Bibliothek

Ihre E-Mail wurde erfolgreich gesendet. Bitte prüfen Sie Ihren Maileingang.

Leider ist ein Fehler beim E-Mail-Versand aufgetreten. Bitte versuchen Sie es erneut.

Vorgang fortführen?

Exportieren
Filter
  • Chemical Engineering  (17.974)
  • Engineering General  (9.884)
  • Nuclear reactions  (4.460)
Materialart
Erscheinungszeitraum
Schlagwörter
  • 201
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 3175-3192 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A model of a continuous digester was developed as an extension of the well-known Purdue model. A lumped-parameter approximation is used to describe the flow transport mechanism of the digester, and a model based on the fundamental principles of mass and energy is derived. Mass bases and volume fractions are defined to allow fewer simplifying assumptions in the model derivation than in previous model versions. The steady-state profiles and dynamic responses of the digester model are compared with a previous version of the Purdue model, and the significant differences between the two models are highlighted. The digester model is also compared to the Weyerhaeuser benchmark digester model, and a parametric sensitivity analysis to several model parameters is performed. Physical explanations are given for the demonstrated model behaviors. Model implementation is straightforward, making it useful for process control, optimization and design studies.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 202
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 3223-3231 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The standard industrial process for the purification of natural gas is to remove acid gases, mainly hydrogen sulfide and carbon dioxide, by the absorption and reaction of these gases with alkanolamines, but the lack of reliable and accurate vapor-liquid equilibrium (VLE) data impedes the commercial application of more efficient alkanolamine systems. The objective of this research was to develop an FTIR apparatus and an in-situ technique capable of making VLE measurements of acid-gas-aqueous alkanolamine systems and to improve the accuracy of vapor-liquid equilibrium measurements at low hydrogen sulfide and carbon dioxide concentrations. The new FTIR apparatus and technique were tested in VLE measurements of low concentrations of carbon dioxide and hydrogen sulfide in aqueous mixtures of diethanolamine.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 203
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1545-1550 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Homogeneous thermal cracking of ethane, which is an endothermic and hence energy-intensive process, was carried out in the presence of limited O2 under different process conditions (at 600°-850°C; O2/ethane ratio of 0-0.2; H2O/ethane ratio of 0-3.3; and space velocity of 2,000-11,000 h-1). The influence of a sulfur additive in the feed and reactor material on the process performance was also investigated. Noncatalytic oxycarcking of ethane in the presence of limited O2, greatly enhances not only the total conversion of ethane but also the conversion of ethane by purely thermal cracking. This process also occurs at a much lower contact time than that required to achieve the same conversion for the thermal cracking process. Also, both the exothermic oxidative conversion and the endothermic thermal cracking of ethane occur simultaneously, which makes this process very energy-efficeint, with a drastic reduction in external energy requirement and coke formation. By manipulating the process conditions, particularly the temperature and O2/C2H6 ratio, the overall process can be made almost thermoneutral, mildly exothermic, or mildly endothermic.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 204
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1717-1726 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Cylindrical internal reflectance infrared spectroscopy (CIR-FTIR) was used for the determination of the transport properties of hydrocarbons in zeolite L at high temperatures and pressures. This was the first time that the intracrystalline diffusivity of hydrocarbons in microporous media could be determined under supercritical conditions by using a dynamic technique. The study investigated the self-diffusion of n-heptane, the counterdiffusion of n-hexane and 1-hexene, and the codiffusion of n-heptane and pyxlene in zeolite L under subcritical and supercritical conditions. The diffusion time constants obtained for the single and binary systems showed that the diffusion within the pore was reduced significantly under supercritical conditions (i.e., liquidlike behavior) as the hydrocarbon density within the pore was increased.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 205
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1763-1784 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A nonlinear model-predictive control scheme based on the autoregressive-plus Volterra model is proposed. A “plant-friendly,” yet persistently exciting, input sequence is designed for model identification. A second feature of this work is that the control action is determined by solving a less computationally burdensome nonlinear programming problem than the optimization problems associated with Newton-type controllers and polynomial ARMA model nonlinear MPC. A third contribution is that semiglobal closed-loop stability conditions are derived and are shown to be less conservative than those previously published. The control scheme is shown to outperform a feedback strategy using proportional integral control and a linear model-predictive control design for the control of two polymerization reactor case studies. The complex features of the latter case study [multivarible (3 × 3), recycle loop, high-order (24) dynamics] motivate the applicability of this approach for industrial problems.
    Zusätzliches Material: 20 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 206
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1797-1812 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: ZSM-5 zeolite membranes with reproducible properties were prepared by in-situ synthesis on porous α- and γ-alumina tubular supports and characterized by XRD, SEM and electron microprobe analysis. Single-gas permeances for H2, CH4, N2, CO2, n-butane, and i-butane increase over some temperature range, but some gases exhibit maxima or minima. The highest ideal selectivities at room temperature are 299 for N2/SF6, 392 for H2/n-butane, and 2,820 for H2/i-butane. These membranes can separate n-butane/i-butane, H2/n-butane and H2/i-butane mixtures. All n-butane/i-butane separation selectivities have maxima as a function of temperature and are higher than ideal selectivities because n-butane inhibits i-butane permeation. Thus, separation is not by size selectivity, but is due to pore blocking. Temperature depenencies of single-gas permeances and separation selectivities depend strongly on the location of zeolite crystals and the location is determined by preparation procedure. Ideal selectivities also depend strongly on the preparation procedure. When the zeolite forms a continuous layer on the inside surface of the support tubes, pure i-butane permeates faster than pure n-butane so that the single-gas permeances are not determined just by molecular size. The i-butane permeance also increases much more with temperature than the n-butane permeance. The permeation behavior may be the result of permeation through nonzeolitic pores in parallel with zeolite pores. When zeolite crystals are dispersed throughout the pores of α-alumina supports, permeances are lower and gas permeation and separation properties are quite different. Ideal selectivities are lower, pure n-butane permeates faster than i-butane, and the permeances increase much less with temperature. Separation selectivities are lower but can be maintained to higher temperatures.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 207
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1861-1873 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Volatile species are removed from polymers by devolatilization. Foaming experiments using corn syrup and low-density polyethylene were carried out to investigate effects of volatile content, operating vacuum level and stripping agent in devolatilization. When foaming and rupture occur, a limiting foam volume growth was observed for a polymer regardless of the volatile content and the addition of stripper bubbles. A mathematical model was also developed to study the effect of stripper bubbles in polymer devolatilization. Based on the cell model for bubble growth, a bimodal model for foam growth is developed as the first step to describe the initial formation and growth of the volatile and stripper bubbles in polymer during devolatilization. When foaming and breakup occur at a critical foam volume expansion, a film model for mass transfer is used to model the second step of devolatilization. A numerical factorial study shows that the devolatilization section should be designed and operated to provide the screw channel sufficient free volume and residence time for the desired foam expansion.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 208
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1914-1920 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 209
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1921-1921 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 210
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1925-1934 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Thin polymer coatings produced from water- and organic-solvent-based precursor liquids are ubiquitous components of industrial and consumer products. Design and optimization of dryers for these coatings require accurate predictions of their drying rates. Accurate drying predictions for many polymer/solvent coatings require a satisfactory description of the polymer/solvent mutual diffusion coefficients. A method is proposed ot determine a satisfactory description of the diffusion coefficients by effective free-volume theory parameters. The effective parameters are determined from gravimetric data measured in a bench-scale drying apparatus. The application of the method to a poly(vinyl acetate)/toluene solution shows that the effective free-volume parameters give diffusion coefficients that agree with published data. The method is also applied to a rubber-based adhesive in industrial-grade heptane by treating the complex adhesive as a pseudobinary solution. For both systems, the effective parameters lead to quantitatively accurate drying predictions in a pilot-scale oven.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 211
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2187-2193 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: After an aqueous solution containing Sr2+ was flowed through a bed packed with particles of activated charcoal for a very long time, the flow was abruptly switched to deionized water. The variation in ionic concentration at the outlet with time was characterized by the power law, Cout ∼ t-α, for sufficiently large t. This fractal-like behavior we reported previously has further been studied theoretically and experimentally. A major concern is to examine dependency of α on experimental conditions. Adsorption sites predominate over dead-end pores or spaces as “trappers” in our case where Sr2+ or Ba2+ is adsorbed on activated charcoal. The experimental results can well be explained by our theoretical model. It has been found, however, that the response curve for Sr2+ deviates from the power law after a very long time. This deviation can be explained by introducing the assumption that there exists a maximum value of the activation energy for the desorption process. The curve for Ba2+, on the other hand, exhibits no such deviation until Cout decreases to the detection limit of the analytical device used.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 212
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2373-2375 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 213
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2376-2380 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 214
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997) 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 215
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2393-2404 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Direct numerical simulations were used to investigate turbulence structure and scalar transfer across a shear-free, nonwavy gas-liquid interface (free surface) in stably stratified turbulent flows. These simulations solve the Navier-Stokes and thermal-energy conservation equations, using a finite difference approximation. The relation between the turbulence structure in the stably stratified turbulent boundary layer and organized motion near the free surface are discussed. In addition, scalar transfer across a free surface is investigated by solving a passive scalcr conservation equation after both velocity and temperature fields are fully developed. The effects of stable stratification on the scalar transfer process in a region very close to the free surface are also discussed.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 216
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2424-2431 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A laser Doppler anemometer was used to measure velocity components for the flow of a Newtonian fluid in a reversing section of a pilot-scale corotating twin-screw extruder. Measurements were made at a fixed axial position in the intermeshing (nip) region and the translational region (áway from the nip). Tangential and axial velocity profiles reached a maximum in the middle of the screw channel, indicating pressure flow. Leakage flow through the gaps between screw flights and backflow toward the hopper were observed only in the nip region. No reversal of flow was detected in the translational region. Measured velocity profiles showed substantially higher shear rates in the reversing section of the screw as compared to those in the forward-conveying section.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 217
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2415-2423 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The miscible displacement of aqueous lignin solutions (model black liquor) by water from beds formed from glass beads was studied as a function of the presence of cationic polymer in the wash water, bed structure, lignin concentration, and superficial flow rate. The displacement behaviors in homogeneous beds formed from fine beads (121 μm) were compared with results of experiments using a channel bed consisting of a bed formed from fine beads surrounding a channel of coarse beads (638 μm) running the length of the bed in the flow direction. Washing efficiencies, defined as the fraction of lignin removed when one pore volume of eluate was collected, were 84-93% for homogeneous beds washed with water compared with 31-33% for the channel bed; the range in efficiencies reflects the influence of other variables. The presence of cationic polymer in the wash water enhanced the washing efficiency by 1.7 to 2 times with a corresponding 20 to 35% decrease in the permeability of the central channel in the channel bed. The improved washing with polymer was due to selective plugging of the central channel with precipitate formed from complex formation between anionic lignin in the black liquor and the cationic polymer. Breakthrough curves obtained from 12 microconductivity probes located throughout the bed showed that mixing of lignin in the black liquor and the cationic polymer. Breakthrough curves obtained from 12 microconductivity probes located throughout the bed showed that mixing of lignin solution (high conductivity) with wash water (low conductivity) in the displacement front, as expressed by a mixing length, was a maximum in the coarse bead channel and was decreased when the wash water contained cationic polymer.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 218
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2471-2478 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The adsorption selectivity, Si, j = (Xi/yi)/(xj/yj), is examined in a 1-D model of a mixture of hard rods adsorbing on a linear substrate. The adsorbed components are characterized by their length, li, and equilibrium constant, ki. We derive an expression for the bulk-phase pressure Po, for which there is no separation of components i and j, S,i, j = 1, in terms of these parameters. The selectivity of the smaller component always increases with the bulk pressure, which results in a selectivity reversal if, as is usually the case, the larger component is more strongly adsorbed at low surface coverages. In a binary mixture, when P 〈 Po, the selectivity of the smaller component decreases with increasing bulk-phase mole fraction, y1, while for P 〉 Po, the reverse is true. The effect of varying the molecular parameters on the selectivity is also studied.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 219
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2456-2470 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The isotope exchange technique (IET) can be used to simultaneously measure multicomponent gas adsorption equilibria and self-diffusivities of the components in a single isothermal experiment without disturbing the overall adsorbed phase. An experimental protocol for the IET and corresponding data analysis procedures is described. Isotherms and self-diffusivities for adsorption of N2 as a pure gas were measured on commercial samples of a carbon molecular sieve and a 4-Å zeolite using IET, as well as those of O2 and N2 from their binary mixtures. The carbon molecular sieve did not exhibit thermo-dynamic selectivity for air separation, but had a kinetic selectivity of O2 over N2 Mass-transfer resistances for self-diffusion of N2 and O2 on the carbon molecular sieve were controlled by pore mouth restrictions in the carbon, but those for adsorption of N2 into the 4-Å zeolite by Fickian diffusion inside the adsorbent. A linear driving force model described the uptakes of N2 and O2 in the carbon molecular sieve. The Fickian diffusion model described the N2 uptake in the 4-Å zeolite. Mass-transfer coefficients for both O2 and N2 on the carbon molecular sieve increased linearly with increasing gas-phase partial pressure of these gases, and the pressure of O2 did not affect mass-transfer coefficients for N2. The self-diffusivity of N2 in the 4-Å zeolite decreased with increasing adsorbate loading.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 220
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2488-2508 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The concept of standing concentration waves is introduced to derive design equations for continuous moving bed (CMB) processes. For linear isotherm systems, simple equations are derived from the analysis to link product purity and recovery to zone lengths, bed movement velocity, flow rates, column capacity factors, and mass-transfer coefficients. Once product purity, recovery and feed flow rate are specified for a given system, the zone flow rates and bed movement velocity that provide the highest throughput and the lowest solvent consumption can be determined from the solutions. In a given system, there is a trade-off between product purity and throughput. If bed volume and product purities are fixed, the longer the zone lengths, the higher the throughput. Simulations based on a linear driving force model that considers axial dispersion and lumped film and intraparticle diffusion are used to compare the column profiles and effluent histories of CMB and simulated moving bed (SMB). A numerical algorithm is introduced to allow simulation of both CMB and SMB operations using the same program. The comparison shows that the design equations derived for CMB systems are applicable to SMB systems. Finally, the standing wave solutions are used to analyze an experimental SMB system from the literature (Ching et al., 1991). Simulations agree closely with the data and the predictions of the theoretical analysis.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 221
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2571-2578 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A new two-phase swirl-flow monolithic-type reactor was designed to study the kinetics of heterogeneous photocatalytic processes on immobilized semiconductor catalysts. True kinetic rate constants for destruction of a textile dye were measured as a function of wavelength of light intensity and angle of incidence, catalyst layer thickness, and the effect of absorption of light by liquid film on the overall rate of photocatalytic degradation. Photocatalytic activities of two commercially available TiO2 catalysts (Degussa P25 and Hombikat UV 100) were also compared for different light intensities and catalyst layer thickness. Residence time distribution and mass-transfer limitations were evaluated. This new reactor appears to be an attractive choice for kinetic studies of heterogeneous photocatalysis.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 222
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2601-2604 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 223
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2889-2902 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A model for a pneumatic-conveying dryer is presented, with the focus on the superheated steam drying of wood chips, although it can also be used for other porous materials and drying media. It includes a comprehensive 2-D model for the drying of single wood chips, which accounts for the main physical mechanisms occurring in wood during drying, including coupled transport of water, air, vapor and heat. This model allows for features such as initial condensation and flashing at the outlet, as well as the falling rate period when the drying is controlled by internal transport. External drying conditions in the dryer are calculated by applying mass, heat and momentum equations for each incremental step in dryer length. A plug-flow assumption is made for the dryer model, and single-particle and dryer models were solved iteratively. The irregular movement and nonspherical shape of wood chips are accounted for by measuring drag and heat-transfer coefficients.Model calculations illustrate the complex interactions among steam, particles, and walls that occur in a flash dryer. The drying rate, the slip velocity, and temperature vary in a complex manner through the dryer, necessitating the use of a comprehensive single-particle model, as in this case. Previous experimental data on the drying of bark chips in a pilot dryer was used to verify the model. The predicted temperature and pressure profiles, as well as the final moisture content of the material, agreed well with the measurements. Thus, the model provides a useful tool for the design and scale-up of pneumatic-conveying dryers. Effects of steam and material properties on the drying were investigated with different design parameters.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 224
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2932-2943 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Inverse gas chromatography (IGC) was used to measure diffusion and thermodynamic parameters of volatile compounds in polymers. A comprehensive model for IGC is proposed, and a numerical solution for it is developed. Four capillary columns were prepared using PDMS and EPDM as the stationary phase. Toluene, ethanol, water, and some chlorinated compounds were the probes for the chromatographic experiments. Limitations of the IGC technique, although not reported in the literature, are explained. Nevertheless, the results for the systems chosen were satisfactory and agreed with the literature. The effect of adsorption on the column wall is important when water is used as a solute. The adsorption effect was incorporated into the model. The parameters obtained for water using the modified model became more reliable. The parameters obtained with IGC were used to get further understanding of the pervaporation process.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 225
