摘要:

The ability of the rationalized SCLC model to correlate data on the salt effect in vapor-liquid equilibria is examined in this work. For a system consisting of two miscible solvents the effect of salt in altering the relative volatility is represented by the model with four adjustable binary interaction parameters. The model is shown to correlate vapor-liquid equilibria of several alcohol-water-salt systems satisfactorily.

ISSN:0098-6445    

DOI:10.1080/00986449508936280

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The Redlich-Kwong (RK) equation of state introduced in 1949 has been considered the most accurate two-constant-parameter cubic equation of state. The other cubic equations which are more accurate than the RK equation contain either three, or more, parameters and/or their parameters are temperature- dependent. A New two-constant-parameter cubic equation of state, $ is introduced using a simplified molecular theory of hard-sphere fluids for its repulsive term. This two-constant-parameter cubic equation of state appreciably increases the accuracy of thermodynamic property predictions and phase equilibria of pure fluids and flluid mixtures over the equations of this category.

ISSN:0098-6445    

DOI:10.1080/00986449508936281

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Batch-reactor input profiles are normally obtained under the assumption of knowledge of a parametric model. When this assumption does not hold, parameter deviation from the nominal value can severely impair performance of the nominal optimization. The minimax optimization offers an allernative that accounts for parameteric uncertainty, but its inherent worst-case assumption degrades its performance near the nominal parameter value compared to that of the nominal optimization. This work presents a new optimization procedure that offers robustness similar to the minimax optimization while retaining nominal performance similar to the nominal optimization. Given a probability distribution for the uncertain process parameters from a previous identification step, the method optimizes the expectation of cost function for the entire parameter space instead of optimizing the cost function for the expectation of the parameters. In this way increased robustness towards uncertain or time-varying parameters is obtained without unduly compromising the nominal performance. Since evaluation of the proposed objective function involves numerical integration, an efficient strategy is presented for obtaining its exact gradient indirectly, thereby rendering the method numerically reliable and computationally attractive, and less demanding than the minimax approach, in general. For the special case where the nominal parameter value is assigned probability one, the method reduces to the well-known control vector iteration procedure, a numerical optimization strategy based on Pontryagin's maximum principle. Two examples demonstrate the advantage of the new method over the conventional approaches, namely, nominal optimization, minimax approach and local-sensitivity-based approach.

ISSN:0098-6445    

DOI:10.1080/00986449508936282

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The hydrodynamic behavior of particles in circulating fluidized beds has been studied by means of a Boltzmann-like kinetic model. Two main regimes of flow: a homogeneous and a heterogeneous regime have been delimited. In the homogeneous regime, for concentrations below a critical value, the flow consists of upward moving solids. Above the critical concentration, clusters appear. Particles velocity distribution at different values of the solid concentration and the ratio of particles being in clusters to those being in homogeneous flow are calculated for different solid mass fluxes, particle size distributions and superficial gas velocities. Slip factors and the effect of gas radial velocity profile have been predicted. Qualitative agreement with experimental data is obtained.

ISSN:0098-6445    

DOI:10.1080/00986449508936283

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper describes the prototype of an expert system for the technical analysis of cement kilns. Technical analyses are complex tasks performed by an expert to diagnose malfunctions, to evaluate the effects of recent modifications on the plant, or simply to strike a detailed balance of normal plant operation. The expert system is composed of three modules. The first module deals with flowsheet description through the SPI interface. SPI is a general package which can be used in applications to graphically describe a flowsheet and to automatically generate an internal object-based representation of the flowsheet from its graphical description. Moreover, procedures for automatic deductions can be implemented within SPI, in order to help the user provide the application with relevant data in an economic way and to ensure flowsheet consistency. The goal of the second module is to plan the measurements campaign according to the plant structure and the purpose of the analysis. The third module performs the measurements processing by analysing the process parameter's trend and normality. After the module's contents have been described, the knowledge representation is discussed. The first module relies extensively on object oriented programming while the two others use production rules. Taxonomies for process elements and diagnosis concepts are described, and abstracts of sessions giving examples of rules used in the knowledge bases are provided. Synergy between objects and rules is highlighted. The importance of flowsheet representation and input is highlighted. Finally, it is pointed out that knowledge acquisition has been enhanced by the competence of the expert system designer both in computers sciences and in chemical engineering. The programme presented here is a prototype which takes into account the diversity and the variety of the analysis task, although it does not envisage all the possible cases. It has proved the suitability of the expert system approach for tackling the technical analysis of cement kilns.

