褶型空气过滤介质微观结构三维建模及其含尘性能模拟

基于实际熔喷纤维电镜扫描(SEM)图像,建立了不同褶间角、层数、直径、纤维个数、曲率的褶型空气过滤介质微观结构模型,实现了对褶型空气过滤介质微观结构的动态控制.通过计算流体力学和离散单元法(CFD-DEM)耦合的方法对褶型过滤介质含尘过滤阶段的过滤特性进行模拟,将模拟结果与相关经验关联式比较.结果表明,所建模型与实际过滤介质电镜图像基本相似,压力损失模拟值与计算值误差在10%以内,表明CFD-DEM耦合计算方法可行;在含尘过滤阶段,同一进口风速(v)下随颗粒沉积量增加,压力损失非线性增大;不同进口风速下的压力损失增加均随过滤时间增加而增大,v=0.6 m/s时压力损失增加最大,为0.214 Pa,v=0.4 m/s时压力损失增加最少,为0.133 Pa.当3.216 ms时,颗粒出现明显沉积与团聚,纤维彼此贯穿的区域沉积更明显,表明纤维的排列方式对颗粒的沉积影响显著.     

基于微观结构的褶式滤芯拟态化模型及其过滤性能的数值模拟

基于随机多层纤维过滤介质算法建立褶式滤芯三维拟态化结构模型,对褶式滤芯内部气-固两相流动进行数值模拟,计算不同运行参数及结构参数下滤芯的压力损失及过滤效率,并与文献计算值进行比较. 结果表明,压力损失随过滤风速增大呈线性增加;随褶尖角增大,压力损失呈先减小后增加,压力损失计算值与文献计算值吻合较好. 褶尖角和过滤风速一定时,过滤效率随粒径增加先减小后增大,在给出的颗粒直径范围内存在最易穿透颗粒直径(MPPS). 不同过滤风速下,当颗粒粒径小于0.5 mm时,扩散作用使过滤效率随过滤风速增加而减小;大于0.5 mm时,惯性作用使其随过滤风速增加而增加;MPPS随风速增加而减小;本计算值与文献计算值趋势一致. 不同褶尖角下,当颗粒粒径小于1 mm时,扩散作用使过滤效率随褶尖角增大而减小;大于1 mm时,惯性作用使其随褶尖角增大而增加.     

基于阻力的V型褶式滤芯结构参数的响应面法优化

应用计算流体力学方法建立褶式滤芯阻力的二维计算模型,对其气相流场进行了数值模拟,并与文献结果比较. 在此模型基础上,利用响应面法研究了褶高(h)、褶间距(W)和过滤风速(Vf)对V型褶式滤芯阻力的影响,得出了预测模型,并对滤芯结构参数和运行条件进行了优化. 结果表明,滤芯阻力的模拟值和文献计算值变化趋势一致;h, W及Vf对滤芯阻力均有影响,但影响显著性Vf>W>h;滤芯阻力随Vf近似呈线性增大,当Vf一定时,存在最优W值使滤芯阻力最小,且最优W值随h增大而增大;在本研究的各参数范围内,最佳结构参数h=25 mm, W=10.899 mm,最佳运行参数Vf=0.005 m/s.     

空气滤清器过滤阻力多元关联式的研究

为减低空气滤清器过滤阻力,对空气滤清器流场特性进行的实验测试和模拟计算,旨在于为空气滤清器的优化设计提供相关的理论指导和依据。采用CFD模拟技术,结合实验测试的方法,建立了空气滤清器的CFD模拟的两维和三维模拟模型,计算机模拟计算结果与实验测试结果吻合,计算得出空气滤清器的过滤阻力与其各自影响因素的变化规律,通过数值模拟计算结果的回归分析,给出了空气滤清器总成过滤阻力与其显著影响因素的单因素关联式。利用大量的过滤压降与不同滤清器结构参数、过滤速度和过滤介质特性参数的模拟数据,回归得出总成过滤阻力与入口速度、滤芯褶数、进气管长、进气管径、出气管长、出气管径和滤纸厚度的无量纲的多元关联式。     

数值研究壁面参数对单纤维捕集效率的影响

基于开源OpenFOAM软件模拟单纤维过滤介质内气-固两相流运动,着重研究了单纤维过滤介质壁面参数与捕集效率之间的关系,即为纤维过滤介质的碰撞恢复系数和碰撞阻尼系数的变化对捕集效率的影响。将模拟结果与经验关联式进行对比验证,且具有很好的一致性。模拟结果表明:固体颗粒物的捕集效率随着碰撞恢复系数的增大呈现先减小后平稳的变化趋势,而碰撞恢复系数为0.5之后捕集效率基本保持稳定;颗粒物捕集效率随着碰撞阻尼系数的增加,固体颗粒物的捕集效率呈现先增大后平稳的趋势,且在碰撞阻尼系数在0.7以后,捕集效率基本趋于稳定。     

静电纺纳米纤维复合梯度型空气过滤材料的研究进展

概述了静电纺纳米纤维及其复合梯度过滤材料的特性,详述了国内静电纺纳米纤维复合梯度型空气过滤材料的制备、过滤模型理论及数值模拟等研究进展。基于不同纤维层过滤不同粗细颗粒物,每一层纤维网发挥各自独特作用,可采用多种结构和折叠结构复合,增大过滤面积,制备多层梯度的静电纺纳米纤维复合滤材,使滤材具有高效低阻、容尘量大、使用寿命长等特点,是未来空气滤材的重点研发方向;同时应加强过滤模型设计与数值模拟研究,通过滤材的应用数据不断修正模型,促进滤材性能的改进。     

工业常用孔的流动特性研究进展

孔流系数是孔特性研究的重要参数之一,其特性研究在工程实际中非常重要。可以由理论公式、实验数据拟合或关联式及数值模拟等方法表示。常用孔的形状可以分成普通孔(圆孔、方孔)与特殊孔(如U型孔,V型孔等)两大类,笔者对常用工艺孔孔流系数的不同研究方法及适用条件进行了综述,分析发现,孔流系数C0=F(孔形状、雷诺数Re、厚径比δ/d0)。薄壁小孔的孔流系数可以近似为0.62~0.63;厚壁孔的孔流系数可以近似为0.82;流量系数C0与流速系数CV、收缩系数ε、阻力系数ξ的关联式可以表述为简单孔孔流系数关联式为:C0=εCV,收缩系数ε=AA1c,CV=11 ξ流速系数。笔者认为,前人对特殊孔的研究相对较少,今后对孔流系数的研究应借助先进实验方法,采用数值模拟技术,拓宽研究领域和适用范围,特别是应加强对特殊孔的研究,以加快新设备的开发与利用。     

粘性颗粒在单纤维体上流动特性的模拟方法

分别采用CFD-DEM耦合、基于EDEM软件的API接口加载曳力模型以及开源软件Open FOAM三种模拟方法对颗粒在单纤维上的沉积特性进行了数值模拟,对比分析了颗粒物的沉积形态、纤维的过滤性能(包括压力损失和过滤效率)和模拟计算成本,结果表明,基于开源软件Open FOAM模拟方法最优,无论是模拟粘性颗粒物在纤维体上的沉积形态和纤维体的过滤性能,还是模拟计算成本都优于其他两种方法;而基于EDEM软件的API接口加载曳力模型的模拟方法无法得到气相参数及压力损失、CFD-DEM耦合的模拟方法由于计算量大应谨慎选取。     

三角形布管折流杆换热器壳程性能模拟与实验研究

三角形布管折流杆换热器是一种有别于传统方形布管折流杆换热器的新形式,其性能评估与算法都没有现成的资料。文中应用CFD软件Fluent进行分段模型的流动与传热研究,将数值模拟的局部流动与传热数据综合整理得到了整体法关联式,经与文中的实验数据和C.C.Gentry提出的实验关联式进行对比,发现方形布管的模拟结果与C.C.Gentry关联式符合良好;三角形布管的模拟结果与本文改进的C.C.Gentry关联式比较,发现传热关联式精度很高,而压力降关联式的平均误差也可以接受。由此提出了三角形布管壳程的折流杆换热器流动与传热设计评估的计算方法。验证还发现,包含E间隙的换热器模型模拟更符合实测数据结果。     

新型静态混合器压力降研究

在SK型静态混合器的基础上提出了三种组合螺旋形式的静态混合器,利用专业CFD计算流体力学软件Fluent对这三种静态混合器内流场进行了数值模拟,得到了不同流速下的压力降数值,绘制了压力降随速度的变化曲线,并针对三种静态混合器和特定的介质给出了压力降与速度的关联式。     

Experimental study of pleated fabric cartridges in a pulse-jet cleaned dust collector

Six pleated filter cartridges with different base media and geometrical dimensions were tested in a full-size dust collector periodically cleaned by a short burst of pulse-jet. The evaluation was performed under two different cleaning modes called clean-on-demand (to clean the filter once the pressure drop reaches a preset value) and clean-on-time (to clean the filter at a fixed time interval). The filter performance was evaluated by the effective residual pressure drop and downstream particle concentration. The results showed that the pleat ratio, defined as the ratio of pleat height to pleat pitch, had a great influence on the preferred operating mode for cleaning the filter. Clean-on-time mode demonstrated better performance for filters with a high pleat ratio (> 4.0), while clean-on-demand mode performed better for filters with a low pleat ratio (< 4.0). The test results also showed the tank pressure was critical for cleaning the pleated filter cartridges, whereas the pulse duration only had a small effect on the cleaning efficiency. With the same base media, cartridges with surface treatment such as fine fiber were superior to those without surface treatment. Pulse-jet cleaning could also promote particle penetration through filter media. The downstream particle concentration during cleaning was at least twice of that during filtration process for all pleated filter cartridges tested. Further, the downstream particle concentration was independent of the applied cleaning mode and the cleaning intensity in this study.     

Optimization of Pleated Filter Designs Using a Finite-Element Numerical Model

A numerical model has been developed to optimize the design of pleated filter panels. In this model, the fluid flow is modeled by a steady laminar flow and the filter media resistance is governed by the Darcy-Lapwood-Brinkman equation. A finite element method with a nine-node Lagrangian element is used to solve the governing equations. For the rectangularly pleated filter panel, the numerical results agree well with the analytical model of Yu and Goulding (1992) and with his experimental data. The pressure drop increases at small pleat count due to increased media face velocity, and at large pleat count due to increased viscous drag in the pleat spacings. Therefore, an optimal pleat count for minimum pressure drop exists at a certain pleat height for each filter media type. The optimization of rectangular pleated filters, e.g., mini-pleated filter panels, has been performed for six commercial filter media. The optimal pleat count is shown to increase with decreasing media permeability of the filter media. A generalized correlation curve has been found for the six filter media by using a nondimensional parameter analysis. The results can be used to design pleated filter panels with minimum pressure drop.     

玻纤滤材过滤阻力的预测

过滤阻力和过滤效率是玻纤空气滤材的关键参数。实际应用中,为了优化滤材阻力和效率之间的矛盾,通常会选择多种尺寸的纤维搭配使用。对这种滤材的过滤阻力进行预测,对于高性能滤材的研制具有重要意义,而目前对玻纤滤材过滤阻力的理论计算大部分还局限于单种纤维的理想情况。本文将针对由多种玻纤原料制备的滤材,根据不同玻纤的比表面积,利用Kozeny-Carman方程计算由此制备的滤材过滤阻力。这种方法计算的过滤阻力理论值与实际测量值非常接近,相关系数R2=0.996 9,可为过滤材料的优化设计提供一定的依据。     

Influence of Diameter on Surface Dispersive Free Energy of Polyethersulfone Nano-fibers

Nano-fibers have been applied in many fields because of their unique properties. Quantifying and characterizing the surface free energy and researching the influence of fiber diameters on surface free energies is important. In this paper, three kinds of polyethersulfone nano-fibers with the average diameter of 873, 567 and 254 nm were successfully fabricated by electrospinning at room temperature. The surface dispersive free energy of the three fibers and polyethersulfone (PES) macro-size particles were measured by inverse gas chromatography technique at 30, 40 and 50°C. It was found that the surface dispersive free energy decreased with decreasing fiber diameter. The rationality of the measured values of surface free energy was validated with a BSA adsorption experiment.     

芳纶的制备 微观结构与测试方法

介绍芳纶的制备工艺 (包括一步法和两步法工艺及芳纶浆粕型纤维的制备 ) ,并对聚对苯二甲酰对苯二胺 (PPTA )纤维的几种主要微观结构形态 ,包括皮芯层有序微区结构模型、轴向排列褶裥层模型和片晶柱状原纤结构模型 ,进行了较详尽的论述。应用碳纤维的结构形成原因推测了芳纶结构也应存在多样性 ,讨论可能影响其结构的因素。对用于芳纶微观结构分析的表面力显微镜和介电学谱技术进行了简介。     

A study on the effects of laminating temperature on the polymeric nanofiber web

The use of fine fiber has become an important design tool for filter media. Nanofibers-based filter media have some advantages such as lower energy consumption, longer filter life, high filtration capacity, easier maintenance, low weight rather than other filter media. The nanofibers-based filter media made up of fibers of diameter ranging from 100 to 1,000 nm can be conveniently produce by electrospinning technique. Common filter media have been prepared with a layer of fine fiber on typically forming the upstream or intake side of the media structure. The fine fiber increases the efficiency of filtration by trapping small particles, which increases the overall particulate filtration efficiency of the structure. Improved fine fiber structures have been developed in this study in which a controlled amount of fine fiber is placed on both sides of the media to result in an improvement in filter efficiency and a substantial improvement in lifetime. In the first part of this study, the production of electrospun nanofibers is investigated. In the second part, a different case studyis presented to show how they can be laminated for application as filter media. Response surface methodology (RSM) was used to obtain a quantitative relationship between selected electrospinning parameters and average fiber diameter and its distribution.     

Electrospun nanofibers with application in nanocomposites

The use of fine fiber has become an important design tool for filter media. Nanofibers-based filter media have some advantages such as lower energy consumption, longer filter life, high filtration capacity, easier maintenance, low weight rather than other filter media. The nanofibers-based filter media made up of fibers of diameter ranging from 100 to 1,000 nm can be conveniently produce by electrospinning technique. Common filter media have been prepared with a layer of fine fiber on typically forming the upstream or intake side of the media structure. The fine fiber increases the efficiency of filtration by trapping small particles, which increases the overall particulate filtration efficiency of the structure. Improved fine fiber structures have been developed in this study in which a controlled amount of fine fiber is placed on both sides of the media to result in an improvement in filter efficiency and a substantial improvement in lifetime. In the first part of this study, the production of electrospun nanofibers is investigated. In the second part, a different case studyis presented to show how they can be laminated for application as filter media. Response surface methodology (RSM) was used to obtain a quantitative relationship between selected electrospinning parameters and average fiber diameter and its distribution.     

Nanofibrous chitosan non-wovens for filtration applications

Chitosan containing nanofibrous filter media has the advantage of filtering material based on both its size and functionality. They can be potentially applicable in a wide variety of filtration applications ranging from water purification media to air filter media. We have fabricated nanofibrous filter media by electrospinning of chitosan/PEO blend solutions onto a spunbonded non-woven polypropylene substrate. Filter media with varying fiber diameter and filter basis weight were obtained. Heavy metal binding, anti-microbial and physical filtrations efficiencies of these chitosan based filter media were studied and correlated with the surface chemistry and physical characteristics of these nanofibrous filter media. Filtration efficiency of the nanofiber mats was strongly related to the size of the fibers and its surface chitosan content. Hexavalent chromium binding capacities up to 35 mg chromium/g chitosan were exhibited by chitosan based nanofibrous filter media along with a 2-3 log reduction in Escherichia coli bacteria cfu.     

Figure of Merit of Composite Filters with Micrometer and Nanometer Fibers

We investigate the filtration performance of composite filters composed of micrometer and nanometer fibers. The filter quality is evaluated using the figure of merit, also known as the quality factor. We use analytical expressions for the pressure drop and filtration efficiency to compute the figure of merit. The effects on the figure of merit by fiber diameter, solidity, and thickness of nanometer and micrometer fibers and face velocity are investigated. Experimental data obtained using conventional filter media and nanofiber composite filters are then used to verify the calculated results. We find that for large particles (approximately 0.1 μm and above), nanofibers can improve the figure of merit compared to conventional filters. Smaller fiber size, larger solidity, and thickness of the nanofiber layer lead to better filtration performance in this size range. For small particles (approximately below 0.1 μm), nanofibers do not improve the figure of merit compared to conventional filter media. Larger fiber size, smaller solidity, and thickness of the nanofiber layer are preferred in this size range. We demonstrate that our procedure using analytical expression is a fast and effective tool for filter media design.     

Clogging modeling in pleated filters for gas filtration

A model of clogging of a pleated filter in gas filtration is presented. The model is obtained by combining a semi-analytical model of the flow in a pleated filter and an empirical model of clogging of the planar filter medium applied locally along the pleated filter channels. The model takes into account the formation of a filtration cake of variable thickness at the porous wall of the pleated filter entrance channels and the resulting evolution of the entrance channels aperture distribution during the filtration/clogging process. Based on the numerical predictions, two main clogging scenarios are identified and analyzed. The optimum pleat density, defined as the pleat density maximizing the filter capacity, is determined and shown to be greater than the pleat density minimizing the pressure drop for a clean filter. Predictions of the evolution of overall pressure drop across the pleated filter due to clogging are compared with experimental data.