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.     

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。     

DETERMINATION OF FIBER CHARGE DENSITY OF ELECTRET FILTERS

Particle collection in electret filters is enhanced by electrostatic forces resulting from the embedded charge on the fibers of the filters. Currently, there is no simple method available for determining the charge density on the electret fibers. Since charge on the fibers can degrade with loading or during storage, a simple evaluation technique is desirable. Aerosol consisting of organic oil mist generally used for testing HEPA filters should not be used for evaluating electret filters since organic aerosol droplets rapidly degrade the electrostatic charge effect. In this study experimental measurements of penetration were made on electret filters challenged with monodisperse, polystyrene latex spheres, PLS, of known size and charge. The experimental data on penetration were used to separate the contributions of the individual collection parameters and to determine the effective density of charge on the fibers. Collection efficiency due to mechanical filtration mechanisms was measured using filters in which the electret charge had been effectively neutralized by loading the filters with an oil aerosol. Collection due to dielectrophoretic force was obtained using aerosol with zero charge. The effective charge density on the fibers was determined by comparing measurements of penetration for particles having known size and charge with the predictions of available theoretical equations. Details of this method of determining the density of charge on the fibers are described here. Experimental determinations of charge density showed reasonable agreement with the charge densities given by the manufacturers of the tested filters.     

电晕放电注入双向拉伸聚丙烯薄膜驻极性能的探讨

以一种双向拉伸聚丙烯（ＢＯＰＰ）薄膜在不同温度下进行恒温处理，然后进行负电晕驻极。结果表明，ＢＯＰＰ薄膜随恒温处理的温度升高，热刺激电流（ＴＳＣ）峰值愈低。利用经验方法，估算了它们的活化能，并探讨了导致ＴＳＣ峰温变化的原因。     

"水的映像"国际海报集

Luba LuKova是纽约著名的艺术家和设计师。她的艺术作品经常运用比喻、象征和文字的形式来表达与人类有关的主题。曾为纽约时报、Adobe、华尔街杂志、索尼公司、哈佛大学、时代NTU及抗战联盟工作。作品在美国许多杂志书刊发表,并获联合国教科文组织的国际海报沙龙大奖、纽约One Club的金笔奖、ICOGRADA的优秀奖和Fort Collins公司的荣誉桂冠。她的艺术具有魅力,作品曾在世界各地举办展览,并被多家博物馆收藏。2006年Clay＆Gold Editions将出版她的艺术书籍。     

FORMATION OF FILTER CAKES WITH PARTICLE PENETRATION AT THE FILTER SEPTUM

The mass of solid particles entering the formation is an important factor in industrial cake filtration operations. Predictions of the concentration at the filter septum require the ability to predict the mass transport of solid particles under variety of conditions.

This study analyzes cake formation, including particle penetration at the filter septum. In addition to the total instantaneous mass balance equation, mass balance equations for captured and suspended particles and the fluid phase are averaged along the cake thickness taking into account conditions at the surface and the septum. Capture mechanisms, such as surface straining, and internal cake erosion and particle capture are included in the analysis.

The results are ordinary differential equations in terms of thickness, concentration of suspended particles in the filtrate, average particle concentration, average porosity, and such operational parameters, as slurry concentration, injection rate, and volumetric solid fraction.

To test tbe validity of the analysis presented here, the numerical results are compared to results for a simplified case. The conclusions from the sensitivity analysis conducted in this study agree with earlier conclusions. Results show that the concentration of suspended particles in the filtrate increases rapidly and then decreases gradually until it reaches zero after 13 hours. This yields that after 13 hours we have a clear filtrate.     

汽油滤清器泄漏原因分析

汽油滤清器在整车进行24个循环试验后发生泄漏。利用宏观分析、金相检验和扫描电镜及能谱分析等手段对汽油滤清器泄漏原因进行了分析。结果表明,缝隙腐蚀和电偶腐蚀是造成汽油滤清器罐体早期泄漏的主要原因。汽油滤清器罐体与支架在最初阶段由于接触区域存在缝隙,发生了缝隙腐蚀,致使汽油滤清器罐体铝发生点蚀、支架镀层局部脱落;镀层脱落后,滤清器罐体铝与支架基体由于电极电位的不同进而发生了电偶腐蚀,加速了滤清器罐体腐蚀的进程,导致汽油滤清器发生泄漏。     

石墨层间化合物GICs的形成机理探讨

将ＧＩＣｓ形成过程划分为熔融、活化、扩散和成键等阶段,分析了各阶段反应的主要影响因素,以氯化铜、氯化镍、ＧＩＣｓ的合成实验为基础,根据ＳＥＭ对石墨膨胀前后,插层后的形貌分析,以及膨胀石墨合成ＧＩＣｓ反应前后体积变化分析,认为ＧＩＣｓ的形成过程中,主要有三个机制起作用：     

AIGA 设计师作品选辑2

AIGA中国设计之旅 2008年美国平面设计师协会跨文化设计中心（AIGAXCD）的中国设计之旅（从5月10日至5月24日）标志着AIGA遵守自己的承诺,即致力于展开世界各地设计师之间更广泛深入的沟通与交流,并以实际的方式去欣赏在我们的生活中设计是如何与文化相互交融的。     

AIGA设计师作品选辑1

AIGA中国设计之旅 美国设计师协会跨文化设计中心（AIGA XCD）旨在帮助美国设计师成为全球设计界不可缺少的一部分。尽管还不是所有的美国设计师看到与全球沟通的重要性,但是选择加入2008年5月AIGA中国设计之旅的设计师们却对与全球沟通抱有极大的热情,他们将此次中国设计之旅看作与中国设计师建立联系的极为重要的第一步,并希望籍此开始理解中国在全球扮演的重要角色。     

穿孔结构流体滤波器参数优化设计研究

本文提出了利用遗传算法对穿孔共振结构的滤波器进行了多参数优化计算 ,得出在已知脉动频率下 ,不同的流体介质中 ,穿孔共振结构滤波器的最优参数 ,为穿孔共振结构流体滤波器的使用提供了较好的设计方法。本文还对一实际穿孔结构滤波器进行了实验研究 ,证明本文的理论计算与参数优化方法的正确性     

A STUDY OF SHEAR FATIGUE CRACK MECHANISMS

Abstract— Studies have been made of the micro-and macroscopic features of a transverse shear fracture and a longitudinal shear fracture. The fatigue crack propagation mechanisms of mode-II and mode-III are described, which can be used to explain both fracture features and the crack shape. Finally a series of comparisons are made of mode-I, -II and-III fatigue crack propagation mechanisms.     

机敏柔性机构振动控制方法研究

本文利用柔性连杆构件粘贴压电材料和粘弹性材料，研究了柔性机构振动智能控制的方法，导出了粘贴压电材料和粘弹性材料构件的有限元方程；并对具体柔性机构的振动响应控制进行了计算机数值仿真，结果表明：机敏柔性机构控制方法的控制效果明显优于传统的主动控制或动控制方法，且只需要较低的控制电压输入。     

气动弹性剪裁的机理和效益

本文综合介绍了当前复合材料的飞机结构在气动弹性剪裁方面的概况及其理论基础。着重阐述了气动弹性剪裁的机理,即气动弹性剪裁赖以实现的基本原理。并且通过一系列曲线展示了由此产生的对飞机性能的影响.当引起的影响有益时,就表明了气动弹性剪裁的性能效益。      

FAILURE MECHANISMS IN IMPACT FATIGUE OF METALS

Abstract Impact fatigue tests were performed with smooth and notched specimens of low carbon steels under various impact loading conditions. The characteristic failure mechanisms in impact fatigue was discriminated by comparison with those in non-impact, ordinary fatigue. The fatigue life of smooth specimens was uniquely related to the range of plastic strain at the middle of the fatigue life in both impact and non-impact fatigue, although the characteristics of micro-structural deformation and cyclic stress-strain relationships were markedly different. The growth rate of a fatigue crack in impact fatigue of notched specimens was higher than that in non-impact fatigue when compared at the same stress intensity factor. Fractographic observations with scanning electron microscopy and the X-ray diffraction technique revealed more abundant cleavage facets and a smaller spread of the plastic zone beneath the fracture surface made by impact fatigue. Both nucleation and propagation lives in notched specimens were much shorter in impact fatigue than in non impact fatigue when compared at the same values of nominal stress and stress concentration factor.     

晶须增强增韧聚合物基复合材料机理研究进展

简介了晶须增强增韧聚合物基复合材料研究的现状;并较全面地介绍了各种增强增韧机理,主要包括:裂纹桥接、裂纹偏转、拔出效应等机理。晶须增强增韧聚合物基复合材料主要表现在:(1)晶须导致基体局部应力状态改变;(2)晶须对基体结晶行为产生影响。文中还简要介绍了在实验过程中影响聚合物基晶须复合材料性能的几个重要的因素,如与界面相关的一系列因素和晶须在基体中含量、晶须在基体中的分散程度、晶须长径比以及在基体中的排列方向等。     

气动伺服弹性系统结构陷幅滤波器优化设计

为解决飞机气动伺服弹性耦合频率低且随飞机重量构型变化大,使用结构陷幅滤波器改善飞机气动伺服弹性稳定性易于影响飞机操稳特性的问题,建立了一种基于多目标遗传算法的结构陷幅滤波器优化设计方法。以气动伺服弹性系统的弹性模态频响峰值最小作为优化目标,刚体模态频响特性作为设计约束,通过设计罚函数修正个体适应度对陷幅滤波器的频率与阻尼参数进行优化。结果表明：该文方法能够兼顾飞机的气动伺服弹性与刚体运动特性,有利于充分利用高增益控制系统提升飞行性能。