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2641-2649 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The morphological evolution of flame-generated “primary” spherules and inorganic aggregates was studied at low particle volume fractions [O(10-1 ppm)] in a welldefined/characterized laminar nonpremixed combustion environment which produces particle heating rates of 104 K/s. Pure Al2O3 particles synthesized in an Al(CH3)3 (TMA-) seeded atmospheric pressure laminar counterflow diffusion flame “fueled” with CH4/O2/N2 were used as the model material/combustion system. Experimental techniques included spatially resolved laser light scattering (LLS) and thermophoretic sampling/transmission electron microscopy. Local aggregate morphology was characterized in terms of spherule (“grain”) size, aggregate size, aggregate shape and fractal structure. Effects of flame temperature and TMA concentrations on particle inception location, sizes and morphology studied systematically were interpreted based on parallel theoretical studies. LLS signals and TEM images show particle/aggregate size and morphology evolution as a result of two competing rate processes. Mean spherule diameters prior to high-temperature coalescence are explained in terms of the strong size dependence of nanoparticle restructuring kinetics due to surface melting, even at 500 K. Mean fractal aggregate sizes reached only 15-27 spherules near a local temperature of only 1,250 K. Final particulate products were isolated spherical particles resulting from complete “collapse” of the aggregates in an interval of only 24 ms immediately upstream of the maximum gas temperature (2,280 K). Experimental results are compatible with the characteristic times governing each participating “unit” rate process. Some of these methods can be applied in controlling the larger-scale synthesis of valuable nanopowders and guide rational extensions into the domain of turbulent nonpremixed combustors generating ultrafine particles of tailored composition and morphology at high mass loadings.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 226
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2688-2697 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The chemical reaction mechanism and fine particle generation during atmospheric pressure chemical vapor deposition with the tetraethylorthosilicate/ozone system were studied experimentally and theoretically for a flow-type vertical-tube reactor. For the thermal decomposition of ozone, numerical simulations obtained using reaction rate constants for a batch reactor explained experimental results well. The activation energy of chemical reaction between TEOS and the oxygen radical, O· was evaluated from the particle generation rate (2.18 × 105 J/mol). Particle population balance equations, based on the simplified reaction coagulation model, were coupled with equations for the thermal decomposition of ozone and chemical transformations of TEOS and solved numerically. Calculation results for particle number concentration and size agreed with experimental results for temperatures below 430 K. For temperatures above 430 K measured concentrations agreed well with calculated values, but measured sizes were significantly smaller than calculated sizes. Thermal desorption spectra from particles generated at 423 K revealed a peak from C2H4 at ∼ 800 K, presumably from ethoxy groups. This emission explains, at least in part, the observed decrease in particle size at high temperatures.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 227
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2724-2730 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Mordenite (MOR) and ferrierite (FER) membranes without any pinhole and crack were synthesized by a vapor-phase transport method. The permeance of H2, He, CH4, N2, O2 and CO2 was determined at 290-400 K, which showed minimum with increasing temperatures for most cases. In the parallel diffusion model was proposed, molecules adsorbed in a micropore are assumed to diffuse in parallel through the central region of the pore and along the wall region of the pore. This parallel diffusion model accounts for the effect of pore size of MOR and FER on the permeation and expresses the experimental data well. The interaction between gas molecules and pore walls are evaluated for each gas.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 228
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2715-2723 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Asymmetric membranes consisting of palladium, ruthenium and platinum deposited on the surface or inside the pores (average size, 200 nm) of a tubular alumina membrane were prepared by the chemical vapor deposition (CVD) technique. Sublimation and decomposition temperatures of their acetylacetonato complexes used as metal sources for CVD were important factors in preparing the membranes selected for hydrogen separation. Among the membranes prepared by CVD, the palladium membrane gave the highest flux of hydrogen and was about 1.6 times higher than a dense palladium membrane with a thickness of 4.5 μm prepared by an electroless plating technique. The hydrogen permeation through the membranes prepared by CVD are related to the surface diffusion of spillover hydrogen.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 229
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 145-156 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The dynamics of semibatch reactors is often neglected in the literature despite their industrial importance. This article analyzes the stability and dynamic behavior of semibatch polymerization reactors operated according to a flow scheduling strategy designed to impart a steady-state nature to the dynamics of these essentially transient reactors. It can also improve the operation of these reactors, especially the quality of the polymer produced (such as molecular weight distribution and polymer composition). In the proposed strategy of flow rate scheduling, the intensive states of the reactor can be made to reach steady-state values. A comparison of the dynamics of the proposed and classical operating strategies illustrates this possibility. Further dynamic analysis reveals the emergence of phenomena characteristic of continuous operation in a CSTR. Examples are multiplicity of the trajectories, limit cycle oscillations, as well as nonhomogeneous oscillations belonging to a period doubling cascade. Operation in a sequential semibatch mode is discussed, as well as the importance of selecting parameters for the fillup and discharge operation. In this mode of operation either periodic or chaotic behavior is obtained. The effect of both on polymer properties is studied in detail.
    Zusätzliches Material: 22 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 230
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 655-664 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Frequency-domain measurements of photon migration were conducted in concentrated polystyrene suspensions to assess their use for on-line particle sizing in undiluted process streams. Using a numerical inverse algorithm, particle-size distributions (PSD) and volume fractions of three latex suspensions with differing distributions were recovered from phase-shift measurements at 15 or less visible wavelengths. Comparison to dynamic light-scattering measurements show excellent agreement. Since it is the propagation characteristics of multiply scattered light instead of the amount of light detected that is employed to solve the inverse problem, the measurement technique provides a self-calibrating (and therefore especially suitable) method for on-line process monitoring of PSD in the chemical-based industries.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 231
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1426-1435 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The turbulence structure of the liquid phase near a wavy gas-liquid interface in stratified flow was experimentally investigated in a 50 mm (H) × 100 mm (W) rectangular duct. The characteristic parameters of the organized motion under the liquid waves such as the frequency of appearance and length scale were estimated by using the variable-interval time-averaging and the photochromic dye activation techniques. These characteristics were used in a hybrid surface renewal-eddy cell model to predict the interfacial heat- and mass-transfer coefficients in stratified two-phase flow. The predictions for cocurrent and countercurrent flows agreed reasonably well with experimental data available in the literature.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 232
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1838-1848 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Opportunities exist to exploit the unique properties of carbon dioxide to process polymers for advanced applications. The diffusion of deuterated water in poly(methyl methacrylate) films swollen by carbon dioxide at 35°C over the pressure range 0 to 90 bar (corresponding density range: 0.0 to 0.66 g/cm3) was measured using in situ FTIR spectroscopy. The mechanism and time scale of the diffusion of deuterated water in PMMA are easily controlled by manipulation of the applied CO2 density. The enhancement of mass transport rate is consistent with the degree of plasticization of the polymer due to the absorption of carbon dioxide.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 233
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1884-1893 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Clathrate phase equilibria for the ternary water-phenol-carbon dioxide system containing one-guest and two-host components were studied. Three four-phase equilibrium loci for this ternary system were determined over wide temperature and pressure ranges. A quintuple point, thermodynamically unique, and invariant condition appeared in this type of ternary system, was carefully measured, and were 293.7 K and 57.2 bar. At this quintuple point, five individual phases of water-rich liquid, phenol-rich liquid, carbon dioxide-rich liquid, phenol clathrate, and vapor could coexist in equilibrium. A new experimental technique was used to determine the liquid-phase compositions coexisting with phenol clathrates at the isobaric conditions of 30.0 bar and six temperatures ranging from 278.2 and 303.2 K. A potential applicability of the clathration process to phenol separation from aqueous solutions was demonsrated in terms of phenol concentrations based on carbon dioxide-free concentration. In particular, phenol separation by using high-pressure carbon dioxide as a clarthrate-inducing agent could be applied even to multiphase aqueous solutions over an entire range of phenol concentrations.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 234
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 3241-3252 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Hydrodynamics of foam films in a porous medium depend strongly on the pore geometry, foam quality, foam flow rate, surfactant formulation, rheological properties of the film, and the capillary pressure in the medium. These dynamics were studied numerically by simulating the behavior of a foam film as it traverses a periodically constricted sinusoidal pore. Different regions of film behavior exist depending on its rheological properties. For a film with rigid (immobile) surfaces, the entrainment effect leads to a thickening film consistent with related phenomena such as Bretherton's (1961) analysis of a bubble moving in a capillary tube. A film with mobile surfaces, however, stretches and thins while remaining uniform in thickness and may become unstable under certain conditions. The dependence of limiting capillary pressure on the foam flow rate and rheological properties is explained quantitatively.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 235
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 3253-3256 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 236
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 3271-3273 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 237
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2609-2609 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 238
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 3274-3274 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 239
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2657-2664 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Silica and stannic (tin) oxide powders were synthesized by oxidation of their respective chlorides in single and double (inverse) diffusion flame reactors. The effect of reac-tant gas mixing on the characteristics of these powders (size and morphology) was investigated by altering the position of the fuel (CH4) and oxidant (air or O2) streams in the burner. Reactant gas mixing plays a key role in controlling particle size since it affects the temperature history, residence time, and initial particle concentration in the flame, thus, yielding a simple technique for particle-size control over a wide size range in flame reactors. The different material properties (such as sintering) of silica and stannic oxide result in particles of different size and morphology, although they were made at nearly identical flame conditions. Moreover, the oxidant composition affects significantly the properties of silica particles.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 240
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2679-2687 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The combined phenomena of SiO2 particle generation and deposition were analyzed theoretically and experimentally in a tubular flow reactor. The deposition tube was directly connected to a high-temperature tube furnace reactor by a flange and the deposition characteristics of SiO2 particles were measured. The SiCl4 conversion and deposition efficiencies were calculated, solving the mass and energy balance equations and the aerosol dynamic equation in the tubular flow reactor. Effects of process variables such as furnace set temperature, inlet SiCl4 concentration and total gas-flow rate were examined. Experimental results agreed closely with theoretical prediction. Effects of natural convection are significant at low gas-flow rate. Tube wall temperature profiles inside the deposition tube were proposed for uniform coating of SiO2 particles. The study shows that the tube furnace reactor can be used to coat the inside wall of the deposition tube with ultrafine particles uniformly by adjusting tube wall temperature profiles.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 241
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2698-2703 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Experiments were conducted to test the theory of nucleation-controlled growth of spherical particles in a turbulent jet. Dibutyl phthalate (DBP) particles were formed in a bench-scale jet apparatus with nozzle diameters 0.235 cm and 0.375 cm. Size distributions and number concentrations of the particles were measured at different DBP vapor concentrations, jet velocities, and positions. There is evidence that the DBP particle nucleation was confined to the shear layer of the jet and that the particles grew by condensation as they moved away from the nozzle. Trends in the data suggest that for low rates of particle formation in jets, the final aerosol concentration can be predicted from simple scaling laws.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 242
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2704-2709 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Vapor-phase synthesis of ultrafine TiO2 particles was investigated experimentally in the simultaneous hydrolysis and oxidation of TiCl4. Experiments were made for the control of particle size, size distribution and phase composition of ultrafine TiO2 particles with the preheating of reactants. The molar ratio of H2O/TiCl4 was adopted as a variable for the control of particle size and size distribution in various reaction systems such as TiCl4-H2O, TiCl4-H2O-O2, and TiCl4-H2O-air. As the molar ratio of H2O/TiCl4 increased from 2 to 12, the average particle size decreased from 45 nm to 19 nm, and the rutile content of TiO2 powders increased from 21% to 54% in the TiCl4-H2O system. Changes in the average particle size were the same in the TiCl4-H2O-O2 system as in the TiCl4-H2O system, but particle-size distributions were narrower in the TiCl4-H2O-O2 system. The same tendencies of average particle size, size distribution and rutile content were also found in the TiCl4-H2O-air system. A high production rate of ultrafine TiO2 particles was obtained at the condition of high mole fraction of TiCl4 and low gas-flow rate in the presence of water vapor and preheating of reactants.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 243
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Parameters and/or processes responsible for the stability of catalyst supports and ceramic membranes are discussed. Two major parameters/processes were identified which are responsible for the stability of sol-gel derived nanostructured oxides at elevated temperatures. They are metastable-to-stable phase transformation and structure and packing of primary particles within the aggregate. Based on these observations, strategies to develop thermostable nanostructured oxides for high-temperature membrane and catalyst applications are discussed by taking titania and titania-alumina nanocomposites as examples.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 244
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2870-2873 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The atomic structure of amorphous silicon nitride fibers produced by two different methods is revealed using the technique of neutron scattering. Polymer-derived fibers are found to contain excess crystalline silicon and disordered carbon, and fibers annealed in N2 for 100 h contain a cristobalite phase that becomes amorphous under 200-kV electron irradiation. Fibers grown from the gas phase, however, are shown to consist of almost pure amorphous Si3N4, with a small crystalline a-Si3N4 component.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 245
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2-12 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Effects of elongation on the radiation heat transport down a spheroidal cavity, located in a conducting solid with a diffusely reflecting cavity-solid interface, are examined. An effective conductivity λe and a void radiation conductivity λr are obtained as a function of cavity eccentricity α; and surface emissivity ε. To facilitate the calculations and produce readily applicable equations, a rigorous variational principle is used. Exact solutions are generated in the neighborhood of the spherical cavity (α2 → 0) for any ε 〉 0, a long needle-shaped void (α2 → 1) for any ε 〉 0, and a perfect reflector (ε → 0) for arbitrary elongation (0 ≤α2 ≤ 1). Significant differences arising from the shape change are observed. The α2 → 0 edge demonstrates a linear increase in λr with ε. At the opposite edge α2 → 1 and positive ε, λr is a horizontal line independent of ε, much like the long cylinder, whose conductivity is a factor of 32/(9π) (= 1.13) larger. In the neighborhood of ε 0, λr is always zero for any 0 ≤ α2 ≤ 1. The emissivity slope for ε → 0 starts from unity at α2 = 0 and increases monotonically with elongation to a singularity 3π[16(1 - α2)]-1 as α2 → 1 for the long needle.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 246
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 547-554 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A method for testing the thermodynamic consistency of binary and isothermal vapor-liquid equilibrium data at moderate and high pressures is proposed, using a φ-φ approach. The Redlich-Kwong-Soave equation of state with Huron-Vidal mixing rules at infinite pressure is used in the data-reduction procedure, and a Margules equation is used to calculate the activity coefficients at infinite pressure. This model is shown to be thermodynamically consistent. The proposed method allows us to check consistency of vapor-liquid equilibrium data in the presence of components at the gaseous and supercritical states.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 247
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 535-546 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: This article completes the analysis of high-temperature mutual solubilities of hydrocarbons and water. Part I (Tsonopoulos and Wilson, 1983) presented benzene, cyclohexane, and n-hexane, while Part II (Heidman et al., 1985) extended the investigation to ethylbenzene, ethylcyclohexane, and n-octane. Part III presents experimental data up to the three-phase critical end point for C6, C8, and C10 1-alkenes, n-decane, n-butylcyclohexane, m-diethylbenzene, p-diisopropylbenzene, cis-decalin, tetralin, 1-methylnaphthalene, and 1-ethylnaphthalene. The thermodynamic analysis of Henry's constants for hydrocarbons in water is extended to the critical temperature of water, while the solubility and volatility of water in hydrocarbons are successfully correlated with several modifications of the Redlich-Kwong equation of state.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 248
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 196-211 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Plausible stoichiometries for solvation and association complexes in binary mixtures of chloroform and one of six organic diluents (n-hexane, p-dioxane, acetone, diethyl ether, tri-n-butyl phosphate, or triethylamine) are examined parametrically. A range of stoichiometric assumptions based on hydrogen bonding are examined, but only a few such combinations yield statistically significant fits to the experimental vapor-liquid equilibria and NMR chemical shift data. Hydrogen bonding considerations and the “true” chemical species are much more important than nonspecific physical factors such as molecular sizes, shape differences, and regular solution terms. Thermodynamic equilibrium constants are presented for the most significant chloroform solvation complexes. Nonspecific dilution shift is important and more helpful in fitting NMR data than the assumption of a chloroform dimer. Physical effects and an orientation factor are used to predict excess enthalpy in chloroform/n-hexane mixtures where no solvation or association reactions occur. Model parameters are used to predict excess molar volumes and enthalpies. Commonly reported stability constants are concentration dependent.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 249
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 715-726 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A prototype computer program SOLIDS has been developed for the simulation of processes with solids processing steps. In addition to heat and mass balances, the equipment units are modeled with discretized population balance equations. Any transformation mechanisms for the particle-size distribution (PSD) - nucleation, growth, dissolution, agglomeration, and breakage - can be represented. With the sequential modular code, the PSD can be tracked from unit to unit in a complete plant. To provide maximum flexibility for further development, new or improved equipment models and discretization techniques can be included as additional subroutines. Case studies show that accounting for the PSD can lead to improved equipment design and a more complete description of the interactions among the units in the plant.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 250
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 693-702 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Centrifugal partition chromatography (CPC) is a relatively new preparative chromatographic technique. To understand, predict, and optimize CPC separations a model is needed, describing the effluent concentration profile as a function of the phenomena that determine the separation efficiency (mass transfer, mixing, and partitioning). The model presented in this article describes experimental effluent concentration profiles accurately. Partition coefficients, Stanton numbers, and Péclet numbers were obtained by comparing model simulations to experimental pulse-response data. The fitted partition coefficients agree well with those obtained from shake-flask experiments. Mass-transfer limitation is the major reason for peak broadening. The inverse mass-transfer coefficient is a linear function of the partition coefficient. The model will be a valuable tool in determining the influence of mass transfer as a function of various experimental conditions.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 251
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 727-739 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: In this article we present a method for the on-line identification and modeling of full profile disturbance models for sheet forming processes. A particular principal components analysis technique called the Karhunen-Loève expansion is used to adaptively identify the significant features of the profile. In addition, we show how the temporal modes of the reconstructed profile can be modeled using low-order linear autoregressive (AR) processes. By simulation examples, the effect of the order of the AR model is studied, as well as the window size of the data used in the on-line application of the KL expansion, the effect of data weighting, the importance of the correct selection of the number of modes, and the frequency of updating the parameters of the AR models. Identified disturbance models can be easily incorporated into model-predictive control algorithms.
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 252
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997) 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 253
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 893-901 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: This article deals with prediction of turbulent flows in ducts of noncircular cross sections and, in particular, assessment of the performance in such flows of two very different models of turbulence. One model is of the two-equation, eddy-viscosity type, which is used in conjunction with a non-linear stress-strain relationship. The other is a complete Reynolds-stress transport closure that involves the solution of a differential transport equation for each of the six components of the Reynolds-stress tensor. The flows considered are characterized by the presence of secondary motions that are largely driven by the turbulence anisotropy and whose prediction remains a severe challenge to turbulence closures. Data from several experiments involving such flows are used here to assess the overall performance of the two models. It is found that the two models yield very similar results that are also of adequate engineering accuracy - an outcome that argues in favor of the use of the nonlinear two-equation model in practical computations.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 254
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 328-338 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Past research shows that for the same power per unit volume, flocculation performance varies with tank size and impeller type. This study was performed to characterize effects of scale and impeller design on turbulence produced in the flocculation process. The study was performed with a Rushton turbine and an A310 foil impeller in three square tanks of 5-, 28- and 560-L volume. Fluid velocities were measured using a dual-channel laser Doppler velocimeter with an enhanced burst spectrum analyzer. Flocculation tanks were operated at a constant average unit-mass energy-dissipation rate of 0.0016 m2/s3. The results show that the turbulence intensity and local turbulent energy-dissipation rate were higher for the Rushton turbine than for the A310 impeller. The turbulence intensity was found to increase with increasing tank size regardless of impeller type. The local turbulent energy dissipation rate decreased for the Rushton turbine and remained constant for the A310 impeller with increasing tank size.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 255
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 357-362 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: When a fluidizing gas is switched from a low-density gas to a high-density gas, particles in the emulsion phase agglomerate and bubbles disappear. At the same time, channeling occurs and a decrease in the pressure drop over the bed is observed. The disturbance of fluidization is temporary, and normal fluidization is restored after several minutes. The study of mechanisms of the transient phenomena shows that the difference in diffusion rates of the two gases in the emulsion phase caused the agglomeration of particles. Because the mobility of particles was reduced, channels were formed and the fluidizing gas bypassed through them. Effects of the properties of the fluidizing gases and particles on the intensity of the transient phenomena were also studied. The intensity increased with increasing difference in the densities of the two gases. The transient phenomena were considerable for small- and light-particle systems.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 256
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 398-408 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Vacuum membrane distillation is a membrane-based separation process considered here to remove volatile organic compounds from aqueous streams. Microporous hydrophobic membranes are used to separate the aqueous stream from a gas phase kept under vacuum. The evaporation of the liquid stream takes place on one side of the membrane, and mass transfer occurs through the vapor phase inside the membrane. The role of operative conditions on the process performance is widely investigated in the case of dilute binary aqueous mixtures containing acetone, ethanol, isopropanol, ethylacetate, methylacetate, or methylterbutyl ether. Temperature, composition, flow rate of the liquid feed, and pressure downstream the membrane are the main operative variables. Among these, the vacuum-side pressure is the major design factor since it greatly affects the separation efficiency. A mathematical model description of the process is developed, and the results are compared with the experiments. The model is finally used to predict the best operative conditions in which the process can work for the case of benzene removal from waste waters.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 257
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 374-387 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The attainable region approach for reaction - mixing systems is combined with geometric methods for the feasibility of separations. The result is a systematic approach to identify the feasible compositions that can be achieved in processes combining simultaneous reaction, mixing, and separation. An activity-based formulation for both nonideal VLE and reaction-rate expressions is applied to develop hybrid reactor-separator models for the multiphase CSTR and PFR with simultaneous vapor removal. A reaction-separation vector is defined that satisfies the same geometric properties as the reaction vector. Therefore, the attainable region can be constructed following the existing procedure for reaction-mixing systems. This approach provides a method to generate feasible process alternatives. The technique is demonstrated on two nonideal ternary mixtures: the production of dimethyl ether by dehydration of methanol, and the production of methyl tert-butyl ether from isobutene and methanol. It is shown that for hybrid reaction-separation devices the entire composition space is not always attainable. In such cases, combining a hybrid device with traditional nonreactive separation is required to attain certain products.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 258
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 448-463 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Continuous solution copolymerization is an important industrial process in the manufacture of commodity and engineering plastics. The addition of comonomers and solvent, and the rate of heat exchange must be simultaneously manipulated to maintain safety, operability, and the product quality adequately, yielding a process with nonlinear behavior, strong and asymmetric input-output multivariable coupling, and potential for open-loop instability and state multiplicity, as shown in earlier dynamics and control studies. Accordingly, the key control objectives of the copolymerization reactor are: the compensation of interaction, the preclusion of input multiplicity and the robustness (i.e., tolerance to modeling and tuning errors) of the controller. In principle, these control issues should be considered within a nonlinear setting. Otherwise, the reactor may have to be operated with a conversion that is conservatively below what can be handled by standard mixing and heat-exchange equipment. To assess the inherent control possibilities and limitations of a given copolymerization reactor, a methodology to address the control problem is proposed such that the nonlinearity, interaction, input multiplicity, and robustness issues are explicitly confronted. The result is a linear multivariable interaction compensator whose tuning can be done with notions and tools from conventional control. This method is tested with the copolymerization of vinyl acetate with methyl methacrylate, dissolved in ethyl acetate.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 259
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The low-temperature oxidation chemistry of linear and branched alkanes is discussed with the aim of unifying their complex behavior in various experimental systems using a single detailed kinetic model. New experimental data, obtained in a pressurized flow reactor, as well as in batch- and jet-stirred reactors, are useful for a better definition of the region of cool flames and negative temperature coefficient (NTC) for pure hydrocarbons from propane up to isooctane. Thermochemical oscillations and the NTC region of the reaction rate of the low-temperature oxidation of n-heptane and isooctane in a jet-stirred flow reactor are reproduced quite well by the model, not only in a qualitative way but in terms of the experimental frequencies and intensities of cool flames. Very good agreement is also observed for fuel conversion and intermediate-species formation. Irrespective of the experimental system, the same critical reaction steps always control these phenomena. The results contribute to the definition of a limited set of fundamental kinetic parameters that should be easily extended to model heavier alkanes.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 260
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1309-1318 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The substitution reaction of hexachlorocyclotriphosphazene, N3P3Cl6, with phenol was performed to synthesize the partially substituted (phenoxy) chlorocyclotriphosphazenes, N3P3Cl6 - i(OC6H5)i, i = 1 - 6 by phase-transfer catalysis (PTC) in an organic phase/alkaline solution. The steric hindrance effect plays a crucial role in this reaction. The reaction system was controlled by both chemical kinetics and mass-transfer effects. The mass transfer of the catalyst between two phases was investigated by a pseudosteady-state liquid-liquid PTC (LLPTC) model. Also, the intrinsic reaction-rate constants of the series substitution and the overall mass-transfer coefficient of the catalyst from the organic phase to the aqueous phase were determined by a combined model. In addition, the corresponding energies, enthalpies, and entropies of activation of the series substitution were also estimated.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 261
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1357-1361 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 262
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1390-1402 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Liquid circulation in bubble columns influences many system properties such as mass transfer and catalyst dispersion. Conditions favorable for liquid circulation often exist only for highly turbulent slurries. Experiments under conditions of lowered surface tension proved conclusively that uniform circulation can exist even in the bubbly-flow regime. Moreover, the measured circulating velocity profile is more plug-shaped in the center core than traditional models, which take a parabolic shape. These observations led to the application of a circulation theory based on an energy-dissipation model for turbulent eddy viscosity, which can be easily computed as a simple function of superficial-gas velocity. Two length scales were used in model calculations depending on flow regime: bubble diameter for bubbly flow and column diameter for churn turbulence. The liquid-velocity profile contained a tuned dimensionless proportionality constant, which resulted in two different average values, k = 2.51 for bubbly flow and 0.0242 for churn turbulence, when tuned to experimental data. The integral average eddy viscosity is numerically equivalent to the eddy dispersion coefficient for bubbly flow. Predicted liquid velocity compared very favorably with new measured values under conditions of low surface tension and with literature values.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 263
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 598-608 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The traditional way of determining the slip velocity of molten polymers is the classic Mooney technique, which utilizes experimental data obtained from a capillary rheometer. However, measurements of the rheological properties of polymer melts in capillary flow at high shear rates are often complicated by viscous heating, which is not taken into account by this method. A data analysis procedure based on a mathematical model for nonisothermal capillary flow of molten polymers is developed. Conduction, convection, and viscous heating are included, together with the effect of wall slip. The technique provides detailed velocity and temperature fields in the die, and can be used to determine the slip velocity at high shear rates corrected for the effect of viscous heating. It is tested for the capillary flow of several polymers, including polystyrene, polypropylene, high-density, and linear low-density polyethylenes.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 264
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1448-1457 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A revised machine learing methodology is applied to a simulated crystallization process flowsheet for continual imporvement of its performance by generating and analyzing process data. The aim is to identify bands of crucial decision variables leading to zones of best average process performance. The methodology comprises two components: symbolic induction and case-based reasoning. It uses an incremental algorithm to update performance classification rules, which not only improves the efficiency of the symbolic induction of the classification rules by eliminating the need for their periodic reinduction, but also simplifies the case-based reasoning step. The new concepts and procedures are illustrated by application to a potassium nitrate crystallization process comprising a mixed-suspension, mixed-product-removal crystallizer, a hydrocyclone, and a fines dissolver, By identifying and establishing ranges for the most crucial decision variables, namely, feed concentration, flow rate, and cooling stream temperature, three zones leading to an improvement of nearly 12% on nominal average performance are detected within two generations of the classification rules.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 265
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1559-1568 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Thermochemical data of mineral oil fractions are scarce. Due to the complex structure of natural hydrocarbon mixture, standard heat and Gibbs free energy of formation depend on the sample. A procedure for predicting these properties is presented. Both properties depend on the hydrocarbon type and on its molecular weight. The double-bond equivalent (DBE) and the number of olefinic double bounds are the important characterization parameters of the model. DBE can basically be calculated from molecular weight and elemental composition. Alternatively, boiling point and atomic H/C ratio can be used if the model is applied to mineral oil fractions from which boiling curves can be obtained. A criterion for testing the reliability of the estimated DBE value is available, because DBE is also a function of structural group distribution.The relevance of the DBE concept is shown with regard to hydroprocessing of mineral oil fractions. The model can be applied to total average molecules as well as to an arbitrary number of pseudocomponents and continuous mixtures. The difference between feed and product DBE is equivalent to the amount of hydrogen consumed for hydrogenation of unsaturated hydrocarbons. Further properties of the product can be predicted.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 266
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1569-1578 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: For the first time, a model for dynamic adsorption and tension of diffusion-controlled systems has been extended to binary premicellar mixtures of nonionic surfactants of different adsorption capacities and nonideal interactions in the monolayer. Local equilibria between subsurface concentrations and adsorbate densitities are modeled using the nonideal adsorbed solution theory, which describes these two elements. The model shows that larger molecules (those with the smaller adsorption capacity) tend to be preferentially adsorbed at low times, if they have equal adsorption equilibrium constants and diffusivities, and smaller moleules at longer times. This adsorption selectivity is reduced when larger molecules have a much larger adsorption equilibrium constant, or when there are negative deviations from ideality in the monolayer. This model's predictions are compared to tension data for two nonionic surfactants, C12E5 and Triton X-100, at 25°C. The data are represented well by the diffusion-controlled model with a finite diffusion-layer thickness, which describes the faster decrease in tension observed with the bubble surfactometer, compared to data with other techniques. With this model, surface coverages and concentration profiles are calculated, thus elucidating the adsorption selectivity of molecules of different adsorption capacities. Synergistic effect in dynamic tension and adsorption can be predicted. Mild synergism in dynamic tension lowering by the preceding nonionic surfactants is also observed.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 267
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1597-1604 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Hartree-Fock theory and density functional theory were used to compute the enthalpy and entropy changes of dimerization for a number of hydrogen-bonding compounds. In Part 1, the calculational methods and procedures use for the water dimer are described, and the results obtained are compared with those of others and with experimental estimates in the literature. Here, a variety of organic compounds that can self associate and/or cross associate are considered. The results obtained for the self-association of these compounds are compared with estimates obtained from various types of experimental data. The results are also used to examine the validity of group-contribution methods for hydrogen-bonding mixtures and to test a simple estimation procedure for cross dimerization that can reduce the number of calculations, such as those described here, that need to be done.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 268
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1611-1626 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A comprehensive composite database for distillation sieve-tray efficiency is used to develop point efficiency and entrainment correlations based on a model that considers the fluid on the distillation tray to be contained in a liquid-continuous region near the tray deck and a vapor-continuous region on top of the liquid-continuous region. This model allows estimates of the portion of the mass transfer that occurs in each region and the mass-transfer resistance that occurs on the liquid side and vapor side of the interface. For most cases, most of the mass transfer occurs within the liquid-continuous region. The liquid side resistance is often significant.The entrainment correlation is consistent with the work of Bennett et al., which relates entrainment to the ratios of the liquid to vapor density and the froth height to the tray spacing. A simple liquid continuous-only mass-transfer model containing only four empirical parameters correlates the point efficiency data to within 6.4%. Despite a twofold change in vapor Schmidt number, no dependency on vapor Schmidt number is seen. Important dimensionless groupings are the Reynolds number based on the hole velocity, effective froth density, ratio of the liquid inventory to the perforation diameter, and fraction of the tray area perforated. Mathematically simple and accurate methods allow the prediction of the section efficiency for trays operating in cross or parallel flow. They address vapor and liquid mixing, entrainment and a criterion to avoid significant degradation of the tray efficiency due to weeping.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 269
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1641-1648 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 270
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1649-1651 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 271
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1653-1661 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Pulsed magnetic field gradient stimulated echo NMR measurements are performed for diffusion and flow of an aqueous phase both within a sample of packed spherical beads and within a 25% porosity Fontainebleau sandstone. The stimulated echo dependence on the gradient pulse area q is used to derive the displacement probability distributions PΔ(X) for fixed observation times Δ. The shape of PΔ(X) as a function of Δ is simulated for computer-generated porous media, and a good agreement is obtained between the experimental NMR data and the simulations.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 272
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1675-1683 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: In gas-liquid flows through tee junctions, because of the difference in inertia between the phases, the flowing mass fractions for an individual phase at the outlet sides differ from those at the inlet. This phase separation is an important consideration in delivering fluids and energy through pipe networks in the power and process industry. In this work, air-water and steam-water flows through branching and impacting tee junctions are considered. Under certain conditions (when the volumetric fraction of the liquid drops does not change appreciably and their bulk density is much higher than the gas density, and when the flow rates and/or the gas volumetric fraction are high), these flows can be approximated as irrotational flows of incompressible, inviscid fluids and are amenable to potential flow methods, for example, conformal mapping. For the general case of gas-liquid flows through a branching or impacting tee, a CFD code is utilized to conduct transient flow simulations. Predictions of phase separation for both types of tee junction agree well with experimental data.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 273
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 761-776 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Experimental breakthrough results of methane, ethane and propane in activated carbon and silica gel obtained over a wide range of gas compositions, bed pressures, interstitial velocities, and column temperatures were analyzed using a dynamic, nonisothermal, nontrace column breakthrough model. A linear driving force (LDF) approximation is used for particle uptake, and the Langmuir-Freundlich isotherm represents adsorption equilibrium. The LDF mass-transfer-rate coefficient (and, hence, effective particle diffusivity) and column-wall heat-transfer coefficient were determined. The results show that hydrocarbon transport in the activated carbon particles used is essentially by Knudsen and surface flow, while for the silica gel used the transport is primarily by Knudsen flow. For activated carbon, the experimentally derived LDF coefficients for all three sorbates are well correlated using an average effective diffusivity value. With regard to heat transfer, the column-wall Nusselt number is approximately constant for the range of Reynolds numbers considered. Simulations of multicomponent breakthrough in the activated-carbon bed based on independently measured single-component kinetic parameters and the extended Langmuir-Freundlich isotherm agree very well with experimental results. The computational efficiency gained by adopting the simpler extended Langmuir isotherm model is also investigated.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 274
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 785-791 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A novel approach for stabilizing the intermediate steady state of a continuous stirred-tank reactor (CSTR) is proposed by using a special type of periodic forced operation, the so-called mediating operation. The mediating operation enables new additional steady states for which one of the new intermediate steady states is stable to be produced. Thus the proposed approach employs a periodic forcing for stabilization of a selected steady state by control of a steady-state multiplicity. The feed flow rate is considered to be a manipulated variable. Changing CSTR multiplicity is investigated for two-step control inputs. It is shown, analytically, that under two-step control CSTR can exhibit at most five steady states with a stable intermediate steady state. A constructive procedure is proposed for finding control parameters corresponding to maximal multiplicity, that is, for stabilizing an intermediate steady state by two-step control.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 275
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 802-810 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Polymer degradation occurs when macromolecular chains are broken under the influence of thermal, mechanical or chemical energy. Chain-end depolymerization and random- and midpoint-chain scission are mechanisms that have been observed in liquid-phase polymer degradation. Here we develop mathematical models, unified by continuous-mixture kinetics, to show how these different mechanisms affect polymer degradation in solution. Rate expressions for the fragmentation of molecular-weight distributions (MWDs) govern the evolution of MWDs. The governing integrodifferential equations can be solved analytically for realistic conditions. Moment analysis for first-order continuous kinetics shows the temporal behavior of MWDs. Chain-end depolymerization yields monomer product and polymer molecular-weight moments that vary linearly with time. In contrast, random- and midpoint-chain scission models display exponential time behavior. The mathematical results reasonably describe experimental observations for polymer degradation. This approach, based on the time evolution of continuous distributions of chain length or molecular weight, provides a framework for interpreting several types of macromolecular degradation processes, particularly how bimodal MWDs can evolve during degradation.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 276
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1627-1636 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Supercritical water oxidation of isopropyl alcohol was investigated in a pilot-scale reactor. A computational fluid-dynamics model developed reveals the detailed flow field, chemical-component distribution, temperature distribution, and salt-particle trajectories in the reactor flow domain. The near-wall fluid temperature from the numerical analysis was compared with experimental temperature data. The temperature comparison was within a 3% error band. The effect of the chemical kinetic rate was investigated for four different rates. Turbulent salt-particle trajectories were also calculated to investigate the effect of particle sizes on salt deposit on the wall. Also, a method of calculating the adiabatic reaction temperature was developed to estimate reaction temperatures prior to a full numerical simulation.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 277
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1637-1640 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 278
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1180-1189 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Accurate detection of minimum liquid fluidization is essential to the successful operation of gas-liquid-solid fluidized beds, especially when particle or liquid properties evolve. A gas-liqid-solid system of 3-mm glass beads exhibits three distinct flow regimes as the liquid velocity is increased: compacted, agitated and fluidized-bed regmes. Measurements showed that the bed is not fluidized in the agitated bed regime. Pressure gradient and bed height measurements do not provide the minimum liquid fluidization velocity; instead, they offer the velocity between the compacted and agitated bed regimes. Time-averaged signals are not reliable for determining the minimum liquid fluidization velocity. It can be obtained from the standard deviation, the average frequency, the Hurst exponent and the V statistic of the cross-sectional average conductivity, which can be measured under many industrial conditions.
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 279
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1227-1241 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: An application of wavelets and multiresolution analysis to density estimation and process monitoring is presented. Wavelet-based density-estimation techniques are developed as an alternative and superior method to other common density-estimation techniques. Also shown is the effectiveness of wavelet estimators when the observations are dependent. The resulting density estimators are then used in defining a normal operating region for the process under study so that any abnormal behavior by the process can be monitored. Results of applying these techniques to a typical multivariate chemical process are also presented.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 280
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1319-1324 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The Ergun equation based on the effective spherical diameter is universally valid for various shapes of granular packings. It, however, was derived from the assumption of infinite tube-to-particle diameter ratio without considering the wall effect. Although some improvements were made by Mehta and Hawley (1969) to correct this, the application of the Ergun equation is still restricted to cylindrical columns with a packing porosity of less than 0.5. To modify the Ergun equation to noncylindrical flow space with or without a wall, it was substituted into the empty tube pressure drop equation by introducing an effective tube diameter so that the pressure drop can be predicted just from the free flow space and the wetted area involved. This treatment offers the basis for a new method in velocity distribution prediction.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 281
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2343-2352 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: This work determines the rate constant of hydrogen peroxide decomposition in supercritical water. Experiments were conducted at pressures ranging from 5.0 to 34.0 MPa and for temperatures up to 450°C. The rate of the homogeneous decomposition reaction is distinguished from the rate of the catalytic decomposition on the reactor surface by conducting experiments at different surface-to-volume ratios. The rate constant of H2O2 decomposition follows the expression k(s-1) = 1013.4 ± 1.2 exp[(- 180 ± 16 kJ/mol)/RT], providing a higher value than that derived from RRKM calculations. Comparison between experiments at supercritical conditions (P = 24.5 and 34.0 MPa) and experiments in high-pressure steam (P = 5.0 and 10.0 MPa) show that the efficiency of the catalytic surface reactions decreases significantly under supercritical conditions. The rate constant just mentioned was incorporated into a methanol oxidation model and the new prediction is compared with the experimental data of Rice et al. (1996), showing a distinct improvement compared to the original prediction.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 282
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2359-2367 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: When a supercritical (SC) solution infiltrates through micropores, its pressure will fall off considerably along the flow direction, and significant solute supersaturation can be obtained inside the pores. Thus the solid solute can deposit onto the pore surface due to nucleation. The supercritical solution infiltration (SCSI) method was applied to modify porous ceramic membranes. A mathematical model was used for the membrane poresize change during the SCSI process. Numerical solution of this model showed that for a membrane with initial pore-size distribution (PSD), its average pore size could be increased or decreased due to dissimilar kinetics of the solute precipitation under different conditions, α-Al2O3 microfiltration membranes were modified by the SCSI method using SC solution of the aluminum isopropoxide/propane system under different conditions. The PSD change was determined for the modified membranes after hydrolysis and sintering. With the reduction in permeability, the average pore size was reduced when the process conditions were more favorable for homogeneous nucleation and increased under the opposite conditions. Experimental results qualitatively coincided with those by the proposed model.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 283
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2381-2384 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 284
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 3257-3259 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 285
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 3042-3058 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Polymer reactor control problems often lack frequent measurements of polymer properties, while other reactor environment measurements, such as temperatures, are readily available. The experimental application of a new estimator for handling such multirate measurement systems is presented. The estimator, in conjunction with a detailed nonlinear model and all measurements at their respective sampling rates, is able to provide frequent predictions of the process variables related to the quality (weight-average molecular weight) and quantity (monomer conversion) of the polymer product. The experimental application of a multivariable, nonlinear model-based predictive controller using reactor temperature and initiator flow rate as the manipulated variables for controlling weight-average molecular weight and monomer conversion is presented. The control strategy is designed to handle control nonaffine systems (nonlinear in the manipulated variables), while allowing for the incorporation of rate and amplitude constraints on the manipulated variables. A continuous methyl methacrylate solution polymerization pilot plant was used for the experiment.
    Zusätzliches Material: 23 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 286
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 3095-3104 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A mathematical model for a catalytic membrane reactor for oxidative coupling of methane (OCM), in which the membrane acts as an oxygen distributor to a bed of catalyst, is presented. From experimental data obtained using several silica membranes impregnated with Li and/or Na, which were prepared by the sol-gel method using alumina supports, the catalytic activity of the membrane was included in the so-called real membrane reactor (RMR) model. Then, the RMR performance was compared with that of the ideal membrane reactor (IMR), whose membrane was supposed to have no activity for the OCM and with experimental data obtained in membrane reactors. Since the membrane activity was implemented in the RMR model, for the first time in the literature, maxima in the hydrocarbon selectivity-methane conversion curves were predicted in agreement with previous experimental trends. Besides, the IMR performance was compared with that of the fixed-bed reactor (FBR), giving the maximum improvement of a membrane reactor over the FBR. Key factors for the future improvement of the performance in this kind of membrane reactor are deduced from these simulations.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 287
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997) 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 288
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 3133-3146 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: In slide coating of photographic films, liquid layers flow down an inclined plane, across a small gap under a pressure differential (vacuum), and onto a fast-moving substrate. Process interruptions to allow splices of adjoining rolls of substrate to pass through the coater result in significant waste. Coating over splices fails due to air entrainment and/or two free-surface flow instabilities during the necessary gap widening: (1) standing waves (ribbing) or rupture of the liquid bridge when vacuum is kept high or (2) lateral contraction when vacuum is lowered. The problem of coating over splices is solved here by reducing it to a fluid-mechanical stability problem. First, air entrainment was eliminated by serrating the splice trailing edge and lateral contraction by prewetting the substrate with liquid streams. Avoiding rupture of the liquid bridge then reduces the problem to finding the vacuum at which the bridge becomes unstable to small disturbances. This “critical” vacuum is found by finite-element stability analysis of the quasi-steady 2-D free-surface flow to small 2-D and 3-D disturbances, direct tracking of critical points, and verification by solving the transient 2-D skip-out process. Three modes of failure are predicted if the vacuum is not sufficiently reduced with gap widening. Implementation of a computed vacuum strategy in a production line gave sufficient latitude for coating over imprecise splices.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 289
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 3215-3222 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Depletion and structural interactions between dilute, large, nearly hard-sphere colloidal particles in a fluid dispersion containing much smaller nearly hard spheres were investigated as a function of small-particle concentration in sedimentation experiments. It shows that low concentrations of fine particles can destabilize larger particles due to the attractive depletion forces, while at higher concentrations of small particles, the surface-induced structural forces prevent large-size particles from approaching each other and thereby stabilize the large-particle suspension. A theoretical model based on the Ornstein-Zernike method was used to calculate the interparticle interactions in a bidis-persed colloidal system in which small particles are polydispersed. The theoretical re-sults explain the experimental observations.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 290
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 3260-3263 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 291
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2636-2640 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 292
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2616-2623 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Electrostatic adhesion processes are used in preparing composite aerosol particles with the electrostatic adhesion force acting between electropositively-charged and electronegatively-charged particles. This process enables one to disperse the core and subcomponent particles more uniformly and to control the amounts of subcomponent particles adhered to the surface of individual core particles by adjusting the charging voltage. Using the composite particles prepared by the electrostatic adhesion process as a starting powder for sintering, a composite bulk body of the Ba2YCu3O7-X oxide superconductor with BaZrO3 inclusions is produced. BaZrO3 particles with diameters less than 100 nm are uniformly dispersed in the Ba2YCu3O7-X matrix. The composite bulk body shows improvement in critical current density, which is based on the uniform dispersion of fine BaZrO3 particles as magnetic flux pinning centers. These advantages are attributed to the uniform dispersion of BaZrO3 over the whole starting powder.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 293
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 419-424 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The separation of air for nitrogen production can be carried out by pressure-swing adsorption over a carbon molecular sieve. The separation is kinetically based, since the equilibrium adsorption of both oxygen and nitrogen is very similar, but the oxygen is adsorbed faster. Several theoretical and experimental studies have been reported, but mainly dealing with nitrogen purities below 99.9%. The objective of this article is to study experimentally the effect of different process variables on the performance of a rate-induced PSA process in the high-purity region. The effect of cycle time on both the yield and the specific product per unit cycle become more significant as the purity increases. On the other hand, the specific feed per unit cycle is almost insensitive to product purity, particularly as the cycle time increases. These results agree very well with predictions from a theoretical model.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 294
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 464-474 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Rate parameters and gradient correlations of proteins are very important to engineering investigations of gradient-elution chromatography. Before carrying out computer simulations for gradient process, these rate parameters and gradient correlations must be determined from experimental data. This work presents a systematic method for estimating and determining these parameters and correlations using experimental data and computer-simulation results based on isocratic runs. The values determined were then employed in gradient-elution studies by putting them into the rate model to perform computer simulations. Experimental runs under gradient conditions using the parameters and correlations just referred to were carried out in a DEAE Sepharose CL-6B ion-exchange chromatography. Comparisons between the experimental data and the simulation results show good agreement.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 295
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 902-912 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Simple first-order closure models for covariances of concentration fluctuations, for use in modeling turbulent flow reactors, were tested by direct numerical simulations. Concentration covariances and other statistical functions were evaluated for a series parallel reaction scheme in decaying, homogeneous turbulent flow. The simulations involve solving the unsteady Navier-Stokes and mass conservation equations by a pseudo-spectral method in a 643 wavenumber domain, with initially segregated reactants, for an initial turbulence Reynolds number of 29.9. Simulation results show that covariances of concentration fluctuations normalized with respect to mean concentration values are almost constant and that the time dependence of concentration covariances can be estimated if the mean concentrations are known at any one time after the initial time. Predictions of the first-order closure models of Bourne and Toor, Brodkey and Lewalle, Li and Toor, and Dutta and Tarbell were compared to simulation results. While none of these closures are satisfactory for all the conditions tested, the Brodkey-Lewalle closure agrees best with the simulations.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 296
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 959-970 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The application of electric fields can be a very effective means of removing deposits from membrane surfaces. Such a means of process improvement has usually been applied to cross-flow filtration, allowing efficient operation at low cross-flow velocities. In the limiting case of dead-end filtration (zero crossflow) it is possible to use electric-field pulses to release the filter cake for collection. Experimental data are presented for the dead-end ultrafiltration of silica colloids and the protein bovine serum albumin and for the dead-end microfiltration of titania dispersions taking as variables the magnitude of the applied field, the pulse interval, the pulse duration, and the feed conditions (pH, ionic strength, concentration). The data identify the conditions when pulsed electric fields can be used as an efficient means of releasing filter cakes for collection. A force balance model is developed to predict the filtration rate at the end of the release process, taking into account electrophoretic, electroosmotic, and hydrodynamic forces. The model shows excellent agreement with the experimental data for ultrafiltration and reasonable agreement with the experimental data for microfiltration. The use of pulsed electric fields to release filter cakes in dead-end membrane processes is a promising technique that is most likely to find application in the clarification of process feeds containing low dispersed solutes.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 297
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1032-1040 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: For the simulation and optimization of large-scale chemical processes, the overall computing time is often dominated by the time needed to solve a large sparse system of linear equations. A new parallel frontal solver that can significantly reduce the wallclock time required to solve these linear equation systems using parallel/vector supercomputers is presented. The algorithm exploits both multiprocessing and vector processing by using a multilevel approach in which frontal elimination is used for the partial factorization of each front. Results of several large-scale process simulation and optimization problems are presented.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 298
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: In this work, on-line calorimetry was used to estimate the conversion and the copolymer composition in emulsion polymerization systems. Real-time feedback control of the polymer composition during the semibatch emulsion copolymerization of vinyl acetate and butyl acrylate was carried out. Both homogeneous copolymers and copolymers with previous defined composition profiles were obtained. It was shown that the feedback control was able to avoid monomer accumulation in the reactor, and hence potentially dangerous thermal runaways, without any deleterious effect on the polymer composition, when a sudden inhibition was caused by deliberately adding a solution of hydroquinone. The use of feedback control for the maximization of the production rate under safe conditions in the unseeded emulsion copolymerization of vinyl acetate and VeoVa10 (an alkyl vinyl ester from Shell) is also presented.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 299
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1125-1140 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Expression of the time-averaged equations for the conservation of momentum and energy in terms of the fractions of the local shear stress and heat flux density, respectively, due to turbulence is shown to result in greatly simplified representations for fully developed flow and convection in round tubes and parallel-plate channels as compared to those in terms of the eddy viscosity, eddy conductivity, or mixing length. On the other hand, the turbulent Prandtl number is shown to be a fundamental characteristic of flow and convection rather than simply an artifact of the eddy diffusional model. The new simplified representations provide the basis for improved predictions of the velocity distribution, the friction factor, the temperature distribution, and the Nusselt number. The adaption of these new representations for other geometries and for developing convection is discussed briefly.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
  • 300
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1141-1152 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A dynamic model has been developed to predict the transient behavior of the temperature, the heat removal rate by the in-bed heat exchanger, and the flue-gas oxygen concentration for a circulating fluidized-bed (CFB) combustor. The model was incorporated into a control simulator to reproduce the combustion process within the overall program. The simulator predicts the behavior of the combustor under manual or automatic control to allow testing of control strategies. The model is validated by comparison with step-response tests carried out on a pilot CFB combustor. Discrepancies are attributable to unmodeled disturbances. Further validation, necessary to ensure the applicability of the simulator to control development, is provided by comparing control models identified experimentally using the pilot CFB to those obtained by simulation. Favorable comparison suggests that the dynamic model is suitable for use in control simulation.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
Schließen ⊗
Diese Webseite nutzt Cookies und das Analyse-Tool Matomo. Weitere Informationen finden Sie hier...