铝及铝合金无铬钝化的研究进展

研究并开发实用性强、环境友好的铝及铝合金无铬钝化工艺是未来发展的趋势。综述了国内外铝及铝合金无铬钝化体系的研究状况及其特点,为铝及铝合金无铬钝化的后续研究提供参考,并展望了未来的研究方向。     

浅述我国水泥助磨剂的研究及应用

本文简要介绍了我国水泥助磨剂的研究及应用现状，重点从助磨剂的作用机理、国内研究及应用的水泥助磨剂两方面进行综述，并结合自己近几年从事水泥助磨剂的研究、生产及使用工作的体会提出今后对水泥助磨剂进一步研究的方向及需解决的技术方案，并对我国水泥助磨剂的研究及应用进行了论述。     

黑色混凝土制品研究新进展

文章综述了黑色混凝土制品的研究新进展。介绍了黑色混凝土制品的研究意义和基本概念。对黑色混凝土制品的最新研究内容及发展方向进行了说明。仔细介绍了几种黑色颜料的性质及应用情况并进行分析。并对黑色混凝土制品的研究进行了总结。     

热交换器管子－管板的胀接性能

对锅炉、热交换器管子－管板胀接结构的安全及可靠性进行了实验研究。研究范围包括胀接结构的连接强度，密封即耐压性能，疲劳强度等。作者提供了初步的研究结果及试验数据，为设计、制造及研究工作者进一步认识胀接结构的特性，修改现行规范中的有关规定提供了依据。     

非金属材料化学镀镍工艺与镀层性能研究

综述了近年来非金属材料化学镀镍工艺及其性能研究的最新成果。介绍了预处理阶段的主要步骤及化学镀镍的典型配方。对影响化学镀镍工艺的有关因素,镀层性能研究的基本方法和新的手段进行了较详细地论述。指出了化学镀技术新的应用前景及今后的研究方向。     

新型乙炔氨推进剂研究进展

阐述了新型乙炔氨液体推进剂的特点。重点介绍了俄罗斯的研究计划、进度及我国对乙炔氨的研究情况,包括理论能量计算、安全特性研究、传热特性研究、热点火试验等。分析了我国开展乙炔氨研究工作的必要性及未来发展前景。     

水体中重金属的生物有效性

简要评述了水体中重金属的生物有效性及研究现状,介绍了水体中藻类及动物的重金属的生物有效性．并提出了其研究过程中的一些问题,对其研究趋势作了展望。     

蕨淀粉的开发与应用

对蕨淀粉的微观形状，粒微及分布，糊化温度，粘度，冷凝行为及抗腐败能力进行了表征与研究。研究了蕨淀粉的氧化降解、脱色及化学改性工艺过程，研究了蕨淀粉在冰衣，粘合剂，高效蓄能材料方面的应用。     

SHS技术发展的概况

本文概括介绍了SHS技术原理、工艺特点及研究现状,并提出了SHS工艺存在的问题及今后研究的重点。     

聚酯热熔胶的应用及研究进展

综述了聚酯热熔胶的研究历史及发展概况,介绍了聚酯热熔胶的结构、性能、应用,探讨了聚酯热熔胶的研究方向及发展前景。     

Numerical simulation of local and global mixing/segregation characteristics in a gas–solid fluidized bed

Researches on solids mixing and segregation are of great significance for the operation and design of fluidized bed reactors. In this paper, the local and global mixing and segregation characteristics of binary mixtures were investigated in a gas–solid fluidized bed by computational fluid dynamics-discrete element method (CFD-DEM) coupled approach. A methodology based on solids mixing entropy was developed to quantitatively calculate the mixing degree and time of the bed. The mixing curves of global mixing entropy were acquired, and the distribution maps of local mixing entropy and mixing time were also obtained. By comparing different operating conditions, the effects of superficial gas velocity, particle density ratio and size ratio on mixing/segregation behavior were discussed. Results showed that for the partial mixing state, the fluidized bed can be divided into three parts along the bed height: complete segregation area, transition area and stable mixing area. These areas showed different mixing/segregation processes. Increasing gas velocity promoted the local and global mixing of binary mixtures. The increase in particle density ratio and size ratio enlarged the complete segregation area, reduced the mixing degree and increased the mixing time in the stable mixing area.     

Mixing of large particles in two-dimensional gas fluidized beds

The fluidization and solids mixing characteristics of very large particles were investigated in a two-dimensional gas fluidized bed. Bubble or slug induced drift and gross solids circulation appeared to be the predominant solids mixing mechanisms in this large particle bed. The contribution from wake mixing appeared to be negligible and radial mixing was more rapid than axial mixing. Apparently, segregation in the axial direction resulted from preferential transportation of the lighter particles upwards with rising bubbles and from interparticle competition to fill the voidage created by the rising bubbles. No appreciable segregation occurred in the radial direction. A nonstationary random walk model has been developed to characterize mixing and segregation of fluidized large particles.     

宽粒体系液固流态化随机理论数学模型

用快速切割流化床研究了宽粒级液固流态化的轴向混合和分离,测定了粒度分布、平均粒径和空隙度沿床高的变化.证实了颗粒的运动有随机性.用马尔柯夫过程建立了一个随机游走模型,描述了流化床中宽粒体系的混合和分级特性.对钛铁矿和石英砂(粒径0.04～0.40mm)进行了检验.结果表明,体系的初始流态化速度、膨胀性质、粒度分布以及平均粒径和空隙度沿床高的变化的测定结果,同模型的预测值很好符合.     

基于EMMS介尺度模型的双分散鼓泡流化床的模拟

双分散气固鼓泡流化床中颗粒通常具有不同粒径或密度,导致产生颗粒偏析等现象,影响传递和反应行为。颗粒分离和混合与气泡运动密不可分,其中相间曳力起关键作用。最近Ahmad等提出了一种基于气泡结构的双分散介尺度曳力模型,能成功预测双分散鼓泡流化床的床层膨胀系数。本研究耦合该曳力模型与连续介质方法,模拟了两种不同的双分散鼓泡流化床,通过分析不同流化状态下的气泡运动、颗粒浓度比的轴向分布等参数,进一步检验模型的适用性。研究表明,当双分散颗粒处于完全流化状态时,耦合双分散介尺度曳力模型可合理预测不同颗粒的分离现象;而其处于过渡流化状态时,新曳力模型和传统模型均无法获得合理结果,此时调节固固曳力可改进模拟结果。     

Particle mixing/segregation in gas-solid fluidized bed of ternary mixtures

The particle concentration profiles and minimum fluidizing velocity of ternary mixtures were investigated experimentally. All the experiments were carried out in an 88 mm I.D. transparent acrylic column containing fluidized beds of ternary particles of different sizes, densities and shape. Mixing/segregation patterns were visualized under different operating conditions. The experimental results are compared with empirical relationships for mixing index and take-off velocity. A new definition of the mixing index, including particle minimum fluidizing velocity and density predicted the mixing/segregation behaviour reliably. The proposed correlation of take-off velocity agrees with the experimental results very well.     

Mixing–segregation phenomena of binary system in a fluidized bed

A study on mixing–segregation phenomena in a gas fluidized bed of binary density system was performed by analysis of the residence time distribution and mixing degree. The effect of particle mixing on the residence time distribution and solid mixing was studied in a binary particle system with different densities. Residence time distribution curve and mean residence time of each particle were measured according to the flotsam particle size, mixing ratio and gas velocity in a gas fluidized bed (0.109 m I.D., 1.8 m height). The characteristics of residence time distribution and the deviation of mean residence time of each particle are consistent with previous mixing index based on the axial concentration of jetsam. From this study, mixing index of binary particle system with different densities should be considered by not only axial concentration distribution of jetsam particle but also characteristics of residence time distribution. This result suggests that the solid movement by fluidization gas is more important than solid axial dispersion.     

An index to characterize gas-solid and solid-solid mixing from average volume fraction fields

A mixing index based on solid volume fraction fields is developed for gas-solid flows. Conventional mixing indices are based on particle realizations of granular mixing and are applicable to experimental data or discrete element method simulations. However, these indices cannot be used as-is for multifluid models, and an index for characterizing mixing in gas-solid flows from continuous fields is needed. The performance of the new mixing index is tested in two applications. The first is a 3D simulation of the mixing of biomass and sand in a fluidized bed reactor, and the second is a 2D simulation of binary particle segregation in a fluidized bed. The simulations are performed using OpenFOAM®. The mixing index is used to quantify gas-solid mixing using solid volume fractions and solid-solid mixing using solid fractions. The formulation of conventional mixing indices is extended to be used with solid volume fractions fields, and methods for performance improvement are presented.     

Numerical Simulation of Particle Segregation in Vibration Fluidized Beds

The influence of vibration parameters on the segregation phenomenon of a binary mixture in a vibration fluidized bed is investigated. Initially, the mixture composed of spherical balls with different densities but same diameter is in a perfect mixing state in the bed. The motion of particles is simulated based on the discrete element method. The effects of friction coefficient, vibration frequency, amplitudes, and gas velocity are analyzed. The coefficient of segregation to the degree of particle segregation is calculated for different operating conditions. The segregation degree in the vibration fluidized bed is found to be higher than that in the bed without vibration. The curve for the segregation degree exhibits a single peak value which represents the optimal segregation result.     

Density segregation of dry and wet granular mixtures in gas fluidized beds

The Discrete Element Method combined with Computational Fluid Dynamics was coupled to a capillary liquid bridge force model for computational studies of mixing and segregation behaviors in gas fluidized beds containing dry or wet mixtures of granular materials with different densities. The tendency for density segregation decreased with increasing fluidizing velocity, coefficient of restitution, and amount of liquid present. Due to the presence of strong capillary forces between wet particles, there was a high tendency for particles to form agglomerates during the fluidization process, resulting in lower segregation efficiency in comparison with fluidization of dry particles. Particle‐particle collision forces were on average stronger than both fluid drag forces and capillary forces. The magnitudes of drag forces and particle‐particle collision forces increased with increasing fluidizing velocity and this led to higher mixing or segregation efficiencies observed in dry particles as well as in wet particles at higher fluidizing velocities. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4069–4086, 2015     

Discrete particle simulation of solids motion in a gas–solid fluidized bed

The solids motion in a gas–solid fluidized bed was investigated via discrete particle simulation. The motion of individual particles in a uniform particle system and a binary particle system was monitored by the solution of the Newton's second law of motion. The force acting on each particle consists of the contact force between particles and the force exerted by the surrounding fluid. The contact force is modeled by using the analogy of spring, dash-pot and friction slider. The flow field of gas was predicted by the Navier–Stokes equation. The solids distribution is non-uniform in the bed, which is very diluted near the center but high near the wall. It was also found that there is a single solids circulation cell in the fluidized bed with ascending at the center and descending near the wall. This finding agrees with the experimental results obtained by Moslemian. The effects of the operating conditions, such as superficial gas velocity, particle size, and column size on the solids movement, were investigated. In the fluidized bed containing uniform particles better solids mixing was found in the larger bed containing smaller size particles and operated at higher superficial gas velocity. In the system containing binary particles, it was shown that under suitable conditions the particles in a fluidized bed could be made mixable or non-mixable depending on the ratios of particle sizes and densities. Better mixing of binary particles was found in the system containing particles with less different densities and closer sizes. These results were found to follow the mixing and segregation criteria obtained experimentally by Tanaka et al.