摘要:

AbstractSpontaneous combustion may occur in a coal stockpile when the heat generated within the pile cannot be dissipated at near ambient temperature. Under practical conditions, natural convection enhances the rate of heat removal from the bed and shifts the ignition to lower particle sizes (higher reactivities). Analysis of three limiting cases of a one‐dimensional model yields criteria predicting the conditions under which ignition occurs as well as those for which a low‐temperature (extinguished) state exists for all particle sizes. A simple asymptotic relation predicts the ignition point at large Rayleigh numb

ISSN:0001-1541    

DOI:10.1002/aic.690340302

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA three‐dimensional radiation model coupled with two‐dimensional mass balances for the intervening chemical species is solved for the photochemical chlorination of ethane. The analysis was carried out using the full mechanistic kinetic sequence and employing polychromatic radiation for a process conducted in a tubular reactor placed inside an elliptical reflector.Theoretical predictions were compared with bench‐scale experiments and showed excellent agreement. Using the validated model, computational experiments were conducted to explore the influence of reactor design and operational parameters upon the degree of chlorination. Dichlorination reactions were also added to the kinetic model to analyze reactor behavior from the viewpoint of selectivity. Thea prioridesign method described can be applied from first principles and requires no experimentally adjustable param

ISSN:0001-1541    

DOI:10.1002/aic.690340303

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractBifurcation problems with slowly varying control parameters are of interest in several research areas, including catalyst deactivation, combustion, and lasers and other nonlinear optical devices. Significant theoretical work has been devoted to the study of these dynamic phenomena, but very little directly relevant experimental information is currently available. Results are presented here from an experimental study of the dynamic behavior of a catalytic reaction system due to a deliberately slowly varied control parameter. Attention is focused on the dynamics due to slow passage through simple limit and Hopf points.

ISSN:0001-1541    

DOI:10.1002/aic.690340304

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe structure of the wavy interface on a falling liquid film is studied for conditions of countercurrent gas flow in order to investigate mechanisms for flooding. Measurements taken just below the liquid feed and at 1.7 m down the tube show that under all conditions, including flooding, the waves propagate only downward and are never of such amplitude as to bridge the tube. These observations are in contrast to speculations in the literature that upward flow of waves or bridging of liquid due to waves cause flooding. In the mechanism suggested, flooding is due to flow reversal in the film just at the liquid entry.

ISSN:0001-1541    

DOI:10.1002/aic.690340305

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe ideal adsorbed solution (IAS) theory of adsorption of gas mixtures is extended to the case of energetic heterogeneity. A heterogeneous ideal adsorbed solution (HIAS) behaves ideally on a particular site, but energetic heterogeneity causes a segregation in the composition of the adsorbed phase. Equilibrium properties are obtained by integrating over a multivariate energy distribution based upon perfect positive correlation of site energies. The fact that predictions from HIAS are always an improvement over IAS indicates that heterogeneity is a factor that must be considered in theories of mixed‐gas adsorption. Errors in HIAS predictions may be caused by steric exclusion of the larger molecules from micropores accessible to smaller molecule

ISSN:0001-1541    

DOI:10.1002/aic.690340306

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractAdvancing and colliding flow fronts are important fluid mechanical problems in injection mold filling. These are small‐scale, transient free‐surface flows with a significant impact on the molecular orientation of molded parts. This paper describes a numerical technique for the simulation of transient free‐surface flows. The algorithm combines a Galerkin/finite‐element discretization of the governing equations with a predictor‐corrector scheme for integration in time, and determines simultaneously the flow field and the free surface at every time step. The method is applied to the start‐up of a fluid flow initially at rest and impingement of two flow fronts to form a weldline. Comparison of simulation with available experiments on the start‐up problem shows very good agreement. Numerical tracking of fluid elements clarifies various aspects of flow‐induced deformation

ISSN:0001-1541    

DOI:10.1002/aic.690340307

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA novel amidoxime‐group‐containing adsorbent of hollow‐fiber form (AO‐H fiber) was prepared by radiation‐induced graft polymerization of acrylonitrile onto a polyethylene hollow fiber, followed by chemical conversion of the produced cyano group to an amidoxime group. Distribution of the amidoxime group was uniform throughout the hollow‐fiber membrane. The fixed‐bed adsorption column, 30 cm in length and charged with the bundle of AO‐H fibers, was found to adsorb uranium from natural seawater at a sufficiently high rate: 0.66 mg uranium per g of adsor

ISSN:0001-1541    

DOI:10.1002/aic.690340308

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractGas separation behavior of permeators containing asymmetric cellulose acetate hollow fibers with the dense skin on the outside, facing the feed gas, has been investigated experimentally and theoretically using a sweep gas technique. Two systems were studied: CO2‐N2, and O2‐N2(air). If the membrane structure is assumed to be symmetric or homogeneous, the model complies with the present data much better, compared to the assumption that the membrane is asymmetric.Separation was carried out with the high‐pressure feed outside the fibers as well as inside the fibers. In both cases the data were well predicted by the homogeneous model. No concentration polarization effects were found when the feed flowed inside the fibers. The inherent membrane separation capability appeared practically the same whether the feed was inside or outside the fibers. Internal pressurization did not damage the membrane performance for the low pressure range used.These findings enable the operation of asymmetric hollow‐fiber permeators with the feed inside the fiber lumen, which gives better separation in high stage cut sit

ISSN:0001-1541    

DOI:10.1002/aic.690340309

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe effect of pore structure on the gasification of two chars impregnated with potassium carbonate catalyst is investigated. Well‐characterized char samples were reacted with carbon dioxide, water vapor, and oxygen. The effects of catalyst on the magnitude of the gasification rate as well as on the entire rate vs. conversion pattern are reported. Reactivity and structural data are analyzed to obtain a meaningful comparison of the gasification behavior for all char‐gas pairs. Initial intraparticle catalyst dispersion was strongly influenced by the pore structure of the chars. During gasification with carbon dioxide and water, the catalyst appeared to redistribute itself in accordance to the accepted reaction mechanism, leading to superior catalytic activity. The reported measurements indicate that both the pore structure of the chars and the chemistry of a particular reaction are key factors in determining the overall catalytic performa

ISSN:0001-1541    

DOI:10.1002/aic.690340310

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA detailed mathematical model is used to predict local and effluent properties within an axisymmetric, entrained‐flow gasifier. Laboratory experiments were conducted to provide local properties for four coal types from a gasifier operating at near‐atmospheric pressure. Effects of selected model parameters and test variables were examined and compared with measurements in most cases. The comparison of predictions and measurements provides the first evaluation of capabilities and limitations of a comprehensive model for entrained‐flow gasi

ISSN:0001-1541    

DOI:10.1002/aic.690340311

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY