Random particle packing with large particle size variations using reduced-dimension algorithms

We present a reduced-dimension, ballistic deposition, Monte Carlo particle packing algorithm and discuss its application to the analysis of the microstructure of hard-sphere systems with broad particle size distributions.We extend our earlier approach (the “central string”algorithm) to a reduced-dimension, quasi-3D approach. Our results for monomodal hard-sphere packs exhibit a calculated packing fraction that is slightly less than the generally accepted value for a maximally random jammed state. The pair distribution functions obtained from simulations of composite structures with large particle size differences demonstrate that the algorithm provides information heretofore not attainable with existing simulation methods, and yields detailed understanding of the microstructure of these composite systems.     

几种动态注射成型方式的比较

在分析传统静态保压注射过程中聚合物取向特点的基础上,介绍了“推－拉”注塑、双塞移动保压和螺杆直射动态保压等几咱动态注射成型方式,并对各种动态注射成型方式的特点及适用性进行了探讨。     

A particle packing algorithm for pellet design with a predetermined size distribution

In this paper a particle packing algorithm is proposed which is to be used to predict the behaviour of pellets in the blast furnace on a first principal basis. Pellets consist of particles of various mineralogical composition and the structure in which they pack together to form a pellet is dependant on the size distribution of the particles and the pellet porosity. This packing structure can result in isolated volumes within the pellet where the local composition deviates from the overall average composition. This can result in, for example, melt formation at lower temperatures than expected, which will have a detrimental effect on the pellet strength. These local compositions result from the contacts between particles of different minerals and can thus be quantified by the coordination number of the particles. By using a validated coordination number model, which is unique for a particle packing algorithm, virtual pellets were created for a range of particle size distributions and porosities. The algorithm used the Monte Carlo method combined with the simulated annealing minimisation algorithm to solve the pellet simulations. The objective function is a combination of two functions, one describing the deviation from the target coordination number of the particles and the other the average fraction of overlapping volume of the particles per contact. In this way a realistic pellet structure was maintained while at the same time controlling the coordination number of the particles.     

Moisture adsorption characteristics of a thin bed of polycrystalline potash pellets: Part I. Experimental study

This study is an experimental investigation of heat and moisture transfer within a packed bed of polycrystalline, porous potash pellets. Experiments were first performed to determine the moisture uptake characteristics on individual pellets subject to a step-change in relative humidity. Then a bed of pellets was subjected to flows of humid air on the upper boundary and a cold impermeable surface on the lower boundary resulting in a temperature gradient across the bed. Temperature and moisture content were measured within the bed. It was found that moisture uptake is less for potash pellets and they are less likely to cake than granular and standard potash when subjected to the same ambient air conditions. This is due to the porous nature of the pellet and its nearly uniform size and spherical shape.     

An exact method for determining local solid fractions in discrete element method simulations

A novel solid fraction algorithm is presented which accounts for the partial volume of a sphere straddling cuboidal bin boundaries. The algorithm accounts for spheres intersecting a single plane (face), two perpendicular planes (edge), or three perpendicular planes (corner). Comparisons are made against the more common algorithm in which the solid fraction is determined by assigning the sphere's total volume to the bin in which the sphere's center of volume (COV) is located. Bin size‐to‐sphere diameter ratios >30 must be used to give errors <5% when using the traditional method when applied to simple cubic (SC) and hexagonal packing assemblies. Bin size‐to‐sphere diameter ratios larger than five are required for random sphere packings. Although time averaged solid fraction measurements are similar using either the exact or COV solid fraction schemes, the scatter in the COV method is much larger than for the exact method. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Shape influences on the packing density of frustums

