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  • Chemistry  (10,474)
  • Inorganic Chemistry  (602)
  • 1995-1999  (10,474)
  • 1950-1954
  • 1996  (10,474)
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Publisher
Years
  • 1995-1999  (10,474)
  • 1950-1954
Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of science education and technology 5 (1996), S. 193-201 
    ISSN: 1573-1839
    Keywords: Chemistry ; chemistry education ; multiple intelligences ; imagery ; visual-spatial thinking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Natural Sciences in General , Technology
    Notes: Abstract Chemistry has evolved from a science dominated by mathematics into a science highly dependent on spatial-visual intelligence. Yet the chemical content of introductory courses remains taught essentially the same as 40–50 years ago. Chemistry, today, is recognized by chemists as the molecular science. Yet, school chemistry is alienated from that perception. Thanks to the computer, young people are more comfortable with visual imaging than their instructors were at the same age. Thus the time is rife to reinvigorate chemistry education by means of the visual-spatial approach, an approach wholly in conformance with the way modern chemistry is thought about and practiced.
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  • 2
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 10-22 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Formation of asphalt aggregates and their deposition on the pore surfaces of a porous medium, which alter the structure of the medium and its effective properties, is a critical problem to catalytic and oil recovery and refinery processes. Extensive new experimental data for the amount of precipitated asphalt formed with crude oil and various solvents are presented. Results indicate that, contrary to the previous assumptions, asphalt formation is at best partially reversible. A thermodynamic model based on the Flory-Huggins theory of polymer solutions is used, together with the Soave equation of state, to predict the data. Critical evaluation of the model shows that its predictions do not agree well with our data. As an alternative, we propose a new model that employs a scaling equation, somewhat similar to those encountered in aggregation and gelation phenomena. The scaling function takes on a very simple form, and its predictions are in very good agreement with the data. It also predicts that the onset of precipitation may obey a simple universal equation.
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  • 3
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 55-67 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The competition between drying and reactions in a liquid coating containing precursors to a random network polymer can give rise to a variety of drying phenomena. Solidification, or gelation, of the polymer may occur before, after, or during the removal of solvents from the coating. Rates of drying and reaction are probed by solving the equations of mass transfer by diffusion along with chemical reaction in one dimension. Solutions to this system of equations are obtained by Galerkin's method with finite-element basis functions and entail large-scale computation. Skinning, or solidification at the surface of the coating while the bulk is still liquid, occurs in thick coatings when the diffusional resistance to drying is significant, that is, at high mass-transfer coefficients. Homogeneous solidification occurs in thin coatings at low mass-transfer coefficients. Drying regime maps represent these solidification phenomena as regions in parameter space.
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  • 4
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 96-130 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Recent and ongoing research in the distillation of nonideal mixtures is reviewed focusing on advances in the methodologies for the synthesis, design, analysis and control of separation sequences involving homogeneous and heterogeneous azeotropic towers. Maps of residue curves and distillation lines are examined, as well as geometric methods for the synthesis and design of separation sequences, trends in the steady-state and dynamic analysis of homogeneous and heterogeneous towers, the nonlinear behavior of these towers, and strategies for their control.Emphasis is placed on the methods of computing all of the azeotropes associated with a multicomponent mixture, on the features that distinguish azeotropic distillations from their zeotropic counterparts, on the potential for steady-state multiplicity, and on the existence of maximum and minimum reflux bounds. Important considerations in the selection of entrainers are examined. For the synthesis of separation trains, when determining the feasible product compositions, the graphical methods are clarified, especially the conditions under which distillation boundaries can be crossed and bounding strategies under finite reflux. The application of geometric theory to locate the fixed points, at minimum reflux, is reviewed in connection with homotopy-continuation algorithms for this purpose. The use of homotopy-continuation algorithms, especially for the steady-state simulation of heterogeneous azeotropic distillations, is justified. Methods for phase stability analysis are reviewed in connection with the location of real bifurcation points at phase transitions, an important feature of algorithms for the dynamic simulation of heterogeneous azeotropic distillations.
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  • 5
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 187-203 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Discrete-time nonlinear feedback control laws are derived for multivariable nonlinear processes, whose “delay-free” parts are minimum phase. These include mixed error-and state-feedback, error-feedback, and mixed error- and output-feedback laws, which can induce linear input-output closed-loop response. This study is carried out within the framework of the discrete-time globally linearizing control. The broader class of nonlinear processes, in which controlled outputs as well as some other process variables are measured, are also considered. A mixed error- and output-feedback control law is derived for this class of processes. The conditions under which the mixed error- and output-feedback can be applied to a process operating at or around an open-loop unstable equilibrium point are determined. The application and performance of the derived control laws are illustrated by the numerical simulation of a chemical reactor.
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  • 6
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 214-231 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The long-time behavior of a reaction mixture containing infinitely many species in isothermal continuous stirred tank reactors (CSTRs) is analyzed and contrasted with that in a plug-flow reactor (PFR). The reaction kinetics considered are irreversible first-order, irreversible coupled pseudo first-order, and reversible first-order. Asymptotic lumped kinetics for the mixture as a whole are developed as a function of feed properties and reactor type. Such lumped kinetics in many cases are of the power law form, with the exponent for a CSTR being lower than that for a PFR. Conditions under which non-power-law kinetics arise are given. Due to the wide spread of reactor residence times, the mixture in CSTRs admits a much richer variety of asymptotic possibilities than in the PFR. The results uncover some behavioral differences and relationships between CSTRs and a PFR for converting complex mixtures such as petroleum distillates or coal liquids.
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  • 7
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 258-258 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 8
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996) 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 9
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    AIChE Journal 42 (1996), S. 319-331 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A unified network model is formulated for predicting effective Fickian diffusivities of condensable vapors in porous media where capillary condensation and adsorption-desorption hysteresis occur. The model unifies the equilibrium theory based on the poreblocking interpretation of hysteresis in the interconnected network of pores and the percolation model of mass transport in the network with randomly interspersed regions for capillary condensation and surface flow. The Bethe network is used to represent the porous medium, and the effective medium theory is employed to obtain the effective diffusivity. Using the information on the connectivity and the positions of the closure points of the hysteresis loop enclosed by the equilibrium primary adsorption and primary desorption isotherms, the concentration dependence of the effective diffusivity is predicted. The model is applied to the systems water vapor-silica gel, water vapor-activated alumina, and literature data. It successfully predicts the concentration dependence of the effective diffusivity in the whole range of relative pressures for systems both with and without a peak in the diffusivity.
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  • 10
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    AIChE Journal 42 (1996), S. 359-368 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A model of simultaneous heat and mass transfer presented describes drying with internal heat generation. Since a liquid expulsion phase is observed, a numerical procedure was developed to account for saturated and unsaturated zones and to model the liquid expulsion. The model was validated by a drainage experiment. An experimental rig was built to conduct microwave drying experiments in well-controlled conditions using capillary porous body (light concrete) as test material. Two types of drying (high and low power) were distinguished, depending on whether or not boiling occurred in the sample. The heat source term in the medium was determined from the experimental results. The numerical results agree with the experimental observations in terms of drying kinetics and transfer mechanisms. This allows a very accurate description of the transport phenomena and the liquid expulsion phase associated with high-power drying.
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  • 11
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 277-284 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 12
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    AIChE Journal 42 (1996), S. 259-268 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A simple model was developed to describe the absorption of SO2 in a circulating dry scrubbing (CDS) process, which is a semidry, lime-based, flue-gas desulfurization (FGD) process that utilizes a circulating fluidized bed arrangement for contacting a sorbent with SO2-laden flue gas under “coolside” conditions. The reaction chemistry is thought to be similar to that of spray-drying absorption. The liquid-phase mass-transfer coefficient was successfully modeled as a function of the sorbent particle spacing on the wetted surfaces. Gas-phase mass-transfer resistances were assumed to be insignificant. Due to the high surface area available in a CDS reactor, the evaporation rate of water from the slurry was modeled as “constant-rate” drying according to classic spray-dryer theory. However, the “falling-rate” and “diffusion” evaporation stages were negligible in CDS since sorbent particle bunching at the surface of the slurry is nonexistent.
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  • 13
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    AIChE Journal 42 (1996), S. 271-276 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 14
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    AIChE Journal 42 (1996), S. 298-300 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 15
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    AIChE Journal 42 (1996), S. 332-346 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The flows generated in vessels stirred by two Rushton impellers were investigated in two vessels of diameter (T) 100 and 294 mm with impellers of diameter D = T/3 using flow visualization, power consumption, mixing time, and 360° ensemble-averaged and 1° angle-resolved LDA measurement techniques. The flows depended strongly on the clearance of the lower impeller above the base of the vessel (C1), the separation between the impellers (C2), and the submergence (C3) of the upper impeller below the top of the liquid column height (H). When these distances were varied, three stable and four unstable flow patterns were observed. Comparisons between the two LDA techniques showed that while the 360° ensemble-averaged measurements are useful for characterizing the overall flow structure and turbulence levels in the vessel, care must be exercised when interpreting such data, since in the impeller region they include periodic variations in the mean velocity in addition to the turbulent fluctuations. The trailing vortex structure and flow periodicity produced by the Rushton impellers is shown to decay significantly within a cylindrical region of height 1.2D and radius 1.0D centered around the middle of the vessel, when C1 = C2 = T/3. The turbulence structure within this region is anisotropic, while outside this region it might be considered mostly isotropic. The main flow features scaled well between the vessels.
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    AIChE Journal 42 (1996), S. 369-382 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A computer-aided simulator of steady-state two-phase flow in consolidated porous media is developed. The porous medium is modeled as a 3-D pore network of suitably shaped and randomly sized unit cells of the constricted-tube type. The problem of two-phase flow is solved using the network approach. The wetting phase saturation, the viscosity ratio, the capillary number, and the probability of coalescence between two colliding ganglia are changed systematically, whereas the geometrical and topological characteristics of the porous medium and wettability (dynamic contact angles) are kept constant. In the range of the parameter values investigated, the flow behavior observed is ganglion population dynamics (intrinsically unsteady, but giving a time-averaged steady state). The mean ganglion size and fraction of the nonwetting phase in the form of stranded ganglia are studied as functions of the main dimensionless parameters. Fractional flows and relative permeabilities are determined and correlated with flow phenomena at pore level. Effects of the wetting phase saturation, the viscosity ratio, the capillary number, and the coalescence factor on relative permeabilities are examined.
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    AIChE Journal 42 (1996), S. 431-439 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The crystallization of phenanthrene from toluene with carbon dioxide as the antisolvent gas is described. In the GAS process, a pressurized gas is dissolved into a liquid solvent, where it causes a volumetric expansion and lowers the solubility of the solute. Theoretical models are presented for the liquid-phase expansion and the solubility as a function of pressure and temperature. The Nývlt theory for batch crystallization is adapted to predict the pressure profile in the crystallizer needed to maintain a constant supersaturation and growth rate. Generation of seeds is accomplished via a pressure pulse at the saturation pressure. The average particle size of the phenanthrene could be varied from 160 to 540 μm. Creation of seeds doubles the particle size and reduces the coefficient of variation significantly. The residual amount of toluene in the crystals without treatment is approximately 70 ppm. The particles are agglomerates of phenanthrene crystals.
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  • 18
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    AIChE Journal 42 (1996), S. 440-454 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The high throughput and operating cost of the reactor provide the economic incentive in considering the on-line optimization of the LDPE tubular reactor. For an on-line optimization procedure it is crucial to develop a flexible and adaptive on-line parameter estimator, which based on the appropriate measurements from the reactor will adjust certain key model parameters so that the model can capture the actual reactor operation and reliably be used for the real-time optimization of the reactor performance. Various issues involved in developing the on-line estimator for such applications as the mathematical modeling of the reactor, the selection of the adjustable model parameters and reactor measurements, the decomposition of the problem according to the characteristic time constants of various disturbances, and the efficient and robust solution of the mathematical problem are discussed. The tools developed were successfully used on an EXXON high-pressure LDPE tubular reactor. Results from the numerical experiments that are compared with scaled data from a real reactor show that the estimated temperature profiles agree remarkably with those observed at various phases of the reactor operation.
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    AIChE Journal 42 (1996), S. 595-598 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 42 (1996), S. 601-612 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A previously developed mathematical wetting model is generalized and applied to the following two closely related situations: the spreading of a liquid over a prewet solid surface and the receding contact-line motion with a microscopic residual film, remaining behind the contact line. An analytical expression for the velocity dependence of the dynamic contact angle is derived. Macroscopic characteristics (the dynamic contact angle and drag force) and the flow field corresponding to the spreading of a liquid over a wet solid surface differ considerably from those calculated for a dry surface. Under certain conditions the flow in the reference frame fixed with respect to the contact line has a region with closed streamlines. The region appears due to the flow-induced Marangoni effect, the reverse influence of the surface tension gradient along the liquid-solid interface caused by the flow on the flow, which gives rise to the gradient. The results are compared qualitatively with experimental data.
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    AIChE Journal 42 (1996), S. 683-690 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Simulated countercurrent chromatography is a continuous flow method for separation of binary mixtures or for separation of multicomponent mixtures into two fractions. Countercurrent flow is simulated by moving the feed point past several fixed adsorbent beds at a rate between the single column breakthrough time of each component. The number of columns and the location of the inlet and outlet port were varied to investigate product purity and productivity. Concentration profiles of the effluent product streams were measured. The maximum product concentration exceeds the feed concentration during part of the feed-switching cycle and drops to zero during part of the cycle. Three configurations were tested with the total number of columns varying between three and eight. For the test separation chosen, gaseous propylene and dimethyl ether on Chromosorb 101, high purity (〉 99%) product streams were obtained with an optimal four-column configuration using three desorbent streams.
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    AIChE Journal 42 (1996), S. 700-712 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The frequency response method measuring the temperature and pressure of an adsorbent sample determines the mass- and heat-transfer kinetics in adsorbents, especially in zeolites. The temperature of the sample (large crystals or monolayers of pellets) is measured by infrared detection. The main aspects of the in-phase and out-of-phase functions as given by an analytical bidispersed model are described. They depend on characteristic times related to kinetic paprameters. Experimental results on adsorption of water on NaX zeolite (crystals or pellets) show that this method allows heat transfer to be very clearly delineated from mass-transfer modes and the separation of different mass-transfer modes. For a bidispersed sample, macro- and microporous mass-transfer parameters may be obtained with the same sample. Results on a contaminated 5A zeolite-propane system show the presence of mass-transfer resistance at the pellet surface. The infrared temperature measurement associated with the frequency response appears to be powerful in determining kinetic adsorption, and gives more information than the pressure measurement.
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    AIChE Journal 42 (1996), S. 742-752 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: With the growing environmental concern, it is necessary to improve process simulation and develop design tools to account for environmental factors in the synthesis of large-scale chemical processes. A major obstacle in tackling this problem is uncertainties in some of the technical and economic parameters, which lead to uncertainties in design, plant performance, and cost estimates. Further, a conceptual process design involves the identification of an optimal flowsheet structure from many alternatives stituting the “superstructure.” Synthesis and optimization of large-scale processes involving uncertainties often require considerable computational effort. A novel algorithm presented here is based on simulated annealing for the process synthesis of large-scale flowsheets having several configurations and considers uncertainties in the process design systematically. This new “stochastic annealing algorithm,” provides an efficient approach to stochastic synthesis problems by incorporating a penalty term in the objective function and balances the trade-off between accuracy and efficiency based on the annealing temperature. It has been used to study a benchmark synthesis problem in the HDA process. Savings of up to 80% in CPU time has been achieved without significant loss of solution precision with stochastic annealing, compared to simulated annealing with a fixed sample size. It can be applied to analyze efficiently any complex process flowsheet and provide valuable insights into process feasibility based on optimal design, plant performance, and uncertainty issues.
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    AIChE Journal 42 (1996), S. 777-790 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Most advanced control applications rely on good dynamic process models. The performance of the control system depends on the accuracy of the model used. Typically, such models are developed by conducting off-line identification experiments on the process. These identification experiments often result in input-output data with small output signal-to-noise ratio, and using these data results in inaccurate model parameter estimates. Prefilters are used to separate useful information from the noise in the input-output data and to improve parameter estimates. A systematic design procedure for selecting a prefilter using discrete wavelet transforms is presented. The design procedure provides explicit information on the compromises in prefilter design, interpreted in terms of parameter variance and bias. The prefilter design procedure is then applied to identify a second-order output error model.
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    AIChE Journal 42 (1996), S. 820-828 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The new application of nuclear magnetic resonance imaging (MRI) techniques for characterizing fractures and flow in fractured media is investigated. Specifically, a relaxation-weighted imaging technique is used for selectively highlighting either fracture or porous matrix regions. Many advantages over conventional spin-density MRI techniques for characterizing fractured media are demonstrated. Its use to speed image acquisition is also demonstrated. In addition, a multislice profile imaging technique is used to investigate imbibition and drainage displacement experiments in fractured porous media. These images demonstrate that the fractures can have profound effects on the fluid distributions in multiphase flow.
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    AIChE Journal 42 (1996), S. 861-875 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A primary constituent in high-temperature (120-140°C) milk fouling residues is calcium phosphate in the form of calcium phosphate dihydrate (brushite, CaHPO4 · 2H2O) and hydroxyapatite [Ca5(PO4)3OH]. The removal of these mineral-rich deposits from stainless steel occurs by dissolution and mechanical cleaning. This research uses a novel solid scintillation technique to noninvasively and continuously investigate the removal of P32-labeled mixtures of calcium phosphate from inner surface of stainless steel tubes. The proposed mass-transfer model suggests that the film is initialy removed by dissolution, when compared to the experimental results. An alternative first-order model presented includes the effects of the solvent flow rate and solvent pH on decontamination rates. This model agrees with the experimental cleaning data over the range of pH and flow rates studied.
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    AIChE Journal 42 (1996), S. 884-888 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 42 (1996), S. 896-900 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 42 (1996) 
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    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 42 (1996), S. 927-931 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The sedimentation velocity of multiparticle suspensions was investigated experimentally for cases where the column wall is likely to have a nonnegligible effect. The experiments demonstrate that the container wall diameter influeces the falling velocity only for dilute systems, which is in contrast with a widely used, established empirical relationship.
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    AIChE Journal 42 (1996), S. 953-959 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The formation of a filter cake during mechanical dewatering (filtration and expression) of sludge is studied using one-dimensional nuclear magnetic resonance (NMR) imaging of porosity profiles. The experiments clearly showed the formation of a porosity gradient during filtration and the disappearing of this gradient during expression, forming a cake with a uniform porosity. This technique makes it possible to investigate the material behavior of the porous medium, which is needed before any model calculations can be performed. The results indicate that NMR imaging is useful in nondestructive monitoring of the filtration and expression process of sludge.
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    AIChE Journal 42 (1996), S. 973-982 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A model that makes it possible to evaluate the secondary nucleation rate in a pilot-scale industrial crystallizer is presented. It relates the secondary nucleation rate directly to the volume rate of attrition of large parent crystals. Two other terms are included in the equality, one that expresses the distribution formed by the attrition fragments, and the other that expresses a survival efficiency accounting for the percentage of attrition fragments that grow out after the attrition step. The model is further tested on a 970-L draft-tube-baffled evaporative crystallizer with ammonium sulfate as the model material used for crystallization and having an on-line crystal size-distribution measuring device.
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    AIChE Journal 42 (1996), S. 1010-1032 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A generalized modeling framework for process synthesis alternatives is proposed, based on fundamental mass/heat-transfer principles. A multipurpose mass/heat-transfer module is introduced as the building block of the framework, whereas basic block-superstructure rules (such as splitting, mixing, and bypassing) are used to develop a systematic representation of process units and process structures, conventional or not. Process synthesis procedures are explored within this modeling framework, where synthesis alternatives are not postulated as process unit networks, but explored simultaneously without predefining synthesis schemes, as combinations of mass/heat-exchange stream matches. The representation potential of this framework is illustrated with examples from unit operations, whereas synthesis example problems are presented to show the broad range of process alternatives that can be modeled, identified, and optimized.
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    AIChE Journal 42 (1996), S. 1041-1068 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The study of spatial structures in heterogeneous reactors is a challenging academic topic, revealing patterns that differ from those known to exist in reaction-diffusion systems exposed to uniform conditions, as well as a practical problem that should affect design and operation procedures of commercial reactors like the catalytic convertor. Experimental observations and mathematical models of spatiotemporal patterns in high-pressure catalytic reactors are reviewed. Patterns in high-pressure reactors, in which thermal effects provide the positive feedback, as well as the long-range communication, usually emerge due to global interaction. Patterns are classified comprehensively by considering reactors of increasing degree of complexity: a wire or ribbon exposed to uniform conditions, a globally coupled catalyst in a mixed reactor or in a control loop, and a fixed bed in which interaction by convection occurs only in one direction. Catalytic wires are not expected to exhibit sustained patterns in the absence of global interaction. Global interactions by external control or gas-phase coupling are shown experimentally and analytically to induce a rich plethora of patterns. Complex motions were simulated to occur due to the interaction of convection, conduction and reaction in a fixed-bed; only a few of these patterns were experimentally observed. Directions for future research are suggested.
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    AIChE Journal 42 (1996) 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 42 (1996), S. 2-9 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Diffusion of carbon dioxide through silicone-polycarbonate membranes containing oriented mica flakes is proportional to the square of the volume fraction of the flakes, to the square of the aspect ratio, and to the square of the cosine of the angle at which the flakes are oriented. These experiments are consistent with Monte Carlo simulations. The simulations allow investigation of more complex geometries, including other flake orientations and polydisperse flake sizes.
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    AIChE Journal 42 (1996), S. 42-54 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A laser-Doppler velocimetry (LDV) apparatus and a computational fluid dynamic (CFD) software package (FLUENT) were used to experimentally determine and numerically predict the velocities in a baffled vessel agitated by one or two 45° pitched-blade turbines. The flow characteristics in the impeller regions were measured by LDV and used as boundary conditions in the numerical computations. Turbulence effects were simulated using either the k-ε model or algebraic stress model (ASM). The CFD predictions were compared to the LDV measurements in terms of average velocities in all three directions as well as turbulent kinetic energies. Predictions based on ASM were typically in closer agreement with the experimental data than those based on the k-ε model. Flow patterns in both configurations were dominated by the axial and tangential components. The presence of the upper impeller altered the flow considerably, producing a strong vertical recirculation pattern between the impellers and significantly reducing the circulation flow below the lower impeller.
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    AIChE Journal 42 (1996), S. 87-95 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Liquid-solid fluidization characteristics of irregularly shaped Biobone particles were studied in a fluidized bioreactor column 2.35 m high and 0.1 m dia. The wet biobone particles had a density of 1,890 kg/m3. Two size ranges were studied: 1.70-2.36 mm and 1.25-2.36 mm. The Biobone is a natural cheap material composed of collagen, which is a strong protein structure, embedded with microcrystals of hydroxyapatite and calcium phosphate, and it is an excellent matrix of commercial importance used for the immobilization of enzymes, whole cells and other biocatalysts. Fluidization characteristics of Biobone particles, which include measurements of pressure drops, holdups, minimum fluidization velocities, particle entrainment, and residence time distributions at different water superficial velocities, are reported. Because of the highly irregular shape of Biobone particles, new fluidization behavior was observed, which was much different from the fluidization behavior of spherical particles reported in the literature. A new channeling index, Ic, is proposed to quantify the channeling characteristics of fluidized Biobone particles, and a new parameter, α, was developed to distinguish the transition between fixed and fluidized states of the Biobone particles.
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    AIChE Journal 42 (1996), S. 147-153 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: L-Isoleucine and the isomorphic amino acids L-leucine and L-valine serve as a model system in the examination of the effects of impurities on the purity and morphology of crystals recovered from batch crystallizations. Factors are determined that influence crystal purity and, concomitantly, crystal size and shape. Characteristics of the L-isoleucine crystal are determined by X-ray analysis and compare favorably with the literature. These and literature characteristics of L-leucine and L-valine are used in simulations to evaluate possible mechanisms by which lattice substitutions with impurities lead to size and morphological changes.
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    AIChE Journal 42 (1996), S. 154-160 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This article is intended as a complement to a recent article in this journal, “Comparative Study of Flow Schemes for a Simulated Countercurrent Adsorption Separation Process” by Ching et al. (1992). These authors carried out experiments on continuous separation of three carbohydrate mixtures with both the usual four-section scheme and a three-section scheme: fructose dextran (MW ≌ 9,400), raffinose dextran (MW = 6,000), and fructose-raffinose. These two schemes were modeled as equivalent true countercurrent systems. From the experiments and model results they conclude that the equivalent true countercurrent model is fully adapted to represent the four-section scheme, but a major discrepancy arises with the three-section scheme: the raffinate concentration is not correctly predicted.From these results it may be concluded that when a physically meaningful modeling of the equivalent true countercurrent is realized, the apparent discrepancy disappears. From another standpoint, such a mismatch between the experiments and model predictions would not have been observed with a model that considers the periodic port motion. Such a model foresees a cyclic steady state where extract and raffinate compositions vary throughout the period T; they can be considered as constant only when averaged over the period. It is worth comparing the results of these two models, especially when the equivalent countercurrent representation is not very close to the physical phenomenon it should represent.We agree with their major finding that a three-zone scheme represents necessarily a higher desorbent demand than a four-zone scheme.
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    AIChE Journal 42 (1996), S. 176-186 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A stable adaptive control strategy is suggested for a class of continuous-flow bioreactor processes described by Monod kinetics with two unknown parameters, one of which appears nonlinearly. Similarly, as in the case of the previously reported adaptive controllers, the parametrization of the process model, in conjuction with the adaptive exponential feeding strategy and corresponding adaptive algorithms, results in a stable system in which the convergence of the output errors to zero is guaranteed. In the former, however, two major problems are encountered: (1) both output errors were used to adjust the controller parameters, which may yield unacceptable performance of the resulting adaptive system; (2) conditions under which the process output can assume only positive values are difficult to derive. Hence, a design of a stable adaptive controller is suggested, whose parameters are adjusted using only one of the output errors and that yields acceptable performance of the control system. With this method, conditions under which the process outputs can assume only positive values can be readily derived. These conditions in turn guarantee that the control input saturation at value zero cannot occur. In this context, two adaptive controllers are suggested, such that the resulting adaptive systems are stable and the control objective is met. The adaptive controller design relies on a convenient coordinate transformation, while the proof of stability is based on suitably chosen Lyapunov functions. The performance of the adaptive system is evaluated through computer simulations.
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    AIChE Journal 42 (1996), S. 204-213 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Simultaneous effects of physisorption, diffusion, and reaction were characterized by dynamic experiments for propene metathesis over rhenium oxide/γ-alumina catalyst in a Berty reactor. Single-component sorption isotherms from steady-state experiments for ethene, propene, and 2-butene were used to predict multicomponent physisorption by the ideal adsorbed solution theory. Effective diffusivities were determined from molecular, Knudsen, and surface-diffusion coefficients, including bimodal pore-size effect and tortuosity factors. Transient sorption diffusion experiments were conducted with inactivated catalysts. The reaction rate expression, derived from elementary steps of carbene mechanism, was identified by solving the inverse problem with step test data. The direct problem was solved by orthogonal collocation within the method of lines. Model predictions agreed with responses from dynamic experiments carried out under conditions different from those used for estimating model parameters.
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    AIChE Journal 42 (1996), S. 239-248 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A thermodynamic framework is developed for calculating wax precipitation in petroleum mixtures over a wide temperature range. The framework uses the experimentally supported assumption that precipitated wax consists of several solid phases; each solid phase is described as a pure component or pseudocomponent that does not mix with other solid phases. Liquid-phase properties are obtained from an equation of state. Calculated wax-precipitation data are in excellent agreement with experimental results for binary and multicomponent hydrocarbon mixtures, including petroleum.
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    AIChE Journal 42 (1996), S. 269-270 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 42 (1996), S. 290-295 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 42 (1996), S. 285-289 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 42 (1996), S. 296-297 
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    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 42 (1996), S. 301-318 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experiments conducted quantify the macroscopic hydrodynamic characteristics of various scale 2-D bubble columns, which include dispersed and coalesced bubble regimes characterized by two flow conditions (4- and 3-region flow) with coherent flow structures. Hydrodynamic behavior is analyzed based on flow visualization and a particle image velocimetry (PIV) system. Columns operated in the 4-region flow condition comprise descending, vortical, fast bubble and central plume regions. The fast bubble flow region moves in a wavelike manner, and thus the flow in the vicinity of this region is characterized macroscopically in terms of wave properties. In columns greater than 20 cm in width, the transition from the dispersed bubble flow regime to the 4- and then to 3-region flow in the coalesced bubble regime occurs progressively with gas velocities at 1 and 3 cm/s, respectively. The demarcation of flow regimes is directly related to measurable coherent flow structures. The instantaneous and time-averaged liquid velocity and holdup profiles provided by the PIV system are presented in light of the macroscopic flow structure in various 2-D bubble columns. Numerical simulations demonstrate that the volume of fluid method can provide the time-dependent behavior of dispersed bubbling flows and account for the coupling effects of pressure field and the liquid velocity on the bubble motion. Comparison of computational results with PIV results for two different bubble injector arrangements is satisfactory.
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    AIChE Journal 42 (1996), S. 347-358 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The velocity and pressure fields and the effect of wall flux on these fields in a spiral channel are presented. As fluid flows inward through a spiral channel with constant gap and permeable walls, the streamwise flux decreases while the curvature increases. Thus, by balancing the stabilizing effect of wall suction with the destabilizing effect of increasing curvature, established vortices can be maintained along the spiral channel. This approach is used to prescribe spiral geometries with different wall fluxes. Using a weakly nonlinear stability analysis, the influence of wall flux on the characteristics of Dean vortices is obtained. The critical Dean number is reduced when suction is through the inner wall only, is slightly reduced when suction is equal through both walls, and is increased when suction is through the outer wall only. The magnitude of change is proportional to a ratio of small numbers that measures the importance of the effect of curvature. In membrane filtration applications the wall flux is typically 2 to 5 orders of magnitude less than the streamwise flow. If the radius of curvature of the channel is of the order of 100 times the channel gap, the effect on the critical Dean number is within 2% of the no-wall flux case. If the radius of curvature is sufficiently large, however, it is possible to observe effects on the critical Dean number that approach O(1) in magnitude for certain parameter ranges.
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    AIChE Journal 42 (1996), S. 383-390 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Multiple diffusion reactions are frequently encountered in the modeling of heterogeneous catalytic reactors. Obtaining an accurate estimate of the yield and selectivity in such reactions is crucial for an optimal design of reactors. Due to the inadequacy of analytical techniques in handling nonuniform catalyst shapes and mixed boundary conditions, numerical techniques are often employed to compute these design parameters. Among other numerical techniques, the boundary element method (BEM) is a superior method to solve linear diffusion reaction problems. The integral nature of the BEM formulation allows for boundary-only discretization of the particle, thus reducing the computer execution time and the data preparation effort. A boundary element algorithm is developed to solve a network of linear diffusion reactions in porous catalyst particles in two dimensions. For this purpose, a matrix of fundamental solutions is defined and derived. The developed algorithm is applied to complex reaction networks to obtain the yield of intermediates for nonregular catalyst shapes and nonuniform boundary conditions. The method can be used as a design tool to study particle scale modeling in detail and can be incorporated into an overall reactor model.
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    AIChE Journal 42 (1996), S. 409-421 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A novel gas purification technique called rapid pressure swing absorption (RAPSAB) was developed by integrating the best features of membrane contacting, gas-liquid absorption, and pressure swing adsorption (PSA). In this cyclic separation process, a well-packed microporous hydrophobic hollow-fiber module was used to achieve nondispersive gas absorption from a high-pressure feed gas into a stationary absorbent liquid on the module shell side during a certain part of the cycle followed by desorption of absorbed gases from the liquid in the rest of the cycle. The total cycle time varies between 20 s and upwards. Separation of mixtures of N2 and CO2 (around 10%) where CO2 is the impurity to be removed was studied using absorbent liquids such as pure water and a 19.5% aqueous solution of diethanolamine (DEA). Three RAPSAB cycles studied differ in the absorption part. Virtually pure N2 streams were obtained with DEA as absorbent demonstrating the capability of bulk separation to very high levels of purification. Numerical models developed predict the extent of purification for pure water and the DEA solution for one of the simpler cycles. Model simulations describe the observed behavior well.
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    AIChE Journal 42 (1996), S. 493-502 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Neural-network-based control schemes are generally designed by replacing standard elements of the classic control schemes by feedforward neural networks. The introduction of discrete time recurrent networks, which are inherently dynamic systems, into those schemes can simplify the design of neural controllers. The concept of applying recurrent networks in indirect adaptive control schemes is described. A combined network cluster consisting of the control network and the model network is constructed to allow the use of the real-time recurrent learning algorithm. To demonstrate the feasibility of the method two simulation examples are presented.
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    AIChE Journal 42 (1996), S. 516-523 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The one-sided single-pellet dynamic technique introduced in this article is shown to be a very effective and simple method for the analysis of adsorption and diffusion in porous solids. Moment expressions are presented for reversible and irreversible adsorption processes. Since the adsorption equilibrium constant is the only unknown parameter in the first moment expression, this parameter can be evaluated from a single set of pulse-response experiments. This technique to evaluate the adsorption equilibrium constant is illustrated using ethylbromide as tracer. It is also shown that for a very strongly adsorbing tracer, such as 1,2-dichloroethane in soil, modified moment expressions derived with a semiinfinite boundary condition are necessary unless a criterion developed in this work is satisfied.
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    AIChE Journal 42 (1996), S. 538-546 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Nuclear magnetic resonance (NMR) spin-lattice relaxation measurements are used to investigate pore structures and fluid phase distributions in porous media. A new method for estimating relaxation time distribution functions from measured relaxation data is presented using a B-spline basis to represent the distribution function and Tikhonov regularization to stabilize the estimation problem. Surface relaxivity, which is required to convert relaxation time distributions to pore-size distributions of fluid phase distributions at partial saturations, is determined using pore volume-to-surface-area ratios estimated by NMR diffusion measurements. This approach was validated by analyzing certain model porous media with known pore volume-to-surface-area ratios. The method is demonstrated by determining pore-size and fluid phase distributions of sandstone and carbonate samples, as well as by comparing the pore-size distributions of chalk samples obtained by this methodology with those estimated by mercury porosimetry.
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    AIChE Journal 42 (1996), S. 571-584 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The recently developed formalism for describing the solute-induced effect in dilute near-critical mixtures is extended to fluids composed of anisotropic molecules through the statistical mechanical interpretation of the derivative (∂P/∂x2)T,p∞ whose critical value is the Krichevskii parameter.Rigorous expressions for Henry's constant and the solute distribution factor along the orthobaric curve are derived in terms of the volumetric and entropic solute-induced local effects, and the quasi-linear behavior of their orthobaric density dependence away from the solvent's critical point is rationalized.The formalism is illustrated with integral equation calculations of the orthobaric density dependence of several solvation thermodynamic quantities for an infinitely dilute volatile solute in near-critical solutions of hard-sphere Yukawa fluids.
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    AIChE Journal 42 (1996), S. 649-659 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Drop breakup mechanisms inside a cavity flow are presented for two immiscible fluids. Due to the nonuniform flow condition of the cavity, the breakup mechanism varied along the streamlines. The streamlines were characterized by stream zones A and B, where zone A possessed a methodical transient breakup governed by Tomotika's breakup via capillary instabilities, and the breakup mechanism of stream zone B consisted of tip streaming breakup, an inefficient breakup mechanism. The flow behavior near flight region had a significant role in the drop breakup mechanisms. The study of the evolution of drop dispersion showed that the matrix viscosity is critical in controlling the transient breakup process and that the shear rate increase had little or no effect on the drop breakup.
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    AIChE Journal 42 (1996), S. 671-682 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The absorption of Cl2 into aqueous bicarbonate and aqueous hydroxide solutions was studied both experimentally and theoretically. The rate coefficient of the reaction between Cl2 and OH- was estimated over the temperature range of 293-312 K and fitted by the Arrhenius equation: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{24} = 3.56*10^{11} \exp \left({\frac{{ - 1,617}}{T}} \right) $$\end{document}.If Cl2 were assumed to react only with water and OH- in an aqueous bicarbonate solution, the predicted absorption rate would be much lower than that experimentally measured. This suggests that Cl2 reacts with HCO3- in an aqueous bicarbonate solution. The rate coefficient of the reaction between Cl2 and HCO3- was estimated over the temperature range of 293-313 K and fitted by the Arrhenius equation: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{21} = 5.63*10^{10} \exp \left({\frac{{ - 4,925}}{T}} \right) $$\end{document}.More importantly, under absorption conditions, the amount of hydroxide consumed for absorbing a specific amount of Cl2 into an aqueous hydroxide solution is almost twice the amount of bicarbonate consumed for absorbing the same amount of Cl2 into an aqueous bicarbonate solution.
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    AIChE Journal 42 (1996), S. 727-741 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new discretization procedure for the agglomeration equation is presented. The intrinsic problems caused by discretization of the particle-size distribution are mitigated by using proper probability functions. Thus, the new discretized equation predicts the same total number of particles as its continuous counterpart and guarantees conservation of mass. This general method can correctly predict any two properties simultaneously and is not limited to number and mass. Simulation results with various agglomeration kernels show that the new method provides significant improvements over the conventional discretization method. Furthermore, the new method allows the user to choose equal-size intervals or geometric-size intervals with any geometric ratio to cover the particle-size range. In addition to flexibility, the latter feature leads to better accuracy in particle-size distribution predictions.
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    AIChE Journal 42 (1996), S. 753-766 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new methodology for gage control of sheet and film processes is presented. A linear process model is developed that is capable of describing many of the interesting features of the process, including a noisy and moving gage sensor, significant process noise, strong coupling between the gage in different lanes, constraints on the actuators, and significant time delay between the actuators and the sensor. An automatic control of this process given this model form is designed. Novel features of the controller are that it can contend with information from a moving sensor and handle hard constraints on the actuators. Control performance and robustness to noise are demonstrated favorably via simulations.
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    AIChE Journal 42 (1996), S. 809-819 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A general theory for the adsorption of self-associating molecules in microporous structures is developed. The approach is similar to the “chemical” interpretation of nonideality of vapor and liquid phases. The theory displays Type 5 isotherm behavior and can explain Types 1 and 5 transition. Isothermal data are represented by only three parameters: Henry's law constant, saturation capacity, and reaction constant for “cluster” formation in the micropores. When isotherms at different temperatures are available, the theory can be used with five temperature-independent parameters to describe the entire phase behavior including the heat of adsorption. Water adsorption on activated carbon, the most common display of Type 5 behavior, is used to test the theory. Analysis of several data sets indicates that the theory can closely correlate data, provide physically meaningful parameter values in line with carbon properties, and it is highly effective in correlating temperature variation. The reaction enthalpy for water dimerization in the carbon micropores is lower than that in vapor phase. This preliminary conclusion with the theory needs to be supported with more accurate data when available.
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    AIChE Journal 42 (1996), S. 829-836 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Many living organisms store iron in solid form, Fe(III), as a crystal in the inner cavity of the ferritin molecule. When iron is needed for biosynthesis, a reducing agent reduces Fe(III) into the soluble form Fe2+ released by ferritin. Crystallization and release processes are reversible, and their rates evolve in an identical way as a function of the number n of iron atoms in the molecule. The rate increases with n, showing a maximum value when n is approximately 1,300, and then stabilizes for the highest values of n, which can reach 4,500. On the other hand, plotting the amount of released iron as a function of time gives curves with a sigmoid shape. The proposed model was based on the theoretical description of different steps involved in crystal growth inside the protein shell: several independent crystals grow freely at the inner protein wall, and then a distribution function takes into account possible overlapping of different crystallite clusters, whose further growth is limited by diminution of the available space inside the cavity. The kinetics derived was then used to calculate the release curve as a function of time. Solving the system of differential mass-balance equations was simplified by describing the ferritin population as a large discrete distribution of species. The model fully fitted and explained the variation in the crystallization rate with n, and the sigmoid shape of the release curve as a function of time obtained experimentally in a thin-layer electrochemical cell.
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    AIChE Journal 42 (1996), S. 850-860 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Cartilage constructs were grown using isolated chondrocytes and biodegradable polymer scaffolds made of fibrous polyglycolic acid in the form of 1-cm-dia × 5-mm-thick discs. The scaffolds were seeded in a mixed cell suspension and cultured for up to 8 weeks under static or mixed tissue culture conditions in petri dishes and spinner flasks. Turbulent mixing significantly improved the biochemical compositions and altered morphologies of the cartilage constructs, which were the thickest ones cultured to date in vitro. Constructs from mixed cultures were more regular in shape and contained up to 70% more cells, 60% more sulfated glycosaminoglycan, and 125% more total collagen when compared to constructs from static cultures. Mixing also induced the formation of an outer capsule with multiple layers of elongated cells and collagen fibrils around the inner tissue phase, while statically grown constructs consisted of round cells embedded in cartilaginous matrix. Mixing during cell seeding and tissue culture is thus an important parameter for the cultivation of tissue-engineered cartilage in a range of sizes, shapes and compositions for a variety of clinical applications (e.g., fibrous cartilage for reconstructive surgery or articular cartilage for joint resurfacing).
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    AIChE Journal 42 (1996), S. 889-891 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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    AIChE Journal 42 (1996), S. 910-920 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: New data on the variation of the diffusion coefficient with concentration in binary nonideal liquid mixtures are presented. The diffusion coefficients were measured with laser holography with an improved analysis procedure and are primarily in systems that form two liquid phases. The results show that for such systems the diffusion coefficient is constant if a chemical-potential driving force is used. If, however, the miscibility gap is wide, the Schreiner equation (Schreiner, 1922) is shown to be more accurate than relations that consider the variation of viscosity. Cluster theories developed for diffusion behavior near critical points were found to explain the data well only in water-organic systems on the water-rich side.
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    AIChE Journal 42 (1996), S. 767-776 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Identification of low-order linear multiinput/multiouput models can lead to accurate descriptions of the dynamic behavior of a continuous crystallization process. While open-loop experiments exhibit an oscillating crystal size distribution, improved experimental conditions can be established through stabilization of the process with a simple single-loop feedback controller. The resulting closed-loop identification problem is studied using low-order linear multivariable input-output models. Two closed-loop identification methods are applied, one of which was recently introduced to provide accurate approximate models in general closed-loop process configurations. Identification and validation data are obtained from an evaporative pilot crystallizer, and the identified models are validated in terms of time- and frequency-domain responses. A fourth-order, three-input three-output model is shown to describe accurately the process dynamics. The results are compared with a linearized and reduced first-principles model.
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    AIChE Journal 42 (1996), S. 1-1 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
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    AIChE Journal 42 (1996), S. 23-41 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An integral-spectral formulation for laminar reacting flows in tubular geometry (tubular Poiseuille flows) is introduced and performed within an operator-theoretic frame-work where the original convective-diffusive differential transport problem coupled with reaction is inverted to give an integral equation. This equation is of second kind and of the Volterra type with respect to the axial coordinate of the tube with a kernel given by Green's function. Green's function is identified by a methodology that gives the Mercier spectral expansion in terms of eigenvalues and eigenfunctions of the Stürm-Liouville problem in the radial variable of the tube. Eigenvalue problems for both Dirichlet and von Neumann boundary conditions are solved in terms of analytical functions (Poiseuille functions) and compared with the values found in the literature. The groundwork is set for future applications of the methodology to solving a wide variety of problems in convective-diffusive transport and reaction. Examples with wall and bulk chemical reaction are given to illustrate the technique.
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    AIChE Journal 42 (1996), S. 68-86 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Mass transport of n-heptane, n-nonane, and n-dodecane in zeolite T was studied using a gravimetric uptake technique. The sigmoidal shape of the uptake curves indicated the existence of a nondiffusional resistance in the transport process. To compute the transport parameters, an approach based on the temporal moments of the uptake curves was developed. A model involving an external resistance dependent on the local slope of the sorption isotherm best represented the data. No evidence of the “window effect” reported by Gorring was found. The measured diffusivities decrease with chain length, while the activation energies remain essentially constant. Both resistances (diffusional and nondiffusional) depend strongly on lattice loading, and their relative contributions for the transport time change as saturation is approached.
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    AIChE Journal 42 (1996), S. 131-146 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Recuperative parametric pumping in adsorptive membranes, a cyclical adsorptive separation process, can lead to two distinct mechanisms of separation: rejection and preferential transport. During rejection, the adsorptive membrane rejects an adsorbing solute while permitting the transport of nonadsorbing solutes. During preferential transport the reverse occurs; the adsorptive membrane selectively transports an adsorbing solute while preventing the transport of nonadsorbing solutes. Switching from rejection to preferential transport can be accomplished by merely decreasing the ratio of the stroke volume (cyclical volume of solution pumped into and out of the membrane) to the membrane void volume. Preferential transport, earlier called an “inverse separation,” results from the adsorbing solute crossing over from an adsorbing to a desorbing region in the interior of the membrane and is governed by the shape of the equilibrium isotherms and by process variables. In experiments with lysozyme and a membrane chromatography cartridge, selectivities obtained by preferential transport were on the order of 5 and agreed with theoretical predictions. Theoretical predictions suggest that to further improve separation by preferential transport, experiments need to be conducted on low dispersion membranes (Pe 〉 104) and that both rejection and preferential transport can lead to continuous concentrated streams of the adsorbing solutes.
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    AIChE Journal 42 (1996), S. 161-175 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new approach to cation-exchange kinetics views ion-exchange resin as an aggregate of uniform cylindrical pores. Ion exchange occurs at the pore surface. The counterions dissociate only partially from the fixed sites, and the charge created on the pore surface is balanced by the counterions in the electrical double layer. Thus, any cross section of a pore consists of an annular double-layer region and a central core region. Electroneutrality prevails in the core region through an influx of coions. Diffusion of ions through both regions is considered. The complete model incorporating these ideas for kinetics of monovalent cation exchange was tested with our experimental data as well as with the reported data. The pore diffusion coefficients used in the model are free ionic diffusion coefficients corrected for the tortuosity factor of the pores. Unknown parameters of the model are the degree of dissociation of counterions from the fixed sites of the pore (fσ), and the film thickness (δ). Both parameters are insensitive to the type of counterions, solution concentration, and the direction of exchange. Further, fσ appears to be a characteristic property of resin alone. Superiority of the developed model over the previous models is established.
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    AIChE Journal 42 (1996), S. 232-238 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Dissolution and crystal growth on the (010) cleavage surface of mineral gypsum have been studied by scanning force microscopy, which allows observation of surfaces while they are in contact with aqueous solutions. Etch pits formed on the (010) surface in contact with solutions undersaturated with respect to gypsum are oriented in relation to the [001] zone axis. Edges parallel to [001] are stable or move only slowly. Edges parallel to [100] and [101] move more rapidly. Crystal growth by migration of step edges is observed in contact with supersaturated solutions. The inhibition of crystal growth by phosphonate produces gross changes in the texture of steps and terraces.
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    AIChE Journal 42 (1996), S. 249-258 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Ion-selective electrodes were used to measure the activity coefficients at 298.2 K of individual ions in aqueous solutions of NaCl and NaBr up to of 5 molal and of KCl up to 4 molal. The mean ionic activity coefficients of NaCl, NaBr, and KCl, obtained from the values of the activity coefficients of the individual ions, show good agreement with values reported in the literature. The experimental results show that the activity coefficients are different for the anion and the cation in an aqueous solution of a single electrolyte and that, as expected from the ion-ion and ion-solvent interactions, the activity coefficient of an ion depends on the nature of its counterion. A modified form of the Pitzer's model, which distinguishes between the activity coefficients of the anion and the cation, was used to correlate the experimental results.
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    AIChE Journal 42 (1996), S. 391-404 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mathematical model and numerical algorithm are developed to predict electrodeposition rates from a 2-D jet of electrolyte that impinges on a flat surface. The principal situations of interest are for applied voltages that produce current densities below the limiting current. The motion is assumed to be at high speed with the jet inducing a thin laminar boundary layer on the surface; a progressively thinner concentration layer and an electrochemical double layer near the surface are accounted for. Two cases, corresponding to a submerged and unsubmerged jet, are considered. A boundary integral method is used to compute the current density along the plate in a general iterative numerical procedure coupled to the solution of the hydrodynamic, concentration and electrochemical boundary layers. The results show that relatively high deposition rates occur near the point of impingement and that altering the jet angle relative to the surface influences local electrodeposition rates significantly.
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    AIChE Journal 42 (1996), S. 405-408 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A range of small, medium and large pore zeolite, and their modified forms are studied for their ability to separate di- from monobranched isomers of hexane. The separation studies are carried out using high-temperature (250-350°C) gas chromatography. Beta(H,Ba) is found to be the most effective separator of 2,3-dimethylbutane and 3-methyl-pentane and is therefore studied for its sorption capacities toward the two hexane isomers.
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    AIChE Journal 42 (1996), S. 422-430 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Activated carbon was impregnated with a metal halide, and adsorption and desorption characteristics of CO on the carbon were measured by fixed-bed runs. It was found that the impregnation of PdCl2 or CuCl effectively increases CO absorption. PdCl2/CuCl-impregnated carbons were characterized by N2 adsorption, SEM, EPMA, and XPS. Adsorption isotherms of CO were also measured on these carbons, and the influence of the loading of impregnant on CO adsorption was experimentally elucidated. A selection procedure of impregnant was proposed based on the frontier orbital theory. The perturbation energy for molecular orbital mixing was estimated by the HOMO - LUMO interaction. CO adsorption on impregnated carbons was qualitatively interpreted using the perturbation energy, and the energy was regarded as an index of impregnant selection.
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    AIChE Journal 42 (1996), S. 455-465 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Two issues involving the methodology used for on-line control of product quality in batch manufacturing processes are addressed: the generation of fast, data-driven process models and the use of such process models for on-line feedback control of product quality. The methodology is investigated using the example of the control of dispersity and molecular weight distribution in a batch reactor for emulsion polymerization of vinyl acetate. An artifical neural network (ANN) is used as a model to predict the quality as a function of the manipulated variables and on-line measurements. This model is constructed using an augmented dataset that integrates experimental information and knowledge from a mathematical model. The proposed model is compared with other types such as a theoretical model whose key parameters are fitted to experimental data. The hybrid ANN is superior to the parameter-fitting approach for this case. Experimental and simulation studies confirm the advantage of using the proposed model and the predictive control algorithm.
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    AIChE Journal 42 (1996), S. 477-492 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Effective utilization of measured process data requires efficient techniques for their compact storage and retrieval, as well as for extracting information on the process operation. Techniques for the on-line compression of process data were developed based on their contribution in time and in frequency using the theory of wavelets. Existing techniques for compression via wavelets and wavelet packets are inconvenient for on-line compression and are best suited for stationary signals. These methods were extended to the on-line decomposition and compression of nonstationary signals via time-varying wavelet packets. Various criteria for the selection of the best time-varying wavelet packet coefficients are derived. Explicit relationships among the compression ratio, local and global errors of approximation, and features in the signal were derived and used for efficient compression. Extensive case studies on industrial data demonstrate the superior performance of wavelet-based techniques as compared to existing piecewise linear techniques.
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    AIChE Journal 42 (1996), S. 524-531 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effect of high levels of coke deposit on catalyst properties and mass transport through the pores space was studied using commercial catalysts, Pt-Al2O3 and Ni-Mo-Al2O3. Changes in porosity, pore-size distribution and internal surface area of several aged catalysts were compared to those of fresh catalyst. Effective diffusivity was also measured by pulse chromatography. For Pt-Al2O3, which shows a high initial porosity (0.93) and a relative high mean pore radius (300 Å), catalyst properties remain unchanged while coke content increased. For the Ni-Mo-Al2O3 catalyst (with initial porosity of 0.53 and mean pore radius of 50 Å), however, with an increase of 15% in coke content, isolated void regions appear, and porosity, internal surface area and effective diffusivity decrease sharply. Pore and stochastic models were used to interpret the effective diffusivity experimentally measured. A structural parameter in each case, tortuosity factor in pore models, and coordination number in the percolation model were calculated. When coke produces significant changes in catalyst morphology, the tortuosity factor almost doubles its initial value for a coke content of 20%. On the contrary, the percolation model seems to predict changes accurately in porosity, mass trasport coefficient, and an isolated prosity growing from the coordination number matched for a fresh catalyst.
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    AIChE Journal 42 (1996), S. 547-561 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Emulsion liquid membrane separation processes remain excessively vulnerable to one or more of four major problems. Difficulties lie in developing liquid membranes that combine high levels of both stability and permeability with acceptably low levels of swelling and ease of subsequent demulsification for membrane and solute recovery. This article provides a new technique for simultaneously overcoming the first three problems, while identifying physical indications that the proposed solution may have little adverse effect on the fourth problem (demulsification) and may even alleviate it. Numerous benefits of optimized conversion of the membrane phase into suitable non-Newtonian form are identified, their mechanisms outlined, and experimental verifications provided. These include increased stability, retained (or enhanced) permeability, reduced swelling, increased internal phase volume, and increased stirrer speeds. The highly favorable responsiveness of both aliphatic and aromatic membranes to the new technique is demonstrated.
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    AIChE Journal 42 (1996), S. 466-476 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Suppressing the influence of external disturbances on a process is the most common objective of a controller in a chemical plant. A control system that can keep the controlled variables at or near their set point and the manipulated variables lower than their prespecified maximum bounds in the face of load disturbances is wanted. A method is presented to design controllers with disturbance rejection specifications and limits over the control energy. This methodology is based on a special strategy to shape the structured singular value of a closed-loop transfer function matrix.
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    AIChE Journal 42 (1996), S. 503-515 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The safeguarding methodology of chemical plants is usually based on controlling the instantaneous values of process state variables within a certain operating window, the process being brought to shutdown when operating constraints are exceeded. This method does not necessarily prevent chemical reactors suffering from a runaway during dynamic operations because (a) excessive amounts of unreacted chemicals can still accumulate in the process, and (b) no means are provided to the operating personnel to identify hazardous process deviations. A model-based startup and safeguarding procedure is developed for an industrial adiabatic tubular reactor to improve process safety during startup. The trajectories of manipulated variables are calculated by minimizing the amount of one of the main reactants in the reactor effuent. It is concluded that proper control of the initial reactor temperature profile is critical for a safe startup while the impact of other manipulated variables is relatively smaller than that of the initial reactor temperature profile.
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    AIChE Journal 42 (1996), S. 532-537 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Radiation absorption at the surface of catalytic particles is the initial step of photocatalytic oxidation reactions currently considered for their potential effectiveness in the treatment of polluted water with traces of highly toxic organics. Owing to the presence of catalyst particles within the fluid phase, the radiation field within a photocatalytic reactor results from the absorption and scattering within the participating medium. An annular reactor with a coaxial central lamp was considered, and the resulting 2-D radiation field was analyzed using a Monte Carlo technique to solve the radiative transfer equation. Results are discussed based on the relevant optical parameters, and a heuristic is derived for the design and rating of a photocatalytic reactor. To exploit the reaction volume effectively, the order of magnitude of the optical thickness should be close to unity, and for a given value of the absorption coefficient the catalyst with the lowest albedo should be selected; however, a precise evaluation of the phase function is not crucial to a relable representation of the radiation field.
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    AIChE Journal 42 (1996), S. 562-570 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A generalized four-parameter quartic equation of state (EOS) proposed by Shah and coworkers (1992, 1994) was extended to polar fluids. To use the new generalized quartic EOS for polar fluids, only four characteristic properties of the pure compound are required - critical temperature, critical volume, acentric factor, and dipole moment. For nonpolar fluids, the previous equation is recovered and its superior performance for nonpolar fluids is retained. A new set of coefficients for polar fluids for the EOS was determined from multiproperty regressions using literature data for various physical and thermodynamic experimental properties of 30 pure compounds. These regressed coefficients, which are functions of the critical temperature, critical pressure, acentric factor, and the dipole moment of the fluid, were generalized. The accuracy of this equation of state is evaluated with the new set of regressed coefficients to predict thermodynamic properties of pure polar compounds, including vapor pressure, density, residual enthalpy, enthalpy of vaporization, and second virial coefficient. The capability and accuracy of this quartic equation of state are also compared with the well-known Peng-Robinson EOS.
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  • 84
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 585-594 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A comprehensive equation of state was developed to represent the phase equilibria and volumetric properties of aqueous calcium chloride solutions at temperatures above 523 K. The equation consists of a reference part and a perturbation contribution. The reference function is developed from the statistical mechanical theory for mixtures of dipolar and quadrupolar hard spheres, which agrees well with the Monte Carlo simulation results. In this treatment, calcium chloride is described by the completely undissociated model. The empirical perturbation function is a truncated series of virial expansion terms. Thus, mixing rules are guided by those of virial coefficients, which are derived rigorously from statistical mechanics. The equation reproduces experimental saturated vapor pressures and volumetric data within experimental uncertainty for temperatures to 623 K. At higher temperatures, few and less accurate experimental data are available, but values of the saturated vapor pressures of the liquid have been reported and are represented satisfactorily.
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  • 85
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996) 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 86
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 638-648 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The full Navier-Stokes equations were employed with a single-fluid model and a front tracking scheme to study a large cylindrical bubble in a free shear layer. A general formulation based on work by Auton et al. of the hydrodynamic forces on a finite Reynolds number large bubble in an unsteady, nonuniform and rotational flow was then used to investigate the effects of nonlinear spatial and temporal gradients on dispersion. The resulting bubble dispersion in the full Navier-Stokes solution significantly differ from that by a conventional bubble dynamic equation based on linear spatial gradients and quasi-steady flow. This was due to the adjunct forces not accounted for by such a formulation, which are related to regions of high nonuniformity and unsteadiness. These adjunct forces in the drag/lift direction were correlated with rapid variations of relative bubble velocity and high gradients of the liquid velocity.
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  • 87
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    AIChE Journal 42 (1996), S. 613-622 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Deterministic cross-stream migration of FENE dumbbells, cyclic trimers and bicyclic tetramers in nonhomogeneous, nonrectilinear flows representative of tortuous pores is analyzed. Identifying the crucial feature of misalignment between a tumbling dumbbell and the surrounding streamlines, Brunn (1983) showed that the dumbbell model requires three reflections in the bead-bead hydrodynamic interaction (HI) for lateral migration to occur: lower-order approximations of the HI are insufficient because they lead only to alignment with the flow rather than tumbling. In any orientation the trimer (tetramer) has at least two (three) “bonds” out of alignment with the flow. Radial migration in rotary Couette flow between concentric cylinders occurs in the freely draining limit, and the simplest, first-order HI is sufficient to cause lateral migration in rectilinear tube flow. Flow through a sinusoidally corrugated pore brings a new convective timescale on which the bead-spring entity moves between converging and diverging flow environments. Since this process outpaces the dumbbell's alignment, even a freely draining dumbbell spends most of its time slightly misaligned with the surrounding streamlines, and migrates toward the walls (higher shear). Tumbling occurs on a much longer timescale, with the dumbbell traveling through many wavelengths of the wall corrugations (and fluctuating in orientation) between successive (rapid) end-for-end flips in the shear field. The flipping time seems to scale inversely with the length of the dumbbell. The trimer and tetramer rotate largely as in rectilinear shear, and exhibit somewhat stronger migration for the same bond length. As a simple model of pore entrance effects, net drift in an oscillatory Sampson flow through a thin orifice is also considered.
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  • 88
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 623-637 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The evolution of a film with insoluble surfactant on a wavy horizontal wall differs from flow without surfactant (the way it usually is studied) in that the film passes through different stages. The first stage is as if the surfactant were absent. Once the surface tension gradient - induced by the nonuniform surfactant concentration adsorbed at the free surface - starts resisting the flow effectively, the evolution enters a transitional stage. A final stage is reached once the free surface becomes rigid due to the surface-tension gradient (high elasticity limit) or becomes virtually leveled before the surface-tension gradient is released (low elasticity limit). The velocity profile through the film changes with time, sol fluid is depleted or accumulated at different strata in the film as the flow evolves. The velocity profile and resulting deformations throughout the film can be influenced significantly by the viscosity distribution or stratification, which occurs, for example, when multiple layers of different viscosity are coated simultaneously. A model and applications for the leveling of such a film are presented. The evolution is described in general terms for a film of uniform viscosity and for a film of two discrete layers of different viscosity. Then the three limiting cases are established. For two of these limits, the effect on the exponential decay rate of the flow and the deformation of the different strata or layers is examined when the viscosity is changed in an infinitesimally thin layer or stratum, and in a layer of finite thickness in films of two and three discrete layers.
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  • 89
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    AIChE Journal 42 (1996), S. 660-670 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The expansion behavior and structural phenomena of fluid-particle systems was simulated using a method analogous to the Monte Carlo method for molecular systems. Individual particles are moved, and the resulting moves are accepted or declined based on the change in the system's potential energy and the average kinetic energy of the system. Several fluid-particle systems have been successfully predicted with the model including colloidal particle concentration profiles and random packing of uniform spheres. Additionally, predictions of steady-state fluidized-bed expansion characteristics for uniformly sized stainless-steel spheres and narrowly distributed nickel and glass spheres show excellent agreement with the theoretical model used in the simulation and satisfactory agreement with experimental data. Dynamic expansion predictions of both bed height and overall bed structure as a function of time also agree with the experimental data.
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  • 90
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    AIChE Journal 42 (1996), S. 691-699 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The importance of spatial variations of the conditions in industrial-scale, agitated, batch cooling crystallizers is investigated by computer simulations. A three-compartment model is developed considering primary and magma density-dependent secondary nucleation. An increasing crystallizer size is described by an increasing suspension turnover time. It is shown that accumulation of larger crystals in the bottom region, localized supersaturation generation and variations in the secondary nucleation rate due to varying local mixing intensity will, under normal conditions, exert a low and often negligible influence on the product-size distribution of an industrial unit. In a batch process, the product-size distribution is governed mainly by the conditions early in the process. During this period the supersaturation half-life is much longer than the suspension turnover time, and the influence of local variations becomes weak.
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  • 91
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    AIChE Journal 42 (1996), S. 713-726 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Protein partitioning kinetics was measured for the semibatch extraction of lysozyme in a laboratory-scale, liquid-liquid spray column. The organic, isooctane phase contained reverse micelles formed from the anionic surfactant, sodium di-2-ethylhexyl sulfosuccinate. For the extraction of protein from aqueous to reverse micellar phases, experiments were performed over a range of dispersed-phase flow rates for cases of the organic- or aqueous-phase dispersion. The influence of aqueous-phase pH and ionic strength, which influence electrostatic interactions between protein and reverse micelles, was also investigated. Results were interpreted in terms of a two-film model of mass transfer. The nature of the dispersed pahse could significantly influence the partitioning kinetics, while study of the droplet hydrodynamics suggested that stagnant drops were formed regardless of which phase was dispersed. Literature correlations for describing the droplet-formation process and droplet hydrodynamics predicted measured values satisfactorily. Attempts wer also made to predict overall mass-transfer coefficients based on existing correlations describing mass transfer during droplet formation, free rise (or fall), and coalescene. Predicted values of KL were 2-10 times greater than measured values, probably because of large concentrations of surfactant used to formulate the reverse micelle phases. This approach did, however, provide detailed information on the quantity of protein transferred during the successive processes of droplet formation, free rise (or fall) and coalescence.
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  • 92
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    AIChE Journal 42 (1996), S. 932-939 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The volumetric flow rate of liquid and gas through small gigaporous particles was measured by a new method that isolates single particles in a test apparatus. To our knowledge, this is the first direct confirmation of flow through gigaporous particles made at pressure drops experienced during normal operation. High-performance liquid chromatography particles from 30 to 50 μm in diameter, previously reported to exhibit convection-enhanced intraparticle mass transfer, were studied. Using a CFD model of the test system, the permeability of individual particles was determined from the pressure-drop-flow-rate relationship. The average measured permeability of the particles studied is 7.89 × 10-15 m2 with no dependence on particle size. This is 4 to 17 times greater than values calculated from models currently used to estimate the permeability of these kinds of particles. No other experimentally measured values of permeability have been reported for particles of this size. The results of this study might imply that the intraparticle structure does not behave like a bed of uniformly packed microspheres, but rather as an inhomogeneous assemblage of microparticles. The measured permeability values offer the possibility of developing better models of the intraparticle flow field under normal operating conditions. Knowledge of the intraparticle flow field is an important step in deriving predictive models of convective mass transfer in these types of particles.
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  • 93
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    AIChE Journal 42 (1996), S. 3523-3532 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The structure of a colloidal deposit retained by a porous wall is described, accounting for surface interactions and hydrodynamic forces. The balance of forces acting over spherical, charged particles allows the calculation of the interparticular distances inside the cake according to the physicochemical conditions (ionic strength, particle potential, pH, particle size) and to the experimental parameters (flux). The model predicts that beyond a critical mass deposited on the porous wall, the structure of the layers near the membrane changes where the particles are in close contact with each other. Experimental data obtained with latex monodisperse particles filtered over various types of ultrafiltration membranes for various physicochemical and flux conditions are compared to the model predictions. These results explain the existence of irreversible colloidal deposits in filtration and suggest strategies to optimize backflush or pulsed pressure procedures often used to improve the efficiency of ultrafiltration or microfiltration.
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  • 94
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    AIChE Journal 42 (1996), S. 3508-3522 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A molecular model based on the integral equation theory of statistical thermodynamics is used to study phase separation in PEG-salt aqueous two-phase systems. PEG molecules are modeled as hard spheres that attract each other through a temperaturedependent Yukawa potential, which mimics the effect of PEG-water hydrogen bonding on the attraction between PEG molecules. The salt ions are modeled as charged hard spheres interacting through a Coulombic potential. Excess thermodynamic properties due to Coulombic and Yukawa interactions are calculated by analytical solutions to the Ornstein-Zernike equation for the mean spherical approximation closure. Yukawa parameters for PEG-PEG interactions are determined by fitting the theoretical phase diagram for a pure Yukawa fluid to the experimental phase diagram for a PEG-water mixture. The model predicts experimentally observed trends: increasing the temperature increases the slope and length of the tie lines; increasing the PEG molecular weight increases the miscibility gap; and increasing the anion charge lowers the salt concentration at which phase separation occurs. Theoretical results allow us to infer the relative importance of ion-PEG interactions, ion-solvent interactions, and the interpenetrable nature of PEG molecules on the phase separation in PEG-salt aqueous two-phase systems.
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  • 95
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    AIChE Journal 42 (1996), S. 3533-3543 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Attempts to model asphaltene solubility with Scatchard-Hildebrand theory were hampered by uncertainty in molar volume and solubility parameter distribution within the asphaltenes. By considering asphaltenes as a series of polyaromatic hydrocarbons with randomly distributed associated functional groups, molar volume and solubility parameter distributions are calculated from experimental measurements of molar mass and density. The molar mass distribution of Athabasca asphaltenes is determined from interfacial tension and vapor pressure osmometry measurements together with plasma desorption mass spectrometry determinations from the literature. Asphaltene desnities are calculated indirectly from mixtures of known concentration of asphaltene in toluene. Asphaltene density, molar volume, and solubility parameter are correlated with molar mass. Solid-liquid equilibrium calculations based on solubility theory and the asphaltene property correlations successfully predict experimental data for both the precipitation point and the amount of precipitated asphaltenes in toluene-hexane solvent mixtures.
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  • 96
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Additional Material: 5 Ill.
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  • 97
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 98
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Additional Material: 5 Ill.
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  • 99
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 100
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    Weinheim : Wiley-Blackwell
    Advanced Materials 8 (1996) 
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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