Performance of Electrically Augmented Fibrous Filters,Measured with Monodisperse Aerosols

A study of the performance of filters in an external electric field has been carried out in controlled conditions using monodisperse aerosols with a charge distribution close to a Boltzmann. The effects of electric field strength, particle diameter, fiber diameter, and filtration velocity have been measured. The results are in basic agreement with existing theory for the capture of particles by polarization forces and indicate that this process is dominant, although other filtration processes are also significant, particularly when the electric field is low. Reasonable correlation between single fiber efficiency and the dimensionless parameter for capture by polarization forces is observed. The agreement is improved by the inclusion of the hydrodynamic factor into the calculation, but this does not remove all discrepancy. If filters are exposed to an electric field for a protracted period, a small persistent residual polarization of the fibers is observed. Loading the filter with aerosol in the laboratory has little effect on its performance, though eventually the aerosol captured in the vicinity of the live electrode causes shorting out.     

袋式过滤器过滤初期阶段滤袋压力特性的实验研究

针对袋式过滤器过滤初期阶段的压力特性,选用高密度聚乙烯粉料进行了实验分析,主要考察过滤速度和入口浓度对滤袋压降的影响。实验结果表明,在过滤初期阶段滤袋的压降上升趋势很明显,这种压降的增大主要来自于残余压降;滞留在滤料内的粉尘改变了滤料内部的流道结构,从而导致了滤袋残余压降的不断升高;过滤速度和入口浓度的增加均可使残余压降增大。最后通过压降组成的分析,提出了滤袋总压降的计算模型。     

聚结式过滤器处理含油污水实验研究

研究采用聚结式过滤器处理含油污水,选取润滑油配制含油污水,研究了初始含油量、流量、静置时间以及乳化程度等参数对分离效果的影响.实验结果表明,初始含油量越高、乳化程度越小、除油效果越好.针对开发的聚结式含油污水过滤器,对其操作工艺参数进行了优化,流量应控制在600L/h左右,静置时间以30min为宜.     

Experimental Study on Electrostatically Enhanced Granular Filters

Filtration of charged aerosols by granular bed filters enhanced by an externally applied electrostatic field was studied experimentally. The filtration efficiencies of latex aerosols by sand beds were measured for various aerosol and bed granule diameters. The results were compared with theoretical solutions. It was demonstrated that high filtration efficiencies of charged aerosols may be achieved when moderate electrostatic fields are applied to a filter.     

Computer Simulation of Monodisperse Aerosol Collection in Fibrous Filters

A computer program has been developed to simulate the filtration process in fibrous filters collecting monodisperse aerosol particles. The model filter is represented by an array of parallel cylindrical fibers and the Kuwabara flow field is employed to determine the particles trajectories inside the filter. The simulation model is based on the Monte-Carlo (self-driven) principle, and a sequence of uniform pairs of pseudorandom numbers is generated representing the initial locations of the approaching particles. The estimation of the initial collection efficiency through the simulation model that considers the deposited particles and the presence of dendrites is in good agreement with published experimental data. The development of the quasi three-dimensional simulation model offers a detailed information about the transient progression of the deposition process. The transient behavior of the pressure drop across the collector system (the fiber and the collected particles) and the morphology of deposit are presented and the results are in good agreement with experimental data.     

Simultaneous Production of Two Monodisperse Aerosols Using a Spinning-Top Aerosol Generator

A relatively simple laboratory technique for the simultaneous production of two monodisperse aerosols of different size has been developed and tested. This technique utilizes a standard May spinning-top aerosol generator that has been modified and enclosed under a special dual-cone fractionator. The fractionator efficiently separates the primary and satellite droplets. Illustrative Nacl aerosol generation data, obtained in a series of experiments, show that satellite droplets can provide an important source of the monodisperse aerosol.     

Comparative Study of the Performance of Nine Filters Utilized in Filtration of Aerosols by Bubbling

A new process of air purification has been developed and studied experimentally (Agranovski et al. 1999). This process is based on passing air through a filter immersed in liquid. It leads to the formation of bubbles within the filter as the carrier gas passes through and thus provides alternate mechanisms for the removal of aerosols. It was identified (Agranovski et al. 1999) that for relatively large particles (0.3-2.7 w m) the efficiency of the filter utilized in wet filtration is higher than for dry filtration. In the current paper, experiments are described that investigate the performance of the technology for particles in the size range of 0.03 to 2.7 w m, to identify the importance of an alternative mechanism of purification (diffusion). Also, 9 different filters were employed to compare the efficiencies of the wet and dry filtration for different applications of the technology.     

