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  • Chemical Engineering  (3,710)
  • Molecular Cell Biology  (640)
  • Wiley-Blackwell  (4,350)
  • 1975-1979  (2,431)
  • 1970-1974  (1,919)
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  • Wiley-Blackwell  (4,350)
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  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979) 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 41-47 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In a Lagrangian frame of reference based on lamina (fluid filament) thickness and in a warped time scale based on a single, flow dependent quantity, mixing, diffusion, and reaction can be described in a relatively simple way. Applications are presented for stretch and fold in taffy pull, egg beater and static mixer, shear stretch, stretch of laminae in a vortex, mixing with diffusion, reaction rate controlled by diffusion of reactant through a product layer, and very fast reactions in a turbulent flow.
    Additional Material: 5 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 48-56 
    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 paper is an experimental and theoretical study of horizontal stratified gas-liquid two phase flow in a circular tube. Both phases are considered to be in turbulent flow, and the liquid phase flow field is modeled by applying eddy viscosity expressions developed for single phase flow. The pressure drop and in situ volume of liquid are predicted from the gas and liquid flow rates, physical properties, and pipe size by means of an iterative procedure which terminates when calculated gas and liquid pressure drops match. The iterative design procedure is compared with new data for air-water flow in a smooth tube of 63.5 mm ID and with data available in the literature. For conditions corresponding to small amplitude interfacial waves, the average deviation between predicted and experimental results is 24.3% for the pressure drop and 7.7% for the holdup. For roll wave conditions, the corresponding average deviations are 4.6 and 26.4% for pressure drop and holdup, respectively. These results are substantially better than the predictions obtained using the Lockhart-Martinelli correlations.
    Additional Material: 16 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 87-100 
    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 operation of two arrangements of multistage adsorption beds, parallel and series, was analyzed, and the optimal design problem of minimizing the capital and operating costs of the multistage adsorption bed systems was formulated. Solution of the optimization problem was obtained by using the Fibonacci search scheme. For the purpose of the study, data on the adsorption of liquid on activated carbon were taken from the literature for both single solute and multisolute adsorption systems and was used to derive the expressions for adsorption rate and the equilibrium relationship. Details of the performance of the optimally designed multistage adsorption bed systems are presented in terms of the physical and design parameters.
    Additional Material: 18 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 100-108 
    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 paper examines the effect of flow maldistribution on the predicted conversion and selectivity in a radial flow fixed-bed reactor. A simple model was developed to relate gas maldistribution to the catalyst bed to the conversion with first- and second-order reactions and to selectivity for first-order reactions in series and parallel. For the cases considered, the conversion debit due to maldistribution of the gas phase was as much as 11%. The model was extended to cover adiabatic conditions for simple first-order reactions. For an exothermic reaction, maldistributions can enhance conversion over that obtained with a uniformly distributed gas phase.
    Additional Material: 10 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 24-32 
    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 time delay compensation techniques, the Smith predictor and the analytical predictor, are used for bottom composition control of a pilot scale methanol-water distillation column. The closed-loop performance of the two predictor schemes is compared to that for a proportional-integral controller in experimental and simulation studies. The predictors resulted in improved control for both set point and feed flow disturbances.
    Additional Material: 11 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 57-64 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Microscopic observations and Coulter counter measurements of the secondary nuclei produced when a parent crystal of potash alum was contacted with a solid rod suggest that these nuclei are born by an attrition mechanism which appears to be dependent on the growth rate of the crystal. The nuclei can be up to 50 μm in size. The nuclei smaller than about 4 μm are relatively insensitive to supersaturation, whereas the number greater than about 4 μm is approximately linear in supersaturation.
    Additional Material: 7 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 131-143 
    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 hydrodynamic behavior of paper pulp slurries in vertical laminar flow has been observed and modeled. Radiotracers were used to tag both the liquid and solid phases of slurries flowing in 4 and 30 cm pipes. Residence time distributions were determined for each phase and were used to derive and compare several flow models. A model consisting of a central core in plug flow circumscribed by a clear Newtonian annulus provides a good representation of the observed slurry behavior. Correlations between the model parameters and the Reynolds number and slurry consistency are presented, and implications of the results on the design of slurry flow reactors are discussed.
