Simulation Analysis of Inhalable Dust Sampling Errors Using a Multi-Component Error Model

Measurements to characterize inhalable aerosol exposure are subject to random error even after sources of systematic error have been eliminated. For a fixed aerosol sampler geometry the random errors are due to the variability of measured and unmeasured parameters including ambient variables, quantification technique, and operation parameters. In this discussion we apply a multi-component error estimation model to size selective aerosol sampling with the well-known Institute of Occupational Medicine (IOM) inhalable aerosol sampler. Random errors due to typical variations in sampler flow control, timing, and mass determination were small, being approximately 3%. Similarly, random errors due to variations in wind velocity were reasonably small at approximately 10%. However, the bias introduced by wind velocity was notable, ranging from peak values of 17 to 27% depending on aerosol mass median aerodynamic diameter and geometric standard deviation. This modeling indicated that the combined influence of variations in sampler flow control, timing, mass determination, and ambient wind velocity on IOM performance appeared to be less than approximately 10%; however, bias at moderate wind velocities was shown to be important for the IOM sampler as suggested by other studies. The effects of sampler placement, angle of incidence of ambient wind velocity on the sampler, and head orientation of the exposed person are unknown at this time and need additional research.     

Characterization of the Velocity Field in a Small,Cylindrical, Low Reynolds Number Aerosol Sampling Cyclone

A laser Doppler velocimeter capable of simultaneously measuring two components of velocity was used to measure the flow field in a 88.9-mm diameter, cylindrical, reverse-flow, multiport cyclone. A third component was measured by reorienting the cyclone. The components measured were those in the radial, axial, and tangential directions with the tangential component being measured in both orientations. The ratio of velocities was ? _θ:? _z:? _R = 100:10:1. At a flow-rate Reynolds number, N _RQ= (4pQ)/(πμD _c), of approximately 860, values of turbulence intensity for each component within the cyclone were on the order of 10% when determined as the component standard deviation normalized to the mean flow. The vortex structure is dependent upon Reynolds number.     

高寿命水雾化喷头的制作

水雾化喷头是增湿塔的关键部件,它的好坏直接影响到增湿塔对窑尾废气的调质效果,对于窑尾收尘器的收尘效率起到决定作用。由于喷头是在较高水压(2-8MPa)下长期连续使用,因此除雾化效果外,喷头的使用寿命问题也越来越受到人们的关注。本文介绍耐磨工具材料--硬质合金在水雾化喷头上的应用及其水雾化喷头的设计改进。     

浸入式水口防堵塞的研究进展

介绍了铝碳质浸入式水口的Al_2O_3堵塞问题及Al_2O_3附着机理,阐述了防止水口堵塞的各项措施,并探讨了浸入式水口的发展趋势。     

连铸水口中钢-耐火材料相互作用的热化学性

通过钢水和耐火材料之间的相互作用,可以在浸入式水口(SEN)内壁上形成沉积或变质层。用化学热动力学分析软件装置进行模拟,热化学反应定量解释了这些相互作用。预期的与从高温静态试验中获得的结果进行比较。在这些试验中,含有和不含有铝的钢在从含有和不含有碳的不同氧化物耐火材料中制得的耐火坩埚内熔融。采用阴极发光(CL)显微技术、反射光(RL)显微技术和扫描电子显微技术(SEM)来研究耐火材料-金属界面试样的特性,以了解相互反应并确定耐火材料和钢成分对堆积物形成的影响。显微技术资料和热动力学预测都表明,含碳耐火材料,尤其是镁碳和铝硅碳,导致大幅度的和钢相互反应。所有无碳和无杂质材料几乎没有什么相互反应。     

Bubble Formation at Variously Inclined Nozzles

Bubble formation at variously inclined submerged nozzles, fed with a continuous gas flow rate, is investigated. The average liquid velocity induced by bubble motion is determined, leading to a simple correlation for estimation of the liquid velocities induced by the repeated passage of bubbles. An effective model for the prediction of bubble sizes at their detachment from vertical nozzle orifices is presented which encompasses a bound expansion stage, followed by an accelerated expansion phase, and ends by an original bubble detachment criterion. The existence of a liquid‐phase effective entrainment velocity, generated by the continuous passage of the bubble stream, is quantified and included in the model. Model predictions are found to correlate well with experimental and literature data.     

A Model for the Prediction of the Collection Efficiency Characteristics of a Small,Cylindrical Aerosol Sampling Cyclone

Velocity data from a previous study were nondimensionalized and used in conjunction with a computer program which solves the equations for particle trajectory to predict the collection efficiency for the cyclone. Results for the prediction of cutpoint at the same Reynolds number as that for which the velocities were measured, both for a large cyclone of 88.9 mm diameter and another geometrically similar at one half the scale, are excellent. The model predicts cutpoints of 10 μm and 5.1 μm for the large and small cyclone, respectively, while the actual cutpoints determined from aerosol tests were 9.9 μm and 5.2 μ m. The efficiency curve generated by the model was steeper (geometric standard deviation of 1.1) than the efficiency curve determined through the aerosol testing (geometric standard deviation of 1.4). A simplification of the Dirgo and Leith equation fitting Barth's design curve is suggested which provides a significantly better fit of the aerosol data (geometric standard deviation of 1.3). At 1.5N _{R Q}, where N _{R Q} = (4pg)/(πμD _c), the error in prediction of the cutpoint in the large cyclone is less than 8% while at 04N _{R Q} the error is less than 2%. Although results are good over a limited range of Reynolds numbers, the model is strictly applicable only for flows which are dynamically similar to those studied here.     

Structure Optimization of SENs and Upper Nozzles

The structure of SEN and upper nozzles was optimized and simulated. Relevant trials were conducted on site during the casting of Al-killed steel. These optimizations effectively solve the nozzle clogging and reduce the defects of the casting slab.     

Simulation of Droplet Generation by Mixing Nozzles

In various chemical processes thorough homogeneous mixing is of great importance. Due to their small characteristic dimensions, micromixers have a great potential to achieve fast and uniform mixing. However, in the field of powder synthesis from precipitation processes the use of standard micromixers is severely limited because of rapid clogging of the microchannels. As an alternative, mixing nozzles which are less susceptible to fouling can provide a sufficient mixing quality. The flow field and fluid distribution inside multi‐fluid droplets during droplet formation is simulated. Depending on the geometry and flow rates, complex velocity fields and flow distributions are found and the impact on the mixing efficiency is qualitatively deduced. Furthermore, we point out how the tendency of fouling can be further reduced with the help of improved nozzle geometries.     

Customized Vibrating-Membrane Nozzles for Enhanced Fluid Atomization

Copyright 2015 American Association for Aerosol Research     

提高钛材喷嘴的使用寿命

针对硫磺雾化喷嘴存在磨蚀快、高温蠕变明显的现象,提出了喷嘴氮化热处理的方法。实践证明这是延长喷嘴使用寿命的有效方案。     

A Partial Theory of Atomization in Internal Mix Swirl Nozzles

The aspiration of spherical particles which are suspended without sedimentation in an ideal fluid that flows past a thin-walled sampler is investigated. A recent experimental study showed that secondary aspiration caused by particles bouncing off the walls of the nozzle and subsequently entering the nozzle inlet is of importance in determining the aspiration efficiency of samplers in many situations. Therefore the extent of oversampling caused by particle rebound is investigated using a numerical method. Three situations are considered, namely, when the particles (1) adhere to the sampler surface on impact, (2) bounce off the surface and all those that hit within a certain area, known as the stagnation area, are eventually sampled, and (3) bounce off the surface with no loss of energy. Results for the three cases are compared and they are found to display the same trends as found in the experimental investigations.     

设备管口载荷计算的准确模拟

设备与设备外部的管道相互作用,会对设备管口产生一个作用力,运行时设备管口的受力不能超过设备的允许值,因此设备管口受力值的准确计算很重要.化工设备有多种形式,但按设备内部管道可分为三种典型形式:直管、U型管和环管.文章以某项目的三种典型设备为例,应用CAESAR Ⅱ应力计算软件中的“虚拟刚体”对设备进行模拟,并在此模型上,增加设备管口的约束条件.完成后的模型将设备与管道连成了一个整体,能直接计算设备滑动端的位移,也能在计算中考虑设备管口的约束条件.通过对设备热胀位移的计算验证了模型的准确性,计算结果体现了设备与管道的相互作用,并能同时计算多个工况的受力值,因此能提供更准确的设备管口载荷.     

柱型水力旋流器柱段长度的研究

针对柱型水力旋流器,以能量损失最小和最佳分离效率为目标函数,运用Fluent软件进行数值模拟,获得旋流器柱段的最佳长度以及柱段长度和溢流管插入深度的最优关系。     

汉代乐舞俑的艺术特色

汉代陶俑艺术在中华民族史册上占有非常重要的地位,活灵活现的乐舞俑更是涌动着蓬勃的生命力,它那古朴稚拙、取大势去繁缛及写实和写意相结合的艺术特色在历史上也是极为罕见,以至于汉代陶俑艺术对我国现代陶瓷的发展也产生了深远影响。     

Dilatational Relaxation in Cylindrical Seals

This paper presents a viscoelastic thermal stress analysis which illustrates the importance of dilatational stress relaxation in cylindrical seals. When the core is elastic and the cladding is glass, dilatational stress relaxation has no significant influence on the stresses in the seal. However, when the core is glass and the cladding is elastic, this relaxation has a profound effect. For the latter seal, the setting temperature is weakly dependent on seal dimensions. In fact, stress development during cooling can be accurately predicted from the "fluid core" analysis by Scherer and Cooper, using the fictive temperature of the glass as the setting temperature.     

Stress Measurement in Cylindrical Vessels

An analysis is presented of the birefringence patterns observed in the walls of cylindrical glass objects when viewed tangentially in a matching index fluid. The patterns to be expected from a combination of parabolic and bending stresses, resulting from asymmetric cooling, are calculated. Experimentally measured patterns are shown to illustrate the theory. A simple method is presented whereby the stresses at the outside and inside surfaces of tempered ware can be calculated from the observed pattern.     

Random Errors in Dyeing

The differences in colour from the target of a dyed material which are due to known weighing errors are calculated using computer match-prediction techniques. The results, which are presented in the form of a colour map, show that the sensitivity is dependent on the target colour and the colours of the constituent dyes in the recipe.     

Fluent在气液两相雾化喷嘴模拟分析中的应用

Fluent模拟软件广泛应用于气液两相雾化喷嘴的设计和分析。文章主要综述了近年来国内气液两相雾化喷嘴数值模拟的研究进展,分析了各种模拟方法的特点。