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1.
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. 相似文献
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K. B. TENNAL M. K. MAZUMDER A. SIAG R. N. REDDY 《Particulate Science and Technology》2013,31(1-2):19-29
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. 相似文献
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数据采集系统中温度数据的数字滤波算法分析 总被引:1,自引:0,他引:1
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。 相似文献
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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. 相似文献
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鲁希华 《高分子材料科学与工程》1994,10(2):124-127
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。 相似文献
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Nelly M. Abboud 《Particulate Science and Technology》1993,11(3):115-131
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. 相似文献
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. 相似文献
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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。 相似文献
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石墨层间化合物GICs的形成机理探讨 总被引:12,自引:5,他引:12
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: 相似文献
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A STUDY OF SHEAR FATIGUE CRACK MECHANISMS 总被引:1,自引:0,他引:1
Hu Zhizhong Ma Lihua Cao Shuzhen 《Fatigue & Fracture of Engineering Materials & Structures》1992,15(6):563-572
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. 相似文献
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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。 相似文献
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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。 相似文献
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FAILURE MECHANISMS IN IMPACT FATIGUE OF METALS 总被引:1,自引:0,他引:1
H. IGUCHI K. TANAKA† S. TAIRA† 《Fatigue & Fracture of Engineering Materials & Structures》1979,2(2):165-176
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. 相似文献
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晶须增强增韧聚合物基复合材料机理研究进展 总被引:21,自引:0,他引:21
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。 相似文献