    Additional Material: 15 Ill.
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  • 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: For every viscoelastic fluid studied in the contraction geometry, it was found that increasing the flow rate beyond a certain limit resulted in disturbance to the stable entry flow patterns described in Parts I and II. An examination of the development of the entry flow disturbances was carried out using still and cine photography. Still photographs are presented to illustrate the characteristics of the unstable flow patterns. The time varying nature of the flow has been recorded on a cine film Flow Patterns in Abrupt Entry Flow of Viscoelastic Fluids which is available for loan. Critical condition criteria for the onset of the periodic flow disturbances were obtained in terms of the fundamental fluid properties and are presented and compared with other suggested criteria for the onset of unstable entry flow of viscoelastic fluids.
    Additional Material: 9 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 170-179 
    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 theoretical investigation of ultrafiltration through hollow fibers used in artificial kidney applications is presented. The hollow fibers are considered to be cylindrical tubes with ideally selective semipermeable walls which retain cellular particles (red and white cells, platelets) and plasma proteins in the blood perfusing the fibers. In contrast, water and species of low and medium molecular weight can freely permeate the membranes. The assumption is made that secondary flows avoid the formation of concentration boundary layers at the wall. Proper nondimensionalization of the equations for axial and radial transport results in the identification of parameters which are important in the characterization of the ultrafiltration through semipermeable tubes. Perturbation analyses for small values of these parameters lead to sets of differential equations which were solved analytically. These closed form solutions demonstrate the influence of hydraulic conductivity of the fiber walls, geometry, and axial and transmembrane pressure drop on the efficiency of hollow fiber artificial kidneys.
    Additional Material: 9 Ill.
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  • 11
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 190-192 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 1 Ill.
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  • 12
    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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  • 13
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979) 
    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
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 258-266 
    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 equation of motion for the two phase flow within a bubble column, operated within the recirculation flow regime, has been solved, and the profile of liquid flow has been determined. Nicklin's relation for the bubble flow regime has been extended to the recirculation flow regime.Data analysis shows that the mean slip velocity between bubble and liquid is approximately constant and that the kinematic turbulent viscosity increases rapidly with increasing diameter of the column. These observations lead to the conclusion that scale-up has but little influence upon the mean gas holdup.
    Additional Material: 8 Ill.
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  • 15
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    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 272-283 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Rates of hydrogenation of α-methyl styrene were measured at 40.6°C and 1 atm in a recycle, trickle-bed reactor using a palladium/aluminum oxide catalyst. Data for different hydrogen concentrations in the gas and liquid feed streams suggested that except, at high liquid flow rates, on part of the outer surface of the catalyst the mass transfer limitation was very small, indicating a gas covered type of surface. A procedure was developed for evaluating effectiveness factors for the nonuniform boundary conditions existing when part of the particle surface is covered by gas.
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  • 16
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 306-311 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Removal of sulfur, nitrogen, and oxygen from heavy gas oils is affected by the chemical composition of supported molybdate catalysts. Cobalt and nickel, when added to these catalysts, have a promoting effect on these reactions. However, the relative rates always follow the same trend; that is, the hydrodesulfurization is the fastest, followed by hydrodenitrogenation and hydrodeoxygenation.
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  • 17
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 320-327 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Continuous pH parametric pumping separations of a haemoglobin-albumin-CM Sepharose system were experimentally investigated. The parapump has a feed containing the protein mixture to be separated, introduced alternately to the top and bottom of the chromatographic column. The top and bottom products are withdrawn from the apparatus, respectively, during the bottom and top feed. It is shown that under certain conditions the pH driven parametric pump has the capacity for removal of protein components from one product fraction and large enrichment in the other fraction. Moreover, the continuous process can be operated with a large feed throughput.
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  • 18
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 549-551 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Ill.
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  • 19
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 202-202 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Tab.
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  • 20
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    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 207-208 
    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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  • 21
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 362-365 
    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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  • 22
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 370-373 
    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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  • 23
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 376-381 
    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 solution is obtained to the kinetics of a fixed-bed adsorber in response to a step change in feed concentration for a linear equilibrium system with consideration for the resistance to mass transfer in both the mobile and stationary phases. The differential equations of continuity and mass transfer are integrated upon simulating the intraparticle concentrations with a parabola. The results agree with Rosen's rigorous but complex solution in the range of conditions of practical interest. The present solution is more convenient for computer application for the calculation of breakthrough curves.
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  • 24
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 384-384 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
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  • 25
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 385-395 
    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 simulation procedure for predicting the dynamic behavior of a deep bed filter over the entire practicable range of filter operation is developed. The method is based on synthesizing available quantitative results relating to filtration, and to porous media flows, within an overall framework which views the process to consist of two principal stages dominated by appropriate limiting deposition modes. Evaluation of the results through comparison with available data indicates, to the extent the nature of these types of data permits, that the method is surprisingly effective and even capable of predicting on satisfactorily quantitative basis some intricate details of observed filter behavior.
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  • 26
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 423-429 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Starting from a conventional distillation system without heat integration, a series of bottlenecks from the viewpoint of energy conservation is sequentially found by a thermodynamic analysis using a heat availability diagram, and modified systems are evolutionally synthesized as the result of debottlenecking. The present approach has made possible a unified interpretation of various energy integrated distillation systems with multieffect columns, intercondensers/interreboilers, heat pumps, etc.
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  • 27
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 439-446 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Data on the ice formation rate are presented for a salwater drop suspended by drag forces in a flowing cold organic liquid. The effects of refrigerant undercooling, salt concentration, drop size, and time were studied. Ice formation rates in drops of 3 wt % sodium chloride solution were two to three times lower than in pure water drops. A parallel plate model was used to correlate the data and predict ice formation rates for other drops and refrigerants.Dispersing drops of brine or fruit juices in a countercurrent cold organic refrigerant is a method of desalination (or freeze concentration) that deserves further study.
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  • 28
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 352-354 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 1 Tab.
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  • 29
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 358-359 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 30
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 365-367 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 1 Tab.
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  • 31
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 32
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 382-383 
    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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  • 33
    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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  • 34
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 405-415 
    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 turbulence intersities and spectra in water very close to an air interface have been measured with a hot wire anemometer. The turbulence in the water has been induced in three ways: with a stirrer, by a submerged jet, and by flow of a thin film of water over inclined plates, both rough and smooth.We find that the root-mean-square fluctuation velocity Ṽx′ shows for the first system no regular trend with the distance y below the surface, while for the second system Ṽx′ increases markedly as the surface is approached. In water films over the rough plates, Ṽx′ can be as high as four times the shear stress velocity.The turbulence energy spectra close to the surfaces in the first and second systems show (Figure 6) no extended region of slope -5/3, whereas for flow over the plates, there is an appreciable subrange of this slope (Figures 8 and 9).Intensities of turbulence in the surface region are as high as 30 to 50% in the first system, up to 100% in the second system, and 17% over smooth plates and up to 60% over rough plates.These turbulence characteristics can be related to the rates of mass transfer for oxygen absorbing into water by comparing plots of k/D1/2 with the square roots of the different eddy frequencies. The Levich treatment [interpreted by Equation (15)] gives good agreement with the stirred cell and jet results. For the smooth and rough plates, mass transfer depends on eddies intermediate in size between the x directional and the y directional large eddies. In all cases, the Kolmogoroff eddy frequencies are much too high to correlate with mass transfer rates.Further, the energy spectra show that 60 to 80% of the total eddy energy lies in the larger eddies, with only 1% (or less) in the Kolmogoroff range.We conclude that the Prandtl sized eddies, and even larger eddies, determine mass transfer rates at a free surface.Direct measurement of concentration fluctuation frequencies, using platinum microelectrodes, was found to be unsatisfactory because of the poor frequency response of the amplified signals.
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  • 35
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    AIChE Journal 25 (1979), S. 447-455 
    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 kinetics of ethylene hydrogenation to ethane are studied in a 7.0 cm diameter fluidized packed-bed reactor. The fixed packing, 1.27 cm nickel on alumina catalyst, is used in conjunction with both -48/+100 mesh alumina and -50/+170 mesh glass inert fluidized particles. Reactant mixture is passed through the reactor at velocities sufficient to fluidize the inerts. Conversions from 0 to 91% are observed over the temperature range 56° to 261°C and flow rate range 10 to 800 cm3/s.The mass transfer coefficient and reaction rate constant are simultaneously evaluated from integral conversion data. The mass transfer coefficient between the interstitially fluidized bed and the catalyst surface is correlated in dimensionless form asNsh = 0.77 NRe0.418 NSc1/3The correlation is significant at the 95% confidence level that is, r = 0.59, p′ 〉 0.Predictions of conversion using both the mass transfer coefficient correlation and a Langmuir-Rideal reaction expression are in good agreement with experimental data. The effects of contact time and catalyst diameter on conversion are also presented. Film diffusion influences become limiting at temperatures above 100°C at the velocities studied. Diffusional resistances were found to be important at Reynolds numbers below 100, at 186°C. No significant difference in reaction rate was found between fluidized alumina and glass inert particles under comparable operating conditions.
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  • 36
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 469-478 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Coupled diffusion generated countergradient transport through membranes is analyzed by experimental and theoretical means. Membrane wedge interferometer experiments on an ethanol—water-cellophane membrane system show that net countergradient mass transfer of the less permeable component ethanol may be generated over a wide concentration range. A theoretical analysis of an idealized membrane separating two binary bulk solutions is developed to display further the major features of diffusional coupling effects, and good agreement between observed and predicted countergradient transport characteristics is shown.
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  • 37
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), 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: Equations describing phase volumes in multicomponent, multiphase systems in the neighborhood of critical points are derived to aid in the location of such critical points. The theory is in good agreement with experiments for three ternary systems and four surfactant systems of the type used for tertiary oil recovery.
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  • 38
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 516-521 
    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 use of helical ribbon agitators to mix viscous non-Newtonian fluids has been investigated. A generalized model, based on an appropriate definition of effective viscosity, is proposed to predict power consumption. This model is most successful with fluids that do not have a high degree of elasticity.It was found that the efficiency of mixing of pseudoplastic fluids was about half of that of Newtonian fluids in the same mixer, while the efficiency of mixing viscoelastic fluids was still lower and approximately independent of the mixer geometry. Blade width was the primary variable affecting the mixing efficiency on inelastic fluids.
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  • 39
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 542-544 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 40
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
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  • 41
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 552-554 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 1 Ill.
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  • 42
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 560-560 
    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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  • 43
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979) 
    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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  • 44
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 583-591 
    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 present research concerns mechanism and rate of reaction between dissolved ozone and phenol in homogeneous solutions. The stopped-flow technique was employed to obtain absorbances during reactions; the kinetic experiments were conducted at temperatures varying from 5° to 35°C in aqueous solutions with pH values ranging from 1.5 to 5.2.The kinetic data indicated that the absorbance of a mixed solution increased rapidly in the very early portion of the reaction and then declined slowly in the remaining period. The rate of reaction in the early period was first order with respect to both phenol and ozone concentrations. The rate constant increased with pH value and temperature, and an activation energy of 5.74 K cal/mole was obtained. Further tests showed that the dissolved ozone was consumed completely in the first period and that in the second period the intermediate products were decomposed without depletion of ozone. Catechol, o-quinone, hydroquinone, oxalic acid, humic acid, and a dimer were identified from mass spectra as products of the ozonization reaction.A free radical mechanism, with initiation of an electrophilic reaction for the formation of catechyl radical, has been proposed to explain the experimental data for phenol-ozone reaction in aqueous solutions. According to the proposed mechanism, the reaction path through the attachment to ortho position is much more favorable compared with that through the paraposition because of geometric advantage, though quinones and hydroxyphenol can be formed through parallel paths. The products of reaction detected in this research, therefore, are accountable by this mechanism. A rate equation derived on the basis of this mechanism also agrees well with that observed from the kinetic experiments.
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  • 45
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 600-609 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Mathematical modeling of a periodically cycled plate column has been completed by using a liquid bypass model to describe nonideal liquid draining. A numerical solution over a wide range of parameters provides a closed envelope of feasible solutions. A region of this envelope encloses favorable operating values of the parameters, while the other region is unfavorable. Measurements of the parameters for nonideal liquid draining in a 600 mm diameter column fitted with sieve plates lead to predictions of only small improvements in separation performance. Modifications to the column intervals are required to move the parameters into a more favorable position in the solution envelope.
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  • 46
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 609-615 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Sparse linear systems in bordered block-triangular form can be efficiently solved by block-triangular splitting, a new technique that provides a drastic reduction in the fill-in (loss of sparsity) that occurs in the direct solution of such systems. This technique is applicable in the iterative solution of the large systems of nonlinear equations that arise in the equation oriented approach to process simulation and design calculations.
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  • 47
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979) 
    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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  • 48
    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 formulation is presented describing the reduction of iron oxide pellets with hydrogen in a counterflow moving-bed arrangement under conditions such that both the gaseous and the solids streams may be maldistributed. This maldistribution is imposed on the system by prescribing a radial variation in the void fraction and the particle size, together with a radial variation in the axial velocity of the solid stream.In the formulation, allowance has been made for realistic chemical kinetics and nonisothermal behavior. Computer results are presented for both the maldistributed system and for base line cases where uniform gas and solids flow have been postulated.It was found that maldistribution may play a very marked role in affecting the performance of the system, in particular, when the gas and the solid streams are mismatched, for example, preferential flow of gas near the walls and preferential flow of solids in the central core.
    Additional Material: 11 Ill.
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  • 49
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 843-855 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Drag coefficient and relative motion correlations for dispersed two-phase flows of bubbles, drops, and particles were developed from simple similarity criteria and a mixture viscosity model. The results are compared with a number of experimental data, and satisfactory agreements are obtained at wide ranges of the particle concentration and Reynolds number. Characteristics differences between fluid particle systems and solid particle systems at higher Reynolds numbers or at higher concentration regimes were successfully predicted by the model. Results showed that the drag law in various dispersed two-phase flows could be put on a general and unified base by the present method.
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  • 50
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 831-838 
    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 temporal variation of particle size and chemical composition of a marine aerosol exposed to SO2, NH3, NO, NO2, H2SO4 and H2O vapor is studied to determine the effect of these parameters on the sulfate and nitrate levels in the particle. Results show that, for gas phase SO2 oxidation to sulfate, and liquid phase nitrate formation, those parameters that enhance sulfate formation tend to inhibit nitrate formation, and vice versa. Further, for the situation considered, the ratio predicted for sulfate and nitrate ions to ammonium ions is very nearly that found if all these ions were present in the form of NH4NO3 and (NH4)2SO4. This compares favorably with data on sulfate, nitrate and ammonium levels in the Los Angeles area. The model used is capable of representing a general growing, reacting aerosol; other cases studied by this approach are briefly outlined. Limitations of its use are discussed.
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  • 51
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 893-895 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 5 Ill.
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  • 52
    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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  • 53
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 885-890 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 6 Ill.
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  • 54
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    AIChE Journal 25 (1979), S. 663-676 
    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 theory for predicting the effective axial and radial thermal conductivities and the apparent wall heat transfer coefficient for fluid flow through packed beds is derived from a two-phase continuum model containing the essential underlying and independently measurable heat transfer processes. The theory is shown to explain much of the confused literature and pinpoints the remaining major areas of uncertainty, further investigation of which is needed before secure prediction is possible.
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  • 55
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    AIChE Journal 25 (1979), S. 686-697 
    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 paper considers the transfer of mass or heat between a fluid and a small amplitude solid wavy surface. A periodic variation of the transfer rate can occur because of wave induced variations of the normal convective flow and of the properties of the turbulence. Solutions of the mass balance equations are presented for the laminar flow at a large Schmidt number or Prandtl number and for turbulent flow at large and small wave numbers. For turbulent flows at intermediate wave numbers, the prediction is limited by inadequacies of present theories that model the wave induced variation in the turbulent diffusion of heat or mass. In order to provide guidance for this modeling, new measurements on the variation of the mass transfer rate along a solid wavy surface are presented for a Schmidt number of 729. An analogy between momentum and mass transfer is explored as a means for evaluating the turbulent diffusion terms.The amplitude of the function describing the mass transfer variation is found to decrease with decreasing wave number and the phase to increase with decreasing wave number. The phase angle and the amplitude of the variation in the mass transfer rate relative to the average mass transfer rate are insensitive to changes in Schmidt number or Prandtl number. For turbulent flows, the phase change can be large enough that the maximum in the mass transfer rate can exist somewhere in the trough of the wave. This result is of considerable significance in interpreting wavelike dissolution patterns.
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  • 56
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    AIChE Journal 25 (1979), S. 697-701 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In a previous paper, we have examined the variation of the mass transfer rate along a small amplitude wavy surface which is exchanging mass with a turbulently flowing fluid. We now use these results to show that a soluble flat surface is unstable in the presence of a turbulent flow. The wavelength of the most rapidly growing surface disturbance, made dimensionless with respect to the friction velocity and the kinematic viscosity, is found to be a very weak function of the Schmidt number. These results provide a possible explanation for wavelike dissolution patterns observed in caves and on the underside of river ice. The analysis predicts that deposition patterns should be quite different from dissolution patterns in that the most rapidly growing wave for deposition has a length of zero.
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  • 57
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 1006-1015 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Methods for estimating the properties of electrolytic solutions are reviewed, with emphasis on molecule-molecule, molecule-ion, and ion-ion interactions. The algorithms of Parts I and II, to search for global minimum in Gibbs free energy, are extended to handle electrolytes and compared with an algorithm using k-values. Results are presented for SO2-H2O and H2S-NH3-H2O systems and agree with experimental values.
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  • 58
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    AIChE Journal 25 (1979), S. 1057-1064 
    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 overall heat transfer rates to stationary spheres of highly-polished molybdenum (2 to 5.6 mm in diameter) in a confined argon plasma jet were experimentally measured. The effects of large temperature differences and large variations of the fluid property on the heat transfer process are investigated. The sphere Reynolds number range between 10 and 80, and the sphere temperature between 1,200 K and 2,400 K, with temperature differences between the gas and the sphere in excess of 2,000 K. These conditions are within the range commonly encountered in industrial plasma processing. The experimental values of the heat transfer coefficients are in reasonably good agreement with the predictions of a theoretical analysis of variable-property flow and heat transfer previously reported by the authors.
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  • 59
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 1077-1080 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Calculations for the high Peclet number, entrance region (Lévêquelike) packed bed, mass transfer coefficient using a sinusoidal periodically constricted tube model for the void structure of the bed are presented. An inverse cube root dependence of the mass transfer coefficient on the bed depth is predicted. This length dependence is anticipated only at very low Reynolds numbers. Calculations which assume a mixing region between successive periods are also presented. No bed length dependence is anticipated in these coefficients.
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  • 60
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    AIChE Journal 25 (1979), S. 1081-1082 
    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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  • 61
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    AIChE Journal 25 (1979), S. 948-958 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Secondary nucleation kinetics for potash alum in draft-tube baffled crystallizers have been determined from steady state crystal size distributions measured down to about 5 μm. Differences in nucleation rates were found for crystallizers of similar geometry but different capacity. Models relating the frequency of crystal/propeller collisions to crystallizer geometry and operating parameters were compared. In general, these successfully accounted for the observed differences in nucleation rates.
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  • 62
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Solubilities of ethane, carbon dioxide, and hydrogen sulfide have been measured in propylene carbonate, N-methyl-2-pyrrolidone and tetramethylene sulfone (sulfolane); and in mixtures of these physical solvents with monoethanolamine and diglycolamine, in the range -10 to 100°C. Thermodynamically consistent equations are given for gas absorption with chemical reaction at equilibrium. Henry's law describes physical equilibrium between the acidic gas in the vapor phase and free acid solute in the liquid phase. Equilibrium constants describe chemical equilibria for the absorbed gas and the chemical solvent.Preliminary design calculations for sweetening natural gases by absorption with mixed solvents suggest that, under some circumstances, mixed-solvent absorption may be more economical than using conventional aqueous alkanolamine.
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  • 63
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    AIChE Journal 25 (1979), S. 1015-1024 
    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 is proposed for mass transfer of gases across surface-active films and into an aqueous phase. The interfacial region (1) obeys local equilibrium conditions, (2) has a capacity for the dissolved gases greater than the solubility in water, and (3) has a diffusion coefficient three orders of magnitude less than for that in water. The model is solved for and compared with three different experiments: the transient diffusion through monomolecular films into quiescent liquids studied by Plevan and Quinn (1966), the gas absorption through surfactant films into falling liquid films investigated by Emmert and Pigford (1954), and the frequency response of concentration pulses in surfactant films reported by Whitaker and Pigford (1966). The model consistently describes these experiments previously explained by three different models that either ignored the capacitance of the film or assumed local non-equilibrium.
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  • 64
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    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 1073-1077 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 65
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Unlike fibers, planar reinforcements, such as flakes and ribbons, provide reinforcement in two directions. If such reinforcements are arranged parallel to their principal plane in a composite material, they thus provide a distinctly higher performance than fiber reinforcements for two-dimensional loading conditions. This higher performance amounts to about a factor three for the Young's modulus and a factor two for the tensile strength. However, in spite of this obvious advantage, composites with planar reinforcements are as yet relatively unknown. This is mainly due to the fact that planar reinforcements are not as readily available as fiber reinforcements and therefore not much work has been done on them. The present article gives first a short outline of the theory of the elastic and tensile properties of composites with planar reinforcements. Then, a non-exhaustive review is presented of the work on composites with planar reinforcements, with particular attention given to recent developments. A final aim of this article is that by showing the merits of planar reinforcements as compared to presently existing fiber reinforcements, it may contribute to their use in the design of composite structures.
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  • 66
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The thermochemical and flammability properties of some thermally stable polymers considered for use in aircraft interiors are described. The properties studied include: (a) thermomechanical properties such as glass transition and melt temperature; (b) dynamic thermogravimetric analysis in anaerobic environment; (c) flammability properties such as oxygen index, flame spread and smoke evolution; and (d) selected physical properties. The thermoplastic polymers evaluated included polyphenylene sulfide, polyaryl sulfone, 9,9-bis(4-hydroxyphenyl)-fluorene polycarbonate-poly(dimethylsiloxane) and polyether sulfone. The thermoset polymers evaluated included epoxy, bismaleimide, a modified phenolic and polyaromatic melamine resin. These resins were primarily used in the fabrication of glass reinforced prepregs for the construction of experimental panels. Test results and relative rankings of some of the flammability parameters are presented and the relationship of the molecular structure, char yield, and flammability properties of these polymers are discussed.
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  • 67
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 19 (1979), S. 45-50 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Statistical mechanical methods can be used to relate not only structure and thermodynamics but also structure and kinetics. Methods are developed for calculating the crystal growth rate kinetic models. When the usual macroscopic thermodynamics are applied, the resulting surface energies, σ and σe extracted from the experimental growth rates are quite comparable to those obtained from kinetic models. However, when one applies small system thermodynamics, a substantially smaller σ is obtained. This latter assumption has the advantage of explaining why extended chain seed crystals do not promote crystal growth and why folded chain crystals grow on such seeds. The statistical mechanical methods in both of these cases predict the observed decrease in the rate constant, Kg with decreasing molecular length without the necessity of a separate theory for varying σe with molecular length.
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  • 68
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The methods of small systems thermodynamics have been applied to the calculation of the entropy barrier to the growth of polymer crystals. The height of this barrier at the equilibrium melting point of polyethylene molecules of typical lengths (X = 4,000 to 10,000 segments) is estimated to be of the order of 4 to 5 Kcal per molecule. This barrier increases linearly with ln X if the crystal is very large but retains the approximate values mentioned for crystals with the lamella thicknesses usually found. This entropy change causes the free energy to go through a maximum as in a nucleation phenomena but no new surface formation is involved. The existence of such a barrier explains why crystallization (or melting) never occurs at the equilibrium melting temperature.
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