摘要:

AbstractMost crude oils contain high molecular weight components, which at low temperatures may precipitate as a wax phase. This may cause plugging of pipes and numerous other problems. This paper presents a solid‐liquid equilibrium based model for the description of wax formation. The model for the Gibbs energy contains a contribution based on Flory's theory of multicomponent polymer solutions and a contribution from a metastable subcooled state which oil mixtures may attain. The latter is formulated in terms of the surface tension of the wax phase. Experimental wax appearance points (temperatures), WAP's, are reported for 17 different stabilized North Sea crude oils. The values predicted by the new model are in very good agreement with the experimental WAP'

ISSN:0001-1541    

DOI:10.1002/aic.690341202

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractNumber of passage distribution (NPD) functions in batch and continuous recirculating systems are presented, and their application to dispersive mixing of plastics and rubber is discussed. Dispersive mixing requires a process of repeated ruptures of the dispersed phase. This is accomplished by repeated passages in special regions of the system where stress levels above a given threshhold value are imposed on the liquid. The application of NPD functions to certain batch and continuous mixers and compounders is discussed.

ISSN:0001-1541    

DOI:10.1002/aic.690341203

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractAlternating current impedance measurements can be used as anin situmethod for characterizing rate‐limiting processes in fuel cell electrodes. Theoretical models have been derived and solved analytically. Theoretical analysis indicates that kinetic information can be extracted from the effect of temperature and gas composition on the size of the kinetic loop. The relative importance of kinetics and mass transfer can be inferred from AC impedance analysis. Several examples are given for the case of molten carbonate fuel cell (MCFC) electrodes. Such electrodes are not accessible to classical kinetic investigation techniques due to the high operating temperature and corrosive environment. Relevant kinetic information about MCFC electrodes has been obtained successfully using thisin situtechniqu

ISSN:0001-1541    

DOI:10.1002/aic.690341204

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe numerical simulation of nonisothermal effects during the filling stage of injection molding is investigated here. Generalized Newtonian fluid flows are simulated within thin cavities of arbitrary shape. The numerical scheme is based on a hybrid spatial discretization: classical low‐order Lagrangian interpolants are used in the midsurface directions, while full polynomials constitute the approximation in the gapwise direction. Discrete equations are obtained by use of the Galerkin finite element method combined with a collocation procedure. Special attention is devoted to the influence of the fountain flow (occurring at the front) on the temperature field. A correct writing of the front thermal boundary condition is derived in agreement with the Hele‐Shaw simplified form of the equations. Some illustrative results are presen

ISSN:0001-1541    

DOI:10.1002/aic.690341205

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractPartial molar properties at infinite dilution for binary Lennard‐Jones mixtures are calculated using Monte Carlo simulation methods. The variation of these properties with density, temperature, and intermolecular force parameters is systematically studied. Simulation pair correlation functions are used to examine the structure of the mixtures at the molecular level. Results are also compared to predictions of the van der Waals I conformal solution theory.Partial molar volume and internal energy are found to be strongly dependent on the isothermal compressibility of the mixture and on the proximity of the mixture state condition to phase boundaries. The van der Waals I conformal solution theory gave good results for the infinite‐dilution chemical potential μ 1∞and reasonable results for the partial molar internal energies and volumes. However, it is suspected that this is limited to the infinite‐dilution case, where the isothermal compressibility of the mixture is well represented by the pure‐fluid equat

ISSN:0001-1541    

DOI:10.1002/aic.690341206

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractMass‐transfer enhancement by a stream of bubbles rising near a planar, vertical surface is resolved spatially and temporally using a micromosaic electrode. A stream of gas bubbles is generated electrolytically, either at a segment directly below and in the plane of the monitoring electrodes, or at a wire tip that can be positioned inside or outside the mass‐transfer boundary layer. The mass‐transfer enhancement resulting from bubbles rising within the mass‐transfer boundary layer is found to be strong and localized, in agreement with trends predicted by a surface‐renewal model. Mass transfer resulting from bubbles rising outside the boundary layer is found to receive a steady, laminar enhancement, correlating well with predictions from an idealization of the bubble stream entraining a cylinder

ISSN:0001-1541    

DOI:10.1002/aic.690341207

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe ways in which modeling uncertainties are described for a particular process critically affects the results obtained in robustness studies. In this paper, four multivariable robust stability methodologies are used to characterize and analyze the effects of model inaccuracy due to non‐linearity in high‐purity distillation processes. The unstructured and structured singular value, numerical range, and a mapping of det(l+GPGc) are compared in terms of their ability to predict the stability of the dual‐composition control system over a wide composition range. The importance of using uncertainty descriptions that include a realistic representation of the phase‐magnitude relationship as well as the corrections between uncertainties in each element of the model is demonstrated. The conservation associated with norm‐bounded uncertainty descriptions reveals itself by the extent of detuning needed to insure stability and the subsequent degradation in control pe

ISSN:0001-1541    

DOI:10.1002/aic.690341208

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractWhen a porous solid is placed in acid, the solid dissolves at its surface. However, the same solid can precipitate or dissolve in pores inside the solid. The internal precipitation is a consequence of a nonlinear solubility product amplified by fast chemical kinetics. The internal dissolution can be enhanced by unequal diffusion coefficients. Both precipitation and dissolution can occur simultaneously but in different regions, mimicking the patterns of mineral found in teeth.

ISSN:0001-1541    

DOI:10.1002/aic.690341209

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe kinetics of dissolution of alumina in aqueous solutions of H2SO4was studied at ambient temperature under continuous‐flow conditions. The results are consistent with a model involving rapid hydration of the surface, adsorption‐desorption of H+to form precursor sites, and rate‐determining parallel reactions of the precursor sites to form dissolved aluminum and an insoluble surface species. The model also involves renewal of a precursor site after each dissolution step.The adsorption‐desorption of H+was represented by a Langmuir isotherm. The dissolution data were correlated by a kinetic equation that was developed by assuming the dissolution step is first order in precursor concentration, and the deactivation step is second order in precursor concen

ISSN:0001-1541    

DOI:10.1002/aic.690341210

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractIn spite of chromate's very high selectivity at acidic pH, fixed‐bed chromate‐exchange processes always suffer from severe gradual breakthroughs of chromate during column runs. Earlier, Sengupta and Clifford confirmed that such a gradual breakthrough is an equilibrium phenomenon and provided the underlying ion‐exchange mechanism. An algorithm, developed with the aid of the governing chromate ion‐exchange mechanism, is presented here to predict the salient properties of chromate‐exchange processes in a multicomponent system. The model predicts the gradual chromate breakthroughs during column runs fairly accurately and also accounts for other unusual characteristics of chromate ion exchange. Average separation factor models, often used for designing fixed‐bed ion‐exchange processes, are unable to predict the gradual breakthrough characteristics of a preferred component suc

ISSN:0001-1541    

DOI:10.1002/aic.690341211

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY