摘要:

AbstractThis investigation was undertaken to determine the rate controlling step in the reduction of iron oxides with hydrogen and carbon monoxide. For the reduction of porous hematite pellets, and bars it was found that the reduction rate is controlled by the counterdiffusion of reactant gas and product gas between the reaction zone and the main gas stream.The reduction specimens were spheres ranging in size from 1.5‐ to 4.4‐cm. diameter and 5.1‐ by 7.6‐cm. bars either 0.69 or 1.24 cm. thick. They were prepared from electrolytic iron powder, partially oxidized in a rotary kiln. The final oxidation of the specimens to hematite was accomplished by firing them at 1,149°C. in an oxidizing atmosphere. The bulk density was 3.5 g./cc. The specific surface area was 0.08 sq.m./g. and the void faction was 0.31. The oxide specimens were reduced in streams of pure hydrogen or carbon monoxide at temperatures between 700° and 1,200°C. The reduction was followed by measuring the sample weight during the reaction. Reduction rates were studied at system pressures of 1 and 2 at.The samples reduced step by step, to magnetite, to wüstite, and finally to iron. A shell of reduction, clearly visible in sections of partially reduced specimens, moved concentrically into the core of the samples. Ahead of the receding interface the specimens were known to be pervious to the reactant gases. This led to the conclusion that the gas composition at the interface was in equilibrium with the oxide phases present.Except for the removal of the last portions of oxygen at the lower reduction temperatures, the course of the reduction followed Fick's first law of diffusion. Values of the diffusion co‐efficients, determined from the experimental data, were in close agreement with values predicted from empirical equations. Varying the total pressure of the system had no effect on the rate of reduction, which is consistent with the equations developed from Fick's law for the diffusion‐controlled reaction under investigation.It is speculated that the retarding of the reduction reaction at the lower reduction temperatures is due to the entrapment of oxide inside shells of iron, which are impervious to the reducing gas. Reduction of the trapped oxide then proceeds by solid state diffusion in a manner proposed

ISSN:0001-1541    

DOI:10.1002/aic.690080114

出版商:American Institute of Chemical Engineers    

年代:1962

数据来源: WILEY

摘要:

AbstractThis study of the factors underlying the mechanisms of particle growth in a fluidized calciner was conducted in a 3‐in. diameter column. In such a calciner radioactive waste liquor from nuclear fuel reprocessing can be converted to a granular solid for disposal. To simulate the octual waste, aluminum oxide as bed material and aqueous aluminum nitrate solution as feed were used. Particle growth was traced through the addition of radiactive seeds. The effects on the growth rate of operating variables and physical properties of the feed were investigated. Statistical analysis of the data substantiated the proposed growth mechanism, and the resulting growth coefficient was correlated with the variables studie

ISSN:0001-1541    

DOI:10.1002/aic.690080115

出版商:American Institute of Chemical Engineers    

年代:1962

数据来源: WILEY

摘要:

AbstractViscosities available in the literature for the gaseous and liquid states of eleven substances have been correlated with reduced density by the use of dimensional analysis and the Abas‐zade expression for the residual viscosity to produce a single generalized relationship which is presented both graphically and analytically. The substances are argon, nitrogen, oxygen, carbon dioxide, sulfur dioxide, methane, ethane, propane,i‐butane,n‐butane, andn‐pentane. The properties required for the calculation of viscosity with this relationship are the molecular weight, the critical constants, and the density of the substance at the temperature and pressure considered.Separate relationships were developed for hydrogen, ammonia, and water which do not follow the consistent behaviour of the other substances. Viscosity values for ethylene calculated with the generalized relationship compared favorably with the corresponding experimental

ISSN:0001-1541    

DOI:10.1002/aic.690080116

出版商:American Institute of Chemical Engineers    

年代:1962

数据来源: WILEY

摘要:

AbstractA simple one‐dimensional transport calculation is made which indicates that latent heat transport, by simultaneous evaporation and condensation at different portions of the bubble surfaces, can account for the major portion of the total heat flux in the neighborhood of the departure from subcooled nucleate boiling (burnout). This differs from the previously held view that the stirring action of the bubbles accounted for most of the heat flow in subcooled nucleate boiling. Other evidence is discussed which favors the latent heat transport theor

ISSN:0001-1541    

DOI:10.1002/aic.690080117

出版商:American Institute of Chemical Engineers    

年代:1962

数据来源: WILEY

摘要:

AbstractAn analysis is given of the role of physical and chemical forces in determining the selectivity of a solvent for different hydrocarbons. The physical contribution to selectivity depends on the polar energy density of the solvent and on the difference in size of the hydrocarbons to be separated; this effect is well‐demonstrated by solvent selectivity data for paraffins where no chemical forces are important. The chemical contribution depends on the ability of the solvent to form acid‐base complexes with the hydrocarbon. Chemical forces leading to complex formation can be detected by measurements on the heat of mixing, the volume change of mixing, and on the ultraviolet absorption of solvent‐hydrocarbon mixtures; some illustrations of such measurements are presented. Finally an equation is proposed for correlating selectivity data in extractive distillation, and its applicability is demonstrated with activity coefficient data for saturated and unsaturated hydrocarbons in various polar sol

ISSN:0001-1541    

DOI:10.1002/aic.690080118

出版商:American Institute of Chemical Engineers    

年代:1962

数据来源: WILEY

摘要:

AbstractStudies of mass transfer with rapid, homogeneous, irreversible reactions between dilute species with equal difusivities are carried out with a device which reduces the system of mass transfer‐reaction equations to the equations for mass transfer in the absence of reaction.A relationship which gives the rate of transfer into stagnant, laminar, or turbulent reacting systems is developed. Under some conditions the reaction increases the transfer rates by a constant factor, while under other conditions the reaction increases the individual or over‐all mass transfer coefficients by a constant factor.Calculations of concentration profiles, conversion, etc. are carried out for the Graetz problem with a homogeneous reaction between a dilute species in the fluid and a dilute species diffusing from the tube wall. Reaction completion times for various stagnant elements in infinite media are given.Although the flux into a turbulent reacting fluid is related to the time average behavior in the absence of reaction, the time average concentrations depend also upon the relative intensity of the concentration fluctuations in the absence of reaction. This latter dependence is obtained from a relationship of Hawthorne, et al.Surfaces on which the time average composition is stoichiometric and the reactant concentrations are proportional to the relative intensity of the concentration fluctuations in the absence of reaction are obtained for turbulent flow in a tube with a homogeneous reaction between the fluid and wall. Distances for almost complete reaction are estimated.The time average conversion is related to the accomplished mixing for the case in which two dilute reactants are turbulently mixed. In a uniform, stoichiometric mixture the fractional conversion equals the accomplished mixing. Calculations are carried out for uniform, nonstoichiometric mixtu

ISSN:0001-1541    

DOI:10.1002/aic.690080119

出版商:American Institute of Chemical Engineers    

年代:1962

数据来源: WILEY

摘要:

AbstractThis study forms part of a project aimed at obtaining a better understanding of the behavior of nonideal permselective membranes. The object here was to determine the applicability of the Nernst‐Planck equations for studying the behavior of ions in aqueous solutions surrounding such a membrane during electrodialysis.Attention was confined to stagnant and laminar flow systems. The processes studied were transfer of hydrogen ions, silver ions, and mixtures of the two through the cation exchanging membrane Nepton CR‐61. The bulk solution concentrations on either side of the membrane varied from 0.01 to 0.20 N, and in all cases the only anions present were nitrate ions. Limiting currents for solutions of silver nitrate were predictable within 15%, with much of the uncertainty resulting from the difficulty in defining the limiting current. For mixtures of silver nitrate and nitric acid the limiting currents were predictable within the range of experimental accuracy but were found to be quite sensitive to small changes in the operating conditions. This sensitivity results from the very high relative mobility of the hydrogen ions. The relative transport of the two cations was primarily a function of relative concentration, relative diffusivities, current density, and ion exchange equilibria and was predictable with an accuracy limited only by the uncertainty of the ionic diffusivities and the ion exchange equilibria.The diffusivities of the cations in the membrane relative to the diffusivity of nitrate ion were estimated to be about ten times lower than in solution. This was explained by assuming that the cations tended to concentrate about the anionic fixed charges of the membrane thereby portially screening their effectiveness and reducing the mobility of the cations. In mixtures, the membrane diffusivity of the silver ions relative to the hydrogen ions was lower (by a factor of 1.4 to 3.6) than the relative diffusivity in solution. This indicated that silver ions were more easily concentrated about the fixed charges and thereby screened them from both the anions and hydrogen i

ISSN:0001-1541    

DOI:10.1002/aic.690080120

出版商:American Institute of Chemical Engineers    

年代:1962

数据来源: WILEY

摘要:

AbstractA study has been made of the second virial coefficients of binary gas mixtures containing one or two polar components. Methods for calculating these coefficients are presented. The interaction coefficientBijfor a polar‐polar interaction cannot be calculated with the Stockmayer potential with pure component parameters only; such calculations tend to underestimate the strong forces of attraction between dissimilar polar molecules. It is shown that the characteristic distance for the reduced dipole moment for two dissimilar polar molecules is less than the arithmetic average of the distance parameter of the similar molecules by an amount which can be related to the enthalpy of complex formation. When this corrected collision diameter is used in the Stockmayer potential, good results can be obtained for interaction coefficientBij. In the case of a polar‐nonpolar mixture the coefficientBijdepends on dispersion and on induction forces. Techniques are proposed for estimating these forces from pure component parameters, and it is shown that for accurate calculation ofBijit is necessary to correct for the displacement of the dipole from the center of the polar molecule. The paper concludes with some illustrations of how these ideas may be applied to typical chemical engineering probl

ISSN:0001-1541    

DOI:10.1002/aic.690080121

出版商:American Institute of Chemical Engineers    

年代:1962

数据来源: WILEY

摘要:

AbstractMass transfer coefficients were measured for particles suspended in agitated, baffled tanks. The coefficients for a given particle size and a given fluid vary with the 0.10 to 0.15 power of the power dissipated per unit volume. The coefficients, which cover a one hundred fold range, are about 1.5 to 8 times those predicted from the correlations for fixed particles if the terminal vilocity is used to calculate the particle Reynolds number. The measured effects of particle diameter, diffusivity, viscosity, and density difference cannot be described by a simple expenential equation or by previous empirical correlations. The effects of these variables can be explained by using a slip‐velocity theory combined with a modified penetration theor

ISSN:0001-1541    

DOI:10.1002/aic.690080122

出版商:American Institute of Chemical Engineers    

年代:1962

数据来源: WILEY

摘要:

AbstractMass transfer coefficients are reported for particles of boric acid and benzoic acid dissolving in water in a 2‐in. pipeline. For water velocities of 1 to 4 ft./sec. the coefficients are 1.2 to 2 times the values predicted for freely falling particles. The coefficients are slightly less than those obtained in agitated tanks at the same power per unit volum

ISSN:0001-1541    

DOI:10.1002/aic.690080123

出版商:American Institute of Chemical Engineers    

年代:1962

数据来源: WILEY