采矿方案综合评价研究

在采矿方案的选择上进行了一些分析和研究，提出了一种综合评价采矿方案优劣的方法．     

Operando systems for the evaluation of the catalytic performance of NOx storage and reduction materials

Operando measurements were carried out in a quartz reactor to evaluate the catalytic performance of NO_x storage and reduction materials containing Pt and Ba supported on Al₂O₃. Carbonates present on the surface after activation were removed after the first exposure of the sample to the nitration flow. Nitrite species bound to barium were observed at low temperatures. Barium nitrates are the predominant species in the studied temperature range under wet and dry conditions. These species are not stable at temperatures above 723 K. The presence of water inhibits the formation of alumina nitrates favoring the coordination of nitrates with the barium sites.     

喷雾式汽车加热器数值模拟的综合性能评价

针对汽车加热器在工程实际中各单一性能指标可能产生互相影响,因而很难通过几个单一性能评价指标准确地评价加热器性能的优劣的问题,通过数值模拟方法分析了不同柴油喷口半径的喷雾式汽车加热器的各单一性能,包括加热器出口平均温度、加热器温度场均匀性、壁面平均温度、出口柴油组分含量、一氧化碳排放量以及氮氧化物排放量,并利用主成分分析法对数据进行了分析,最终降维得到两个主成分评价指标:P_1和P_2。其中,P_1反映了加热器出口平均温度、加热器温度场均匀性、壁面平均温度、出口柴油组分含量、一氧化碳排放量这几个单一性能指标的综合优劣性;P_2反映了出口柴油组分含量以及氮氧化物排放量的综合优劣性,并在此基础上构建了汽车加热器综合性能指标的评价方法,提出了综合评价函数P,不仅全面考虑了各个单一性能指标,更在此基础上得到了更为直观的加热器优劣排序。     

减阻剂乳液的合成与性能评价

采用水分散聚合法制备了一种应用于滑溜水中的水溶性减阻剂乳液,对减阻剂溶液的粘弹性、耐温耐剪切性和降阻率进行了测试.结果表明,该减阻剂溶液具有明显的粘弹性特征,耐温耐剪切性能良好,0.2％的减阻剂水溶液的最大降阻率超过70％,表现出了良好的降阻特性,能够作为滑溜水用减阻剂使用.     

A numerical study of the Jacobson-Oksman algorithm

The Jacobson-Oksman algorithm is a method for finding the unconstrained minimum of homogeneous functions. The optimal solution is obtained by solving a set of (n + 2) linear equation by a method based on Householder updating. The method has some very attractive features including robustness and rapid convergence, and it does not require accurate one dimensional searches. However, to date, little if any use has been recorded in the literature.We have studied the properties of the algorithm and also compared the method with the Fletcher-Reeves and Davidon-Fletcher-Powell methods. We have found the Jacobson-Oksman method to be superior to the former and comparable to the latter on general nonlinear functions. Therefore we recommend the Jacobson-Oksman algorithm as a competitive alternative to the celebrated class of quasi-Newton methods for unconstrained minimization.     

A numerical study on structure of premixed methane-air microflames for micropower generation

Structure of premixed methane-air microflames at normal and elevated temperatures and atmospheric pressure generated on a microtube was computationally studied, in order to understand the fundamental behavior of the microflames for micropower generation. Based on an earlier experimental investigation of the stability limits of the premixed microflames, the distributions of temperature, fuel and radicals for single microflames near the stability limits and in the stable region were predicted using a two-dimensional CFD simulation with a reduced kinetic mechanism and a detailed transport modeling. The predicted structure of microflames along the stability limits due to heat losses showed substantial fuel leaks between the microflame base and the microtube rim. This observation provided the burning mechanism that a microflame can be generated and sustained only if the injected mixture contains a certain concentration of fuel beyond a certain distance from the tube exit that can avoid quenching. The experimentally observed extended stability limits due to elevated temperature were readily explained by the predicted structure showing intensified burning and reduced heat losses. Finally, the predicted microflame structure showed that the predicted microflame length based on the maximum mass fraction of OH radical well represents the observed visible microflame length.     

Wind tunnel study and numerical simulation of dust particle resuspension from indoor surfaces in turbulent flows

Particle resuspension from flooring is an important source of air pollution in the indoor environment. In this work, resuspension of monolayer, polydisperse, irregularly shaped dust particles from various types of floorings was studied via a series of wind tunnel experiments. The range of free-stream velocity needed for resuspension of dust particles was evaluated as a function of particle size and material of particles and surfaces. In addition, a Monte Carlo simulation for predicting the resuspension of dust particles was developed. The resuspension model took into account the effects of particle irregularity, particle surface roughness, and flow characteristics. The dust particle resuspension from different floorings for several particle sizes was evaluated. The model predictions for resuspension fractions were compared with the experimental data and good agreement was observed. The study provided information on the role of airflow velocity on irregular dust particle resuspension from common floorings.     

On the mechanisms for drag reduction: A viscoelastic evaluation based on a bead-spring model

Two possible drag reduction mechanisms were examined by studying the viscoelastic effects of polymer solutions for the separate cases of oscillatory shear flow and elongational flow. The constitutive equation used was based on a modified dumbbell molecular model which predicts non-Newtonian viscosity and both the primary and the secondary normal stress differences. It can be shown that when this constitutive equation is arranged in the form of the Oldroyd model, the latter becomes a special case of this more general equation. The present results show that viscoelastic effects on the mean local rate of energy dissipation of a fluid element in an oscillatory motion are negligibly small. However, such effects introduce very large increases in the elongational viscosity as the stretching rate exceeds a certain limiting value and the flow time exceeds the terminal relaxation time of the fluid. The relative merits of these findings as possible explanations of turbulent drag reduction are briefly discussed.     

A critical evaluation of reaction calorimetry for the study of emulsion polymerization systems: thermodynamic and kinetic aspects

Protocols were examined for the measurement of rates and enthalpies of polymerization (ΔH_p) using reaction calorimetry. ΔH_p was determined to be 70.2 kJ mol⁻¹ for a series of seeded styrene emulsion polymerizations under typical emulsion conditions, in good agreement with literature values. However, there was a significant deviation from this value for small-particle systems, which is ascribed to surface effects, i.e. environmental effects on ΔH_p. Careful comparison between rate data obtained by calorimetry and by dilatometry leads to recommended procedures for obtaining reliable and accurate rate data using the former technique.     

A study on the micromixing performance in microreactors for polymer solutions

Microreactors are widely applied for various polymerization processes to produce polymers with controlled molecular weight and structures. In this work, the mixing of polymer solutions in capillary microreactors was investigated with the aid of the biazo‐coupling reaction system and high‐speed camera. A smaller inner diameter, a higher Dean number and a lower Torsion number could promote the micromixing performance in microreactors. Unlike the mixing of Newtonian fluids in microreactors or micromixers, the mixing of polymer solutions follows different mechanisms and it is more difficult to reach homogeneous condition. However, the good micromixing performance in capillary microreactor systems for polymer solutions still could be obtained with high shear rates and long enough capillary length at relatively high correlated Reynolds numbers (N_Re > 29). Furthermore, the micromixing time in the capillary microreactors was evaluated based on a modified stretching efficiency model and its value was in the range of 0.1–8.0 ms. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3479–3490, 2018     

A numerical study on warm deep drawing of polypropylene

Warm deep drawing of polypropylene, a semi-crystalline thermoplastic polymer, is studied using finite element analysis. In this process, a circular polypropylene blank is preheated to a temperature much below its melting temperature and deep drawn into the shape of a flat-bottom cylindrical cup using a punch-die combination, both initially at 25°C. The material model used for the analysis considers the effects of varying temperature and strain rate during the deep drawing process on the depth of draw. The effects of blank holder force, initial blank temperature, blank diameter, and die and punch corner radii on the depth of draw are determined. Thickness, temperature, and strain variations in the drawn cups, punch forces, and failure modes are also determined.     

还原参数对铁基催化剂F—T合成性能的影响

在浆态床反应器中详细考察了还原参数对工业铁基催化剂在F—T合成反应中的影响。研究结果表明：提高还原气体中CO／H2的比值有助于提高烯烃的选择性;提高还原气体的空速可以提高催化剂的活性,但是烯烃的选择性有所降低;升高还原温度在一定程度上可以提高催化剂的活性,但是温度过高容易造成催化剂积炭活性下降,适宜的还原温度范围为210～260℃。     

A control oriented study on the numerical solution of the population balance equation for crystallization processes

The population balance equation provides a well established mathematical framework for dynamic modeling of numerous particulate processes. Numerical solution of the population balance equation is often complicated due to the occurrence of steep moving fronts and/or sharp discontinuities. This study aims to give a comprehensive analysis of the most widely used population balance solution methods, namely the method of characteristics, the finite volume methods and the finite element methods, in terms of the performance requirements essential for on-line control applications. The numerical techniques are used to solve the dynamic population balance equation of various test problems as well as industrial crystallization processes undergoing simultaneous nucleation and growth. The time-varying supersaturation profiles in the latter real-life case studies provide more realistic scenarios to identify the advantages and pitfalls of a particular numerical technique.The simulation results demonstrate that the method of characteristics gives the most accurate numerical predictions, whereas high computational burden limits its use for complex real crystallization processes. It is shown that the high order finite volume methods in combination with flux limiting functions are well capable of capturing sharp discontinuities and steep moving fronts at a reasonable computational cost, which facilitates their use for on-line control applications. The finite element methods, namely the orthogonal collocation and the Galerkin's techniques, on the other hand may severely suffer from numerical problems. This shortcoming, in addition to their complex implementation and low computational efficiency, makes the finite element methods less appealing for the intended application.     

Micro-simulated moving bed (μSMB) systems: A numerical study

Continuous chromatographic separation processes like simulated moving bed (SMB) systems have been employed in petrochemicals, sugar, and more recently, in pharmaceutical industries by virtue of their superior separation efficiency. Miniaturization of chromatography-based analytical techniques (e.g., high performance liquid chromatography, micro-HPLC or μHPLC) has already been successfully demonstrated in the last few years owing to the rapid development in MEMS technology. With such a rapid progress in technology, it is definitely possible to realize the miniaturization of a powerful continuous chromatographic process such as SMB. Micro-SMB (μSMB) systems could not only inherit the merits of μHPLC, but also provide efficient separation of compounds such as isomers and enantiomers that are otherwise very difficult to isolate. In this paper, new simulations of the performance of a μSMB system for the separation of a mixture of phenol and o-cresol, using a robust numerical algorithm developed that mimics the dynamic operation of the μSMB system, are presented. A systematic parametric sensitivity analysis that addresses the effects of various process parameters on the performance of the μSMB system is also presented. High purities and yields of both phenol and o-cresol is achieved in the μSMB by judicious choice of process parameters.     

Design and performance evaluation of plasma air cleaning systems for removing yellow sand dust

Yellow sand dust (Asian dust storms) causes harmful damage indoors and outdoors during the springtime, and the removal of Yellow sand dust has become an issue for suitable indoor conditions. An air cleaner is required to remove Yellow sand dust efficiently to improve indoor air quality, and the removal characteristics of Yellow sand dust should be studied. The size distribution and mass concentration of Yellow sand dust observed in China and Korea are analyzed, and the removal efficiency of a plasma air cleaning system based on the principle of electrostatic precipitation is evaluated by using Yellow sand dust. Mass median diameter of Yellow sand dust sampled in Beijing and Seoul ranges from 7.0 to 8.0 μm with a mass concentration of 300-1,462 μg/m³. For a single-pass test, the efficiency of dust removal increases with increasing particle size and decreasing flow rate. The removal efficiency of Yellow sand dust in a plasma air cleaning system at a face velocity of 1.0 m/s is higher than 80%. For a multi-pass test in occupied spaces, the operation time required to reduce Yellow sand dust concentration from an initial concentration of 300 μg/m³ to 150 μg/m³ is 10 minutes for a test room of 27 m³.     

Experimental and numerical study on compressive performance of perforated brick masonry after fire exposure

This paper discusses the compressive performance of perforated brick masonry after fire exposure. Compressive strength tests of the mortar, clay perforated brick, and perforated brick masonry specimens were performed in accordance with ISO834 fire tests of different durations. The temperature distribution of the masonry materials and specimens was simulated using the finite element software ABAQUS, with the thermal parameters of masonry materials recommended by European standard Eurocode 6 and related literature. The compressive strength reduction factors of mortar and clay perforated brick exposed to different fire durations were calculated via the layered method suggested by European standard Eurocode 1. In addition, the compressive strength reduction factors after cooldown were obtained from the experimental data of the masonry materials, and by considering further reductions in the compressive strength after cooling from high temperatures. Experimental data of the masonry specimens were compared with the numerical results obtained using the reduction factors proposed in this work. The comparison revealed an overall acceptable approximation. Thus, the method presented in this paper can be used to evaluate the residual capacity of masonry structures after fire.