Understanding the role of restructuring in flocculation: The application of a population balance model

The effect of shear on floc properties was observed through population balance to comprehend the mechanisms of flocculation, in particular the role of restructuring. Little fundamental attention has been given before to the shear influence responsible for creating compact aggregates, while the floc characteristics might differ in other conditions. It is crucial to understand how aggregates evolve to steady state, if their properties are to be ‘tailored’ to suit subsequent solid-liquid separation. From a previous experimental study (Langmuir 18(6) (2002) 1974), restructuring was observed to occur extensively in the flocculation of latex particles in couette-flow, and was proposed to be responsible for the decrease in floc size on their transition to equilibrium. On the other hand, flocs of larger primary particles were more susceptible to breakage, with densification occurring as a result of fragmentation and re-aggregation. Denser flocs were found when structural deformation dominated, particularly in the initial stage of the process, while comparatively tenuous ones were observed when formation and breakage kinetics were the governing mechanisms. The distinct manners in which aggregates of different primary particle sizes evolved with time, were replicated with a population balance that incorporated the floc structural variation; verifying that restructuring indeed played a crucial role under certain flocculation conditions.     

基于Web挖掘的用户兴趣建模方法的研究

基于用户兴趣的不同,研究如何针对用户的浏览行为来获取用户的有效兴趣数据,并根据现有用户兴趣模型存在的不足,结合Web挖掘中的相关技术,先显式构建用户兴趣模型,后隐式更新用户兴趣模型,从而实现能适应用户兴趣变化的用户兴趣模型。     

寿州窑瓷器造型文化研究

江淮名窑寿州窑,创烧于我国南北朝时期,兴盛于隋唐,衰落于五代宋。在其悠长的发展历程里,寿州窑烧制了许许多多的陶瓷用品,大致可分为饮食器、盛储器、酒具、文具、寝具、玩具、建筑用瓷等,釉色崇尚黄、黑釉,造型浑厚饱满,古朴沉稳,姿态万千,多样的的造型符号传递了当时的社会文化背景、瓷器制作水平和审美文化,为深入研究中国古陶瓷文化提供了珍贵的资料,对当今的文创产品开发也大有裨益。     

Film model for coated cement concrete

The performance of a polymer concrete coated cement concrete under sulfuric acid environment was studied for 3 years. Both dry and wet concrete specimens were used in this study. The mass transfer coefficient ratio of cement concrete to polymer concrete was over 12. Coated cement concrete cylinders with pinholes were used to study the chemical resistance of the coated concrete under sulfuric acid environments to represent the worst sewer condition. Effects of pinhole sizes on the performance of coated concrete were studied, and changes in weight of the coated concrete specimens were measured regularly. The weight change in coated cement concrete was modeled using a film model and the effect of the pinhole sizes on the performance of the coated concrete was quantified.     

Effect of the geometry and pattern of the flow channel on the performance of polymer electrolyte membrane fuel cell

This research focuses on the effect of the geometry and patterns of the gas flow channel on the PEM fuel cell performance. Simulation was conducted and the results were verified by experiments. Three-dimensional, single phase, compressible and isothermal models of 5 cm² electrodes, anode and cathode, were developed and studied by utilizing a commercial Computational Fluid Dynamics (CFD) software, FLUENT 4.5. Two types of gas flow channel were investigated: conventional and interdigitated. The results showed that the flow channel pattern does not have a significant effect on the anode cell performance, whereas it has a strong effect/influence on the cathode cell performance. The interdigitated design provides a higher limiting current density and cell performance than the conventional design on the cathode side. Moreover, the cell performance does not depend on the inlet and outlet channel widths. On the contrary, for the interdigitated design, it was influenced by the shoulder width. Finally, experiments were conducted to validate the simulation results.     

