Method for Estimating Size-Specific Particulate Emission Inventories

Increasing evidence on the detrimental health effects of suspended fine particulates has prompted the introduction of new ambient air quality standards for particles with diameters smaller than 2.5 and∕or 10 μm and has created the need for size-specific inventories. To address this need, “generic” cumulative weight fraction data have been fitted with lognormal particle size distributions, and the resulting mean diameter dm and standard deviation σg values compiled for many sources of practical interest. In addition, nomographs are developed for assessing the mass fraction of particles with diameters <2.5, 6, 10, 15, and 30 μm as a function of the applicable dm and σg. The above data and tools allow easy extension of total particulate matter emission inventories for uncontrolled sources into size-specific ones. Supplemented with published typical efficiencies of control systems in the ranges 0–2.5, 2.5–6, and 6–10 μm, they also allow easy compilation of approximate size-specific inventories for controlled sources. In addition, used in conjunction with graphical models for selected control systems that predict the total efficiency and lognormal size distribution of penetrating particles, they offer a unique rigorous approach for size-specific inventories from controlled sources.     

Rapid Performance Evaluation and Optimal Sizing of Dry Cyclone Separators

Cyclones are generally less efficient than other kinds of equipment, but their simple construction, low energy requirements, and ability to operate at high temperatures and pressures make them attractive for cleaning up gases. Despite the simplicity in construction and operation, complex mathematical formulations are used for predicting the collection efficiency of particles of a given diameter. These must be numerically integrated, along with the inlet particle-size-distribution functions that are appropriate in each application, in order to obtain the overall cyclone efficiency. In this paper, the above cumbersome procedure is simplified through nomographs allowing rapid, yet rigorous, estimation of the overall cyclone efficiencies based on two alternative and well-established approaches and on the sole assumption of a lognormal particle-size distribution. Along with the above, pressure drop and limiting inlet velocity correlations are also considered, and each of the above nomographs is combined with others, providing direct graphical representation of the so far obscure relationships among cyclone diameter, overall efficiency, and gas pressure drop or flow rate. The paper thus affords an overview of cyclone behavior over a wide range of conditions, offering direct solutions to both cyclone performance and optimal cyclone design problems.     

Effect of Heat Input on Fume Generation and Joint Properties of Gas Metal Arc Welded Austenitic Stainless Steel

 The effect of heat input on fume and their compositions during gas metal arc welding (GMAW) of AISI 316 stainless steel plates are investigated. Fume generation rate (FGR) and fume percentage were determined by ANSI/AWS F12 methods. Particle characterization was performed with SEM-XEDS and XRF analysis to reveal the particle morphology and chemical composition of the fume particles. The SEM analysis reveals the morphology of particles having three distinct shapes namely spherical, irregular, and agglomerated. Spherical particles were the most abundant type of individual particle. All the fume particle size falls in the range of less than 100 nm. Mechanical properties (strength, hardness and toughness) and microstructural analysis of the weld deposits were evaluated. It is found that heat input of 115 kJ/mm is beneficial to weld stainless steel by GMAW process due to lower level of welding fume emissions and superior mechanical properties of the joints.     

A Transfer Function for Relating Mean 2D Cross-Section Measurements to Mean 3D Particle Sizes

It is common practice to estimate mean 3D particle and grain size of polycrystalline materials by multiplying 2D cross-sectional measurements by a multiplication factor. However, the most frequently used multiplication factors apply only to uniform or specific dispersions of particles, and therefore can provide misleading results. In the present work, empirical equations are developed to more accurately predict the mean 3D grain size of a lognormal spherical particle dispersion, regardless of the dispersion’s width. The equations provide an improvement over scalar multiplier values by allowing the effects of particle size distribution to be accounted for using inputs that can be obtained by cross-sectional analysis.     

Modeling of Class I Settling Tanks

Sedimentation is one of the earliest and most important unit operations in water and wastewater treatment. Conventional approaches for studying sedimentation of Class I settling tanks did not present enough information on suspended particle size distribution in the effluent. This information is very important for further treatment units such as filtration. In this research, a relatively simple and practical mathematical model is introduced to study sedimentation of non-uniform particle size in Class I settling tanks. The model is capable of providing such information as removal efficiency, size distributions in sludge and in effluent suspension, and thickness of bottom sludge. If desired removal efficiency is provided, the length of the tank can also be determined. Through numerical experiments, a sensitivity analysis was performed to examine the effects of tank dimensions, overflow rate, and detention time on the removal efficiency. Comparison with other models and a set of experimental data indicates a good agreement.     

A statistical theory of grain growth

By extending the theory of Kurtz and Carpay, a detailed statistical theory of normal grain growth has been developed. The theory utilizes their concept of multiple distributions, i.e. the division of grains into topological classes (14 planar, 34 spatial) but unlike their treatment it does not require the individual distributions of each class to be lognormal. An alternate multiple distribution of grain sizes, where the grains are classified according to a given value of size, rather than a given value of sides, or faces is also proposed. The overall distributions (both in grain shapes and sizes) are then obtained by summing the individual distributions, and are shown to be approximately lognormal. Alternate origins of lognormality are also discussed.     

Image-Based System for Particle Counting and Sizing

A procedure is developed to provide measurements of particle size by adapting parts of a commercially available particle image velocimetry system to obtain in situ digital images of the particles. The procedure is nonintrusive and is able to capture images of the particles as they are mixed, thus avoiding the need for disturbing the flow or withdrawing samples for later analysis. Measured size distributions are shown to compare closely with manufacturer's values for standard polystyrene spherical particles, and particles with diameters as small as 6 μm are resolved. The system also is shown to track changes in particle-size distribution during an aggregation test. In addition, information on particle geometry is obtained, which should be useful for improving the ability to model aggregation processes. A simple modeling framework based on the Smoluchowski equation is presented to demonstrate the use of data obtained with this procedure in particle aggregation modeling.     

Characterizations of pore and constituent particle populations in 7050-T7451 aluminum plate alloys

Although qualitative relationships between fatigue lives and the sizes of the microstructural features, such as pores and particles, are well known, the quantitative models are lacking because of the unavailability of the required detailed microstructural data. The purpose of this work was to obtain such data for the high porosity (HP) and reduced porosity (RP) variants of the aluminum 7050-T7451 thick-plate alloys. Both alloys had similar tensile and fracture properties, but the reduced porosity variant showed superior fatigue performance attributed to the smaller sizes of the fatigue crack initiating particles and pores. Those size differences, as well as the differences in the through-thickness size gradients, have been characterized in this work. The sizes, shapes, and orientations of particles and pores were analyzed first on the plane sections and then converted to the true three-dimensional (3-D) characteristics using the moment method. In the conversions, the particle and pore shapes have been assumed as triaxial ellipsoids and their size distributions as lognormal. The spatial distributions were quantified using the nearest neighbor spacing method. Results confirmed that the reduced porosity alloy had smaller particles and pores than the high porosity variant. The size distributions in the former were also more confined. In both alloys, the largest particles and pores were at the plate centers and the smallest at the surface. Their spatial distributions could be categorized as random with clusters.     

离子型稀土矿土壤粒度分布特征研究——以赣县姜窝子稀土矿山为例

颗粒粒度分布对土壤水分运动和溶质迁移,以及水土流失有重要影响. 利用水洗分筛和激光粒度分析技术研究了江西赣县姜窝子稀土矿土壤颗粒粒度并探讨了土壤颗粒粒度在垂直方向的分布规律. 研究表明,姜窝子稀土矿山土壤颗粒粒度分布受风化程度、颗粒垂向迁移因素的影响,呈如下分布:①离子型稀土矿土壤颗粒按直径分为粗、细、粉、黏粒结构,且土壤粗颗粒以石英为主,稀土矿土壤颗粒粒度呈驼峰式分布,即粒径在粗颗粒（ > 2 mm） 和黏粒（ < 0.075 mm）含量较高,粒径在细、粉粒（0.075~2 mm）含量相对较低;②受风化程度和颗粒垂向迁移的影响,稀土矿土壤细、黏粒组分的含量随深度增大呈先升后降的曲线形态;③黏粒（ < 0.075 mm）激光粒度分析表明,颗粒分布随粒径的大小变化与粒径大于0.075 mm的颗粒在深度上的分布相似.      

The role of particle size on the laser sintering of iron powder

The effects of powder particle size on the densification and microstructure of iron powder in the direct laser sintering process were investigated. Iron powders with particle sizes ranging from 10 to 200 μm were used. It was found that the sintered density increases as the laser energy input is increased. There is, however, a saturation level at which higher density cannot be obtained even at very intensive energy input. This saturation density increases as the size of the iron particles decreases. Meanwhile fine powders with narrow particle size distributions have a tendency toward agglomeration, and coarse powders with broad particle size distributions have a tendency toward segregation, both of them resulting in lower attainable density. In order to investigate the role of particle size, a “densification coefficient (K)” was defined and used. This coefficient depends on the particle size and the oxygen content of iron powder. The results of this investigation demonstrate that the presence of oxygen significantly influences the densification and pore morphology of laser-sintered iron. At higher oxygen concentrations, the iron melt pool is solidified to agglomerates, and formation of pores with orientation toward the building direction is more likely to occur. When the oxygen concentration is kept constant, the densification coefficient decreases with decreasing the particle size, meaning the densification kinetics enhances. This article presents the role of powder characteristics and the processing parameters in the laser sintering of iron powder as a model material. The mechanism of particle bonding and microstructural features of laser-sintered parts are addressed.     

粒度大小对赤铁矿和石英浮选分离的影响

通过浮选试验、DLVO理论计算、聚焦光束反射测量（FBRM）等研究了油酸钠浮选体系下粒度大小对赤铁矿和石英浮选分离的影响。人工混合矿浮选试验表明,窄粒级粗粒或中等粒级的赤铁矿?石英混合矿（CH&CQ和MH&CQ）的浮选效果较好,其中CH&CQ和MH&CQ的分选效率分别为85.49%和84.26%,明显高于全粒级混合矿（RH&RQ）的分选效率74.94%;但窄粒级的细粒赤铁矿?石英混合矿（FH&FQ）的浮选效果则较差,其分选效率只有54.98%。浮选动力学试验表明,赤铁矿的浮选速率和回收率不仅与赤铁矿的粒度有关,还受石英粒度的影响,细粒脉石矿物石英会降低赤铁矿的浮选速率和回收率。DLVO理论计算表明,当矿浆pH值为9.0时,石英与赤铁矿颗粒间的相互作用力为斥力,此时细粒石英很难“罩盖”在赤铁矿表面并通过这种“直接作用”的方式抑制赤铁矿浮选,这也与聚焦光束反射测量（FBRM）的测定结果基本一致;颗粒?气泡碰撞分析表明,在浮选过程中细粒石英可能通过“边界层效应”的方式跟随气泡升浮（夹带作用）,影响赤铁矿颗粒与气泡间的碰撞及黏附,从而降低了赤铁矿的浮选速率和回收率。      

Theory of grain boundary motion in the presence of mobile particles

A theory of grain boundary motion in the presence of mobile particles is put forward. It is shown that the boundary-particle-interaction leads to a hysteresis in the velocity-driving relationship. The extent of the hysteresis depends on particle mobility, which is very sensitive to particle size. The effect of particles is discussed for planar and curved boundaries as well as volume particle distributions. The theory accounts for a smaller limiting grain size during grain growth than predicted by Zener drag. The concept can be generalized to include all kinds of mobile obstacles for boundary migration. In such cases not the distribution of obstacle spacing rather the distribution of obstacle mobilities will control microstructure evolution.     

球磨机介质配比方法的试验研究

对生产中简单实用的主要介质配比方法进行了试验比较。结果表明,确定适宜介质配比的方法是：根据给料粒度组成,先确定各主要窄给别对应的最佳介质尺寸,然后各直径球介质占球荷总质量的百分率等于给料中相应窄级别的产率确定介质配比;如果给料中粗粒级含量低,磨矿时间较长,磨机矿浆粘度较大,可按照各尺寸介质等质量百分比法计算介质配比,以适当增加大球介质的比例,提高磨矿效率。该研究结构对实际生产具有重要的指导意义。     

球磨时间对钨粉粒度分布及形貌影响

通过改变球磨时间,获得不同粒度分布的钨粉颗粒,分析球磨时间对钨粉粒度分布和形貌特征的影响,提高粒度分布在目标区间（5～11 μm）的钨粉颗粒体积分数。结果表明,球磨的前2 h对原料中大颗粒钨粉的影响较大,钨粉颗粒最大粒径由134 μm迅速下降到20 μm左右。随着球磨时间的增加,钨粉粒度分布指标减缓下降,除粒径变小外,颗粒形貌基本无变化,但是在球磨10 h后开始出现团聚现象。综合分析可知,球磨时间的改变对钨粉粒度分布指标影响较大,球磨时间为8 h时,可获得粒度分布最窄的钨粉颗粒,在目标区间的钨粉颗粒体积分数达到75%。     

Compositional Fragmentation Model for the Oxidation of Sulfide Particles in a Flash Reactor

A mathematical model to predict the size distribution and chemical composition of a cloud of sulfide particles during high-temperature oxidation in a flash reactor is presented. The model incorporates the expansion and further fragmentation of the reacting particles along their trajectories throughout the reaction chamber. A relevant feature of the present formulation is its flexibility to treat a variety of flash reacting systems, such as the flash smelting and flash converting processes. This is accomplished by computing the chemical composition of individual particles and the size distribution and overall composition of the particle cloud in separate modules, which are coupled through a database of particle properties previously stored on disk. The flash converting of solid copper mattes is considered as an example. The model predictions showed good agreement with the experimental data collected in a large laboratory reactor in terms of particle size distribution and sulfur remaining in the population of particles. The cumulative contribution and distribution coefficients are introduced to quantify the relationship between specific particle sizes in the feed and those in the reacted products upon oxidation, the latter of which has practical implications on the amount and chemical composition of dust particles produced during the industrial operation.     

Effect of loading condition and stress state on damage evolution of silicon particles in an Al-Si-Mg-Base cast alloy

Damage evolution of Si particles in a Sr modified cast A356(T6) Al alloy is quantitatively characterized as a function of strain under tension, compression, and torsion. The fraction of damaged Si particles, their size distributions, and orientation distribution of particle cracks are measured by image analysis and stereological techniques. Silicon particle cracking and debonding are the predominant damage modes. Particle debonding is observed only under externally applied tensile loads, whereas particle cracking is observed under all loading conditions. The relative contributions of Si particle debonding and fracture to the total damage strongly depend on stress state and temperature. For all loading conditions and stress states studied, the average size of damaged Si particles is considerably larger than the bulk average size. The rate of damage accumulation is different for different loading conditions. At a given strain level, Si particle damage is lowest under compression and highest under torsion. The anisotropy of the damage is highly dependent on the deformation path and stress state. Under uniaxial tension, the cracks in the broken Si particles are mostly perpendicular to the loading direction, whereas in the compression test specimens they are parallel to the loading direction. The Si particle cracks in the torsion and notch-tension test specimens do not exhibit preferred orientations. The quantitative microstructural data are used to test damage evolution models.     

氧化铝回转窑内物料流动与传热数值模拟

在分析氧化铝回转窑传热过程的基础上,运用多相流理论对回转窑内横截面物料流动与传热过程进行数值模拟,研究了不同工况下横截面上的温度分布及流动情况。结果表明,截面上物料温度主要受气体及窑壁传热影响,物料颗粒越小,其内部温度上升越快,流动带起的物料高度也越低,但截面上物料内部温度分布基本趋于一致,并可忽略截面温差。     

Modeling of particle size evolution during mechanical milling

The process of mechanical alloying (MA) involves the repeated deformation, welding, and fracture of powder materials during grinding in high-energy mills. During MA, the size and size distribution of the particles change as a result of the particles’ different fracture and welding rates. The evolution of particle volume distributions during such a combined “fission-fusion” process can be describedvia a differential-integral equation. While analytical solutions are known for systems in which only fusion takes place, there is apparently no such solution for the fission-fusion problem. In this article, we describe a discretized form of the fission-fusion equation and apply it to modeling of particle size distributions during milling of elemental powders using previously determined fracture and welding rates appropriate to the global system of particles. Predicted particle size distributions mimic well those determined experimentally. Formerly Graduate Student, Department of Formerly Graduate Student, Department of Formerly Graduate Student, Department of Formerly Professor, Department of Materials Formerly Professor, Department of Materials     

Ball-Mill Grinding Kinetics of Cement Clinker Comminuted in the High-Pressure Roll Mill

The use of high-pressure grinding rolls (HPGR) prior to ball mills has become a common practice in cement clinker grinding due to significant energy savings in comparison to ball milling alone. The energy savings has been attributed to higher energy efficiency of HPGR at low reduction ratios, smaller particle top sizes in the ball mill feed, and the weakening of particles resulting from compression of particle bed by HPGR. This study attempts to show how the weakening effect changes the kinetic breakage parameters of the HPGR-treated clinker. For this purpose, batch ball mill experiments were conducted with three narrow-size fractions (?3.35 + 2.36, ?1.70 + 1.18, and ?0.85 + 0.60 mm) of the feed and product samples of an industrial HPGR, and the breakage rate and breakage distribution parameters of the samples were compared. The results show that the weakening effect leads to nonlinear breakage rates for all sizes, coupled with abnormal breakage at the two coarsest sizes. The weakening effect leads to increased breakage rates of the HPGR product relative to particles of the HPGR feed. The increased breakage rates are accompanied by coarser progeny distributions for the two coarsest size ranges relative to that of the HPGR feed. The progeny distribution of the finest size of the HPGR product, however, is finer than that of the HPGR feed. Ball milling of size-distributed feeds prepared from the HPGR product and feed samples for the same grinding time produces self-similar size distributions when the size is normalized with respect to the median size.