INVITED REVIEW STABILITY OF COLLOIDAL DISPERSIONS

The stability of colloidal dispersions has traditionally attracted considerable attention in the chemical literature because of its origins in the physical chemistry of electrostatic and steric interactions between surfaces immersed in liquids. Moreover, progress in the physics and chemistry of stability phenomena has a direct impact on chemical engineering research, since stability of dispersions plays an important role in the rheology and transport properties of charged particles in liquids, separation processes (such as membrane filtration and solid/liquid separation), deposition and particulale fouling phenomena and numerous other processing operations. This paper presents a discussion of physical and chemical factors that affect colloidal stability and, in addition, presents an overview of the status of current research needs in this area. In addition to electrostatic and steric effects, some recent studies on the role of bulk motion of the supporting liquid on stability are also discussed. The emphasis throughout is on the stability of dilute dispersions, in which simultaneous interactions between more than two particles are negligible. Some major research needs in the above areas are also identified.     

INVITED REVIEW STABILITY OF COLLOIDAL DISPERSIONS

The stability of colloidal dispersions has traditionally attracted considerable attention in the chemical literature because of its origins in the physical chemistry of electrostatic and steric interactions between surfaces immersed in liquids. Moreover, progress in the physics and chemistry of stability phenomena has a direct impact on chemical engineering research, since stability of dispersions plays an important role in the rheology and transport properties of charged particles in liquids, separation processes (such as membrane filtration and solid/liquid separation), deposition and particulale fouling phenomena and numerous other processing operations. This paper presents a discussion of physical and chemical factors that affect colloidal stability and, in addition, presents an overview of the status of current research needs in this area. In addition to electrostatic and steric effects, some recent studies on the role of bulk motion of the supporting liquid on stability are also discussed. The emphasis throughout is on the stability of dilute dispersions, in which simultaneous interactions between more than two particles are negligible. Some major research needs in the above areas are also identified.     

INVITED REVIEW ABSORPTION OF NOX GASES

Oxidation of nitric oxide is an important step in NO_x absorption. Recent advances namely catalytic oxidation and the use of slrong oxidizing agents have been reviewed. The refinements which have been made in the kinetics of NO oxidation have been discussed. Several liquid phase absorbents have been suggested for the NO removal, particularly for the purpose of pollution abatement. Different models for NO oxidation using nitric acid have been analysed and the limitations of published information have been brought out.

Absorption of tetravalent nitrogen oxide (NO₂ and N₂O₄) has received considerable attention. The absorbents include water, nitric and sulfuric acids, sodium hydroxide, sodium sulfite and sodium chlorite. Absorption in water and nitric acid is important in the manufacture of nitric acid. The published information on the mechanism of NO₂ and N₂O₄ absorption in water has been critically analysed. The problem of nitrous acid decomposition has been analysed on the basis of film theory. The predictions agree favourably with the available experimental data.

A new mathematical model has been developed for a packed column. Performance charts have been prepared which take into account the effects of concentration of nitric acid, superficial liquid velocity, temperature and the partial pressures of various components. A simplified model on the basis of NO oxidation has also been presented.

Various process design aspects have been discussed in detail. Optimum values for various operating parameters exist and basis for their selection has been explained. Some engineering aspects such as the selection of equipment and material of construction have also been discussed. A comparison between semi-batch and continuous modes of operation has been presented. The problem of the manufacture of pure nitrites has been analysed

Specific recommendations have been made regarding the use of equations and procedures in design. The knowledge gaps have been clearly brought out and suggestions have been made for future work     

INVITED REVIEW: FLOW BEHAVIOUR OF COHESIVE MATERIALS

Many problems associated with solids handling originate in the influence of the cohesive forces on the flow behaviour of fine powders. Therefore first it is discussed why and under what conditions the property "cohesion" is of particular interest. The results of measurements relating the dependence of cohesive forces on previous compression are then reported. A theoretical model is derived which takes into account the forces acting in interparticle contacts. The theory especially considers the increase in the adhesion forces transmitted in interparticle contacts with increasing consolidation. Permitted simplification of the theory results in a graphic representation allowing immediate visualization of the basic theoretical parameters. Determination of the latter is possible directly, by means of shear tests on cohesive powders. The usefulness of the theory is demonstrated through the representation of unconfined yield stress characteristics of various powders.     

INVITED REVIEW: FLOW BEHAVIOUR OF COHESIVE MATERIALS

Many problems associated with solids handling originate in the influence of the cohesive forces on the flow behaviour of fine powders. Therefore first it is discussed why and under what conditions the property "cohesion" is of particular interest. The results of measurements relating the dependence of cohesive forces on previous compression are then reported. A theoretical model is derived which takes into account the forces acting in interparticle contacts. The theory especially considers the increase in the adhesion forces transmitted in interparticle contacts with increasing consolidation. Permitted simplification of the theory results in a graphic representation allowing immediate visualization of the basic theoretical parameters. Determination of the latter is possible directly, by means of shear tests on cohesive powders. The usefulness of the theory is demonstrated through the representation of unconfined yield stress characteristics of various powders.     

INTERFACIAL TRANSPORT PHENOMENA INVITED REVIEW

Interfacial transport phenomena include all effects associated with momentum, energy, and mass transfer at phase interfaces.

