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  • Chemical Engineering  (638)
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  • 1
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 393-399 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The univariant element, Q1 P0, and the multivariant elements, Q1+P0 and R2+ P0, are compared for the numerical simulation of the flow in extrusion dies. The pressure distribution obtained by using the Q1 P0 element was found to be afflicted with the checkerboard pressure mode. On the other hand, the multivariant elements, Q1+ P0 and R2+ P0, gave accurate and physically reasonable velocity and pressure distributions. The computed values of the pressure drop across extrusion dies matched well with the pressure drop determined experimentally.
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  • 2
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    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 377-382 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The viscoelastic responses of some molten polymers, and particularly of low density polyethylene (LDPE), are known to vary with processing history. Reasons for the variations include the effects of shear history on morphological states of the polymer, or on its molecular weight parameters. A typical low density polyethylene has been used to test the shear-history dependence concept following a variety of processing steps. The polymer was sheared in single-screw and twin-screw extruders, and in a high speed melter / mixer (Gelimat). Samples also were precipitated from very dilute solutions in trichlorobenzene and in p-xylene. GPC analyses showed that, in general, these procedures did not affect the various moments of molecular weight. An exception was the Gelimat-mixed sample, for which mild reductions in Mn and Mw were noted. In contrast, melt viscosity and elasticity readings, the former from low shear evaluations and the latter from extrudate swelling, were affected by the various procedures. A drop in melt viscosity and in elasticity was observed, being most pronounced for precipitated and twin-screw extruded versions of the LDPE. Reductions also were observed in the specimen sheared in the Gelimat instrument. Following conditioning at the test extrusion temperature (170°C), viscous and elastic responses tended to revert to those of the unsheared control sample, the exception again being the sample sheared in the Gelimat melter / mixer. Of the various mechanisms proposed in the literature to account for transient property changes such as those reported, temporary changes in the degree of chain entanglement appear the most satisfactory explanation. Irreversible alterations in viscoelastic properties may be associated with changes in molecular weights due to processing at high shear.
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  • 3
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 400-409 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A model for the filling stage of injection molding of viscoelastic thermoplastics in cavities of complex shape is presented. The model considers two-dimensional melt flow, with converging and diverging flow patterns induced by complex boundary shape and by the presence of an obstacle. The model is non-isothermal (with the melt loosing heat to the mold walls as it travels into the cavity) and handles a viscoelastic (following the White-Metzner model) material with properties that vary with temperature, shear rate, and pressure. The numerical method is based on finite differences, with boundary fitted curvilinear coordinates used in the mapping of the flow field (which has an arbitrary shape that evolves with time) into a time invariant rectangle. The numerical results reveal geometry-induced asymmetries in the flow and thermal fields as well as the effect of various process parameters on the pressure and temperature profiles in the cavity. The model admits variable cavity thickness, thus allowing for a treatment of the cavity thickness as a process parameter in the simulations.
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  • 4
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 497-500 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The use of polymeric materials in building or construction applications is steadily increasing. Therefore, the potential for these materials to be exposed to fire is also increased. The understanding of the pyrolysis characteristics of these materials is thus a necessity. There are many standard tests used to evaluate materials. Unfortunately, the correlation between these tests and large scale fire is less than desirable. A new bench scale rate of heat release apparatus, the Cone Calorimeter, is now being used more frequently in pyrolysis testing of polymeric materials. This apparatus has been shown to correlate much better between room scale testing and large scale fire testing. The cone Calorimeter provides a pyrolysis profile of a material under ambient oxygen conditions. Characteristics such as ignition time, total heat release, maximum rate of heat release, mass loss during pyrolysis, CO2, CO, and smoke production are determined. In this work several almost neat polymers are examined and the general pyrolysis characteristics of these polymers are discussed. The objective of this work is to provide information of basic polymeric pyrolysis properties of these materials. Variations in the material, i.e., molecular weight, polydispersity, and residual catalysis, along with changes in testing procedures, can have dramatic effects on results. Obviously the addition of flame retardant and flame retardant packages to any of these materials will have dramatic effects on results.
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  • 5
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 6
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 513-521 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The overall isothermal crystallization kinetics for nucleated and non-nucleated isotactic polypropylene (iPP)-dotriacontane systems was investigated. Adipic acid was used as the nucleating agent. Half-time was determined via differential scanning calorimetry as a function of the experimentally controlled variables dilution, crystallization temperature, and the addition of nucleating agent. The influence of these variables on crystallization mechanism and spherulitic structure, as implied by the Avrami analysis, was determined. The influence of these variables on fold surface energy was examined by the Lauritzen and Hoffman analysis.
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  • 7
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The overall non-isothermal crystallization kinetics for nucleated and non-nucleated isotactic polypropylene (iPP) in dotriacontane systems was investigated. Adipic acid was used as the nucleating agent. Crystallization peak temperature was determined via differential scanning calorimetry as a function of the experimentally controlled variables iPP concentration, cooling rate, and nucleating agent concentration. The influence of these variables on crystallization mechanism and spherulitic structure as implied by the Ozawa and Ziabicki analyses was determined. The non-isothermal crystallization kinetics presented here are the first for iPP-diluent systems with and without nucleating agent.
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  • 8
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 543-548 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The static shear strength and static friction of three thermoplastics have been investigated for the case of contact between a bulk plastic sample and a very smooth metallic plate. The minimum tangential force required to shear the interfacial adhesion bonds between the two surfaces was measured and defined as the adhesion component of friction Fa. Experimental results showed that Fa is large when the surface energy is high or the interfacial energy is small and that a correlation may exist between this force and the work of adhesion evaluated from Dupré equation. The real area of contact Ar was also measured using an optical device designed to handle samples and experimental conditions similar to the static friction tests. It was found that Ar is proportional to Pa0.9 where Pa is the apparent pressure of contact and an increase of Fa with Pr was observed. The static shear strength τ has been evaluated as the ratio Fa/Ar, and its relationships with the real contact pressure P approximated by linear functions. It was concluded that τ increases at high P, although it has not been verified for ultra-high-molecular-weight polyethylene. An attempt has been made to explain the observed break in the data. The results indicated that (τ/τb) = κ′(τa/Pa) where b refers to bulk, a to apparent values, and κ′ is a proportionality constant that depends on the plastic material.
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  • 9
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 549-558 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A variety of different styrene monomers [styrene (S), p-fluorostyrene (p-FS), pentafluorostyrene (PFS), p-chlorostyrene (p-ClS), p-bromostyrene (p-BrS), p-methylstyrene (p-MS), p-tert-butylstyrene (p-tBS), p-methoxystyrene (p-MOS), p-ethoxystyrene (p-EOS), and p-propoxystyrene (p-POS)] have been polymerized by radical and cationic mechanisms. Copolymers of S/PFS, S/p-ClS, S/2-vinyl-naphthalene (2-VN), and S/p-phenylstyrene (p-PhS) were prepared by radical polymerization. All polymers were fully amorphous and transparent and exhibited only one glass transition temperature in the temperature range 77 to 141°C. Thin films of the polymers were subjected to external electrical partial discharges (PD). Typically, 20 PD experiments were conducted for each polymer and the data for the time to breakdown were adapted to the two-parameter Weibull distribution function. The resistance towards PD of the various polymers was found to depend strongly on the monomeric structure. Complementary PD experiments on a series of narrow molecular mass polystyrenes confirmed that the minor variation in molecular mass between the different styrene polymers is of no importance for the PD resistance. The PD resistance of the homopolymers decreased in the following order: PS ≍ P(p-MS) 〉 P(p-tBS) ≍ P(p-BrS) 〉 P(p-POS) 〉 P(p-ClS) ≍ P(p-MOS) 〉 P(p-EOS) ≍ P(p-FS) 〉 P(PFS). The time to breakdown for copolymers of S and PFS decreased monotonously with increasing PFS content. Styrene copolymers with low molar contents of 2- VN and p-PhS exhibited a higher resistance towards PD than PS. The results are discussed with reference to various properties of the studied polymers, such as segmental mobility, ionization potential, resonance stabilization, and reactivity of the radicals formed.
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  • 10
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 11
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 614-621 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The glass transition temperatures in bismaleimide-based resins were investigated using different stoichiometric ratios of 1, 1′-(methylenedi-4, 1-phenylene)bismaleimide (BMI) and 4, 4′-methylenedianiline (MDA). The resin cure involves a low temperature primary amine addition to the maleimide double bonds and a high temperature homopolymerization of the maleimide double bonds. The network topology and the glass transition temperature changes with resin composition and curing conditions were determined using differential scanning calorimetry (DSC). An empirical model was used to relate the glass transition temperature to the extents of the amine addition and the homopolymerization reactions in 1:1 and 2:1 BMI:MDA resins. The changes in thermal properties with resin post-cure were also examined.
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  • 12
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 640-644 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Dynamic mechanical properties, tensile properties, and scanning electron microscopy of blends of poly(methyl methacrylate) and polycarbonate were investigated after phase separation above their cloud point temperature by annealing in a hot press. The dynamic mechanical properties show that phase separation proceeds more distinctly for the blends annealed at higher temperature and for longer time. The scanning electron micrographs show that the morphology of phase separated blends varies with the conditions of heat treatment. The tensile properties of phase separated blends deteriorate on account of the coarsening of the brittle dispersed phase over the optimum size and the occurrence of voiding during the heat treatment.
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  • 13
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 665-674 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The packing stage starts at the end of mold filling. During this stage, additional material is forced into the mold to compensate for the shrinkage during subse-quent cooling. Underpacking results in molded parts with dimensional variation. Overpacking causes flash at the parting lines, stick during ejection, and excess residual stresses resulting in warpage. The packing stage is thus extremely important in the determination of the final quality of the product. Despite its importance, analysis of the packing stage has been relatively ignored, particularly the viscoelastic effect. In this work, the analysis of the isothermal packing stage is presented for a Maxwell fluid. A set of governing equations is derived for a two-dimensional mold and solved using the Galerkin finite element method. In addition to the distribution of velocity and pressure, the model predicts the stresses in the planar direction, which could be used for subsequent calculation of the residual stresses.
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  • 14
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 675-685 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The objective this work was to determine the effects of selected polyester catalysts on the reaction of a polyester with epoxy functional polymers. Polyesters containing various catalyst metals were melt blended with either an ethylene-co-glycidyl methacrylate or a styrene-co-glycidyl methacrylate copolymer. The viscosities of the blends were monitored as a function of mixing time using torque rheometry. In addition, the molecular weight distributions of selected samples were analyzed using gel permeation chromatography. Both the torque rheometry and the gel permeation chromatography results indicate that the polyester reacts with epoxy functional polymers. This reaction occurs under conditions and at processing times which are readily obtainable in conventional melt processing equipment. Furthermore, the reaction kinetics of polyesters with glycidyl methacrylate copolymers are dramatically affected by the nature of the catalyst system used to prepare the polyester. Under the conditions used, antimony catalysts are particularly effective at promoting the reaction between polyesters and the epoxy functionality and the activity of the catalysts studied appears to decrease in the following order: antimony 〉 gallium 〉 tin ≃ titanium 〉 germanium. Manipulation of the polyester catalyst system may offer a method to control the extent of reaction obtained in reactive processing of polyesters with epoxy functional compounds.
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  • 15
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 709-715 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The flow kinematics of power-law fluids in fishtail dies is studied. A general isothermal three-dimensional finite element code developed by the authors is used for the flow analysis purpose. The basic geometry of the fishtail die is defined by simple super-elliptical curves, which allows a smooth transition from a circle to a slit. The three-dimensional path line and the residence time distribution (RTD) are calculated from the velocity field obtained from the finite element solution of the conservation equations. The effects of the rheological properties and the die geometry on the path line pattern and the residence time distribution are investigated. The results indicate that as both the length of the transition zone and the fishtail angle increases, the residence time distribution becomes more uniform. However, the power-law index does not affect the residence time distribution significantly.
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  • 16
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 736-741 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The polymers of the aromatic nitrogen compounds N-methyl-pyrrole (P-N-Me-PPY), carbazole (PCarb), and aniline (PANI) have been investigated with electro-optical and surface analytical methods. The in-situ reflection spectra indicate the formation of polarons or bipolarons during electrochemical oxidation, depending on polymer type. The absorption bands can be attributed to changes in the electronic structure with regard to the applied potential. Photocurrent spectra of P-N-Me-PPY and PCarb show a p-type semiconducting behaviour for the polymers in the reduced state. The transition to the oxidized state with quasi-metallic properties is indicated by a significant shift in the Fermi level energy and can be followed with XPS and UPS measurements.
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  • 17
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    Polymer Engineering and Science 33 (1993), S. 838-844 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Extruded films of liquid crystalline polymer (LCP)/fluoropolymer blends were melt drawn to develop uniaxial orientation of a microfibrillar dispersed LCP phase. The anisotropy of the films increased with increasing draw and LCP content in the blend. Laminated composite plates were prepared using the extruded sheets as prepreg. The mechanical properties and coefficient of thermal expansion (CTE) of the prepreg and laminates agreed well with predictions from composite lamination theories. The potential for replacing glass fiber reinforced fluoropolymers with LCP/fluoropolymer blends in applications such as microwave circuit boards is discussed.
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  • 18
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 19
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    Polymer Engineering and Science 33 (1993), S. 865-876 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This review presents a general picture of suspension, dispersion, and interfacial polycondensation processes employed for the preparation of beaded resins, dry powders, and high solid dispersions. The polymer systems covered include polyamides, polyesters, polycarbonates, polyurethanes, and phenol-formaldehyde and urea-formaldehyde resins. Basic features of heterogeneous polycondensation processes are outlined, and different mechanisms of particle formation in suspension, dispersion, and interfacial polycondensation are discussed. Effects of manufacturing parameters such as feed ratio, droplet/particle stabilizer, and stirrer speed on product characteristics are also briefly covered.
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  • 20
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    Polymer Engineering and Science 33 (1993), S. 781-788 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The extrudate swell and the dynamic rheological properties of poly(butylene terephthalate) (PBT) and polyamide 6 (PA6) binary blends were investigated at 240°C. The extrudate swell of the blend varies with the viscosity ratio and composition of constituents, and it is several times larger than that of homopolymers when the viscosity ratio of constituents is around unity. The dynamic oscillatory data could be interpreted by Oldroyd's emulsion model proposed by Graebling, et al. These results suggest that the extrudate swell is caused by the shape recovery of the dispersed particles. A semi-empirical method to estimate the terminal relaxation time with experimental data was introduced, and a clear correlation between the extrudate swell and the terminal relaxation time was obtained.
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  • 21
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    Polymer Engineering and Science 33 (1993), S. 819-826 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Much work in recent years had focused on the improvements of the impact properties of engineering thermoplastics by the addition of a low modulus modifier that contains polar moieties as a result of polymerization or that has been modified to contain polar moieties as a result of various grafting techniques. Styrenic block copolymers (styrene-ethylene/butylene-styrene) functionalized with maleic anhydride have proved useful as impact modifiers and compatibilizers in blends with engineering thermoplastics. This paper focuses on the use of these functionalized elastomers to modify nylon 6. In such compositions, a nylon material with unique mechanical performance may be achieved using the functionalized elastomer either alone or in combination with an unfunctionalized styrenic block copolymer. The optimization of performance in these rubber toughened polyamide blends using various types of styrenic block copolymers is discussed. The morphology as it pertains to performance is also reviewed. The information contained herein may prove useful in obtaining a better understanding of the mechanisms of compatibilization and modification of nylon 6 systems.
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  • 22
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    Polymer Engineering and Science 33 (1993), S. 827-837 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Oriented blends of poly(ethylene terephthalate) (PET) and high density polyethylene (HDPE) with and without compatibilizing agent have been studied with regard to orientation temperature, stretch rate, extension ratio, mode of orientation, and blend composition. These oriented blends have been characterized using infrared spectroscopy and differential scanning calorimetry. The tensile and tensile impact properties were also investigated. The results show that blends with compatibilizer show strain hardening upon orientation, whereas the blend without compatibilizer does not strain harden upon orientation. The blends with less PET content have been difficult to orient. The morphology of these blends show fibril structure, highly oriented in the direction of stretch. Infrared measurements show that PET within the blend has undergone strain induced crystallization upon orientation. It has also been observed that the mechanical properties, such as the modulus and ultimate stress, show improvement upon orientation. Simultaneously stretched blends show better physical properties than sequentially oriented blends.
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  • 23
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    Polymer Engineering and Science 33 (1993), S. 895-900 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper illustrates the factors that control brittle failure under fatigue loading for test specimens cut from medium-density polyethylene pipes for gas distribution. A square bar specimen cut from a pipe with a notch was made and a fatigue test was conducted to cause a brittle failure. To obtain the correlation among stress range, frequency, temperature, and cycles to failure in this fatigue test, Coffin-Manson's frequency-modified fatigue life equation was adopted and the material constants were determined. By gradually lowering the frequency, the resistance to creep can be estimated because cycles to failure - indicating the fatigue damage - decreased, and the actual loading time - indicating the creep damage - increased.
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  • 24
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    Polymer Engineering and Science 33 (1993), S. 923-930 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The interfacial tension, phase morphology, and phase growth was determined for four polymer blend systems: polyethylene/polystyrene, polyethylene/polyamide-6, polystyrene/polyamide-6, and polystyrene/poly(ethylene terephthalate). Generally, high interfacial tension correlates with coarse phase morphology and rapid phase coalescence. The addition of various potential compatibilizing agents to these binary blend systems results in lowered interfacial tension, finer and stabilized phase morphologies. The characteristics of different compatibilizing agents were compared for several of the blend systems. We also look at the influences of compatibilizing agents on mechanical properties of the blend systems. Some compatibilizing agents are able to produce substantial improvements in ultimate properties.
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    Polymer Engineering and Science 33 (1993), S. 937-943 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Unidirectional sheets were extruded of an in-situ composite of thermotropic liquid crystalline Vectra B950 in a matrix of polyphenylene-ether and polystyrene. Three important processing parameters were systematically varied: draw-ratio, slit opening and extruder throughput. Morphology and mechanical properties of these films were determined, and qualitatively related to the processing conditions.
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    Polymer Engineering and Science 33 (1993), S. 959-970 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: It is of great importance to accurately measure or predict the Residence Time Distribution (RTD) in designing extruders and/or in setting up a proper operating condition, because chemical reactions depend significantly on the RTD and temperature when chemical reactions take place during the extrusion process. A previous method to predict the RTD can analytically determine RTD, Residence Time Distribution Function f(t) and Cumulative Residence Time Distribution Function F(t), based on a simplified two-dimensional velocity field in an extruder. However, this previous method cannot accurately take into account the three-dimensional circulatory flow inside the extruder. The present paper suggests a new method to accurately determine the RTD taking into account the three-dimensional circulatory flow and presents a new formula derived to calculate f(t). In order to demonstrate the applicability of the new method including the circulatory flow effect, RTD, f(t) and F(t) were calculated based on a three-dimensional velocity field obtained via a quasi-three-dimensional finite element analysis. It was found that the previous method has a tendency to underestimate the RTD, owing to the neglect of the three-dimensional circulatory flow in comparison with the new method.
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    Polymer Engineering and Science 33 (1993), S. 980-988 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Experimental data confirm the utility of the following simple equation in predicting the spin coating behavior of polyimide precursor solutions: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm h} = {\rm c\beta }_{\rm 0} {\rm k}^{{\rm \beta }_{\rm 1} } {\rm \omega }^{{\rm \beta }_{\rm 2} } {\rm t}^{{\rm \beta }_{\rm 3} } \quad\quad\quad\quad{\rm (1)} $$\end{document} in which \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {c = {\rm polymer\, solution\, solid\, weight\, fraction;}} \\ {\beta _i = {\rm fitted\, coefficient\, (Greek\, letter\, beta)};} \\ \quad{h = {\rm film\, thickness\, after\, cure\, or\, solvent\, removal};} \\ \quad{k = {\rm polymer\, solution\, kinematic\, viscosity, centistokes};} \\ {t = {\rm time},{\rm and;}} \\ \quad{\omega = {\rm wafer\, spin\, speed, rpm (Greek\, letter\, omega)}.} \\ \end{array} $$\end{document}.
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  • 28
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Ternary systems consisting of polypropylene (PP), ethylene-propylene-dieneterpolymer (EPDM) and different types of inorganic fillers (kaolin, BaSO4) have been investigated with respect to their mechanical behavior. On the basis of an Interphase model, it was possible using the modified van der Poel equation to describe the temperature dependence of the storage modulus G′(T) and the loss modulus G″(T). The interphase properties G′(T) and G″(T) could be calculated.
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    Polymer Engineering and Science 33 (1993), S. 1251-1260 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Signal deterioration of optical discs depends strongly on the substrate surface roughness. Characteristics of surface roughness of the molded substrate have been studied in order to clarify the transcription mechanism of smooth surfaces in injection molding of polycarbonate resin. When the melt temperature, mold temperature, and injecting rate are low, microscopic flow marks more than 5 nm deep are observed on the surface. These flow marks are formed when the melted resin near the mold wall is cooled to the no-flow temperature of resin before it comes into contact with the mold wall. Molding transcription improves by optimizing the molding conditions for preventing these flow marks. As a result, the surface roughness of the molded substrate obtained is 3.2 nm in maximum height Rmax, which is nearly equal to that of the mold stamper at 2.7 nm in Rmax.
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    Polymer Engineering and Science 33 (1993), S. 1279-1287 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A finite element numerical analysis of preform inflation associated with the injection blow molding process has been developed using a neo-Hookean constitutive model. The analysis is capable of predicting final wall thickness distributions for axisymmetric mold geometries. Experimental studies were conducted on a Uniloy injection blow molding machine (Model 189-3 and Model 122). A twelve ounce (355 mL) cylindrical bottle mold was instrumented with contact sensors, thermocouples, and pressure transducers. Visualization studies of the inflation process were performed using specialized tooling and high-speed video cameras. The experimental studies provide justification for analyzing the deformation by means of a static elastic approach. The predicted wall thickness distribution is in reasonable agreement with the experimental data. Nonuniformities in the temperature distribution in the preform were found to have the most significant impact on the inflation behavior and the resulting wall thickness.
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    Polymer Engineering and Science 33 (1993), S. 1301-1307 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Dielectric α-relaxation of a bisphenol-A type epoxide oligomer has been investigated in the vicinity of the glass transition temperature (Tg) by the direct current (DC) transient method. The logarithm of the DC transient current for the oligomer was well approximated by the third order function of the logarithm of time. The complex dielectric constant was calculated through the Fourier transformation of that approximation function according to Simpson's integration rule in a frequency range of 10-5 - 1 Hz. At the temperature around the Tg (45°C), the dielectric α-relaxation process of the oligomer was found to be governed by the Havriliak-Negami equation. The relationship between the DC conductivity (σ) and the dielectric relaxation time (τ), σ·τm = const, is valid near and above the Tg of the oligomer. The DC transient current method combined with the DC conduction and the dielectric bridge measurements is considered to be a practical tool for analyzing the dielectric α-relaxation process of the epoxide oligomer over a wide frequency and temperature range.
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    Polymer Engineering and Science 33 (1993), S. 1329-1335 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this study, styrene-(ethylene-co-butylene)-styrene (SEBS) triblock copolymer (Kraton G-1652) was modified with maleic anhydride (MA). The maleated SEBS was used as compatibilizer for the blends of Nylon 6 (PA6) and SEBS. The morphology and impact strength of the blends were measured as functions of concentration and MA graft ratio of maleated SEBS. The compatibility and fracture mechanism of the blends were evaluated from the SEM micrographs of the xylene-etched surfaces and of fractured surfaces. Some of the blends exhibited an impact strength up to about 30 fold greater than neat PA6. The fracture involved both both cavitation and shear yielding. The mechanism of compatibilization of maleated SEBS in the ternary components blends was proposed.
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    Polymer Engineering and Science 33 (1993), S. 1341-1351 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper reports on the theoretical and experimental studies of structure formation and strengthening (stiffening) of flexible-chain polymers. Two techniques of strengthening relying on the melt extrusion, i.e., orientational crystallization (crystallization initiated by melt extension) and drawing (uniaxial stretching of a crystallized polymer) are analysed by theory. The experiments involved preparation and study of melt extruded films and film fibers of linear polyethylene formed by the two techniques mentioned above. The effect of the degree of orientation and other parameters of the formation processes on the mechanical characteristics and the factors limiting the ultimate values of these characteristics are discussed. It is shown that multistage drawing succeeds in achieving a higher tensile strength and elastic modulus (1.2 and 35 GPa, respectively) than the orientational crystallization, which gives 0.8 and 15 GPa. The strengthening by drawing is accompanied by microcrack formation. In contrast, no discontinuities are observed in orientationally crystallized samples up to their ultimate extension.
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    Polymer Engineering and Science 33 (1993), S. 1370-1371 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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    Polymer Engineering and Science 33 (1993), S. 1381-1389 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Because of the inability of existing automotive bumpers to absorb energy during impacts over the supports, energy absorbers have to be used to make bumpers effective in barrier impacts. A parametric analysis of a novel double-beam bumper concept has shown that its performance, in terms of energy absorption and impact forces, is insensitive to the location of the point of impact. Physical realizations of this concept, which may not require more material than existing designs, and which are particularly suited to thermoplastic materials, have been developed.
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    Polymer Engineering and Science 33 (1993), S. 1270-1278 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Flow in a three-dimensional channel with a sinusoidally-wavy, vertical wall is examined for the case of applied down- and cross-channel velocity components. An important parameter for the analysis of the nature of laminar mixing in the flow field occurs when the changes in the downstream direction can be decoupled from the changes in the cross-channel direction, thereby allowing for a two-dimensional solution of the system of equations. This paper shows the effect on the nature of laminar mixing when the decoupling of the momentum equations from a fully three-dimensional case to one where a two-dimensional solution can be performed. Experiments are performed on a channel with sinusoidally varying vertical walls that cover the range of decoupling criteria. Silicone pigmented either white or black was run in the apparatus, cured, and cross-sectioned. The cross sections embody a local, detailed history of the state of mixing as it proceeds down the mixer. The amount of mixing is presented as a function of position at each cross section for the different channel configurations. The nature of mixing changes from a linear growth rate in the amount of interfacial area to an exponential rate as the amplitude of the wave is increased. Results demonstrate the existence of chaos, islands, and the factors affecting the mixing behavior.
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    AIChE Journal 39 (1993), S. 422-433 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The memory integral based on convolution of the unit step response to loading a clean pellet with concentration history at the pellet surface is proposed for computations of mass transfer in adsorption process simulation. Although rate laws are widely used to describe diffusion and sorption in pellets for slow (Glueckauf, 1955) and moderate (Kim, 1989) rates of mass transfer, these models fail to describe mass transfer at short contact times because the concentration history experienced by the pellet is not accounted for. To facilitate memory integral computations, approximations to the unit step response to loading a clean pellet are derived based on a single moving finite element and by asymptotic matching in time. Numerical evaluation of the memory integral is demonstrated on simple cycles which show the merits of this approach.
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    AIChE Journal 39 (1993), S. 397-412 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The problem of bulk, transition and Knudsen regime diffusion in structures of freely overlapping fibers of various orientation distributions was numerically investigated, and the interrelation of the resulting effective diffusivities was examined. Fibers were randomly positioned and oriented in d = 1, 2, or 3 directions. A Monte Carlo simulation scheme was employed to determine the effective diffusivities from the mean-square displacement of random walkers traveling in the interior of the porous structure. The effective diffusivity was found to depend strongly on the orientational distribution of the fibers, porosity of the fibrous structures, and Knudsen number. The tortuosity factor decreased in general with increasing porosity, approaching at the limit of dilute beds the lower bound derived for each direction of diffusion from variational principles. The simulation results agreed well with experimental values of the bulk tortuosity of fibrous beds from the literature. It was also found that the reciprocal additivity or harmonic average effective diffusivity expression (Bosanquet formula), commonly used to estimate transition regime diffusivities from the values at the ordinary and Knudsen diffusion limits, provides an excellent approximation for the effective diffusivity of fibrous beds, except for that parallel to the fibers of a unidirectional structure.
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    AIChE Journal 39 (1993), S. 461-470 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The asymptotic behavior of fixed-point methods in the complex domain is studied. Both direct substitution and Newton's method exhibit stable periodic and aperiodic behavior from real- or complex-valued starting points. Moreover, multiple stable periodic orbits can exist for direct substitution. Traditional trust region (or dogleg) methods, on the other hand, often terminate at singular points, which correspond to nonzero-valued saddlepoints in the least-squares function that can be arbitrarily far from a solution. Furthermore, the basins of attraction of these singular points are usually dispersed throughout the basin boundaries in the complex domain, clearly illustrating that singular points (via the dogleg strategy) also attract either real- or complex-valued starting points.In light of this, an extension of the dogleg strategy to the complex domain, based on a simple norm-reducing, singular point perturbation, is proposed. This extended trust region method removes all forms of nonconvergent behavior and always terminates at a fixed point, even from critical point (worst-case) initial values. Many numerical results and geometric illustrations using chemical process simulation examples are presented.
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    AIChE Journal 39 (1993), S. 446-460 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Most of the advanced nonlinear control algorithms require a model of the system to be controlled. Unfortunately, most of the processes in the chemical industry are nonlinear, and fundamental models describing them are lacking. Thus there is a need for the identification and control of nonlinear systems through available inputoutput data. In this article, we briefly introduce the input-output model used (polynomial ARMA models), and analyze its stability and invertibility. This paves the way to the development of a nonlinear-model-predictive controller. Implementation issues such as modeling of disturbance, state and parameter estimation are discussed. The theory presented is illustrated through examples.
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    AIChE Journal 39 (1993), S. 471-492 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The separation of a binary mixture, using a third component having intermediate adsorptivity as desorbent, in a four section countercurrent adsorption separation unit is considered. A procedure for the optimal and robust design of the unit is developed in the frame of Equilibrium Theory, using a model where the adsorption equilibria are described through the constant selectivity stoichiometric model, while mass-transfer resistances and axial mixing are neglected.By requiring that the unit achieves complete separation, it is possible to identify a set of implicit constraints on the operating parameters, that is, the flow rate ratios in the four sections of the unit. From these constraints explicit bounds on the operating parameters are obtained, thus yielding a region in the operating parameters space, which can be drawn a priori in terms of the adsorption equilibrium constants and the feed composition.This result provides a very convenient tool to determine both optimal and robust operating conditions. The latter issue is addressed by first analyzing the various possible sources of disturbances, as well as their effect on the separation performance. Next, the criteria for the robust design of the unit are discussed. Finally, these theoretical findings are compared with a set of experimental results obtained in a six port simulated moving bed adsorption separation unit operated in the vapor phase.
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    AIChE Journal 39 (1993), S. 505-509 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 39 (1993), S. 513-517 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 39 (1993), S. 518-520 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 39 (1993), S. 510-512 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 39 (1993), S. 1716-1720 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Chabazite zeolites are used at Oak Ridge National Laboratory to decontaminate wastewaters containing 90Sr and 137Cs. Treatability studies show that chabazite can remove trace amounts of these nuclides from wastewaters containing much higher concentrations of calcium and magnesium. The design of ion-exchange columns for multicomponent systems requires a method for predicting multicomponent equilibria from binary, ternary and quaternary experiments, since the number of experiments required for an empirical equilibrium model is not generally feasible. Binary interaction parameters for the Wilson equation are used to predict solid-phase activity coefficients for the five-component system. The sum of squares of deviations between experimental and predicted solution concentrations for the data points available is calculated. The average deviation per data point for the five-component system is lower than for some of the ternary-and four-component data sets containing calcium or magnesium.
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    AIChE Journal 39 (1993), S. 1708-1715 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The limiting current technique was used to measure area-averaged mass-transfer coefficients for surfaces containing many small reactive areas arranged in various patterns. Partially masked platinum electrodes were fabricated using photolithography, and mass-transfer measurements were performed with a rotating disk apparatus. The average mass-transfer coefficient was sensitive to the fraction of the electrode area exposed (ε), declining from values near that for a fully exposed surface for ε = 0.5 to less than 1% of the fully exposed value for ε = 0.001. For any given ε, the mass-transfer coefficient declined with increased spacing between reactive sites. The results were relatively insensitive to details of the site distribution, such as whether the sites were arranged in regular arrays (square or hexagonal lattices) or distributed randomly over the surface. For all conditions studied, the mass-transfer coefficient greatly exceeded that predicted by conventional models which apply the stagnant film approximation to the fluid surrounding a representative active site. This finding is qualitatively consistent with recent computational results, which suggest that convective transport enhances mass transfer at partially active surfaces to an extent not accounted for by adjustments in the effective film thickness.
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    AIChE Journal 39 (1993), S. 1720-1720 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 39 (1993), S. 1272-1280 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An instability analysis has been carried out to elucidate the unsteady flow conditions encountered in the typical circulating fluidized bed units in light of the conveyor-solids feeder interaction. The results successfully predict the critical velocity and the maximum solids circulation rates reported in the literature and explain the origin of such unstable conditions. Furthermore, the simulation, for the first time, reveals the importance of unit structure in improving the performance of circulating fluidized bed systems. Finally, the concept of a high-density circulating fluidized bed is proposed.
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    AIChE Journal 39 (1993), S. 1303-1321 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The product compositions in single-feed distillation columns can be specified only in certain regions of the composition space, which depend only on the pressure, feed, and vapor-liquid equilibrium for the mixture. In nonideal mixtures, even without azeotropes, the regions may allow unusual product distributions. For example, the distillate in a “direct split” is composed primarily of the lightest component. Intuition and experience with relatively ideal mixtures suggest that the next most plentiful component is the intermediate boiler. In nonideal mixtures, however, with or without azeotropes, the next most plentiful component may be the highestboiling species with only trace amounts of the intermediate boiler. For azeotropic mixtures, distillation boundaries may give rise to additional restrictions on the product compositions. We describe how simple distillation boundaries deform into continuous distillation boundaries and, in a limited number of cases, how the simple distillation boundaries can be crossed in continuous columns for certain ranges of the design variables. Unfortunately, such designs may be quite sensitive to model uncertainties or to disturbances in the parameters.
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    AIChE Journal 39 (1993), S. 1377-1388 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Deposition 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.
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    AIChE Journal 39 (1993), S. 1411-1414 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 39 (1993), S. 1415-1419 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 39 (1993), S. 1389-1397 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Rigorous and approximate methods are compared for the simulation of CO2 absorption into aqueous alkanolamine mixtures of methyldiethanolamine and diethanolamine. In addition, data for the mixtures containing monoethanolamine and the simultaneous absorption of CO2 and H2S are presented. For the rigorous approach, the simplified eddy diffusivity theory is used to simulate the liquid-phase hydrodynamic characteristics. The approximation methods examined are the pseudo-first-order approximation, the interpolation approximation of Wellek et al. (1978), the algebraic combined flux (ACFLUX) approximation and the modified combined flux (MCFLUX) approximation. The latter approximation utilizes the reaction zone concept to determine the kinetic preference of the absorbing gas at the gas-liquid interface. Under the range of conditions studied, the MCFLUX approximation predicts very accurately the CO2 and H2S flux rates in mixed amine systems, as compared with the rigorous solution of the differential equations.
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    AIChE Journal 39 (1993), S. 1406-1410 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 39 (1993), S. 1420-1420 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 39 (1993) 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 39 (1993), S. 1431-1443 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A steady-state method recently proposed for measuring two-phase flow properties of a porous medium is supplemented by NMR imaging for measuring the saturation gradients which are allowed to persist in the specimen. The method relies on a strong capillary end effect which is assumed to be enforced by an outlet capillary pressure boundary condition, but direct verification of this has not hitherto been available. For constant flow rates, incremented stepwise, steady-state profiles of hydrocarbon saturation So are obtained which agree with predictions that they be monotonic, nonintersecting, and convex.Using D2O for the aqueous phase allows unambiguous detection of hydrocarbon by NMR, and imaging measurements of transverse relaxation time T2 were included in the protocol. T2 shows a dependence on So which is mild but not negligible for quantitative NMR imaging.
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    AIChE Journal 39 (1993), S. 935-945 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experiment 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.
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    AIChE Journal 39 (1993), S. 954-961 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Variations of perturbation chromatography were used to measure Henry's constants and equilibrium isotherms of various gases on silicalite. Three different adsorbent samples were analyzed (commercial powder and extruded pellets, and laboratory-synthesized crystals), and no discernable differences among the measured parameters were noted. Henry's constants for the linear alkanes were determined from isobaric and nonisobaric chromatography experiments. They were correlated successfully with temperature and the number of carbon atoms per adsorbate molecule. Isotherms were measured from concentration pulse or tracer/concentration pulse chromatography techniques. The Flory-Huggins version of the vacancy solution model was used to correlate pure gas isotherms and predict binary behavior successfully.
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    AIChE Journal 39 (1993), S. 962-974 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Micropore 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.
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    AIChE Journal 39 (1993), S. 855-866 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A nonlinear model-based scheme is developed for product property control in industrial gas-phase polyethylene reactors. The controller regulates instantaneous melt index and density, and provides servocontrol during grade changeovers. Hydrogen and butene feed rates are manipulated to force the product properties onto desired trajectories. During grade changeovers, these trajectories are determined from off-line dynamic optimization studies. Optimal open-loop policies for reactor temperature, bleed stream flow, catalyst feed rate, and bed level are implemented as part of the changeover strategy.The nonlinear feedback controller design is based on global input/output linearization methods. Disturbances are estimated, and plant/model mismatch is removed using an extended Kalman filter. Simulations on a complex mechanistic model of the process reveal that the nonlinear controller performs well for both regulatory and servocontrol. An analogous linear IMC controller is inadequate for disturbance rejection at different operating conditions and for control during grade changeovers. The simplicity of the nonlinear control algorithm makes it an interesting candidate for industrial application. This single controller can be used to control the properties of many grades of polyethylene made in the reactor and to accomplish near optimal changeovers between these grades.
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    AIChE Journal 39 (1993), S. 885-893 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A simple fluid dynamic model is developed which predicts the thinning rate of a viscous film of liquid, in contact with the smooth interior surface of a long cylindrical tube, due to the shearing action of a turbulent flow of an immiscible fluid through the tube. Experiments indicate the degree to which the model provides an accurate means of predicting viscous film removal from the tube. Similar experiments performed with electrochemically roughened tubes elucidate the limitation of this cleaning process due to surface roughness. The observed limitation is consistent with an analysis based on numerical solutions of the equations for shear flow over a rough surface.
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    AIChE Journal 39 (1993), S. 867-875 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A continuous electrochemically modulated complexation (EMC) process was devised to extract and concentrate a class of heterocyclic nitrogen compounds. This design is composed of flow-through electrolysis cells for redox modulation and cycling of the complexing agent and hollow-fiber membrane modules for phase contacting. The extent of both extraction and concentration was found to depend mainly on the magnitude of the distribution coefficients for both steps. Experimental results and modeling of this continuous EMC process are reported, as well as potential applications for this process for other separations.
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    AIChE Journal 39 (1993), S. 1791-1798 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Adsorption rates and thermodynamic parameters were determined for the gasphase adsorption of n-alkanes and benzene derivatives on octadecylsilyl-silica gel (ODS) by chromatographic measurement and moment analysis. Thermodynamic characteristics of adsorption phenomena on ODS were similar to those on the surface. The contribution of intraparticle diffusion to mass-transport resistance was dominant in the ODS column, and the role of surface diffusion was significant for the intraparticle diffusion. The values of the surface diffusion coefficient were of the order of 10-5 cm2/s and could be estimated by assuming that the surface migration on ODS is a tracer diffusion of an adsorbate molecule in n-octadecane.
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    AIChE Journal 39 (1993), S. 1799-1809 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Nonisothermal adsorption is studied by incorporating its mathematical description into a model consisting of the full two-dimensional Navier-Stokes equations and energy and species concentration equations to simulate the processes in fixed-bed industrial adsorbers/regenerators. The model partial-differential equations are solved numerically by using well-established computational fluid dynamics techniques. The equilibrium between gas and solid is considered nonlinear, which is described by Freundlich-type equations. The transport and adsorption of a compound from a solvent to and into an adsorbent are described by a two-step process: transport through the “film” to the outer surface of the particle and diffusion into the porous particle. The effect of fill resistance is discussed, as well as a two-equation turbulence model. Solutions obtained for a typical industrial adsorber/regenerator demonstrate the potential of this method. The computed results for various flow ratios and parameters in the Freundlich equations are shown to be physically plausible.
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    AIChE Journal 39 (1993), S. 1164-1177 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The 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.
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    AIChE Journal 39 (1993), S. 1196-1209 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A model for a pilot-scale chemical vapor infiltration (CVI) reactor in which multiple substrates are densified simultaneously by carbon deposition from a pyrolyzing hydrocarbon is presented. Kinetic expressions and parameters and transport properties for carbon deposition from propylene determined from experimental studies and a single substrate CVI model are incorporated into the pilot reactor model. The two-dimensional transport equations for heat, mass and momentum transfer are solved for the entire reactor to simulate the effects of varied operating conditions on substrate densification throughout the reactor during the CVI process. Of the conditions simulated, the reactor temperature was found to have the most significant impact on both the uniformity of densification and the process time required. As the temperature increased, the uniformity of densification decreased and the time at which pore blockage at the outer surface occurred was shortened. Increasing the hydrocarbon feed concentration shortened the process time, but did not affect the final level of densification, while the feed rate only affected CVI at intermediate times. Comparison between experimental pilot reactor results and model predictions were satisfactory at short and long times, but agreement was less satisfactory at intermediate times.
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    AIChE Journal 39 (1993), S. 1186-1195 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Solid-state film ion exchange (Ag+-Na+) in glass substrates has been investigated for the fabrication of passive, integrated, optical waveguides. A new ion exchange mechanism is proposed which couples the oxidation of silver metal to silver oxide and the diffusion of silver ions into the glass substrate. At high electric fields and/or high temperatures, the growth rate of a silver oxide film limits the formation of mobile silver ions and constrains the diffusion of silver into the glass. This new mechanism is able to predict the dopant distribution profile under those conditions and under conditions where a constant surface concentration is appropriate (infinitely thick oxide film). It also explains the characteristics of the current vs. time curve measured during the ion exchange process. The formation and growth of the silver oxide film were confirmed by X-ray photoelectron spectroscopy and X-ray diffraction analysis.
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    AIChE Journal 39 (1993) 
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    AIChE Journal 39 (1993), S. 1281-1291 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mechanistic model of slug flow based on a set of mass and momentum conservation equations and a number of empirical closure relations is presented. It is then shown that a simplified version of the model, which physically corresponds to the flow of long liquid slugs(long slug model, LSM), can be immediately derived from the general model. The LSM is much simpler than the general model; at the same time, the predictions obtained in the two cases are very similar, when the comparison is limited to the computation of the pressure gradient and the mean liquid holdup. The LSM successfully correlates a large set of experimental measurements relative to three pipe diameters(18, 50 and 90 mm), four inclinations (0°, ±3°, 0.3°), and two pipe lengths(17 and 34 m).
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    AIChE Journal 39 (1993), S. 1322-1329 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We 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.
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    AIChE Journal 39 (1993), S. 1938-1953 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Control structure (strategy) selection consists of the selection and pairing of manipulated and measured variables. This article outlines a procedure that uses such tools as the existence of right half plane (RHP) transmission zeros, the relative gain array, the performance relative gain array, and the closed-loop disturbance gain. The regulatory control system for the fluid catalytic cracking process is used as an example. Several authors found the Kurihara control structure to be preferable to the conventional control structure. The reason is that RHP transmission zeros limit the achievable bandwidth for the conventional control structure. Two other control structures, however, have better controllability characteristics than both the conventional and the Kurihara control structures. The sensitivity of the measurement selection and variable pairing with respect to changes in the operating point and parametric uncertainty is examined, as well as the general objectives of the regulatory control level and its interaction with the higher levels in the control hierarchy.
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    AIChE Journal 39 (1993), S. 1954-1965 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Sufficient conditions for robust closed-loop stability of a class of dynamic matrix control (DMC) systems are presented. The l1-norm is used in the objective function of the on-line optimization, thus resulting in a linear programming problem. The ideas of this work, however, are expandable to other DMC-type controllers. The keys to the stability conditions are: to use an end-condition in the moving horizon on-line optimization; to have coefficients of the move suppression term in the objective function of the on-line optimization satisfy certain inequalities; and to express the uncertainty as deviations in the unit pulse response coefficients of the nominal plant. These deviations and disturbances must also satisfy certain inequalities.An off-line tuning procedure for robust stability and performance of a class of DMC controllers is also included, which determines an optimal moving horizon length and optimal values for coefficients of the move suppression term. The applicability of our approach is elucidated through numerical simulations.
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    AIChE Journal 39 (1993), S. 1976-1984 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We report experimental data showing the effect of temperature on polymer partitioning in the dextran (DEX500)-polyethylene glycol (PEG8000)-water system. Increasing temperature increases the concentration of PEG in the top phase and decreases the concentration of DEX in the bottom phase. A solution thermodynamic model based on local compositions with temperature-dependent parameters correlates the experimental data well, and an efficient Gibbs-free energy minimization algorithm for phase equilibrium calculations is described. The partial molar enthalpies and entropies of each of the solutes, calculated with the model, are negative and decrease in magnitude as temperature increases.
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    AIChE Journal 39 (1993), S. 1966-1975 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Two cationic, copper metal complexes with different ligands were synthesized: ethylenediamine (en) [Cu(C2N8N2) (ClO4)2] and diethanolamine (Deta) {[Cu-C8H21N2O4]ClO4}. These complexes were mounted on Cab-O-Sil using nonaqueous impregnation techniques, and the loadings were determined at which multilayers formed. These samples were analyzed for copper, carbon, nitrogen and hydrogen content to determine if ligand dissociation occurred during the impregnation. Samples were decomposed in a thermal gravimetric apparatus to determine the kinetics of the thermolysis reaction in air, and the evolved gases were analyzed by gas chromatograph-mass spectrometry to determine the products of the thermolysis reaction. The results of these and earlier studies are summarized in a model that describes the effects of molecular structure upon complex-support interactions. Complexes with the ability to form hydrogen bond interactions between the ligand and the support form strong interactions with the surface of silica, whereas complexes without such hydrogen bond interactions are only weakly attracted to the silica surface. Strong interactions with the surface may also arise as a result of ligand dissociation and direct interaction of the metal ion with the surface oxygens. The charge on the complex and its shape play less important roles in determining the affinity of the metal complex with the silica.
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    AIChE Journal 39 (1993), S. 127-139 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Polymer microspheres and fibers are formed with a versatile new process, precipitation with a compressed fluid antisolvent. By spraying a 1 wt. % polystyrene in toluene solution into CO2 through a 100-μm nozzle, microspheres are formed with diameters from 0.1 to 20 μm as the CO2 density decreases from 0.86 to 0.13 g/cm3. The uniform submicron spheres produced at high CO2 density are due in part to the rapid atomization produced by the large intertial and low interfacial forces. Fibers, with and without microporosity, are obtained at higher polymer concentrations where viscous forces stabilize the jet. The effect of CO2 density and temperature on the size, morphology and porosity of the resulting polymeric materials is explained in terms of the phase behavior, spray characteristics, and the depression in the glass transition temperature.
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    AIChE Journal 39 (1993), S. 140-148 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Slit devolatilization of polymers has been considered in a recent work by Maffettone et al. (1991), who have presented a successful model for single slit devolatilization. In this article, the stability of operation of a realistic multislit process is considered. It is shown that the flow rate per slit which can be stably operated may be significantly less than the optimal one for single slit operation. Stability improves as the concentration of volatiles in the feed solution decreases. The non-Newtonian character of the feed solution at high shear rates is discussed in qualitative terms.
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    AIChE Journal 39 (1993), S. 149-162 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A nonintrusive technique for the in-situ measurement of interfacial pH and current efficiency has been developed. A ring electrode, operated potentiometrically at opencircuit, is used to measure the pH change at a rotating disk electrode. The technique takes advantage of the well-characterized hydrodynamics at the rotating disk electrode and has the added advantage that the pH probe, the ring electrode, is not interfering with the flow field and the current distribution on the disk. To determine the pH at the disk electrode by measuring the potential of the ring, the radial transport of hydronium ions across the insulating gap and on the ring is analyzed taking into account the effect of homogeneous dissociation reactions of water and metal-hydroxide ion complexes. Shifts in the ring potential caused by hydrogen super-saturation and ohmic drop are also evaluated. A platinized ring electrode in a hydrogensaturated electrolyte is shown to provide a stable and reproducible hydrogen ion sensor with a Nernstian response to the changes in the bulk pH. Performance of the ring is evaluated by generating hydrogen at the disk electrode from a dilute acid solution, in the absence of other electrochemical reactions. The technique is then applied to determine the interfacial pH of nickel, iron and nickel-iron alloy electrodeposition with concurrent hydrogen evolution. This method was also used to measure the current efficiency of nickel electrodeposition in a fast, nonintrusive and in-situ manner.
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    AIChE Journal 39 (1993) 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 39 (1993), S. 193-196 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 39 (1993), S. 215-223 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A simple statistical-mechanical theory, known as the random-phase approximation, is applied to study liquid-liquid phase separations in solutions of globular proteins. Phase separation may be induced by addition of nonionic polymer or/and ordinary electrolytes. In this analysis, the osmotic-attraction mechanism, whereby the depletion of “solvent” particles between two proteins causes an attractive force, is primarily responsible for phase separation. For one-component models of protein solutions, the theory yields simple algebraic expressions for the equation of state and for the chemical potential of the protein. This analytical theory describes the observed solubility behavior of proteins, including the effect of protein and polymer size, protein charge and concentration, and concentration of simple electrolytes.
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    AIChE Journal 39 (1993), S. 178-187 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 2-Chlorophenol (2CP) was oxidized in near-critical and supercritical water in a high-pressure plug-flow reactor. The global kinetics for 2CP disappearance were described by a rate law that was 0.88±0.06 order in 2CP, 0.41±0.12 order in O2, and 0.34±0.17 order in water. The activation energy was 11.0±3.8 kcal/mol, and the Arrhenius pre-exponential factor was 102.0±1.2 M-0.63 S-1. The uncertainties represent 95% confidence intervals. The products of 2CP oxidation included CO, CO2, HCl, other chlorophenols, chlorohydroxybenzaldehydes, dichlorophenoxyphenols, dichlorobiphenols, and chlorinated dibenzodioxins and dibenzofuran. The molar yields of the organic products were determined for a set of experiments at 380°C and 278 atm. The most abundant products were 2CP dimers such as dichlorophenoxyphenols and dichlorobiphenols, and the highest yield observed for any individual product was 0.6%. Although the yields of these products were low, their selectivities were high. For example, at 3.6 s, the shortest residence time studied under these conditions, about 50% of the carbon in the 2CP that reacted appeared in 2CP dimers, 18% appeared as CO2, and the balance (32%) was presumably in single-ring and ring-opening products. A reaction pathway analysis using the Delplot methodology revealed that the evolution of products from 2CP oxidation in supercritical water was consistent with a reaction network comprising two parallel primary reactions. One primary reaction path led to dichlorophenoxyphenols and dichlorobiphenols whereas the second primary reaction led to single-ring and ring-opening products. The 2CP dimers were convereted to single-ring and ring-opening products, which were, in turn, ultimately oxidized to CO2.
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    AIChE Journal 39 (1993), S. 434-445 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Modeling of reverse osmosis in the presence of strong solute-membrane affinity has always been a challenge due to the complexity of the solute-solvent-membrane interactions and the resultant effect on membrane performance. Most transport models, including all models treating membranes as nonporous and those based on irreversible thermodynamics, are unable to describe or to predict all of the phenomena associated with this case. Recently, the modified surface force-pore flow model has been derived and used to describe the performance of reverse osmosis membranes for solutes which are rejected from the membrane. In the present work, this model is extended to a more general form which can describe the solute-membrane affinity case. For illustration, the extended model, with five adjustable parameters, is used to describe the performance for cellulose acetate membranes and dilute aqueous solutions of toluene, cumene, and p-chlorophenol (data from literature). The model is reasonably consistent with the data. Simulation results of the extended model are also shown.
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    AIChE Journal 39 (1993), S. 1563-1568 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 39 (1993), S. 1569-1573 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 39 (1993), S. 1574-1576 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 39 (1993), S. 1577-1577 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 89
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    AIChE Journal 39 (1993), S. 1581-1591 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Lagrangian statistics are explored as a means of describing the transport of solids in a turbulently flowing liquid. The essential feature of the approach is to represent the concentration field as resulting from a distribution of sources of particles. It is argued that this provides a better framework to understand the physics than the Eulerian analysis currently being used. Fully developed concentration fields are calculated, using the assumptions of homogeneous turbulence and plug flow. It is found that the configuration of solids and the suspended load depend primarily on the ratio of the settling velocity to the friction velocity, which is a measure of the relative importance of turbulence and of settling in depositing particles. The analysis emphasizes the need for a better understanding of the mechanism and the rate of entrainment of particles into a turbulently flowing liquid.
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    AIChE Journal 39 (1993), S. 1592-1602 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The velocity contour profiles within Dean vortices produced by flowing water in a solid-walled curved tube are quantitatively measured. Magnetic resonance flow imaging using flow encoding with spin warp imaging is used in two and three dimensions to obtain these velocities. These experimental measurements are then compared with simulations obtained from solutions of the Navier-Stokes and continuity equations for three axial flow rates. Numerical solutions were obtained with a finite volume method for curved tube Poiseuille flow.
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    AIChE Journal 39 (1993), S. 1603-1610 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mixing length model describes the recently observed (Bilger et al., 1991) effect of chemical reactions on turbulent diffusivities. From this viewpoint, the coupling between microscale reactions and macroscale mixing occurs because the reaction rate is a quasitransferable property which causes more reaction in fluctuating fluid lumps leaving regions of high rate than low rate. The net effect, which raises or lowers reactant diffusivities, depends on a characteristic macromixing time and the rate at which the mean reaction rate changes with mean concentration: \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{{\rm \varepsilon}_A}}{{\rm \varepsilon}} = 1 - \tau _M \frac{{d\bar r_A}}{{d\bar C_A}} $$\end{document}The model shows correct qualitative behavior and appears to agree quantitatively with much of the existing data. It adds an apparent flux, ετM(drA/dy), to the convective diffusion equations which can enhance or hinder the normal turbulent fluxes, but is likely to have little effect on the mean concentration field.
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    AIChE Journal 39 (1993), S. 1611-1620 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An original technique for simultaneous measurements of concentration and velocity in a turbulent liquid flow with and without a chemical reaction is developed by combining a two-component He-Ne laser Doppler velocimeter with a Ar+ laserinduced fluorescence technique. The mass flux and eddy diffusivity of mass are estimated from the simultaneous measurements of concentration and velocity in a liquid shear-free mixing layer downstream of a turbulence grid. The results show that the present measuring technique enables us to simultaneously measure velocity and concentration with high resolutions and that the approximation of the mean gradient diffusion causes about 10% error in estimating the mass flux in a reacting liquid flow.
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    AIChE Journal 39 (1993), S. 1621-1627 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A dispersionless, adsorption equilibrium, plug-flow model of a countercurrent moving-bed chromatographic separator operating at steady state is investigated. The flux of the constituents of a binary mixture is examined via concentration-phase plane plots, which reveal a complex behavior depending on a parameter ó, the ratio of solid- and fluid-phase flow of the mobile phase. When the model is modified by incorporating finite mass-transfer rates, axial concentration profiles exhibit behavior that is characteristic of experimental observations, rather than the predictions of the ideal model. Numerical simulations with the finite mass-transfer model reveal an optimum operating condition.
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    AIChE Journal 39 (1993), S. 1628-1640 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The heterogeneous macropore, surface and micropore diffusion model recently proposed by Hu et al. (1993) for single-component systems is exiended to multicomponent systems in the description of sorption kinetics of gaseous adsorbates in bidispersed (macropore and micropore diffusions), heterogeneous microporous particles. This model describes sorption of gaseous adsorbates with allowance for the energy distribution of adsorption site for both equilibrium and diffusion of the adsorbed species. A uniform distribution is used to describe this energy distribution, and the cumulative energy distribution function is assumed the same for all species in the analysis of multicomponent mixtures. Extensive experimental data of ethane and propane in Ajax activated carbon are collected to study the effects of energy distribution on the binary adsorption, desorption, and displacement dynamics.
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    AIChE Journal 39 (1993), S. 1641-1653 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Measurements of temperatures (secondary outputs) and flows (inputs) are used to estimate product compositions (outputs) in a distillation column. The problem is characterized by strong collinearity (correlation) between temperature measurements and an ill-conditioned model from inputs to outputs. In a linear study, three estimator methods, the Kalman-Bucy filter, Brosilow's inferential estimator, and principal component regression (PCR), are tested for performance with μ-analysis. One can achieve remarkably good control performance with the static PCR estimator, which is almost as good as the dynamic Kalman filter. The quality of the estimate for these two estimators is improved by additional temperature measurements, although the improvement is only minor for more than about five measurements. On the other hand, the performance of the Brosilow inferential estimator may not improve by adding measurements due to sensitivity to modeling errors. For all estimators, the use of flow (input) measurements does not improve the estimator performance and does in fact damage the performance if a static estimator is used.
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    AIChE Journal 39 (1993), S. 1654-1667 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A method of nonhlinear static and dynamic process modeling via recurrent neural networks (RNNs) is studied. An RNN model is a set of coupled nonlinear ordinary differential equations in continuous time domain with nonlinear dynamic node characteristics as well as both feedforward and feedback connections. For such networks, each physical input to a system corresponds to exactly one input to the network. The system's dynamics are captured by the internal structure of the network. The structure of RNN models may be more natural and attractive than that of feedforward neural network models, but computation time for training is longer. Our simulation results show that RNNs can learn both steady-state relationships and process dynamics of continuous and batch, single-input/single-output and multiinput/multioutput systems in a simple and direct manner. Training of RNNs shows only small degradation in the presence of noise in the training data. Thus, RNNs constitute a feasible alternative to layered feedforward back propagation neural networks in steady-state and dynamic process modeling and model-based control.
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    AIChE Journal 39 (1993), S. 1680-1686 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A pseudohomogeneous model is used to analyze the steady state of a sharp reaction front in a porous medium. The reaction rate is described by the flame sheet approximation, and an asymptotic matching analysis is used to determine the temperature, conversion and position of the reaction front. Both adiabatic and nonadiabatic operations are considered, and the effect of radiation is included in the adiabatic case. The results show that there exists a maximum molar flux before blowout occurs. The critical molar flux is decreased by higher activation energies, but it is increased by higher rate constants and flame temperatures. Radiation further stabilizes the flame against blowout. Expressions are provided for the flame temperature, reactant conversion and the conditions when blowout occur. It is also shown that under certain conditions the front has two steady-state positions.
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    AIChE Journal 39 (1993), S. 1668-1679 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Parametric sensitivity of a two-dimensional pulverized-fuel (PF) combustion model is studied extensively for the effect of parametric uncertainty on model predictions. Results show that error in coal devolatilization/oxidation parameters has the dominant effect on predicted burnout, NOx formation, local gas temperature, and coal-gas mixture fraction. Uncertainty in the turbulent particle dispersion parameters appears to have a secondary effect, while error in the particle-gas radiation parameters has little impact on model predictions. Regions of the computational domain exhibiting sensitivity to specific parameters are identified. Specific parameter sensitivity implies the relative importance of various mechanisms in the overall process. Turbulent particle dispersion seems to be important early in the reactor with kinetic processes dominating at and following the predicted ignition point. Radiation appears to be of minor importance. These results indicate the need for a better method of predicting the overall volatiles yield and further understanding of the devolatilization/oxidation mechanism and its role in the overall PF combustion process. The study provides fundamental direction for future comprehensive model development and focuses on experimental work to better quantify critical input parameters.
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    AIChE Journal 39 (1993), S. 1697-1707 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In bulk foams, the dependence of bubble size on time can be deduced from a hypothesis of statistical self-similarity and the scaling characteristic of the volume change rate of a foam bubble. If this rate, \documentclass{article}\pagestyle{empty}\begin{document}$ {\dot v} $\end{document}, scales as the mean bubble volume v to the power α, the total surface area of the foam decreases as an inverse of time to the power 1/[3 (1 - α)]. Coarsening of polyhedral foam scales with α = 5/6, when molecular diffusion limits gas transport across lamellae and liquid drainage through Plateau borders limits lamella thinning. Excess liquid is released by disappearing small bubbles and flows into the lamellae and Plateau borders of growing large bubbles. If none of this liquid accumulates in the foam, coarsening is exponential and α = 1. When resistance to mass transfer at the lamella surfaces is the rate-limiting step, polyhedral foam coarsens with α = 1/3. Coarsening of slowly draining, spherical-bubble foam scales with α = 0. The theory is compared with nine measurements of the total surface area of polyhedral and spherical-bubble foams pregenerated from aqueous solutions of sodium lauryl sulfate, hexadecyltrimethylammonium bromide, alpha-olefin sulfonate with alkyl chain lengths from C14 to C16, and two shaving creams. The theory also proves that the collapse of a two-dimensional, polygonal foam is self-similar and scales with α = l. In all cases, our theory agrees well with experiment and numerical calculations.
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    AIChE Journal 39 (1993), S. 1687-1696 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A combined-conjugated heat-transfer and fluid-flow analysis is presented for coating fibers by CVD in a vertical cylindrical quartz reactor. The numerical model focuses on radiation and natural convection. Three case studies are performed, and the wall temperature predictions are compared to experimental measurements. In the first case, the flowing gas is hydrogen, and conduction is more important than both radiation and convection, in which case measured and predicted wall temperatures agree excellently. In the second, hydrogen is replaced by argon, thus making radiation heat transfer more important than the previous situation. Three radiation models with increasing degrees of sophistication are compared: an approximate nongray model (no wavelength dependence of emissivity), an approximate semigray model, and a rigorous semigray model with view factor calculations. Comparison with experiments suggest that a semigray radiative analysis is needed for correct determination of wall temperatures. The third involves argon at a lower flow rate, where natural convection effects are more pronounced. Checking the validity of the Boussinesq approximation by incorporating the explicit dependence of density on temperature in the model shows a slight difference between the velocity fields predicted using the Boussinesq approximation and those obtained using the explicit dependence of density on temperature. However, there is negligible difference between the temperature fields predicted in the two cases.
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