interpretations of system behavior while guaranteeing inclusion of the steady‐state response. The method is demonstrated by simulating the effects of equipment malfunctions on a model process.
Falling film heat transfer analysis on a bank of horizontal tube evaporator
Authors: Kocamustafaogullari G. , Chen I. Y. 
Published: June 2004

AbstractHeat transfer analysis of falling film evaporation on a bank of horizontal tubes is investigated in this study. Liquid falling from one tube to the next lower one is considered as a thin liquid jet impinging on the top of the tube with a uniform free falling velocity. The hydrodynamic and thermal solutions are obtained by a finite difference method. In these solutions the heat transfer coefficients are modified to account for waviness.Liquid film thickness and local and average heat transfer coefficients are obtained for the constant heat flux and isothermal boundary conditions. Convective heat transfer effects are shown to be dominant as Peclet number increases. Heat transfer coefficients for the tubes in a tube bank decrease from the first tube onwards until the fully developed region is reached. The present predictions agree favorably with the reported heat transfer data.
Multicomponent equilibrium theory for ion‐exchange columns involving reactions
Authors: Hwang Yng‐Long , Helfferich Friedrich G. , Leu Rong‐Jin 
Published: June 2004

AbstractThe multicomponent equilibrium theory for ion‐exchange columns (chromatography) has been extended to systems accompanied by reactions in either or both phases. Based on the concept of coherence of concentration waves in the original theory, the proposed approach includes a systematic way to determine the thermodynamic variance and a general mathematical formulation to construct the composition path grid by means of numerical techniques. With proper adjustments, this approach can be applied as well to adsorption columns involving reactions. As a practical example, a comparison of predicted and observed effluent histories for an anion‐exchange system with dissociation‐association reactions is shown.
Rotational effects on natural convection in a horizontal cylinder
Authors: Yang H. Q. , Yang K. T. , Lloyd J. R. 
Published: June 2004

AbstractA numerical computation is carried out to study the interaction of rotation and natural convection inside a finite horizontal cylinder. The natural convection is due to differential heating on the two ends, while the rotation is along the axis of the horizontal cylinder. The aspect ratio, length of the cylinder to its radius, is 2.0. The Grashof number is fixed at 1.43 × 106 with air as a working fluid. The effect of rotation is examined with Gr/Re2 from 7.0 × 10−2 to ∞, which covers the range from rotation dominated flow to buoyancy dominated flow. It is found that when rotational speed is relatively small or Gr/Re2 » 1, the effect of rotation is to render the spatial heat flux distribution more uniform. As the rotational speed increases, the heat transfer rate distribution on the end surfaces is more homogenous and its level is also reduced. When the rotational speed is sufficiently high (Gr/Re2 « 1.0), heat transfer is by conduction only and the whole fluid inside the enclosure rotates as a rigid body. It is shown that there exists a rotation speed range in which one can have both relatively high and uniform heat transfer rates on the end walls.
Wrong‐way behavior of packed‐bed reactors: II. Impact of thermal dispersion
Authors: Pinjala V. , Chen Y. C. , Luss D. 
Published: June 2004

AbstractA sudden reduction in the feed temperature of a packed‐bed reactor may lead to a transient temperature rise, referred to as a wrong‐way behavior. As expected, the axial dispersion of heat decreases the magnitude of the temperature excursion and prolongs the transient shift to a new steady state. In addition, the thermal dispersion may enable the wrong‐way behavior to ignite a low‐temperature steady state leading to a disastrous runaway of the reactor. Moreover, it may create a transient high‐temperature wave, which moves initially in the upstream direction. The axial dispersion of heat can lead to some behavioral features which are qualitatively different from those of a model which ignores it. The transient temperature excursion does not exceed a value, which can be estimated by a simple analytical expression.
Fluid mechanics of the planar‐flow melt‐spinning process
Authors: Steen Paul H. , Kent Carpenter J. , Yu Ho 
Published: June 2004

AbstractThe planar‐flow melt‐spinning process which is used to rapidly solidify metals from the molten state is shown to be dominated by the fluid mechanics of the “puddle” region even though heat‐transfer limits the overall thickness of the metal ribbon product. The process is modeled to account for the hydrodynamical forces in the molten region with the influence of heat‐transfer entering through a parameter measuring solidification rate relative to wheel speed. It is shown that this parameter H controls the deviation of the flow behavior from classical coating flow solutions; these solutions are recovered in a limiting case of low solidification rate. A perturbation solution in H distinguishes the melt spinning from the coating process and yields the ribbon thickness as a function of wheel‐speed and the other process parameters for a class of contact‐line conditions. Most interesting of these predictions is the result that under certain conditions there is a window of wheel‐speeds for which there is no steady solution. The relationship of predictions with the limited available data from experiment is briefly discussed.
Separation of solutes from aqueous solutions by contained liquid membranes
Authors: Sengupta A. , Basu R. , Sirkar K. K. 
Published: June 2004

AbstractThe hollow fiber contained liquid membrane (CLM) is a thin liquid film contained in the interstices of two sets of intermingled microporous hollow fine fibers. Organic CLM‐s have been used here for the separation of solutes from an aqueous feed into an aqueous strip. Solutes studied are phenol and acetic acid. The separations are carried out in either hydrophilic or hydrophobic hollow fiber CLM permeator modules, using a variety of organic liquids (e.g., decanol, methyl isobutyl ketone, xylene) as membranes. First‐order models have been developed to predict the overall solute transfer coefficients adequately. The transfer coefficient can be enhanced significantly when a chemical reaction is carried out on the strip side using NaOH. The advantages of the CLM structure include operational stability, independent control of membrane phase pressure, automatic replenishment of the lost membrane liquid, and absence of the need for preequilibration. These features are demonstrated here, even for systems with considerable aqueous‐organic mutual solubilities.