Permeation study on the hollow-fiber supported liquid membrane for the extraction of Cobalt(II)

The transport of Co(II) through hollow-fiber-supported liquid membrane containing di-(2-ethylhexyl) phosphoric acid (D2EHPA) diluted in kerosene was examined. The mass transfer rate, expressed as permeability, P, focused on diffusion through the aqueous layer in the feed solution, the organic layer and the aqueous layer in the stripping solution. Experiments were performed as a function of aqueous feed solution velocity (100-500 ml/min), carrier concentration (0.1-20% v/v), aqueous stripping solution velocity (100-1,000 ml/min) and feed concentration (100-1,000 ppm) with 0.1 M HCl in the product phase. pH of the feed solution was 5.0. The measured permeabilities were compared to generally accepted mass transfer correlations. The validity of the prediction was evaluated with the experimental data, and the data were found to tie in well with the theoretical values. The model is the reported describing that the rate limiting step in the transport of the ion was the diffusion through both aqueous films, feed and stripping, whereas the organic resistance of the membrane was negligible. From this study, the model has good potential for the prediction of permeability of Co(II).     

Unsteady temperature fields of monoliths in catalytic converters

This paper measured unsteady temperature fields of uncoated-monolith and catalytic monolith under real engine operating conditions using thermocouples. A multi-dimensional flow model of the turbulence, heat and mass transfer, and chemical reactions in monoliths was established and numerically solved in the whole flow field of the catalytic converter. The purpose of this paper is to study unsteady warm-up characteristics of the monoliths and to investigate effects of inlet cone structure on temperature distribution of the catalytic converter. Experimental results show that the warm-up behaviors between uncoated-monolith and catalytic monolith are quite different. Simulation results indicate that the established model can qualitatively predict the warm-up characteristics. Increasing the inlet cone angle can improve the light-off characteristics of the catalysts due to high flow velocity and high temperature in the center of the monoliths.     

Simulation of reverse flow operation for manipulation of catalyst surface coverage in the selective oxidation of ammonia

A mathematical model has been developed for the simulation of the ammonia oxidation in a reverse flow reactor. Computer simulations were carried out with a kinetic scheme, based upon elementary reaction steps. Aim was to explore the potential of a reverse flow reactor for selective oxidation of NH₃ to produce either N₂, NO, or N₂O via a dedicated operation procedure. Therefore, the conversion of NH₃ and the selectivity toward N₂, NO, or N₂O, were compared for a reverse flow operation and a steady state, once-through operation.A new operation concept of reverse flow operation in combination with a periodically lower feed concentration is proposed. The novel reactor concept shows a better performance compared to normal reverse flow operation and to steady state, once-through operation. The results indicate that reverse flow operation can be applied for manipulation of conversion and selectivity. A periodically lower feed concentration may increase the conversion, even up to levels that exceed the steady state value.     

A model for the adsorption of single metal ion solutes in aqueous solution onto activated carbon produced from pecan shells

Adsorption isotherms for activated carbon made from pecan shells have been obtained at 25 °C and an approximate pH of 3 for a number of metal ion solutes. It was found that the Slips and Freundlich equations were satisfactory for explaining the experimental data. The correlation of metal ion adsorption with the solute parameters of metal ion electronegativity and first stability constant of the metal hydroxide was investigated. In the case of most of the metal ions studied, higher electronegativities and stability constants corresponded to the higher adsorption levels of metal ions onto the activated carbon. A correlation was developed that predicts the constants of the Freundlich equation from the selected parameters of the metal ions, and thus can predict the adsorption isotherms at constant pH. The developed correlation gives results with acceptable deviations from experimental data. A procedure is proposed for obtaining similar correlations for different conditions (temperature, pH, carbon type and dosage). The ratio of equivalent metal ions adsorbed to protons released is calculated for the studied metal ions over a range of concentrations. In most cases, particularly at low concentrations, this ratio is close to one, confirming that ion exchange of one proton with one equivalent metal ion is the dominant reaction mechanism.