Modeling and simulation of a fully air swept ball mill in a raw material grinding circuit

A raw material grinding circuit was modeled using plant data. Samples were collected from around the circuit and, following a crash stop, from inside the mill. The size distributions of the samples were determined down to a few microns. Using the data from inside the mill a modeling approach, based on perfect mixing, was developed. The modelling approach implicitly assumes that the mixture of feed materials broken is homogenous from the breakage point of view. The air classification around the circuit was modeled using the efficiency curve approach. In order to measure the success of the method the circuit performance was predicted by simulation studies while it was operating at different conditions. The results were then compared with the measured data. It is concluded that modeling gives a useful quantitative indication of what may occur in fully air swept mills.     

Implementation of the quadrature method of moments in CFD codes for aggregation-breakage problems

In this work the quadrature method of moments (QMOM) is implemented in a commercial computational fluid dynamics (CFD) code (FLUENT) for modeling simultaneous aggregation and breakage. Turbulent and Brownian aggregation kernels are considered in combination with different breakage kernels (power law and exponential) and various daughter distribution functions (symmetric, erosion, uniform). CFD predictions are compared with experimental data taken from other work in the literature and conclusions about CPU time required for the simulations and the advantages of this approach are drawn.     

Experimental tracking of silica dispersion into silicone polymer

This work deals with the experimental tracking of a dispersion of very fine silica particles in PDMS using a new, easily implemented methodology. The dispersion experiments are carried out in an 8-l capacity mixer equipped with a torquemeter. Using a Couette analogy, the torque-rotational speed data can be converted into process viscosity-effective shear rate data. Simultaneously, the Particle Size Distribution (PSD) evolution is followed through Laser Light Scattering measurements on diluted samples. The PSD evolution allowed us to interpret the dispersion process in terms of different mechanisms, such as breaking-up and erosion of aggregates, as well as, in some cases, re-agglomeration (or flocculation) of particles.     

DETERMINATION OF TIME-DEPENDENT CONSTITUTIVE MODEL PARAMETERS FOR MICROCRYSTALLINE CELLULOSE

ABSTRACT

Material parameters of a time-dependent elasto-viscoplaslic constitutive model, proposed by Adachi and Oka, have been determined for microcrystalline cellulose. Adachi and Oka model has eight material parameters, with five of them (i.e., consolidation index, swelling index, critical index, shear modulus, and Poisson's ratio) same as those in the more commonly used in time-independent modified Cam-clay model, and remaining three parameters account for time-dependency. To measure the time-dependent parameters, constant strain-rate conventional triaxial compression (CTC) test was designed and conducted using Penn Slate's flexible-boundary cubical triaxial tester (CTT) with microcrystalline cellulose as the test material. To deposit the powder, the sprinkle filling method was used in a layer by layer fashion with a small spoon. The three time-dependent Adachi and Oka parameters were determined from these tests. Adachi and Oka model was verified by comparing the predicted values from the model with measured values from the CTT at 0.05 level of significance. Results showed that: 1) there were no significant differences (p > 0.05) between measured and predicted HTC responses at all loading rates; 2) failure values were predicted accurately (p > 0.05); and 3) there were significant differences (p < 0.05) between measured and predicted CTC responses at all loading rates.     

Coagulation of Particles Through Rapid Mixing

As is often assumed, rapid mix effectively distributes the dosed coagulant in suspension to promote subsequent flocculation of suspended particles and coagulant molecules. This study determined that the role of rapid mix is considerably more complex than conventionally assumed. Particles in the raw water samples from the Banxing Water Works of Taipei City were coagulated at high shear environment, during which flocs of size 40-70 μm were produced. The produced floc interior was compacted, and residual turbidity and the amount of dissolved natural organic matter (NOM) in suspension were substantially reduced. The subsequent stage of rapid mix slightly reduces floc size, further compacts the floc interior, and expels fine particles and some adsorbed NOM from the flocs. A sudden reduction in shearing rate produced large sized flocs with not so compact structures. Moreover, this action released fine particles from flocs into the suspension and enhanced adsorption of NOM onto solid surfaces.     

