THEORY OF THE FRACTIONAL COLLECTION EFFICIENCY FOR THE AXIAL FLOW CYCLONE DUST COLLECTOR

A cyclone dust collector is a simple device with no moving parts, so it is applied in many industrial fields. However there is still no satisfied theory to estimate the collection efficiency for a given cyclone with high reliability since it is very difficult to predict the movement of the fine solid particles in the three dimensional turbulent rotational flows in the cyclone. A new model of the fractional collection efficiency including the diffusion effect of the solid particles and the decay effect of the tangential velocity of gas flow along the concave wall surface has been derived. In order to confirm this model, a simplified axial flow cyclone of body diameter D₁ = 99 mm has been constructed and fly-ash particles were used as a test dust. The experimental results of collection efficiency were compared those predicted by the Ogawa model and the Fuchs model.     

DISTRIBUTIONS OF THE TANGENTIAL VELOCITIES ON THE DUST LADEN GAS FLOW IN THE CYLINDRICAL CYCLONE DUST COLLECTOR

The authors measured the distributions of the tangential velocities of the feed dust concentration C_o = 0. 6 ~15. 0 g/ m³ by the hot wire anemometers. The test dust was fly-ash which had the mean diameter Xpn = 2.03 μm. The used cylindrical cyclone had the diameter D1 = 140 mm, the diameter of the exit pipe D2 = 50 mn and the total length HT = 382 mm. In order to measure the fluctuating velocities and the time mean velocity on the dust Iaden gas flow and on the pure air flow, we had applied two kinds of the hot-wires. The flow Reynolds number Rec was Rec = Qo/HiV = 797~5582. The expert mental results sho-ed that there were no distinct differences of the time mean and fl uctuating velocities between the pure air flow and the dust laden gas flow. Then the authors have tried to explain those expert mental results by the response time of the fine solid particles and that of the scale of the nixing length in the turbulent rotational air flow.     

RE-ENTRAINMENT OF DUSTS FROM THE DUST LAYER ON THE THE DEPOSITED DUSTS IN THE CYCLONE DUST COLLECTORS

There were many papers concerning the experimental results of the collection efficiency, but up to this time there are a few papers concerning the experimental results of the re-entrainment or dispersion of the dust particles from the dust layer by the turbulent rotational air flow in the dust bunker for the cyclone dust collector. Then in this paper, the author described the experimental results of the re-entrainment of the test dust ( talc X_R50 = 8.O µm ) for the four kinds of the throat diameter D₃ = 50, 80, 100 and 150 mm. Especially it is very importance to take into consideration of flow rate Qb into the dust bunker which is a function of D₃ and cyclone diameter D₁ and the maximum tangential velocity Vet in the dust bunker which depends on D₁,D₃ and Qb.     

AN IMPROVED SINGLE DROPLET COLLECTION EFFICIENCY FOR THE INTERMEDIATE FLOW REGIME

An improved angle droplet collection efficiency model for the intermediate flow regime is presented in this paper, taking into account both inertial impaction and interception mechanisms. This model uses the equations of motion that has been derived by performing a force balance on a particle interacting with the flow field of a spherical collector. The fluid flow field around the collector is assumed to be the approximate solution as developed by Hamielec and Johnson for Reynolds numbers ranging between 10 and 80 and Tomotika and Aoi for Reynolds numbers less than 1.0.

The results of this work indicate that the collection efficiencies calculated by using potential flow conditions may have overestimated the overall collection of particulate matter. It was identified that the transition from intermediate to potential flow occurs when the Reynolds number is about 80. The interpolation scheme for the single droplet collection efficiency proposed in this work can be used from Stokes flow to potential flow conditions including intermediate flow regime.     

EFFECT OF LOADING WITH AIM OIL AEROSOL ON THE COLLECTION EFFICIENCY OF AN ELECTRET FILTER

Loading of an electret filter changes the distribution of electrical field in the filter from its preloading condition, and, therefore, affects the filtration efficiency of the filter. Liquid droplets collected on electret filters cause degradation of the electrostatic enhancement of filtration efficiency because of charge neutralization and the formation of a dielectric coating over die charged fibers. In this study, calculations were made for the penetration of aerosol particles through a spun-type electret filter as a function of the particulate loading. An assumption was made that each charge collected neutralized one charge of opposite polarity on the fibers of the filter. It was also assumed that the electrostatic charges present on the particles followed the Boltzmann equilibrium charge distribution. The decrease in fiber charge and resulting increase in penetration were calculated as a function of time and of total particulate loading on the filter. The calculated penetrations were compared with experimental measurements of loading on a spun fiber electret filter challenged with monodisperse liquid droplets of bis-Ethylhexyl Sebacate with equilibrium charge distribution and with zero charge. The rate at which the penetration increased was found to be the same for particles with zero charge as for particles with equilibrium charge distribution. For 1 um diameter droplets with equilibrium charge the theory predicted complete discharge of the filter at a loading of around 200 g/m². Experimentally, only about 0.3 g/m² was required. This difference indicates the presence of additional mechanisms for the discharge of the fibers.     

EFFECT OF LOADING WITH AIM OIL AEROSOL ON THE COLLECTION EFFICIENCY OF AN ELECTRET FILTER

ABSTRACT

Loading of an electret filter changes the distribution of electrical field in the filter from its preloading condition, and, therefore, affects the filtration efficiency of the filter. Liquid droplets collected on electret filters cause degradation of the electrostatic enhancement of filtration efficiency because of charge neutralization and the formation of a dielectric coating over die charged fibers. In this study, calculations were made for the penetration of aerosol particles through a spun-type electret filter as a function of the particulate loading. An assumption was made that each charge collected neutralized one charge of opposite polarity on the fibers of the filter. It was also assumed that the electrostatic charges present on the particles followed the Boltzmann equilibrium charge distribution. The decrease in fiber charge and resulting increase in penetration were calculated as a function of time and of total particulate loading on the filter. The calculated penetrations were compared with experimental measurements of loading on a spun fiber electret filter challenged with monodisperse liquid droplets of bis-Ethylhexyl Sebacate with equilibrium charge distribution and with zero charge. The rate at which the penetration increased was found to be the same for particles with zero charge as for particles with equilibrium charge distribution. For 1 um diameter droplets with equilibrium charge the theory predicted complete discharge of the filter at a loading of around 200 g/m². Experimentally, only about 0.3 g/m² was required. This difference indicates the presence of additional mechanisms for the discharge of the fibers.     

圆柱壳中不连续管壁对振动功率流传播的影响

本文以一无限长弹性圆柱壳为研究对象,分析其自由振动特性及壳体中各内力传播的功率流,研究管壁接头对入射波的影响,从能量流的角度分析其振动控制效果.     

声场对流场影响的研究

借助于传声电容、传声放大器等声学测量仪器和热线风速仪等流场测量仪器及计算机数据采集系统,本文实验观察了有无强声场叠加及不同声场强度时流场瞬时速度波形的变化,并对声场作用下的平均速度、脉动速度、速度频谱、速度自相关、脉动速度和脉动声强互相关等流动特征参数进行了计算与分析。发现了强声对流场的调制作用,流动速度会随声音信号同步脉动,且声强越大,速度脉动幅度越大。当声场强度超过约155dB时,声场进入非线性区,波形从正弦波变为锯齿波。声波诱发的大幅度周期脉动及非线性效应,提高了流动的湍流特性。这些发现,将有助于对声凝聚机理的进一步研究。     

中国先进研究堆低温管路冷损模拟试验研究

对CARR中CNS系统使用的低温氦气管路的冷损进行了模拟试验研究,采用热平衡法确定了低温管路的最大可能冷损值,给制冷系统设计提供了可靠的数据支持.结合试验结果,分析了冷损产生途径,提出了减小冷损的办法.     

透平膨胀机新型切向小孔气体轴承稳定性的实验研究

为减小应用于透平膨胀机普通切向小孔供气轴承的耗气量,我们提出了一种新型切向小孔供气轴承,即在原切向小孔供气轴承结构的基础上在两端面增加台阶。本文在对其动特性进行测试及分析的基础上,得到了其最佳结构参数,并且指出了各影响因素的重要程度。实验结果表明这种新型轴承的稳定性较原轴承有较大幅度的提高。     

多孔材料剪切局部化中的尺寸效应

微孔洞的尺寸对于孔洞长大率的影响显著,研究了这种尺寸效应在延性材料的塑性流动局部化中的作用.在拓展的Gurson模型基础上,采用Rice提出的一个简单的模型,剪切带内外的材料在发生塑性流动局部化时分别为不同的响应,讨论了孔洞尺寸a和初始孔洞体积百分比f0的影响.结果表明:考虑孔洞尺寸后单轴拉伸曲线变化比较大,但剪切带角度几乎没有变化.     

平流式冷凝器传热流动性能理论研究

平流式换热器与常规换热器相比有其无可比拟的优点,常用作汽车空调系统中的冷凝器,其制冷剂侧的传热和流动特性与常规换热器有很大不同.本文比较了不同型式冷凝器的结构特点和工作原理,并详细分析了制冷剂在平流式冷凝器多孔扁管内的传热流动机理,希望能为该类换热器今后的研究、设计和校核提供一些依据.     

超声波场致作用在聚合物加工中的最新进展

概述了超声波场致作用在聚合物成型、改性以及橡胶脱硫中的研究进展,介绍了超声波场致作用在降低聚合物粘度、提高挤出产量、改善聚合物的力学性能和外观质量及实现废旧橡胶的脱硫、再生循环利用方面的应用现状。还介绍了超声波场致作用在超声混炼改性方面的研究进展。     

刚性空心管桩屏障对P波和SH波的隔离效果研究

采用波函数展开法和Graf加法定理,根据桩-土界面处总应力和扭矩平衡的边界条件,得到单排非连续刚性空心管桩屏障对入射平面P波和SH波散射系数的理论解。引入无量纲位移和透射系数等概念,绘制了不同壁厚的刚性空心管桩屏障后的无量纲位移等值线、透射系数随管桩间距的变化曲线以及不同数量的管桩组成的屏障后的无量纲位移变化曲线等图件,通过进一步的分析得出单排非连续刚性空心管桩屏障的隔振效果随着管桩间距和壁厚的减小而提高、最佳隔离区域随着管桩数量的增多而增大等重要结论,为非连续刚性屏障的隔振设计提供了理论依据。     

幂律流体偏心环管流动中公转的影响

数值模拟了压力驱动的幂律流体环管流动中,当流动为充分发展层流、且内管在偏心自转时内管公转的影响。结果表明当内管偏心自转时,其同时存在的公转对环管内压强和内管表面剪应力的分布影响显著。和自转同向的公转在一定强度范围内具有使流动阻力减小的效果,这和公转对由内管偏心自转导致的二次流范围的压缩以及幂律流体剪切变稀的特性有关。流动阻力随公转的变化不是单调的,在各偏心率下均存在一个使流动阻力最小的公转强度。     

数据采集系统中温度数据的数字滤波算法分析

数据采集系统已获得广泛应用,在工业生产和科学试验现场的电磁环境比较恶劣、干扰源较多时,一般要对采样数据进行数字滤波。结合数据采集系统中温度数据的特点,选择合理的数字滤波方式。针对具体的数据采集系统,通过试验确定温度数据的滤波参数。实践表明,利用复合数字滤波方法能够有效的提高温度数据的稳定性与准确性。     

低温液体送入热管道后的升压过程

分析了低温液体输入热管道后升压过程，并对输送过程中的临界质量流进行了计算，结合有关文献的实验数据，给出输送过程中的压力计算公式。并提出了减少压力最大值的方法，对于低温液体输送参数的确定，管道的设计提供参考。     

THE EFFECT OF INTERFACIAL PROPERTIES ON THE FLOW STRENGTH OF DISCONTINUOUS REINFORCED METAL-MATRIX COMPOSITES

Abstract

The effect of interfacial properties on the strength of discontinuous reinforced metal-matrix composites is systematically studied by theoretical modelling. The calculations were carried out within the framework of continuum plasticity theory using cell models and the finite element method. A wide range of inclusion aspect ratios, volume fractions, and interfacial strengths were investigated for perfectly plastic and hardening matrices. Interfaces were modelled either as strongly bonded, or as shearable but strong normal to the inclusions, or as debonding at the reinforcement ends but strong on the sides. Additionally, the effects of reinforcement arrangement and extensive damage to continuous fibre composites were addressed. Debonding at the ends of the inclusions was found to have the most deleterious effect on the strength of the composite. When debonding does not occur but interface sliding takes place freely, an amount of strengthening is seen which is a function of the inclusion volume fraction but is primarily independent of the inclusion aspect ratio. For extensively damaged continuous fibre composites, a weak interface yields a steady-state composite flow strength slightly higher than the volume fraction of the matrix times the yield strength of the matrix. This increases linearly with the interfacial shear strength up to the level for strongly bonded composites and can be estimated from the intact fibre aspect ratio, the matrix yield stress, the volume fraction, and the interfacial strength     

化学示踪技术在民用爆炸物品流向监管中的作用

爆炸物品化学示踪技术是由我国自主研发成功的全新成果,其应用方式为将微量示踪剂均匀混合于爆炸物品中,借助每种示踪剂示踪编码的唯一性,为民用爆炸物品建立身份号码,在民爆物品的生产、运输、仓储、使用等各个环节,将民爆物品各有关信息与示踪编码进行绑定。该技术的应用将在民爆物品流向监管中起到多方面的作用,如跟踪记录民爆物品整个生命轨迹、落实责任到位、实现动态监控和预警、追溯民爆物品来源等,从而提升管理措施的实时性、动态性、有效性和工作效率,其首要的特点是实现了民爆物品的本体标识和炸前炸后溯源。