bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of vapor pressure in vapor‐induced puffing
Authors: Johnny Wu P. , Schwartzberg Henry G. 
Published: June 2004

AbstractWater vapor pressure for cornstarch and popcorn grits at a temperature of between 100 and 180° C was determined by measuring vapor pressures generated at various moisture contents in a heated, closed system. At a higher temperature, fugacity of water increased with increasing temperature probably because of melting or partial melting of starch. The apparent heat of sorption for cornstarch changed significantly with moisture content and temperature. Noncondensible gases were produced by heating popcorn grits to temperatures above 150°C. It is not accurate to estimate vapor pressure based on the heat of sorption or extrapolation of currently used empirical isotherm equations to a temperature above 100°C. Vapor pressure inside popcorn at the instant of popping are. roughly 758 to 827 kPa (110 to 120psia).
Removal of VOCs from groundwater using membrane‐assisted solvent extraction
Authors: Hutter Joseph C. , Vandegrift George F. , Nuñez Luis , Redfield David H. 
Published: June 2004

AbstractA membrane‐assisted solvent extraction (MASX) system coupled to a membrane‐assisted distillation stripping (MADS) system for use in decontaminating ground‐water is evaluated. Volatile organic compounds (VOCs) in the groundwater are extracted in the MASX unit using a sunflower oil solvent. In the MADS unit, VOCs are stripped from the sunflower oil, which is recycled to the MASX unit. Thermodynamic data for the sunflower oil‐water‐VOCs system were measured. The results were used along with published membrane mass‐transfer data to design MASX and MADS modules.
Hydrodynamic assist of dynamic wetting
Authors: Blake Terence D. , Clarke Andrew , Ruschak Kenneth J. 
Published: June 2004

AbstractDynamic wetting speeds are limited by the gross entrainment of air between the liquid and the moving substrate. We present experimental data for the curtaincoating method, in which liquid impinges at high speed on the substrate. We also show that air entrainment is strongly affected by macroscopic hydrodynamics and is subject to hysteresis. Using boundary‐layer theory, a simple hydrodynamic model is developed for the flow field in the impingement zone away from the dynamic wetting line. The model approximately accounts for the shear thinning of polymer solutions and for the influence of surface tension. We apply the molecular kinetic theory of dynamic wetting, modified to account for hydrodynamic stress, to the immediate vicinity of the wetting line. The main result is a correlation for airentrainment data.The experimentally calibrated model predicts that the hydrodynamic assist of wetting is greatest when the dynamic wetting line is located beneath the impinging curtain. Flow visualization supports this physical picture.
Optimizing experimental conditions for minimum production cost in preparative chromatography
Authors: Felinger Attila , Guiochon Georges 
Published: June 2004

AbstractOptimum experimental conditions and column design parameters are calculated for most economical separation of binary mixtures by preparative liquid chromatography. The solvent consumption and capital costs are regarded as the two major cost contributions. Calculations were performed by using the numerical solution of the equilibrium‐dispersive model of chromatography and a nonlinear simplex algorithm. Solvent consumption depends only on the column efficiency, the retention factor, and the loading factor. The production rate depends on the particle size, the column length, the mobile‐phase flow velocity, the retention and the loading factors, and can be optimized with or without recovery yield constraints. A hybrid objective function was constructed to find the tradeoffs between the production rate and the solvent consumption.
Solubility of HFC‐134a refrigerant in glycol‐type compounds: Effects of glycol structure
Authors: Tseregounis Spyros I. , Riley Maynard J. 
Published: June 2004

AbstractEnvironmental concerns have dictated the replacement of CFC‐12 refrigerant with HFC‐134a in automotive air‐conditioning (A/C) systems. Since polyglycols are synthetic compounds compatible with HFC‐134a and considered as lubricants for the A/C compressor, interations of HFC‐134a with glycol‐type compounds and thermodynamic properties of the solutions are important in designing an A/C system. In this work, the solubility of HFC‐134a in four glycol‐type compounds was measured at −5 to 80°C and 90 to 960 kPa. HFC‐134a had the greatest solubility in tetraethylene glycol dimethyl ether. HFC‐134a was less soluble in hexylene glycol and tetraethylene glycol and least soluble in triethylene glycol. Mixtures of HFC‐134a with TRIG or TGDE showed phase separation. Solubility data were used to calculate the activity coefficient of HFC‐134a in glycol solutions. An equation of the form, lnγr = (1 − xr)[A + Bxr], was found to correlate γr to the mole fraction of HFC‐134a in the solution where A and B are constants which may depend on the temperature. Based on a model assuming a specific interaction between molecules and using the activity of HFC‐134a, a higher degree of interaction is expected between HFC‐134a and tetraethylene glycol dimethyl ether molecules than between the molecules of HFC‐134a and other glycols. In general, glycols with free ‐OH groups may have less affinity for HFC‐134a. Solubility is discussed in terms of its parameters and chemical structure of the glycols, as well as the effect of temperature on the solubility, the activity coefficient, and the thermodynamic properties of the HFC‐134a/glycol solutions.
Structure of falling film heat and mass transfer on a fluted tube
Authors: Conlisk A. T. 
Published: June 2004

AbstractThe falling liquid film has become a popular means of transferring heat and mass from a vapor to a binary liquid, especially in gas‐fired heat pump systems. Ideally, the required amount of heat and mass transfer can be accomplished by using a simple cylindrical tube; however, increasingly stringent size and weight requirements for the machine prohibit use of the simple cylindrical surface, and other more complex surfaces with higher absorption capacities have been sought. In this article, absorption of a single component and condensation of a binary mixture on an axially fluted tube is considered. The solution to the problem hinges on the energy equation, although the entire energy transfer process is mass‐transfer‐limited. Significant mass transfer is limited to a thin layer near the liquid‐vapor interface. Solutions to the energy equation are obtained for both the conduction‐ and convection‐dominated regimes. In the latter, significant heat transfer occurs within a thin layer near the liquid‐vapor interface which contains the mass transfer layer; this “boundary layer” structure does not appear to have been recognized in previous work in this area. Using the present results, the capacity of a given tube may be predicted as a function of governing geometrical and physical parameters. The principal objective of this work is to develop the theoretical tools from which computations may be carried out during a design process. The theoretical results may be applied to mixtures typical of application in the absorption heat pump industry.
Factors affecting coalescence frequency of droplets in a stirred liquid‐liquid dispersion
Authors: Wright H. , Ramkrishna D. 
Published: June 2004

AbstractLiquid‐liquid dispersions are commonly used for separations and reaction systems, because the added interfacial area due to dispersion aids in mass transfer and chemical reaction rates. Transient coalescence experiments have been performed for a wide range of dispersed‐phase fractions and impeller speeds. A similarity transformation of the experimental drop‐size distribution is possible for most of the experiments. The drop‐size‐dependent coalescence frequency is obtained from an inverse problem procedure previously developed. Over the range of drop sizes encountered in our experiments, the coalescence frequency increases with increases in the size of the coalescing drops, the dispersed‐phase fraction, and the impeller speed. For a dispersephase system of neutrally buoyant droplets of benzene/carbon tetrachloride in water, the coalescence frequency is K(v, v′)= 3.72 (10−3)ϕ1.42N(v1/2+v′1/2) as a function of dispersed‐phase fraction, ϕ, impeller speed, N2, and volumes of the coalescing droplets, v and v′. The results are compared with previous models for the coalescence frequency. Models predicting an eventual decrease in coalescence rates with drop size are disqualified unless this decrease occurs beyond the sizes observed in our experiments.
Oxygen permeation through thin mixed‐conducting solid oxide membranes
Authors: Lin Yue‐Sheng , Wang Weijian , Han Jonghee 
Published: June 2004

AbstractA new approach for developing fundamental equations of oxygen permeation through thin mixed‐conducting oxide ceramic is presented considering both surface reactions on membrane‐gas interfaces and the diffusion of charged species in the bulk oxide. The essence of this work is the coupling of surface reactions with the bulk diffusion using a novel approach which differs from the conventional Wagner. Theory applicable only to limited cases. With this approach, fundamental equations based on various permeation mechanisms can be derived for oxygen permeation through thin mixed‐conducting oxide membranes, which is impossible using conventional approach. In general, the final results are a complex implicit equation correlating the oxygen permeation flux to the driving force, membrane thickness, and rate constants with physical significance in each step. Somewhat simpler theoretical oxygen permeation equations are obtained for some special cases (mixed‐conducting membranes with a rate‐limiting step, ionic‐conducting membranes, ionic‐conducting membranes with a reducing agent in permeate side). Theoretical results derived using this new approach agree excellently with the experimental oxygen permeation data. It is theoretically and experimentally shown that for ionic conductors, the surface permeation parameter measured by the dynamic permeation method is directly related to the oxygen isotope exchange rate constant measured under equilibrium conditions.
Estimation of crystallization kinetics from batch cooling experiments
Authors: Qiu Yanfeng , Rasmuson Åke C. 
Published: June 2004

AbstractA direct optimization method to estimate nucleation and crystal growth rate parameters from seeded batch cooling crystallization experiments is evaluated. The experimental information applied comprises the concentration of the solution and the temperature as functions of time and the final product size distribution. Parameters in kinetic equations are determined by nonlinear optimization of a dynamic model of the experiment, by which intermediate approximations of experimental data are avoided. The optimization objective function includes both solution concentration data and product size distribution data. Kinetics are estimated for succinic acid crystallizing in aqueous solutions. Results from several different cooling crystallizations are simultaneously supplied into one single optimization to determine seven parameters.
A novel reactor for determination of kinetics for solid catalyzed gas reactions
Authors: Borman P. C. , Bos A. N. R. , Westerterp K. R. 
Published: June 2004

AbstractA novel perfectly mixed laboratory reactor for determining kinetics of heterogeneously catalyzed gas‐phase reactions has been developed. Perfect mixing is achieved by circulating the gas in the reactor using an axial flow impeller in a well streamlined enclosure. Pellets are fixed in a rectangular opening in the blades of the impeller. They rotate with the impeller, thus realizing high particle velocities in the reactor. Interparticle mass transfer was studied experimentally by vaporization of naphthalene pellets. The mass‐transfer coefficient in the novel reactor was found to depend on the velocity of a particle in the reactor. Mass‐transfer coefficients in an internal recycle reactor at equal impeller tip speeds are 4–6 times lower than those in the novel reactor, and conditions can be chosen easily where at higher rotational speeds the mass‐ and heat‐transfer rates are 8–10 times higher than in classical recycle reactors. The recycle flow rate in a recycle reactor was found to depend strongly on the resistance to flow caused by the catalyst bed itself. The novel reactor was tested under reacting conditions using the hydrogenation of ethene.
New lattice model for adsorption of small molecules in zeolite micropores
Authors: Van Tassel Paul R. , Davis H. Ted , McCormick Alon V. 
Published: June 2004

AbstractA new adsorption model is developed for small molecules in zeolites whose form is based on features revealed by molecular simulation. Adsorption is assumed to occur onto a 3‐D polyhedral lattice, and both the energy and entropy of the lattice sites are accounted for using a statistical mechanics approach. Energetic interactions are described by an Ising model with both 2‐ and multibody nearest‐neighbor in‐teractions. Entropic interactions are included by an adsorption site volume term which accounts for the loss of traslational freedom associated with lattice crowding.The model is applied to a system of small molecules (xenon, methane) adsorbed in idealized zeolite NaA, where adsorption has been shown by computer simulation to occur on finite, cuboctahedral lattices (Van Tassel et al., 1992). The model quantitavely predicts the simulated isotherm over the entire pressure range. Comparison is made with a Langmuir model and a van der Waals gas model which, although valid at low pressures, fail at high pressures due to overestimation of translational entropy and inaccurate portrayal of sorbate‐sorbate interaction energy.
Ignition and extinction of flames near surfaces: Combustion of CH4 in air
Authors: Vlachos D. G. , Schmidt L. D. , Aris R. 
Published: June 2004

AbstractIgnition and extinction characteristics of homogeneous combustion of methane in air near inert surfaces are studied by numerical bifurcation theory for premixed methane/air gases impinging on planar surfaces with detailed chemistry involving 46 reversible reactions and 16 species. One‐parameter bifuraction diagrams as functions of surface temperature and two‐parameter bifurcation diagrams as functions of equivalence ratio and strain rate are constructed for both isothermal and adiabatic walls. Lean and rich composition limits for ignition and extinction, and energy production are determined from two parameter bifurcation diagrams. For a strain rate of 500 s−1, CH4/air mixtures exhibit hysteresis from ∼ 0.5% up to ∼ 12.5% and from ∼ 5.5% up to ∼ 13.5% near isothermal surfaces and adiabatic walls, respectively. Ignition temperature rises with composition from 1,700 to 1,950 K, without a maximum around the stoichiometric ratio. Under some conditions multiple ignitions and extinctions can occur with up to five multiple solutions, and wall quenching, kinetic limitations, and transport can strongly affect flame stability. Flames near the stoichiometric ratio cannot be extinguished by room temperature surfaces for sufficiently low strain rates. The role of intermediates in enhancing or retarding ignition and extinction is studied, and implications of the effect of catalytic surfaces on homogeneous ignition and extinction are discussed. Removal of H atoms and CH3 radicals by wall adsorption can increase extinction and ignition temperature of 6% CH4 in air by up to 300 K for a strain rate of 500 s−1.
Controlling the morphology of CVD films
Authors: Viljoen Hendrik J. , Thiart Jacob J. , Hlavacek Vladimir 
Published: June 2004

AbstractThe morphology of the gas‐solid interface during typical chemical vapor deposition (CVD) processes is investigated. The dynamic behavior of the interface depends on many factors, including local curvature of the film, reactant diffusion, adsorption equilibrium, surface kinetics, and mobility of adatoms. These factors depend on material properties of the system and reactor conditions, such as the deposition temperature and pressure. A 2‐D model proposed describes the evolution of the interface in Cartesian coordinates under the influence of stabilizing and destabilizing effects. A linear stability analysis is used to predict under which conditions a planar interface becomes unstable. Stability criteria of a simplified 1‐D analysis is not necessarily valid if the real system has more than one dimension. The substrate temperature and reactor pressure are important factors affecting the stability of film growth and thus the morphology of CVD films. An increase in temperature stabilizes planar film growth if the deposition is diffusion‐limited, but destabilizes it if the process is reaction‐controlled. The reactor pressure has a destabilizing effect on planar film growth during a typical CVD process.
Ion adsorption and ion exchange in ultrathin films of fatty acids
Authors: Ahn Dong June , Franses Elias I. 
Published: June 2004

AbstractIon exchange equilibria of ultrathin Langmuir and Langmuir‐Blodgett films of stearic and arachidic acids in contact with aqueous electrolyte solutions were studied experimentally and theoretically. A model considering electrochemical and thermodynamic aspects of the adsoption of protons, calcium, and cadmium ions from solution to the film has been developed. Key parameters are the binding constants (K's) of ions and the mixing characteristics (or Flory‐Huggins interaction parameters x's) of ions in the two‐dimensional film lattice plane. The ternary system can be described by the parameter values determined with binary proton‐calcium ion, proton‐cadmium ion, and calcium‐cadmium ion systems: KCa = 2.9 × 102, KCd = 8.6 × 103, KH = 3.6 × 106, χH – Ca = −0.76, χH‐Cd = 0.13, and χCa‐Cd = 1.0. Competitive ion adsorption was measured by FTIR ATR spectroscopy of either collapsed or ordered LB films. Data for the proton‐calcium‐cadmium ion system agreed well with the model predictions. The results show possible future applications of such thin films as ion sensors or ion exchange materials.
Protein denaturation in nonlinear isocratic and gradient elution chromatography
Authors: Whitley Roger D. , Zhang Xiaomang , Wang N.‐H. Linda 
Published: June 2004

AbstractProtein denaturation, common in hydrophobic adsorption systems, causes misinterpretation of adsorption mechanisms, interferes with analysis in analytical chromatography, and complicates the design of large‐scale adsorption processes. A detailed adsorption model isolates the effects due to denaturation from those due to mass transfer and intrinsic adsorption kinetics. The model is verified using protein gradient elution data. Simulations establish that typical symptoms of denaturation in frontal and elution chromatogrrams include sensitivity to changes in feed composition, column length, particle size, and operating conditions (feed size, flow rate, and column history). When a denatured species adsorbs irreversibly, the elution chromatogram shows decreasing peak area with increasing incubation time and apparent adsorption hysteresis over repeated cycles. In gradient elution, the peak elution order, resolution, and relative peak height depend highly on modulator properties and operating conditions. Interfering species limit solid‐phase induced denaturation by competing for binding sites. Strategies for detecting and minimizing denaturation are proposed.
Competition between TiCl4 hydrolysis and oxidation and its effect on product TiO2 powder
Authors: Akhtar M. Kamal , Vemury Srinivas , Pratsinis Sotiris E. 
Published: June 2004

AbstractThe competition between hydrolysis and oxidation of TiCl4 during vapor‐phase synthesis of titania powders was experimentally investigated. The effects of reactor temperature, reactant mixing and H2O/TiCl4 ratio were studied in a hot wall aerosol flow reactor. The presence of water vapor resulted in rounded particles instead of the faceted ones observed in the absence of water; this effect was most pronounced at lower reactor temperatures. Mixing the water and TiCl4 vapor streams at low temperature resulted in anatase titania. Larger aggregates with smaller primary particles were observed for powders synthesized in the presence of water vapor. The mixing temperature of the water and TiCl4 vapors, as well as the H2O/TiCl4 ratios, did not affect the aggregate size or specific surface area. Analysis of micrographs of titania aggregates made in the presence of water revealed that the fractal dimension increased with process temperature.
Stochastic dynamic approach to transport phenomena
Authors: Laso Manuel 
Published: June 2004

AbstractA stochastic dynamic approach to the equations of change is introduced here, which first is applied to linear equations and is based on the formal analogy between certain forms of the equations of change and the Fokker‐Planck equation. A stochastic differential equation associated with the Fokker‐Planck equation can be derived from the latter and solved numerically, thus yielding the solution to the original equation of change. The proper treatment of boundary conditions is essential for the success of the method. We show that the method is able to handle the eight fundamental types of boundary conditions (Carslaw and Jaeger, 1959; Crank, 1975). In addition, the stochastic dynamic approach provides a deeper insight in the physical processes underlying transport phenomena than do traditional techniques.
Calculating critical transitions of fluid mixtures: Theory vs. experiment
Authors: Sadus Richard J. 
Published: June 2004

AbstractThe progress in predicting critical transitions in fluid mixtures is reviewed. The critical state provides a valuable insight into the general phase behavior of a fluid and is closely linked with the nature and strength of intermolecular interaction. Calculations of critical equilibria have been confined mainly to binary mixtures. The prediction of binary gas‐liquid critical properties was initially limited to empirical correlations. These techniques have been superseded by rigorous calculations of the critical conditions using realistic models of the fluid or equations of state. All of the known types of critical phenomena exhibited by binary mixtures can be, at least, qualitatively calculated. If an optimal combining rule parameter is allowed, continuous gas‐liquid properties can be calculated accurately for a wide variety of mixtures. Similarly, the pressure and composition dependence of upper critical solution phenomena can be accurately predicted. Progress has been achieved in predicting discontinuous critical transitions in polar and nonpolar binary mixtures. There is increasing interest in calculating the critical properties of ternary and multicomponent mixtures. Although the techniques applied to binary mixtures often can be directly extended to ternary mixture calculations, calculated critical properties of ternary mixtures indicate that their behavior cannot be considered as a simple extension of binary mixture phenomena. Consequently, ternary critical calculations are likely to provide a superior insight into the phase behavior of multicomponent fluids.
Theory of convective heat and mass transfer to spherical‐cap bubbles
Authors: Kendoush Abdullah Abbas 
Published: June 2004

AbstractThe forced convective heat and mass transfer to spherical‐cap bubbles were investigated analytically. Potential flow was assumed outside the bubble except at the bubble surface where the boundary layer approximation was adopted. The present analytical study produced the following exact solution:

for the average Nusselt number where Pe is the Peclet number. The derived equation was compared with the available experimental mass‐transfer results.