The shape of a frustum is a bivariate function of aspect ratio (w) and base radii ratio (c). To investigate the shape influences on the packing density of frustums, random packings of cones (c = 0), truncated cones and cylinders (c = 1) with various heights and diameters are studied through numerical simulations. An improved relaxation algorithm with assembly sphere models for non-spherical particles is applied in the numerical simulations, and the randomness of the packings of the frustums considered is verified. Base on the simulation results, the relationship between the packing density and shape parameters is illustrated, and an empirical formula is proposed to reflect the correlation. It shows that, for the particles having the same w, truncated cones can be packed denser than cones, but looser than cylinders. The packing density of truncated cones first increases and then decreases with the growth of w, while the packing density increases monotonically with the increase of c. No obvious peak is found on the curve of packing density versus c for the random packing of truncated cones, which is different from the reported results for ordered packing where a peak was identified. Furthermore, we observe that the packing density of truncated cones is a linear superposition of the c effect on w effect, and the effects of c and w on the packing density can be treated independently. The optimal aspect ratios of truncated cones, which give the highest packing densities, are all around 0.8. The highest packing densities of cylinders and cones are also the upper and lower bound of the random packing density of truncated cones.     

55米跨局部三角形钢架结构设计

介绍一种轻型尿素散装仓库结构设计。根据尿素散装仓库的特点，充分利用新材料的优势，设计了压型钢板屋面、薄壁型钢檩条和局部三角形钢架的轻型钢结构体系。这种结构型式具有耗钢量少、制作安装方便、施工速度快、对地基承载力要求不高及适用范围广等优点。     

Model-based prediction of substrate conversion and protein synthesis and excretion in recombinant Aspergillus niger biopellets

Aspergillus niger grown as biopellets in a submerged culture has been used as an expression system for glucose oxidase (GOD). With regard to mass transfer, substrate utilization and the formation and excretion of the product GOD, the behavior of aggregated cells such as biopellets differed significantly from that of systems with suspended cells. A one-dimensional pellet model has been developed which is capable to describe the relevant processes in the pellet. Experimental results showed a phase with a highly dynamic pellet size distribution during the first 20 h of the cultivation. A stable number of pellets were usually found after this first period. In the model presented this initial process was described by assuming both suspended hyphae and a fixed number of pellets. The suspended hyphae were attached to the pellets and the substrate conversion and product formation was than described with the pellet model. The model predicted the production of GOD by A. niger in a bioreactor very well. The pellet density was identified as a key parameter which has to be provided as input parameter for the simulation runs. A sensitivity analysis with three different classes of pellet sizes showed that the influence of the final pellet size distribution on the simulation result was neglectable. On the other hand, it can be shown that the total pellet number, and thus the average pellet size was an important parameter. The pellet number influenced mainly the pellet surface area and, consequently, the turnover of substrate and formation and excretion of the product.     

Tracer percentage prediction of dive reflex samplers

Instead of the frequently applied monochromatic light probes a whie light fibre optic system was employed at the Laboratory of Mechanical Process Design, TU Dortmund University, in order to exploit the color in formations for concentration measurements within bulk solid.The system is applied to obtain local particle concentrations of blue- and red-colored quartz sand within the bed of a rotary drum. 16 solid mixtures with one or two particle sizes from 100 μm to 2000 μm and different species concentration were analyzed and the relationship between probe measurement values and red sand content was determined by statistical regression methods.After transformation of the data, linear models were found to derive the red sand content from given measurement values. Based thereupon, an all-purpose scheme for mono- and bi-disperse solid mixtures was developed and verified in an example with a mean error of 5%.     

Shear Enhanced Fiber Orientation and Adhesion in PP/Glass Fiber Composites

Summary: In order to achieve better mechanical properties, most work on polymer/fiber composites has been focused on the importance of the chemistry used to modify the surface of the fibers and improving the adhesion between the fiber and the matrix using coupling agents. Our purpose in this study was to determine the effect of shear on the fiber orientation and interfacial adhesion in poly(propylene)/glass fiber composites via dynamic packing injection molding (DPIM), in which the melt is first injected into the mold and then forced to move repeatedly in a chamber by two pistons that move reversibly with the same frequency as the solidification progressively occurs from the mold wall to the molding core part. SEM, TGA, FT‐IR, AFM and mechanical testing were used to characterize the samples obtained. The majority of fibers are aligned parallel to the flow direction along the sample thickness, even at the core, in contrast to the products obtained via conventional injection molding where the orientation of fibers is observed only at the skin. More importantly, we found that shear could enhance not only the fiber orientation, but also the interfacial adhesion between the fibers and the matrix, particularly for samples with higher fiber contents, resulting in an obvious increase in tensile strength and the onset degradation temperature. A possible transcrystallization was evidenced by AFM investigations of the dynamic packing injection molded samples, which is worth further study.

