摘要:

AbstractDispersion‐free solvent extraction using microporous hydrophobic membranes has been extended to hydrophilic and composite hydrophobic‐hydrophilic membranes. Excess phase pressure conditions, if needed for dispersion‐free operation, have been identified. Boundary layer and membrane resistances to solute transport have been isolated and simple relations developed for the overall mass transfer coefficient in such systems. A variety of flat microporous membranes have been utilized. Previous investigations by others had interpreted the membrane mass transfer resistance using the notion of unhindered diffusion through tortuous pores of the membrane. We have studied here the applicability and limitations of such a model for a number of membrane‐solute‐solven

ISSN:0001-1541    

DOI:10.1002/aic.690330702

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractFault diagnosis is the problem of determining the root causes of process upsets. This paper presents a very efficient method of identifying the possible causes of process disturbances using the signed directed graph (digraph) representation of process interactions. The analysis is based on forming logical statements (rules) derived from the process digraph; these are evaluated using on‐line data to yield the diagnosis. Evaluation of rule antecedents is more efficient than the previous algorithmic approach of Shiozaki et al. In the rule‐based approach, the diagnostic criteria are represented explicitly, not hidden by a complex algorithmic procedure. This allows the diagnostic rules to be tailored to reflect the best available knowledge of plant behavior. The rules generated by this technique can be integrated with other rules on plant operations using an expert systems framew

ISSN:0001-1541    

DOI:10.1002/aic.690330703

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractA new method to design adaptive, self‐tuning controllers is presented that incorporates decoupling for multivariable control problems. The algorithm is shown to result from two very different derivations. The first approach employs multiple single‐input/single‐output self‐tuning controllers but with a classical decoupling scheme incorporated; the second approach utilizes a novel selection of design parameters in an existing multivariable self‐tuning control method. The decoupling self‐tuning controller is capable of handling unknown or time‐varying time delays. Simulation studies utilizing two distillation column models show that the controller can provide excellent control even for highly nonlinear and highly interact

ISSN:0001-1541    

DOI:10.1002/aic.690330704

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractAn experimental study of the effect of turbulent mixing on the selectivity of a parallel‐consecutive reaction system (A+B→R;R+B→S) has been carried out in an unmixed feedstream (multijet) tubular reactor. Fluid mechanical characterization of the reactor by pulsed ultrasound Doppler velocimetry reveals that the mean and rms velocity fields are nearly constant over eight‐ninths of the reactor length. Axial profiles of mean product concentration (RandS) have been measured spectro‐photometrically with a fiber‐optic probe under constant hydrodynamic conditions but with variable feed concentration conditions. The concentration profiles (particularly theSprofile) show very large deviations from the perfect mixing (classical plug flow reactor) limit. These data provide a good basis for discriminating among the many models of mixing and reaction available in the literature. This is demonstrated with two examples: the four‐environment model, which fits the data well, and the interaction by exchange with the mean model, w

ISSN:0001-1541    

DOI:10.1002/aic.690330705

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractArrested‐flow chromatography was used to determine intraparticle diffusivities of large‐pore particles packed in columns. Particle and column tortuosity factors were determined for helium tracer in nitrogen carrier gas at 40°C and atmospheric pressure. Semiempirical modifications of Maxwell's, Burger's, Jeffrey's, and Rayleigh's relations for the composite diffusivity of spherical particles in a stationary medium are proposed for the effective composite diffusion coefficient for a packed bed of porous particles. The equations, modified to represent accurately the extraparticle void diffusion based on measurements for beds of nonporous particles, are used to evaluate intraparticle diffusivities from experimental data obtained by arrested‐flow chromato

ISSN:0001-1541    

DOI:10.1002/aic.690330706

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractThe phenomenological equations that govern the nonequilibrium behavior of the ionic diffuse double layer surrounding an isolated, charged coloidal particle are considered. An approximate solution is constructed that is valid when the ratio of the Debye length to the characteristic particle dimension is small. This solution is applicable to a particle that is subjected to an external perturbation composed of an arbitrary linear combination of steady, axisymmetric electrical, hydrodynamical, or concentration gradient fields. Hence, this analysis provides a unified approach to the treatment of the entire class of admissible problems in the thin double layer approximation. Specific applications are shown to the problems of electrophoresis and dilute shear viscosity of a suspension of uniform, noninteracting spherical colloidal particles. Comparison with the numerical results of previous investigators shows that the solutions are accurate over much of the parameter range of practical interest in colloidal suspensions. The role of the zeta potential and the mobilities, valences, and concentrations of the dissolved ions on electrokinetic phenomena are examined.

ISSN:0001-1541    

DOI:10.1002/aic.690330707

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractA high‐temperature heat transfer probe capable of measuring both the total and radiative heat transfer coefficients between an immersed surface and the bed has been designed, fabricated, and tested. Measurements of these coefficients in beds of 559 and 751 μm sand particles at temperatures up to 1,175 K have been made using this probe. A thermal analysis of the probe is developed in order to ensure a reliable interpretation of the measured quantities. The dependence of the total and radiative heat transfer coefficients on such parameters as bed temperature, fluidizing air velocity, and mean bed particle size are investigated. The various models proposed to describe high‐temperature heat transfer are evaluated from this perspective. The models capable of best simulating the heat transfer process with relative ease of computation are identified and evaluated using data generated in the s

ISSN:0001-1541    

DOI:10.1002/aic.690330708

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractSteady states with different flow rates and temperature profiles may exist in a packed‐bed reactor operating under a prescribed pressure drop, due to the coupling among the species, energy, and momentum balances and the change of the physical properties with temperature and pressure. Thisthermoflow multiplicitymay be found even for reactions whose rate is rather insensitive to temperature changes (low activation energy) and may lead to highly undesirable operation of multitube packed‐bed reactors. A hierarchy of models based on different assumptions is used to derive criteria for predicting the conditions under which this thermoflow multiplicity may oc

ISSN:0001-1541    

DOI:10.1002/aic.690330709

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractGeneralized Taylor dispersion theory for nonreactive solutes (Brenner 1980a; 1982) undergoing convection and diffusion is extended to include irreversible first‐order volumetric and surface chemical reactions possessing position‐dependent reactivity coefficients at the microscale. For sufficiently long times the equivalent chemical kinetic description of the rate of solute depletion at the macroscale is shown to manifest itself as a single constant reactivity coefficient K̄* characterizing an apparent first‐order irreversible volumetric reaction. Subtraction of this gross solute depletion rate from the original microscale transport equation permits the resulting Taylor dispersionlike problem to be resolved by a solution scheme closely paralleling that for the comparable nonreactive case. This allows a straightforward determination of the mean global solute velocity vector Ū* and dispersivity dyadic D̄* appearing in the macroscale convection‐diffusion‐reaction equation describing the local‐space averaged mean transport process. By way of example, these three coefficients are explicitly calculated for reacting and diffusing solute particles sedimenting from a solvent flow occurring between two parallel plates onto the reactive surface of one o

ISSN:0001-1541    

DOI:10.1002/aic.690330710

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY

摘要:

AbstractMoldability criteria and process optimization for both reactive and thermoplastic injection molding hinge on the mold‐filling step. The fluid mechanics of the filling step is typically described in terms of a one‐dimensional main flow and a complex two‐dimensional flow near the advancing front, often termed the “fountain flow.” A unique apparatus which permits direct observation of the fountain flow in a rectangular cavity is described. The motion of tracer lines as well as the pathlines have been photographed for both Newtonian and shear‐thinning liquids. The data show clearly the main flow, the transition to the front flow, and the deceleration and acceleration zones in the fountain flow, which lead to a “mushrooming” of the tracer line.In addition, Galerkin finite‐element analysis is used to predict the isothermal free‐surface flow of a Newtonian liquid near the advancing front between parallel plates. The most interesting visualization of the calculated flow is obtained by tracking lines of material, thus producing numerical tracer experiments. The calculations show the widely varying residence times and the complex shear and extensional deformation histories of fluid elements as they move through the fountain flow region. The calculations are in agreement with the experiments and clarify previous results, both theoretical and experimental, that did not capture the details of th

ISSN:0001-1541    

DOI:10.1002/aic.690330711

出版商:American Institute of Chemical Engineers    

年代:1987

数据来源: WILEY