Investigation of air filter properties of nanofiber non-woven fabric manufactured by a modified melt-blowing method along with flash spinning method

Nanofibers are used in various fields and applications, such as medical care, environment protection, apparel, and agriculture; it is believed that they will continue to show substantial growth in the future. In this study, we focused on the filtration application of nanofibers. The filtration performances achieved polymeric nanofiber mass production by a melt-blowing method. First, the filtration performances of the fiber were experimentally tested with different thicknesses. Then, the computational fluid dynamics flow-analyzing software was used to simulate the pressure loss and flow resistivity of the trial-produced filter under the same conditions as those used in the experiment. Then, a three-directional physical model was proposed and used to calculate the fiber's gap size with different diameters under the same filling rate and the assumption that the fibers always exhibit uniform distribution. Consequently, it was confirmed that the trial-produced non-woven filter possessed excellent filtration abilities and that the investigated data can be used as a standard to manufacture non-woven fabric for producing high-performance filters and face masks. However, the manufacturing method of non-woven fabric filters must be investigated to satisfy both high particle filtration efficiency and low pressure loss in order to develop a high-performance filter.     

A Setup for the In Situ Investigation of Gas–Liquid Foams

The experimental setup is intended to investigate the formation and behavior of gas–liquid foams in circumstances simulating the in situ conditions which are characterized by high pressures (>15 MPa) and temperatures (>60°C). Foam is produced in a pressurized chamber by bubbling the air through a layer of foaming solution poured on a fine filter. The foam structure is recorded in the process of the forming and the breakdown of the foam after the end of foaming in real-time mode by the image visualization system using video microfilming through the optical windows in the walls of the work chamber. A high accuracy is achieved in monitoring the variation of the foam dispersion with time and establishing the onset of the foam-bubble extension and the rate of internal foam breakdown, which is required for the determination of the foam's stability and performance characteristics under extreme in situ conditions.     

环形与圆柱形金属橡胶过滤性能对比研究

金属橡胶是一种新型高性能过滤材料,它具有三维网状结构、高精度全连通的孔径和孔隙度范围宽的特点,有着优异的过滤性能。本文采用"多次通过"试验法对环形与圆柱形金属橡胶过滤性能进行了对比研究。研究结果表明环形金属橡胶比圆柱形金属橡胶具有更加优异的过滤性能,在过滤效率相同的情况下,环形金属橡胶滤材过滤压降较低,流体的通过性能更好,在达到极限压降前能够容纳更多的污染物,滤材使用寿命大为延长。     

Filtration characteristics of magnetic fibrous polymer as a new oil filter material for lubrication systems

Magnetic fibrous polymeric filter (MFPF) elements for lubrication systems were obtained by pneumoextrusion of a thermoplastic polymer (polyamide) containing a magnetic particulate filler (barium ferrite), and treating it subsequently in magnetic fields. Using a standard laboratory oil filtration test rig, metallic particle quantifier, and an image analyser system, the dependence of the filtration characteristics of the magnetic filter medium on the magnetic parameters was investigated. The variation of pressure drop and filtration efficiency with the packing density of the lubricating filter elements was measured. A conventional lubricant filter for an internal combustion engine was also tested for comparison with the filtration performance of the magnetised filter medium. Increasing the magnetic force of the filter medium made the MFPF material more effective in filtering fine ferrous particles, without changing the pressure drop. It was concluded that MFPF can be used as an effective filter in lubrication systems.     

Features of ultrasonic shadow testing of foam plastics based on time-amplitude parameters. Part II

Features of ultrasonic shadow testing of hard foam plastics are discussed. Foam plastics are very difficult objects of testing because of their highly inhomogeneous structure depending on the processes of foaming and solidification of polymers. The main conclusion of the reported study is that shadow techniques based on the amplitude and temporal characteristics present a particular case of the more complex time-amplitude ultrasonic shadow testing technique. At low frequencies, flaws can be treated as entities transparent to acoustic waves. With due account of this fact, both the flaw extension and its thickness can be estimated. In addition, variations in the ultrasound velocity due to anisotropy and dominant orientations of cells in foam plastics should be taken into consideration.     