Kinetics of fluidised bed melt granulation V: Simultaneous modelling of aggregation and breakage

The main purpose of this paper is to quantify the aggregation and breakage rates in fluidised bed melt granulation (FBMG) and to subsequently relate them to various experimental conditions. The earlier paper of this series (2004d, Powder Technology 143-144, 65-83) illustrated a sequence of development and verification work on a breakage model for FBMG, based on the population balance modelling work on tracer experimental studies. A new error-weighted integral technique was also developed, which allows simultaneous extraction of the aggregation and breakage selection rate constant, as well as the attrition constant that reveals the relative amount of attrition during FBMG. Further research is conducted here, as the similar modelling strategy is employed to extract the aggregation and breakage kinetics at different operating conditions. A series of plots revealing the influence of operating conditions (binder spray rates, bed temperature, droplet size and fluidising air flow rate) on these extracted constants are therefore established. The aggregation rate constant plots reveal that the particle aggregation rate is dependent on the amount of binder available per unit time, and hence scales directly with the binder spray rate. The aggregation rate is also observed to increase with increased bed temperature when a higher viscosity binder is used, but reveals a maximum aggregation rate for a less viscous binder. The aggregation rate also increases with larger droplet size and lower fluidising air velocity. The breakage selection rate and attrition constant plot both reveal no direct dependence on binder spray rate, due to the separation in time scale over which the granule breakage occurs. The breakage rate and the extent of granule attrition is also found to decrease with increased bed temperature and increased fluidising air velocity. Due to scatter in the data, it is not possible to deduce any sensible trend on the influence of droplet size on its relative breakage rate and attrition.     

Breakage behaviour of spherical granulates by compression

This paper describes the deformation and breakage behaviour of granulates in single particle compression test. Three industrial spherical granulates—γ-Al₂O₃, the synthetic zeolite Köstrolith^® and sodium benzoate (C₆H₅COONa) were used as model materials to study the mechanical behaviour from elastic to plastic range. The elastic compression behaviour of granulates is described by means of force-displacement curves, by application of Hertz-Huber contact theory and continuum mechanics. An elastic-plastic contact model was proposed to describe the deformation behaviour of elastic-plastic granules. The effects of granulate size and stressing velocity on the breakage force and contact stiffness during elastic and elastic-plastic displacement are examined. It is shown that the zeolite granulates with elastic-plastic behaviour have viscous properties as well. Breakage mechanisms of granulates during elastic, elastic-plastic and plastic deformation are also explained. The breakage probability is approximated by Weibull distribution function. The behaviour of the granulate during compression under the repeated loading-unloading conditions was investigated.     

1450热精轧机万向接轴断裂研究

根据部分实测数据 ,从力学分析、扭振测试分析、断口检验等方面对 1 45 0热精轧机万向接轴断裂原因进行分析 ,得出导致万向接轴断裂的主要原因是系统设计、材质和扭振 ,针对断裂原因提出避免断裂的措施 ,对保护轧机主传动系统 ,减少事故发生 ,具有重要的实际意义     

Fracture behavior of framing coated glass curtain walls under fire conditions

Breaking glass and its subsequent fallout may markedly affect enclosure fire dynamics. However, little is known about the thermal fracture behavior of framing glass façades in different installation forms. Sixteen 600×600×6 mm³ solar control coated glass panes, installed in exposed, semi-exposed and hidden frames, were heated by a 500×500 mm² n-heptane pool fire to investigate the influence of frame constraints on glass breakage and fallout. Measurements were taken of the time to breakage occurrence, heat release rates, incident heat flux, central gas temperatures and glass surface temperatures. Measurements in relation to crack initiation and propagation as well as loss of integrity of the glazing assembly were also recorded. The experimental results show that all cracks initiated at the edge of covered sections and intersected rapidly, forming islands. The maximum temperature difference and heat flux that the glass can withstand are primarily in the range of 50–90 °C and 9–15 kW/m². Using the finite element method (FEM), the breakage mechanism is demonstrated, the predictions of which are in reasonably good agreement with the experimental results. Among four different installation forms, semi-exposed framing façades showed better fire resistance than exposed framing façades. Meanwhile, the fire resistance of hidden framing façades may depend on the fire location. It is intended that these results will provide practical guidelines for fire safety design.     

温度对成品烟丝造碎率及尺寸分布均匀性的影响

为研究温度对配方烟丝造碎率及尺寸分布均匀性的影响,采用烟丝结构分布方程分析了不同温度烟丝破碎后尺寸分布规律.结果表明:在试验温度范围内,①烟丝的造碎率随着温度的升高而降低,相同温度下烟丝的造碎率是:三类烟＞二类烟＞一类烟;温度对不同等级烟丝的影响程度不同:一类烟＞二类烟＞三类烟;②不同温度烟丝,其破碎后尺寸分布的差异性...