Removal of Fine Particles from Smooth Flat Surfaces by Consecutive Pulse Air Jets

In order to develop an effective dry surface cleaning method, removal of fine particles by pulse air jets was experimentally investigated. A dimensionless resuspension parameter, F*, which is the ratio of drag force on particles to van der Waals adhesion force, was introduced to correlate the removal efficiency. Resuspension experiments were carried out with monodisperse PSL particles and wax particles with diameter between 0.25 and 1.1 μm on silicon wafer and glass plate. As a result, it was found that deposition process of particles on the surface (gravitational settling and impaction at a relatively low impaction velocity) has little effect on the removal efficiency and that consecutive pulse air jet is effective in the removal of fine particles. Further, F* is the key parameter in determining the removal efficiency. The prediction method for the removal efficiency by pulse air jets with F* is proposed.     

Electrostatic Removal of Particle Singlets and Doublets from Conductive Surfaces

Fine particles can cause significant losses during the manufacture of microelectronic components. Removal of such deposited particles is important in reducing such losses. The repulsive force on a singlet conducting particle on a charged conducting surface is theoretically proportional to the particle area and the square of the electric field. We have removed particles as small as 1 μm by creating high (> 100 kV/cm) electrostatic fields at the surfaces of conductors. We found that members of doublet pairs had removal probabilities (at the same field strength) that were less than the removal probability of singlets. Further, the removal of one pair member made more probable the removal of the other. Likely factors are the adhesion of the particles to each other and the increase in adhesion to the surface resulting from the attraction of each particle to the image charge of the other. The theoretical analyses explain why whole chains of particles were found to be removed under conditions where the probability of the removal of a singlet particle was relatively small.     

空气雾化喷嘴的液滴雾化性能实验研究

采用LSA-Ⅲ型激光粒度仪对一种常用的小流量空气雾化喷嘴的液滴雾化性能进行实验研究。实验主要测定了不同气液比、气相压力和液相压力情况下沿喷雾轴向不同位置处的液滴粒径分布。测定结果表明气液比和气相压力对雾化液滴粒径影响均较大,其中气相压力影响最大,气液比其次,液相压力影响最小。在本实验测定条件下,经过喷嘴雾化后在轴向100、200、300、400和500 mm位置处液滴的表面积平均直径（SMD）和体积平均直径（D43）出现波动性变化。通过对实验测得液滴粒径分布数据的分析,可以得到Rosin-Rammler分布函数中的特征参数和n,为定量计算液滴粒径提供理论基础。     

Adhesion and Removal of Particles from Surfaces Under Humidity Controlled Air Stream

The adhesion and the removal of individual micrometer-sized particles on a plane substrate are studied using an air shear flow cell. Laminar isothermal compressible flow characterization enables us to analyze the effect of various parameters such as particle size, air humidity, surface nature and surface charge on the aerodynamic forces required to remove the particles from the substrate. The results show that the increase of humidity (up to a critical value) favors particle removal when particles adhere under strong electrostatic forces on a non-conductive charged substrate. On the contrary, the existence of a capillary force disfavors particle removal beyond this critical humidity. The increase of the humidity disfavors the removal of particles in contact with an uncharged substrate. The results are interpreted in terms of a global adhesion force using a force and torque balance on a single particle in contact with a plane substrate. Moreover, the use of a high-speed video recording system enables us to determine the particle removal mechanisms as a function of the particle Reynolds number.     

Adhesion and Removal of Particles from Surfaces Under Humidity Controlled Air Stream

The adhesion and the removal of individual micrometer-sized particles on a plane substrate are studied using an air shear flow cell. Laminar isothermal compressible flow characterization enables us to analyze the effect of various parameters such as particle size, air humidity, surface nature and surface charge on the aerodynamic forces required to remove the particles from the substrate. The results show that the increase of humidity (up to a critical value) favors particle removal when particles adhere under strong electrostatic forces on a non-conductive charged substrate. On the contrary, the existence of a capillary force disfavors particle removal beyond this critical humidity. The increase of the humidity disfavors the removal of particles in contact with an uncharged substrate. The results are interpreted in terms of a global adhesion force using a force and torque balance on a single particle in contact with a plane substrate. Moreover, the use of a high-speed video recording system enables us to determine the particle removal mechanisms as a function of the particle Reynolds number.     

Experimental Study of Air Entrainment Rates due to Inclined Liquid Jets

The air entrainment rate due to inclined liquid jet plunging into a pool was investigated experimentally. Three types of fluids with varying physical properties in terms of viscosity and surface tension were utilized. For the impinging jet test section, nozzles with different inner diameters were selected. The inclination angles and liquid jet velocities at the nozzle outlet were varied and the entrained air rate was measured by the soap meniscus method. Taking the falling velocity of the liquid jet as a characteristic velocity, it was found that the air entrainment rate under the present experimental condition largely depended on the Weber number. From the obtained database, a new empirical model dependent on the Weber number and Laplace length scale is proposed which is capable of predicting the air entrainment flow rate at a mean absolute relative deviation of 21.7 %.     

Particle Focusing Characteristics of Sonic Jets

High-speed particle beams have found extensive applications in physical and chemical characterization of airborne particles. Expanding a particle-laden gas through an orifice into an evacuated chamber may generate these beams. Such particle inlets transmit a narrow particle size range, and this optimal size range strongly depends on the nozzle geometry and operating conditions. In this work, the choked flow through the primary focusing element is simulated using the CFD code FLUENT to seek an understanding of the mechanisms behind the formation of particle beams and the governing parameters. The focusing process is simulated to validate experimental results for existing inlet geometries and further used to evaluate novel inlet geometries that obtain higher transmission and focusing efficiencies. The best geometries yield particle transmission rates that are about 13 times higher than current designs.     

Particle Detachment from Rough Surfaces in Turbulent Flows

Two flow structure-based models for particle resuspension from rough surfaces in turbulent streams are developed. It is assumed that the real area of contact is determined by elastic deformation of asperities and the effect of topographic properties of surfaces are included. The JKR adhesion model is used to analyze the behaviour of individual asperities. The theories of rolling and sliding detachment are used and the flow-induced resuspension is studied. The effects of the near-wall coherent eddies, and turbulence urst/inrush motion are included in the model development. The critical shear velocities needed to detach different sized particles from rough surfaces under various conditions are evaluated and discussed. The model predictions are compared with the available experimental data and good agreement is obtained.     

Experimental Study of Alumina Particle Removal From a Plane surface

Micron and submicron alumina particles are often used for the mechanical polishing of the GaAs wafers processed in the microelectronic industry. A better understanding of the adhesion mechanisms is the key factor for the particle removal and for the optimisation of the industrial chemical cleaning. However, the nature and the strength of the complex interactions occurring between asymmetrical alumina particles and the surface remain unclear. Thus, an experimental study of the detachment of asymmetrical alumina particles in adhesive contact with a glass plate was done using a specially designed shear stress flow chamber. A series of experiments was performed to measure the shear stress necessary to remove individual alumina particles (of 3 and 0.3 µm nominal size) under various chemical solutions (diluted ammonia, surfactant and glycerol). Then the effects of the particle size, the resting time, the pH and the nature of the chemical solutions used for the removal of the alumina particles was characterised in terms of percentage of alumina particles detached. Results have shown that the longer the resting time, the more adherent the particles are. Moreover, it was found that the ammonia solution gives the best particle removal rate (80%) because of the strong repulsive electrostatic interactions between the alumina particles and the glass surface, both being charged negatively in a basic solution.     

Experimental Study of Alumina Particle Removal From a Plane surface

Micron and submicron alumina particles are often used for the mechanical polishing of the GaAs wafers processed in the microelectronic industry. A better understanding of the adhesion mechanisms is the key factor for the particle removal and for the optimisation of the industrial chemical cleaning. However, the nature and the strength of the complex interactions occurring between asymmetrical alumina particles and the surface remain unclear. Thus, an experimental study of the detachment of asymmetrical alumina particles in adhesive contact with a glass plate was done using a specially designed shear stress flow chamber. A series of experiments was performed to measure the shear stress necessary to remove individual alumina particles (of 3 and 0.3 µm nominal size) under various chemical solutions (diluted ammonia, surfactant and glycerol). Then the effects of the particle size, the resting time, the pH and the nature of the chemical solutions used for the removal of the alumina particles was characterised in terms of percentage of alumina particles detached. Results have shown that the longer the resting time, the more adherent the particles are. Moreover, it was found that the ammonia solution gives the best particle removal rate (80%) because of the strong repulsive electrostatic interactions between the alumina particles and the glass surface, both being charged negatively in a basic solution.     

Effects of Inceptive Motion on Particle Detachment from Surfaces

The effects of inceptive motion on particle detachment are examined. The critical external forces corresponding to lift-off, slide, and rotation are obtained from JKR's contact theory and force or moment balance. Frequently used experimental techniques to study particle detachment are discussed in light of this simple analysis.     

中空纤维膜基吸收法脱除空气中二氧化碳的研究

以醇胺类水溶液作为吸收剂，采用聚丙烯中空纤维膜组件进行膜基气体吸收脱除空气中CO2的研究。实验 结果表明，在吸收液浓度为2.0mol·L-1，气速小于0.30m·s-1，吸收液流速小于0.01m·s-1的条件下，其吸收CO2的 总传质系数约为0.03～0.06mol·m-2·min-1·(mol·L-1)-1。研究建立了估算吸收总传质系数的数学模型，模型计算 曲线与实验数据曲线基本一致，可用于膜基气体吸收法脱除CO2过程的放大设计。     

Investigation of Particle and Air Flows in a Mixed-Flow Dryer

Even though the mixed-flow dryer is well established on the commercial market for the drying of grain, maize, and rice, there further potential as well as a need to optimize the dryer apparatus and to improve product quality. Unfavorable designs can cause uneven mass flow and air flow distributions, resulting in locally different drying conditions and, hence, uneven grain drying. The aim of the present article is to evaluate traditional designs of mixed-flow dryers by numerical and experimental investigation of particle and air flows and to discover design deficits. For this purpose, the dryer geometry and different air duct arrangements (horizontal and diagonal) were studied using the discrete element method (DEM) and computational fluid dynamics (CFD). Drying experiments were performed to evaluate the grain moisture and temperature distributions. With regard to particle flow, a typical core flow was detected as in silos with a retarded particle flow at the dryer walls and a fast flow region in the center of the dryer. This was caused by the wall friction effect and the half air ducts fixed at the side walls. With regard to the air flow, dead zones were discovered for the diagonal air duct arrangement. Based on the design deficits identified for the traditional geometry, a new geometry for the mixed-flow dryer that is still under development is discussed.     

脉冲电晕脱硫脱硝工艺

文章概述了脉冲电晕放电烟气脱硫脱硝技术的研究状况,对反应机理作了分析,并指出其影响因素和目前存在的一些问题,最后对该技术作了展望。     

Impact of Airflow Characteristics on Particle Resuspension from Indoor Surfaces

Resuspension is an important source of indoor particles. We measured the resuspension of 1 to 20 μm particles on common indoor materials and explored the importance of turbulence to the resuspension process. Experimental variables included materials (linoleum, carpet, and galvanized sheet metal) and bulk air velocity (5, 10, 15, 20, and 25 m/s). At each of these conditions the turbulence intensity in the boundary layer was varied between a low, medium, and high state and ranged from 9 to 34% at the surface. For comparison of resuspension from the considered surfaces and at different flow conditions, we use the relative resuspension, which quantifies resuspension without requiring knowledge of the number of particles initially seeded on the surface. The relative resuspension compares the fraction of particles resuspended at the experimental conditions to the maximum achieved with a controlled impinging jet. In general, the results show that for the ranges considered, increasing velocity caused the largest increase in resuspension, followed by increasing turbulence intensity and then increasing particle diameter. All three material types showed consistent patterns with carpet having the largest resuspension for a given set of conditions, followed by linoleum and then by galvanized sheet metal. High turbulence and high velocity conditions minimized the differences between materials. An understanding of the relative magnitudes of these effects allows for better analysis and mitigation of indoor resuspension.     

Excimer Laser Induced Removal of Particles from Hydrophilic Silicon Surfaces

A pulsed KrF excimer laser was used to remove several types of submicron-sized particles from silicon surfaces. Polystyrene latex particles, 0.1 μm and larger, were removed from silicon surfaces by dry laser cleaning (no water layer condensed on the surface) but SiO₂ particles could not be so removed. However, during steam laser cleaning, in which a thin film of water is deposited on the surface as both an energy transfer medium and an adhesion force reduction agent, these 0.1-0.2 μm SiO₂ particles were almost entirely removed. Calculations of the various forces contributing to adhesion indicate that hydrogen bonds are the major contributor to the adhesion of inorganic particles to substrate surfaces. Photoacoustic detection, using piezoelectric transducers, monitored the surface vibrations induced by the laser pulses.     

Excimer Laser Induced Removal of Particles from Hydrophilic Silicon Surfaces

A pulsed KrF excimer laser was used to remove several types of submicron-sized particles from silicon surfaces. Polystyrene latex particles, 0.1 μm and larger, were removed from silicon surfaces by dry laser cleaning (no water layer condensed on the surface) but SiO₂ particles could not be so removed. However, during steam laser cleaning, in which a thin film of water is deposited on the surface as both an energy transfer medium and an adhesion force reduction agent, these 0.1–0.2 μm SiO₂ particles were almost entirely removed. Calculations of the various forces contributing to adhesion indicate that hydrogen bonds are the major contributor to the adhesion of inorganic particles to substrate surfaces. Photoacoustic detection, using piezoelectric transducers, monitored the surface vibrations induced by the laser pulses.     

Experimental and Theoretical Investigation of Degradation Mechanisms by Particle Coarsening in SOFC Electrodes

Performance degradation data obtained from single solid oxide fuel cells, tested at 850 °C with air and humidified H₂ and using Ni‐YSZ anode supported cells, are presented here. Microscopic investigation is carried out on both anode and cathode to quantify variations in the morphology at different operation times. The comparison between the measurements on the cells and the SEM image analysis allows to conclude that there is no relationship between the initial cell activation and microstructural modifications of the electrodes. On the other hand, it was found that cell degradation is strictly related to the coarsening of Ni particles occurring in the anode. A theoretical analysis based on an electrode micromodel has been performed in order to compare the variation in performance, expected from particle size change, with the observed data. The model confirmed the conclusions of the experimental results.     

煤高温空气气化实验研究

在内径200 mm的固定床气化炉装置上进行了以高温空气/蒸汽作为气化剂的煤高温空气气化实验,考察了空气预热温度、气化温度、空气/煤比和蒸汽/煤比等工艺参数对煤气化指标的影响. 结果表明,在其他条件不变的情况下,空气预热温度由500℃提高到800℃时,煤气热值提高32.5%. 气化温度越高对气化过程越有利,但在固态排渣条件下,气化温度的提高受煤灰熔点的限制. 空气/煤比和蒸汽/煤比对气化指标的影响本质上是通过改变气化温度来实现的. 对于特定的固定床气化工艺,空气/煤比和蒸汽/煤比均存在最佳操作区域. 在本实验条件下,其优化值分别为1.55~1.8 Nm3/kg和0.25~0.35 kg/kg.