ISSN:0098-6445    

DOI:10.1080/00986449508936284

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Fouling due to the deposition of solids on sieve trays was studied in a 153 mm diameter column and a 90 mm diameter simulator. Tests were carried out with various gas-liquid-solid systems to determine the effect of the fouling mechanism on tray performance. For an air-water system containing saturated NaHCO3, fouling from crystallisation occurs due to water evaporation by dry air at the tray holes. For a CO2-water system containing K2C03and saturated KHC03the reaction between C02and K2CO3causes the precipitation of KHCO3at the gas-liquid interface. For the air-water system containing insoluble solids, flour and Ca(OH)2, no fouling was observed for a 48 hour test period. Interesting results on tray performance were also obtained. Test results indicate that (1) trays with larger holes have higher resistance to fouling, (2) fouling does not occur when trays are operated under weeping conditions, (3) fouling rate increases with increasing gas loading, (4) a bed of mesh packing on the sieve tray accelerates the fouling rate. A mathematical model has been developed for predicting the effect of crystallisation fouling on tray pressure drop as a function of time.

ISSN:0098-6445    

DOI:10.1080/00986449508936285

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Gas-phase controlled absorption of ammonia in foams made of solutions of sulphuric acid has been studied experimentally. Effects of gas-phase concentration of ammonia and type of surfactant on the performance of the foam-bed reactor are investigated. Gas-phase controlled absorption from a spherical bubble is anaylzed using the asymptotic value of Sherwood number (Sh = 6·58), for both negligible as well as significant changes in the volume of the bubble. The experimental data are shown to be in good agreement with the single-stage model of the foam-bed reactor using these asymptotic sub-models, as well as the diffusion-in-sphere analysis available in literature. Influence of effective diffusivity on the time dependence of fractional gas absorption has been found to be unimportant for foam columns with large times of contact. The asymptotic sub-models have been compared and use of the rigid-sphere asymptotic sub-model is recommended for foam columns of practical relevence.

ISSN:0098-6445    

DOI:10.1080/00986449508936286

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A recently validated four-compartment model is used to describe intra-cellular dynamics during fermentations with recombinant microorganisms containing temperature-sensitive (run-away) plasmids. The time-dependent sensitivities with respect to the dilution rate have been computed for normal and run-away replication. During normal replication the cells are most sensitive in the early stage of fermentation, and the intra-cellular compartment containing RNA and ribosomes is more sensitive than the other three lumped components. This is explained through a buffering effect. During run-away replication the sensitives are either constant or increase slowly with time, and there is a shift in the relative sensitivities of the intra-cellular components. All sensitivities except that of the substrate increase as the dilution rate increases.

ISSN:0098-6445    

DOI:10.1080/00986449508936287

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A study is made of quasi-steady state natural convection in a vertical annular porous layer when the inner wall is heated by a constant heat flux and the other walls are maintained adiabatic. On the basis of the Darcy-Oberbec-Boussinesq equations, the problem is solved analytically in the limit of a long shallow annulus (A >>1), where A is the aspect (height-to-gap width) ratio. The analytical solution for the flow and heat transfer, based on a parallel flow assumption, is derived in terms of the Darcy-Rayleigh number R and radius ratio K. A numerical study of the same phenomenon, obtained by solving the complete system of governing equations, is conducted to assess the validity of the analytical results. It is demonstrated that the analytical solution predicts well the flow structure and the heat transfer for a wide range of R and K. In the boundary layer regime it is shown that the Nusselt number, based on the gap width of porous annulus, is Nu = R2/5[2K2InK−(K2− 1)2]/lsqb;2(K − 1)2(K + l)6/5]

ISSN:0098-6445    

DOI:10.1080/00986449508936288

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

To determine the liquid-film time constant (τF) of the dissolved oxygen electrode for kLa measurements with the dynamic method in respiring fermentation broths, an approach using the steady-state readings of the electrode in the broths containing respiring and non-respiring cells, respectively, has been established. The results showed that τFin microbial suspensions with high volumetric oxygen uptake rates could be very large under the conditions of low aeration and agitation, indicating the slower response of the oxygen electrode caused by the more difficult penetration of oxygen molecules through the thicker films with active cell respiration. The significance and adequacy of the τFcorrections for kLa measurements were evaluated experimentally.

ISSN:0098-6445    

DOI:10.1080/00986449508936289

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor