ISSN:0001-1541    

DOI:10.1002/aic.690350302

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractExperiments were conducted to study the hydrodynamics of a gas‐liquid‐solid fluidized bed containing low‐density particles. The density and size of the particles employed were comparable to those ordinarily encountered in fluidized‐bed bioreactors for either wastewater treatment or fermentation. A dual resistivity probe and a conductivity probe were employed to study the axial holdup of gas and liquid phases and the bubble size distribution. The behavior of the axial holdup distribution for solid, gas, and liquid phases is reported. A mechanistic model, based on solids entrainment and deentrainment mechanisms by bubbles, is developed to describe the behavior of the axial solids holdup distribution. The model is shown to satisfactorily account for the experiment

ISSN:0001-1541    

DOI:10.1002/aic.690350303

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe approximate equations of Hassler and Brunner and of van Domselaar are often used to deduce the capillary pressure curve of a porous medium from centrifuge data. The use of these equations restricts the centrifuge method to short samples. Also, these equations require differentiation of data. We report here methods to determine the capillary pressure curve by the midpoint and least‐squares solution of the fundamental equation, relating the average saturationS1of liquid in the porous medium to the capillary pressurePc1at the end of the sample nearest the axis of rotation. The methods do not require differentiation of data and are not restricted to short samples. We introduce and evaluate an approximation based on an exact result derived by Rajan. This new approximation requires the same inputs as do the Hassler‐Brunner and the van Domselaar approximations, but it is accurate over a wider range of sample sizes. In addition, an approximate solution which can be used to estimate capillary pressure curves for long cores is develo

ISSN:0001-1541    

DOI:10.1002/aic.690350304

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractSteady states with different flow rates and temperature profiles may exist in different tubes of a multitube packed‐bed reactor due to the coupling among the species, energy and momentum balances, and the change of physical properties with temperature and pressure. Under typical operating conditions if no axial conduction of heat occurs thermoflow multiplicity can be found only for unrealistically high heats of reaction and/or over a very narrow range of exit pressures. However, accounting for the finite but small heat conduction in the reactor tubes leads to multiplicity for typical parameters and a reasonable range of exit pressures. Cooling tends to decrease the region of parameters for which the multiplicity occur

ISSN:0001-1541    

DOI:10.1002/aic.690350305

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA model is developed for fluid‐solid reaction kinetics in a porous solid. The model is based on a convergent‐divergent pore structure and accounts for pore blockage and inside cavities. A numerical study applied the model to the process of coke removal for catalyst regeneration. The calculated results show that in the presence of pore occlusion, the reaction rates are significantly reduced at the beginning of reaction. At higher levels of coke loading the reaction behavior can be especially affected by the volume fraction of the divergent pores. This behavior can be used to select catalysts with pore structures that improve control of the regeneration proc

ISSN:0001-1541    

DOI:10.1002/aic.690350306

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractGas holdups (ϵGR) and liquid‐phase volumetric oxygen transfer coefficients (kLaT) were measured for a bubble column (BC) and three different external‐circulation‐loop airlift (ECL‐AL) fermentors of 50 to 60 L working volume, using viscous non‐Newtonian aqueous solutions of various carboxymethylcelluloses. Some measurements also were done with a viscous Newtonian system (51.8 wt. % sucrose solution).Discussed in this paper are correlations of ϵGRandkLaTwith riser superficial gas velocity (0.02 ≦UGR≦ 0.26 m/s), the ratio of the downcomer and riser crosssectional areas (0[BC] ≦Ad/Ar≦ 0.444), and the effective viscosity of the liquid phase (0.02 ≦ ηeff≦ 0.5 Pa · s), over the parameter ranges indicated. It is shown that both ϵGRandKLaTare highly dependent uponUGRandAd/Ar. The effective viscosity has a significant effect onKLaT, but has only a relatively weak affect on ϵGR. TheKLaTcorrelation developed for non‐Newtonian systems was extended to include the results obtained for the viscous Newtonian system studied by incorporating the effects of liquid‐phase molecular diffusivity, density, and interfacial tension as determine

ISSN:0001-1541    

DOI:10.1002/aic.690350307

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe pipeline mixing of two fluid streams by turbulent jet injection normal to the pipeline has been studied theoretically and experimentally. A simple scaling law for the second moment of the tracer concentration within the pipeline is proposed for the first fifteen pipe diameters down‐stream from the injection point. The similarity solution is derived by assuming that the tracer diffuses in a weak compound jet moving parallel to the pipeline axis. The theoretical results are correlated with all of the available experimental measurements. The results indicate that the second moment of the tracer concentration decreases with increasing jet momentum and distance from the injection point such thatM= 0.25. (lm/D)−2(x/D)

ISSN:0001-1541    

DOI:10.1002/aic.690350308

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe non‐Newtonian viscosities of polymerically stabilized colloidal suspensions are usually predicted and correlated on the basis of data and scaling principles for Brownian hard spheres. Here, the specific effect of the stabilizer layer is investigated using suspensions of monodisperse PMMA particles with a chemically attached stabilizer layer. The ratio between particle radius and stabilizer layer thickness is changed between 5 and 61. At high values of this ratio the data show Brownian hard sphere behavior. At lower values deviations appear. As a first approximation, the “softness” of the particles can be characterized through the concentration at maximum packing. A more detailed comparison with hard sphere data provides a measure for softness that changes with concentration and shear rate. A theoretical estimate of the concentration effect is in line with the experiments. The critical shear stress (or Peclet number) is not a constant but goes through a maximum when the concentration is incr

ISSN:0001-1541    

DOI:10.1002/aic.690350309

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA technique based upon transmission FTIR to obtain rate constants for adsorption and desorption over supported metal catalysts has been developed and tested. The technique requires the use of a sinusoidal perturbation function imposed on steady state linearized adsorption‐desorption kinetics. The measurement of a phase lag between the sinusoidal inlet gas phase forcing concentration and the response of surface coverage, together with a measurement of the maximum amplitudes of the forcing function and surface response enable the calculation of the relevant adsorption and desorption rate constants.The technique has been successfully applied to the measurement of both adsorption and desorption rate constants for CO adsorbed on a 1% Pt/SiO2catalyst. The values obtained for these rate constants at 343 K were:Ka= 0.147 s−1andKd= 7.28 × 10−3s−1. A sticking coefficient corresponding to the adsorption of weakly bonded CO on Pt under conditions of high CO surface coverage was

ISSN:0001-1541    

DOI:10.1002/aic.690350310

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA multiphase model for the flow of dense, noncolloidal, settling slurries through horizontal pipelines, and an associated Galerkin‐finite element numerical scheme to carry out computer simulations based on the model, were developed. The principal elements of the model are: equations for estimation of the velocity distributions for each component; and those for the concentration distributions. In the former, which are derived from the local volume‐averaged, time‐smoothed conservation of mass and momentum equations, the total stress is comprised of components to account for interparticle and particle‐boundary as well as viscous and turbulent interactions. The governing equations for the concentration distributions are derived similarly from the convective diffusion equation, with the eddy diffusivity modified to account for the presence of the solid particles. Numerical simulations and detailed comparisons with experiment for the flow of gypsum, coal, crushed glass, sand and gravel, covering particle sizes from 38.3 μm to 13,000 μm, and pipe diameters from 4 cm to 49.5 cm, were carried out. The agreement between model prediction and experiment is

ISSN:0001-1541    

DOI:10.1002/aic.690350311

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY