摘要:

AbstractTwo‐dimensional chaotic mixing of similar Newtonian fluids in the presence of an advected dissimilar minor phase fluid body with specified size, interfacial tension, and viscosity ratio was numerically investigated. Interfacial tension was sufficiently high to allow only small deformations in the dissimilar minor phase body. Mixing was confined to a rectangular cavity with periodically driven upper and lower surfaces. Regions of regular motion (i.e., islands) of comparable size to the minor phase body were eventually destroyed or replaced by the minor phase body. Islands persisted for longer times when the initial separation distance between the minor phase body and island was large or when the viscosity ratio was small. When interfacial tension was small enough to deform the minor phase body more readily, islands showed little indication of instability. Results suggest opportunities for improving mixing uniformity in practical processes and disclose how interactions between dissimilar fluids affect mixin

ISSN:0001-1541    

DOI:10.1002/aic.690421202

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractShort contact time circulating fluidized beds (CFBs) are high‐performance reactors with great potential of application for fast endothermic reactions. Optimal kinetic conditions require high operating temperature and very short residence time (∼0.15 s), as well as plug flow in the reaction zone, and fast and efficient solid separation before quenching effluents. Hydrodynamics of dilute CFB operated at high gas velocity was simulated in isothermal condition. The gas‐flow field is described using turbulence closure models developed for the single phase and modified to account for particle presence. Numerical computation was compared with experimental results of Arena et al. (1993) and Tinaburri et al. (1996) for two different riser configurations. A parametric analysis was performed to investigate inlet geometry influence on flow pattern along the riser. Internal tube and circumferential gas inlet produced the most promising configuration to realize optimal flow cond

ISSN:0001-1541    

DOI:10.1002/aic.690421203

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractExtensive small‐angle X‐ray and neutron‐scattering data, as well as results of precipitation measurements, are analyzed to delineate the structure of the asphalt and asphaltene aggregates that are formed when a solvent is injected into a system containing crude oil. The two types of data strongly suggest that both small and large aggregates have a fractal structure, with well‐defined fractal dimensions. If the system is aged long enough at low enough temperature, large asphalt particles will have the structure of diffusion‐limited cluster–cluster aggregates with a fractal dimension Df≃ 1.8, while the small ones are similar to diffusion‐limited particle aggregates with a fractal dimension df≃ 2.5. High temperatures increase the rotational motion of the particles, disturb the structure and mechanical stability of the aggregates, and decrease their fractal dimension. Aging and concentration effects of the asphalts in the solution, and the type of the solvent on the structure of the aggregates are also investigated. Implications of these results for the structure, mechanical stability, and molecular‐weight distribution of asphalts and asphaltenes are detailed. A new molecular‐weight distribution for asphalt aggregates predicts the experime

ISSN:0001-1541    

DOI:10.1002/aic.690421204

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractA new semiempirical model for prediction of self‐diffusion phenomena in liquids is proposed. Assuming anlogy between the concept of a free volume in liquids and a porosity of a granular medium, a capillary model of the granular bed and the Kozeny‐Carman theory was applied to determine self‐diffusion coefficients in liquids. The dimensionless free volume in liquids was evaluated using a combination of the proposed dependence and an appropriate formula available in the literature. The new model was tested for 89 sets of data concerning self‐diffusion of different chemical substances at several values of a temperature. The average error of a prediction was between ± 1% and about 3% for some dat

ISSN:0001-1541    

DOI:10.1002/aic.690421205

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractA new spray technique, called ultrasound‐modulated two‐fluid (UMTF) atomization, is based on resonance between the liquid capillary waves generated by ultrasound and those generated by high‐velocity air. The capillary waves generated by ultrasound on the cone of liquid film issuing from a coaxial two‐fluid atomizer are magnified in amplitude by air blowing around them. Atomization occurs when the amplitude of the capillary waves is too great to maintain wave stability, and the resulting drop sizes are determined by the frequency of the ultrasound. Calculations of the relative amplitude growth for the capillary waves of various wavelengths yield predictions that agree remarkably well with experimental results of drop size and size distribution. Specifically, uniform drops with diameter determined by the third harmonic frequency of the ultrasound are obtained in UMTF atomization at high air velocity and large air‐to‐water mass ratio. In contrast, drop‐size distributions with multiple peaks are obtained in UMTF atomization at low air velocity and small air‐to‐water mass ratio. The use of air also allows the liquid jet to atomize at ultrasonic power levels below and liquid flow rates above the threshold values for ultrasonic atomization without air. These new findings provide not only direct evidence of the capillary wave mechanism but also a means of controlling drop size and size distribution in two

ISSN:0001-1541    

DOI:10.1002/aic.690421206

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractNoncohesive granular materials in slowly rotated containers mix by discrete avalanches; such a process can be described mathematically as a mapping of avalanching wedges. A natural decomposition is thus proposed: ageometricalpart consisting of a mappingwedge → wedge, which captures large‐scale aspects of the problem; adynamicalpart confined to the avalanche itself, which captures details emanating from differences in size/density/morphology. Both viewpoints are developed and comparisons with experiments are used to verify the predictions of the models. In this article, we develop a model of granular mixing and show how to extend the model in order that it may: (1) handle complicated geometries, (2) be applicable for 3‐D mixers, (3) rapidly test mixing enhancement strategies, and (4) incorporate differences in particle properties. In addition, an optimal fill level is determined for several 2‐D mixing geometries, and a novel hybrid—geometrical/dynamical—computational technique is proposed. By merging the geometrical and dynamical viewpoints, this technique reduces the computational time of a typical molecular‐dynamics‐type simulation by a factor of 15. The ultimate goal is to provide fundamental understanding and tools for the rational design and optimization of granular

ISSN:0001-1541    

DOI:10.1002/aic.690421207

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractThree binary vapor–liquid equilibrium (VLE) data were measured: tertbutanolethanediol, tertbutanol‐KAc, and ethanediol‐KAc. Experimental data were correlated with the salt‐containing local composition model (SCLCM). For the multicomponent system, VLE data predicted by SCLCM are in agreement with the data in the literature. An industrial plant (3500T/Y) of salt‐containing extractive distillation for the tertbutanol/water/ethanediol/potassium acetate system was simulated by SCLCM and improved the Rose relaxation method. Simulation results agree well with indust

ISSN:0001-1541    

DOI:10.1002/aic.690421208

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractWith increased product specialization within the chemical‐processing industries, the ability to obtain production schedules for complex facilities is at a premium. This article discusses ways of quickly obtaining solutions for industrially relevant, large‐scale scheduling problems. A number of time‐based decomposition approaches are presented along with their associated strengths and weaknesses. It is shown that the most promising of the approaches utilizes a reverse rolling window in conjunction with a disaggregation heuristic. In this method, only a small subsection of the horizon is dealt with at a time, thus reducing the combinatorial complexity of the problem. Resource‐ and task‐unit‐based decompositions are also discussed as possible approaches to reduce the problem to manageable proportions. A number of examples are presented throughout to clarify the

ISSN:0001-1541    

DOI:10.1002/aic.690421209

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractA method to analyze the closed‐loop stability of a system composed of a nonlinear process and a discrete controller is developed. The closed‐loop system is described by a set of difference equations resulting from the discretization of the continuous‐time model. A commonly used method of discretization (forward difference) offers an incorrect relative order compared to exact discretization. The state and input sensitivity equations of the continuous‐time model are used in computing the nominal closed‐loop stability criteria. The nominal stability analysis is extended to the important cases of unmeasured states and uncertain model parameters. A numerical Lyapunov function is used to estimate closed‐loop regions of attraction. A simulation example (a CSTR with input multiplicity) presented illustrates the analysis methods and closed‐

ISSN:0001-1541    

DOI:10.1002/aic.690421210

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY

摘要:

AbstractGray box models combine the short development time of data‐driven black box models with extrapolation properties of knowledge‐driven first principles models (white box), which in (bio)chemical engineering are always based on macroscopic balances. By modeling the inaccurately known terms in a macroscopic balance with a black box model, one naturally obtains a so‐called serial gray box model configuration. The identification data must cover only the input‐output space of the inaccurately known terms, and the accurately known terms can be used for reliable extrapolation. In this way, the serial gray box configuration results in accurate models with known extrapolation properties with a limited experimental effort. This strategy is demonstrated for the modeling and control of a pressure vessel using real‐time experiments. For this case, the strategy is superior to a black box modeling approach that requires much more data and to a parallel gray box approach that results in a model with poor extrapolation properties. Moreover, neural networks are an accurate and convenient modeling tool for the black part in gray box model configurations, because a very fast noniterative training algorithm is used for training neural

ISSN:0001-1541    

DOI:10.1002/aic.690421211

出版商:American Institute of Chemical Engineers    

年代:1996

数据来源: WILEY