基于匹配滤波的液压流体颗粒污染度检测

为准确的确定液压流体的污染状态,及时地对液压系统进行主动预防性维护,提出了采用匹配滤波原理进行微弱颗粒信号幅值检测的新方法。讨论了匹配滤波器的基本原理及匹配滤波器应用于信号幅值检测时滤波器系数的确定方法并进行了检测误差分析。在对检测系统特性进行分析的基础上,设计了广义匹配滤波器并应用于液压流体污染度检测系统。结果表明该滤波器具有设计简单、计算时间短等优点,能够从强背景噪声中提取出微弱的颗粒信号并很好地恢复了原信号的幅值,有效地提高了检测系统的检测精度和在线检测能力。     

Overcoming the Electrostatic Discharge in Hydraulic,Lubricating and Fuel-Filtration Applications by Incorporating Novel Synthetic Filter Media

Electrostatic charge generation occurs in fluid systems as a result of friction between the fluid and system components. The magnitude of charge generated by each component will depend on many interrelated factors, including environmental ones. It can occur during filtration of hydraulic and lubricating oils as well as diesel and gasoline fuels. This effect manifests itself in several ways, the most noticeable effect being an audible noise (clicking sound) as the discharge of electrostatic charge accumulation causes sparking internally within the system. Less-apparent effects involve migration of the electrical charge downstream of the filter, causing damage to system components and the filter itself when the charge dissipates by discharging itself to a grounded surface. Several methods have been investigated to overcome the aforementioned behavior and prevent the damage that can occur if the electrostatic discharge continues to operate unchecked. One of these methods involved adding an antistatic additive to the liquid, but this is restricted to fuel applications. Other methods involved surface modifications carried out directly on the filter media or the use of conducting materials such as meshes made from suitably selected conducting materials that can be incorporated into the construction of filter cartridges. The main aim of these modifications is to affect a discharge from the filter cartridge, before a hazardous potential accrues on the filter media, by lowering the voltage gap. Although this approach eliminates direct damage to the filter cartridge, it does not prevent charge migration into the oil where it subsequently accumulates. The approach we took involves designing the filter material to be electrostatic dissipative, which offers the advantage of eliminating filter damage entirely and significantly reducing migration of charge into the fluid.     

新型金属橡胶孔隙材料过滤机制与性能研究

基于弹性多孔金属橡胶材料的内部组织结构特点,分析了金属橡胶材料对液体中杂质颗粒的过滤机制;对不同制作工艺的金属橡胶元件进行了过滤性能实验研究,测试了油液过滤前后的污染度等级,并分析了金属丝直径、孔隙度和试件长度对过滤性能的影响。结果表明,金属橡胶材料对污染程度较严重的油液具有明显的过滤效果,滤后油液的清洁度显著提高;增加试件长度、减小金属丝直径和孔隙度有利于提高过滤精度,但孔隙度过小会导致流体阻力大幅上升,且试件长度对过滤效果的影响也受孔隙度的限制,当孔隙度较小时,试件长度对过滤精度的影响明显减少。因此要合理选择工艺参数使金属橡胶材料达到要求的过滤精度。     

Controlling contaminant wear through filtration

This paper reveals the state of the technology in both contaminant wear in fluid components and fluid filtration. Through the use of graphical aids, the fundamental relationship influencing contamination control is disclosed. This presentation will show the correlation of filter performance and contaminant ingression on the service life of fluid systems.     

An experimental study of particulate retention by microporous membranes in liquid filtration

A theoretical study on particulate retention by microporous membrane filters during liquid filtration has been investigated. A model to predict particle retention using a multi-layer concept for filter retention by sieving and using flow resistance for cake filtration was developed to predict particle retention as a function of particle diameter and particle loading. Filter efficiency for the 0.45 μm rated membranes predicted 99.95% for the particle diameter of 0.453 μm. Filter efficiency by sieving model decreased with increased particle loading on the filter. After substantial particle loading, filter efficiency was found to increase with increased particle loading due to the combined effect of sieving and cake filtration. Theoretical particle retention modeling showed good agreement with experimental results.     

铝泡沫填充薄壁结构耐撞可靠性优化设计

泡沫填充薄壁结构能有效地改善汽车薄壁吸能部件的耐撞性。为设计更轻与更有效的吸能结构,并满足汽车安全性设计要求,提出一种新颖的轻质铝泡沫填充双管薄壁结构,并对其耐撞性展开确定性最优化设计。但是,由于薄壁结构的厚度、屈服强度以及铝泡沫的密度等设计参数易受到仿真以及制造误差等不确定性因素的影响,导致确定性最优解收敛于约束边界,从而丢失了应有的使用可靠性要求。因此,提出基于Kriging近似模型与一阶可靠性分析方法的铝泡沫填充结构可靠性最优设计方法,并进一步开展基于参数不确定性的铝泡沫填充结构的耐撞性可靠性优化设计研究。优化结果显示,可靠性最优解不仅远离约束边界,而且较好地满足了铝泡沫填充结构的安全性与可靠性设计要求。     

A new approach to develop high temperature foam core sandwich structures using air plasma spraying

Foam core sandwich structures exhibit mechanical performance comparable to conventional materials at much lower weight and potentially lower cost. An advanced production technique for manufacturing foam core sandwich structures with high temperature constituents is introduced. Skin and core are the main components of a sandwich beam. The various manufacturing processes are available to join skins and core to make a sandwich construction. Here, skins are developed on the surface of the core using air plasma spray technique. It is a rapid technique which eliminates joining process. There will be a good adhesion between skin and core due to mechanical and metallurgical bonds. This technique has the capability to be put into series production.     

Particle deposition in random fibrous porous materials: effect of acoustic fields,fibres distribution and porosity

Porous filters are widely used to control air pollution and have different industrial applications since they constitute a reliable and low cost solution to separate particulate matter from an air stream.In this study, the particle deposition within 3D porous filters subjected to low-frequency acoustic fields is studied following a numerical approach. Findings demonstrate that the application of acoustic waves enhançes the deposition of particles, which in turn improves filter performance. It is shown that frequencies ranging from 200 to 1000 Hz (intensity 120 dB) increase particle deposition up to 2.5 times. Besides, the manner in which fibres are distributed in the porous material and the filter porosity affect considerably the number of particles deposited, for filters subjected to the same filtration velocity.     

数控异形泡棉切割机的运动控制

本文主要分析了泡棉切割加工的工艺要求,以及数控加工的轨迹控制,确立了数控异形泡棉切割机的位置控制系统的方案,研究了其硬件配置和软件结构。本课题的研究是数控异形泡棉切割机研制成功的关键,该切割机已研制成功,并交付用户使用,切削效果好。     

Thermal characteristics of graphite foam thermosyphon for electronics cooling

Graphite foams consist of a network of interconnected graphite ligaments and are beginning to be applied to thermal management of electronics. The thermal conductivity of the bulk graphite foam is similar to aluminum, but graphite foam has one-fifth the density of aluminum. This combination of high thermal conductivity and low density results in a specific thermal conductivity about five times higher than that of aluminum, allowing heat to rapidly propagate into the foam. This heat is spread out over the very large surface area within the foam, enabling large amounts of energy to be transferred with relatively low temperature difference. For the purpose of graphite foam thermosyphon design in electronics cooling, various effects such as graphite foam geometry, sub-cooling, working fluid effect, and liquid level were investigated in this study. The best thermal performance was achieved with the large graphite foam, working fluid with the lowest boiling point, a liquid level with the exact height of the graphite foam, and at the lowest sub-cooling temperature.     

泡沫液位传感器的研制

泡沫是一种特殊的两相流形态，其力学、热学、光学等多种性能均与单相气体或液体有很大区别，由于泡沫的形成机理多样、性质变化复杂，至今尚无完善的研究理论体系，泡沫的液位测量在国内外也是一个空白。开发了一种基于传热原理的测量泡沫液位的传感器，介绍了传感器的构造和原理，以及测量误差和动态响应的计算分析。     

用传递矩阵法计算多层泡沫材料的法向吸声系数

泡沫材料在机械噪声控制工程中应用广泛.以方向相反的两列行波为端口参量,研究泡沫材料传递矩阵的实验辨识方法,研究由一层材料得到多层材料传递矩阵的计算方法,形成刚性背衬下多层泡沫材料吸声系数的计算方法.通过实验对测量计算方法进行验证,对材料厚度与吸声系数的关系进行了初步研究.研究结果表明:传递矩阵是材料本身固有的声学属性,不随其声学边界条件的改变而改变,以一层泡沫材料的传递矩阵参数为基础,通过计算可得到多层泡沫材料的吸声系数.     

The use of scanning electron microscopy to quantify the burden of particles released from clean-room wiping materials

A procedure is described for the detection and direct enumeration of the number of particles that can potentially be released from wiping materials. The technique involves the use of a scanning electron microscope (SEM) to count the particles from a wiper, first by releasing them in deionized water and then filtering the entirety of the liquid through a submicron membrane filter. To obtain an accurate count, the filtration must produce a normal distribution of particles on the filter, and hence the details of the filtering technique must be performed in a very precise manner. The counting of the particles on the filter is accomplished by scanning a statistically representative number of fields and averaging the number of particles per field. The results can then be checked for statistical precision and accuracy. Our criterion for successful measurement was ± 10% accuracy at a 95% confidence level. We believe that the SEM method described in this article is sensitive enough to quantify very low levels of total particle burden without succumbing to the variability and limitations encountered with other enumeration techniques. Typically, this technique enables the accurate counting of particles of all shapes from below 0.1 μm to hundreds of micrometers. In addition, the SEM technique allows for morphologic identification of particles as well as chemical identification if an energy-dispersive x-ray system (EDS) is employed.     

A filtration model of microporous membrane filters in liquids

A theoretical study on particulate retention by microporous membrane filters during liquid filtration has been investigated. A model to predict particle retention using a multi-layer concept for filter retention by sieving and using flow resistance for cake filtration was developed to predict particle retention as a function of particle diameter and particle loading. Filter efficiency for the 0.45 μm rated membranes predicted 99.95% for the particle diameter of 0.453 μm. Filter efficiency by sieving model decreased with increased particle loading on the filter. After substantial particle loading, filter efficiency was found to increase with increased particle loading due to the combined effect of sieving and cake filtration. Theoretical particle retention modeling showed good agreement with experimental results.     

Enhancing particle image tracking performance with a sequential Monte Carlo method: The bootstrap filter

One of the common problems of current pattern match and particle image tracking algorithms is the deployment of constant velocity assumption for particle motion between two frames, which would result in serious errors when high velocity gradient flows are measured. To address this issue, a new particle image tracking method—bootstrap filter tracking is proposed. In this new method, a simple nonlinear dynamic model which takes particle acceleration into account is employed and a sequential Monte Carlo method—bootstrap filter is used in conjunction with pattern match algorithm to strengthen the particle image tracking performance. By using the nonlinear system model and bootstrap filter, particle location at next time step can be predicted accurately and the new method is able to measure high velocity gradient flows with better performance than the traditional particle image tracking algorithms. This new method is validated by using numerically generated particle images. Its accuracy in terms of particle image density, out-of-plane displacement and displacement gradient is compared with the Kalman filter tracking (Takehara et al., 2000 [34]) and the Super-PIV (Keane et al., 1995 [30]) methods. The three algorithms are also compared by using a set of real turbulent jet images. The test results demonstrate that the bootstrap filter tracking method is superior than the Kalman filter tracking and the Super-PIV methods for measuring low density, high velocity gradient flows.