Penetration of Monodisperse,Singly Charged Nanoparticles through Polydisperse Fibrous Filters

The article presents experimental results and theoretical analysis of aerosol nanoparticle penetration through fibrous filters with a broad fiber diameter distribution. Four fibrous filters were produced using the melt-blown technique. The analysis of the filters’ SEM images indicated that they had log-normal fiber diameter distribution. Five kinds of proteins and two types of silica particles were generated by electrospraying and were then classified using a Parallel Differential Mobility Analyzer to obtain well-defined, monodisperse, singly charged challenge aerosols with diameters ranging from 6.3 to 27.2 nm. Particle penetration through the filters was determined using a water-based CPC. Experimental results were compared first with predictions derived from the classical theory of aerosol filtration. It is demonstrated that it is inappropriate to apply it to the arithmetic mean fiber diameter, as this results in turn in a huge underestimation of nanoparticle penetration. A better, but still unsatisfactory agreement is observed when that theory was used together with the pressure drop equivalent fiber diameter or when the Kirsch model of nonuniform fibrous media was applied. We show that the classical theory applied to any fixed fiber diameter predicts a stronger dependence of nanoparticle penetration on the Peclet number as compared to experimental data. All these observations were successfully explained by using our original partially segregated flow model that accounts for the filter fiber diameter distribution. It was found that the parameter of aerosol segregation intensity inside inhomogeneous filters increases with the increase in particle size, when the convective transport becomes more pronounced in comparison to the diffusive one.     

Analytic Solutions to Diffusional Deposition of Polydisperse Aerosols in Fibrous Filters

Deposition of polydisperse aerosols by Brownian diffusion was studied analytically using the penetration efficiency of monodisperse aerosols combined with the correlations among the moments of lognormal distribution functions. The analytic solutions, so obtained were validated using the exact solutions, which were applied to recalculate the filtration efficiencies of the existing experimental data for various filtration conditions. It was found that the collection efficiency of a fibrous filter should be corrected with respect to the position in the filter, if the particles are polydisperse. By considering the effect of the polydispersity of particle size, the analytic solutions showed good agreement with existing experimental data. It is believed that the present work makes it possible to determine the filtration efficiency of polydisperse aerosols in fibrous filters and to estimate errors associated with the degree of polydispersity of the particles quickly and accurately for the diffusion dominant regime.     

减小高装填密度发射装药膛内压力波的实验研究

研究了两种能降低某大口径火炮高装填密度发射装药的膛内压力波的点传方案。第一种点传火方案是在制式点传火结构基础上增加横向传火具,增加点火药包;第二种点传火方案是改变制式传火结构为低爆速传火结构,同时增加横向传火具。高装填密度发射装药射击试验表明,这两种点传火方案均能满足点传火要求。第一种点传火方案较制式可燃中心传火管能实现迅速全面的点火,但出现了压力波增大的现象。而第二种点传火方案较第一种点传火方案的传火速度快,能迅速建立点火压力,发射药床的着火延迟时间小,最重要的是能抑制膛内有害压力波。压力波的频谱分析表明在高装填密度装药中,采用第二种点传火方案能削弱和抑制压力波的高频振荡成分,改善其振动特性。     

东亚地区春季有机碳气溶胶分布特征的初步研究

本研究利用一个区域三维化学输送模式模拟研究了东亚地区2001年春季有机碳气溶胶的输送与演变过程.有机碳气溶胶浓度的模拟值与TRACE-P和ACE-Asia观测期间获取的观测值相比,模拟值与观测值之间具有非常好的一致性,模式合理地反映了有机碳气溶胶浓度的时空分布.模拟结果表明,有机碳气溶胶柱含量的高值区(大于16 mg/m2)主要集中在长江中游和西南地区,黄河以南的我国大部分地区柱含量超过了7 mg/m2,并且4 mg/m2的等值线延伸到了西北太平洋深处.     

单分散窄分布聚苯乙烯微球的制备研究

以苯乙烯为单体,聚乙烯基吡咯烷酮(PVP)为分散剂,偶氮二异丁腈(AIBN)为引发剂,甲醇为分散介质,利用分散聚合法制备了微米级单分散聚苯乙烯微球。通过傅立叶红外分析(FT-IR),扫描电子显微镜(SEM),激光粒度分析(LPS)等方法对微球进行测试表征。研究了PVP用量对微球产物的影响。结果表明:单体的转化率随PVP用量的增加而增大,PS微球的粒径随着PVP用量的增大而减小,其粒径分布先变窄后变宽。当PVP用量为1.5%时微球的粒径分布最窄,单分散性最好。改变PVP用量可以得到不同粒径的PS微球。     

单分散交联聚苯乙烯的合成

采用分散聚合法合成粒径单分散交联聚苯乙烯微球,研究了交联剂用量、交联剂加入方式以及补加分散剂和交联剂对聚合物形态的影响。研究表明,交联剂用量小于1％和大于30％时可以用传统分散聚合方法得到聚合物,通过后加交联剂、稳定剂方法可以得到交联度为1％～30％聚苯乙烯。     

Effect of Bi-Modal Aerosol Mass Loading on the Pressure Drop for Gas Cleaning Industrial Filters

The typical size distribution of emission particulates is bi-modal in shape with particles in the fine mode (< 2.0 w m) and the coarse mode. An experimental study of pressure drop across industrial gas cleaning filters has been conducted using a particle mixture of fine alumina and coarse Arizona dusts with a rotating aerosol disperser to generate the bi-modal test aerosol. Pressure drop increased linearly with increasing mass loading. The pressure drop was found to be strongly dependent upon the mass ratio of fine to coarse particles. The measured specific resistances of HEPA filters at a given face velocity of 5 cm/s were 1.18 2 10 6 , 5.89 2 10 5 , 4.67 2 10 5 , 2.65 2 10 5 , and 1.18 2 10 5 s -1 for the mass ratio of fine to coarse particles of fine only, 50%:50%, 25%:75%, 10%:90%, and coarse particles only, respectively. The pressure drop across the loaded filter increased with increasing face velocity. The larger the mass ratio of fine to coarse particles and the higher the face velocity are, the faster pressure drop rises. The fine particles and the greater inertia of the particle moving fast would cause a denser cake formation on the filter surface, resulting in a greater specific resistance to the gas flow.     

水力转轮水动力特性实验研究

研究利用水力转轮带动螺带刮洗搅拌装置旋转,对石英砂过滤器的筛筐进行水力清洗,有效解决筛筐的堵塞和过滤器反冲洗存在死角的问题。通过研究相同翼型不同攻角水力转轮的水动力学特性,得出不同攻角水力转轮的转动角速度和启动转矩随流速的增加而增大,相同的流速下攻角35°水力转轮的达到1 860 r/min最大转速和3.33 N·M最大启动转矩。不同攻角水力转轮的运动阻力系数为一个定值,攻角35°水力转轮阻力系数最大,其阻力系数比水力转轮静止时小。攻角35°水力转轮具有较好水动力学特性。     

Splashing Characteristics of Monodisperse Sprays with Significant Viscosity Differences Impacting a Flat Surface

Drop impingement and splashing as a function of viscosity and, to a lesser extent, temperature are examined here. The working fluid is a mixture of water and glycerin with relative mass percentages varying from 0 to 100%, which spans a viscosity range of three orders of magnitude. First, a criterion that separates “on” and “off” for splashing as a function of glycerin percentage is expressed in terms of both Weber and Reynolds numbers and its highly nonlinear behavior is a function of the change in fluid viscosity. Next, the complex splashing characteristics of a rather simple monodisperse spray injected at a pressure of 2 bars onto a flat, 2-mm-diameter aluminum cylindrical rod are examined. Spatial variations in the fraction of splashed liquid, Sauter mean diameter, splashed droplet size distribution, and splash volume fraction as a function of radial distance for these mixtures are reported.     

Experimental Study of Dispersion and Deposition of Expiratory Aerosols in Aircraft Cabins and Impact on Infectious Disease Transmission

The dispersion and deposition characteristics of polydispersed expiratory aerosols were investigated in an aircraft cabin mockup to study the transmission of infectious diseases. The airflow was characterized by particle image velocimetry (PIV) measurements. Aerosol dispersion was measured by the Interferometric Mie Imaging (IMI) method combined with an aerosol spectrometer. Deposition was investigated using the fluorescent dye technique. Downward air currents were observed near the seats next to the side walls while upward airflows were observed near other seats. The downward airflow showed some effects on suppressing the dispersion of aerosols expelled by the passenger sitting in the window seat. Results show that the cough jet could bring significant amount of aerosols forward to the row of seats ahead of the cougher and the aerosols were then dispersed by the bulk air movements in the lateral direction. The aerosols expelled from a cough took 20–30 s to reach the breathing zones of the passengers seated within two rows from the cougher. Increasing the ventilation rate improved the dilution and reduced the aerosol exposure to passengers seated close to the source, but the aerosol dispersion increased, which heightened the exposure to passengers seated further away. 60–70% of expiratory aerosols in mass were deposited, with significant portions on surfaces close to the source, suggesting that disease transmission risk via indirect contact in addition to airborne risk is possible. The physical transport processes of expiratory aerosols could be used to shed insights on some epidemiological observations on in-flight transmission of certain infectious diseases.     

石油焦与典型煤炭的燃烧特性比较分析

石油焦是是原油提炼后的最终副产品,具有低灰、低挥发分、高固定碳、高热值等特点。作为煤的一种补充或替代燃料用于锅炉燃烧发电、供热是石油焦很好的利用方式,本文采用热重法和马弗炉烧灰法将石油焦与烟煤等其它典型煤样进行燃烧特性对比分析。实验表明石油焦的燃烧特性介于烟煤和无烟煤之间,且接近烟煤,有较好的燃烧特性,即较低的着火温度、较大的反应速率和较集中的放热峰,但其固定碳含量也更高,灰分更低,所以放热更多。     

腾格里沙漠东南缘沙尘气溶胶主要化学组分特征

基于对沙尘气溶胶质量浓度的长期监测,本项研究对沙坡头地区2001～2002年气溶胶样品进行了化学组成分析,结果显示,Si,Al,Fe和Ca等4种元素的氧化物是该地区气溶胶的主要成分,Al和Si的相关系数接近于1,可以认为是沙漠地区大气气溶胶的良好示踪元素;SO3的绝对含量与Al2O3的变化基本一致,但其百分含量与Al2O3的百分含量呈现负相关,表明人类活动对该地区背景大气气溶胶中的S元素具有定常的贡献,冬季燃煤取暖对S的贡献也不容忽视;K元素在7～9月份出现的峰值,可能暗示了农田对沙尘气溶胶的贡献.