SEM micrographs representing the glass fiber after PP in the composites was extracted (GF30, dynamic sample).     

Packing Density of Binary Mixtures of Wet Spheres

An experimental study of the packing of binary mixtures of coarse spheres with the addition of water has been conducted. The results indicate a similarity between dry and wet packings, either in the relationship between the packing density and the moisture content or in the relationship between the packing density and the particle-size distribution. The Westman equation is used to describe the wet packing after necessary modification. The approach is verified by the good agreement between the calculated and measured packing densities.     

填料塔基础理论研究新进展

规整填料塔具有效率高、压降低、放大效应不明显等优点,其成功应用有赖于对二相流动与传质的深入认识。文中综述了规整填料塔内的气液二相流动与分布、返混、气液二相在常压和高压下的传质特性、M arangon i效应以及计算流体力学(CFD)在规整填料塔中的应用等方面的国内外研究进展。填料塔内液体的分布与返混的研究较多,气相的流动分布与返混特性的研究较少,高压传质、M arangon i效应,特别是利用计算流体力学(CFD)模拟填料塔内的液体流动与传质等已逐渐成为研究的热点。     

Effect of the mechanical failure of catalyst pellets on the pressure drop of a reactor

The effect of the mechanical failure of catalyst pellets on the pressure drop across a laboratory-scale catalyst packing has been examined by experiment. Results reveal that, along with the mechanical failure of the pellets, there exists a point of maximum curvature around which the slope of pressure drop increases rapidly. This rapid increase is attributed to a mutation of the packing structure, occurring as the amount of failed pellets reaches a certain critical value. The secondary breakage of the pellets contributes much to the mutation of the packing and to the pressure drop. It has been observed that a trilobite catalyst is more susceptible to a mechanical stress than a cylindrical catalyst, and that a catalyst with a smaller diameter is much easier to result in an increase in the pressure drop. The measurement of the pressure drop across a laboratory-scale catalyst packing as the failure of pellets under a mechanical stress has a satisfactory reproducibility, and has a close meaning to the mechanical reliability of a fixed bed converter, and hence is recommended as a method for catalyst assessment. The multi-scale and multi-disciplinary nature of catalyst mechanical reliability is also discussed.     

波纹填料在高纯度柠檬醛精馏中的应用

采用具有新型塔内件的高效波纹填料塔分离技术,在高真空下精密分馏热敏性物料山苍子油。此方法分离效率高,压降小,操作弹性大,收率高,能直接获得９７％的高纯度柠檬醛。     

浅谈我国塑料包装材料的发展趋势

概述我国塑料包装材料的发展动向；并对我国塑料包装重点产品的发展方向进行了探讨；最后提出发展的对策和措施。     

Void-size distribution in two-dimensional random packings of equal-sized disks

The void-size distribution in a random packed assembly of disks is expressed here as the distribution of the probabilities of finding circular voids of given sizes. A theoretical void-size distribution is derived and compared with the distribution obtained through computer simulation. The two-dimensional case discussed in this paper is applicable to the study of the kinetics of fines transfer and the characterization of the coating layer structure in powder coating systems.     

Mass transfer in structured corrugated packing

The performance of structured corrugated packing has been simulated by establishing mechanistic models for liquid distribution, liquid flow on the packing surface and mass transfer. The models were used to investigate the effect of packing height, liquid load, initial maldistribution as well as differing initial distribution and solid-liquid contact angle on the packed column performance. Wetted surface area is the primary value of interest and the simulated results compare very well with those predicted by Onda (1968). The results clearly demonstrate that the wetted surface area is a strong function of the solid-liquid contact angle. Other predicted values such as mass transfer coefficients and overall height of a transfer unit show reasonable agreement with published data.