I shall begin by examining the nature of the phase interface and associated common lines. I then will develop the general balance equations at each point within a phase, at each point on a dividing surface, and at each point on a common line. Mass conservation, momentum transfer, energy transfer, and mass transfer are treated as special cases.     

INTERFACIAL TRANSPORT PHENOMENA INVITED REVIEW

Interfacial transport phenomena include all effects associated with momentum, energy, and mass transfer at phase interfaces.

I shall begin by examining the nature of the phase interface and associated common lines. I then will develop the general balance equations at each point within a phase, at each point on a dividing surface, and at each point on a common line. Mass conservation, momentum transfer, energy transfer, and mass transfer are treated as special cases.     

INVITED REVIEW ON THE USE OF CHEMICALLY STRUCTURED MODELS FOR BIOREACTORS

An individual cell is an immensely complicated self-regulated chemical reactor that can alter its biosynthetic machinery to meet the demands of a changing environment. The biochemical engineer must build a large macroscopic reactor to harness the cells for desirable chemical conversions. The design and control of such bioreactors would be facilitated with effective mathematical models of the response of the culture to changes in nutrients or other environmental variables. Because of the inherent internal plasticity of the cell, models must reflect the changing structure of the biomass. This paper reviews some examples of models which contain components representing various chemical fractions within the cell. The advantage of these models is their potential ability to predict the dynamic behavior of a cellular population. In addition such models are potential tools for testing hypotheses concerning cellular control mechanisms and consequently the development of more effective cell strains. Models of populations based on a finite-representation technique using an ensemble of chemically structured single-cell models are emphasized. These latter models are capable of accurate a priori prediction of bioreactors to perturbations in flow rates or feed concentrations. Models which aspire to the a priori quantitative prediction of cell population behavior must be sufficiently complex that shifts in growth-rate limiting processes can be taken into account; consequently a high-level of chemical structure will characterize the best models.     

INVITED REVIEW POLYMERIC DELIVERY SYSTEMS FOR CONTROLLED DRUG RELEASE

The use of polymers to provide controlled long-term delivery of drugs and other chemicals is a rapidly emerging field. This review focuses primarily on the applications of these polymeric systems, and their release mechanisms. Examples of applications include clinical, pharmaceutical, biological, agricultural, environmental, and household uses. Release mechanisms considered are diffusive (reservoirs, matrices), chemical (biocrosion, pendent chain), swelling, and magnetic control of drug release from polymers. Advantages and disadvantages of controlled-release technology, and approaches for developing and testing effective polymeric delivery systems arediscussed.     

编织复合材料数值模拟方法

编织复合材料中纤维束在空间分布的复杂性,导致其与层合复合材料力学性能分析的本质差别.本文概述了编织复合材料的力学特点及其一般研究步骤,详细介绍了目前几种常见的数值模拟模型,分析了其存在的优缺点,依此指导计算模型的合理选择,使之能对编织复合材料进行较为精确的力学性能预报,并为今后的研究提供指导.     

INVITED REVIEW POLYMERIC DELIVERY SYSTEMS FOR CONTROLLED DRUG RELEASE

The use of polymers to provide controlled long-term delivery of drugs and other chemicals is a rapidly emerging field. This review focuses primarily on the applications of these polymeric systems, and their release mechanisms. Examples of applications include clinical, pharmaceutical, biological, agricultural, environmental, and household uses. Release mechanisms considered are diffusive (reservoirs, matrices), chemical (biocrosion, pendent chain), swelling, and magnetic control of drug release from polymers. Advantages and disadvantages of controlled-release technology, and approaches for developing and testing effective polymeric delivery systems arediscussed.     

INVITED REVIEW HYDRODYNAMIC AND MIXING MODELS FOR BUBBLE COLUMN REACTORS

The knowledge of the flow patterns of each phase of bubble column reactors is of considerable importance for the rational design and scale-up. The hydrodynamic models for the liquid phase have been reviewed. The models have been based on some form of pressure balance or energy balance. These two approaches have been compared and recommendations have been made regarding the range of applicability of the individual models. A comparison between the predicted and the experimental liquid velocities has been presented whenever possible. The range of variables has been pointed out for which further investigations are needed. The empirical and theoretical models for the mixing behavior of the different phases of bubble column reactors have also been reviewed.     

计算机模拟技术在絮体分形成长研究中的应用

颗粒聚集形成絮体是水处理混凝过程中的中心现象,絮体的结构、行为和性能与混凝效果密切相关。计算机模拟为研究颗粒聚集过程提供了一条新的途径,而分形理论则提供了新的理论观念。本文对絮体的分形结构模型、絮体成长过程的计算机模拟方法和模拟结果的分析方法进行了系统的介绍,以期推动此项技术的应用研究。     

单晶金属平面微裂纹扩展模拟及其软件开发

以分子动力学为基础,开发了一个用于模拟单晶金属裂纹扩展现象的仿真软件包（CSMD100）。软件包括模型建立、模型计算、结果处理等三个模块。通过仿真可以对实验中很难观察到的现象进行研究并探索其机理。模拟结果揭示了裂纹在扩展过程中的形状变化特征及扩展路径。为预测在一定条件下单晶金属中微裂纹的扩展行为提供了一个有效的可视化的手段。