折褶滤芯过滤阻力的数值模拟与分析

由于滤芯折褶结构过于微小,再加上温度和环境等因素的存在,运用试验测试这种方法来研究折褶滤芯的过滤阻力有一定弊端。采用CFD技术对过滤器进行数值模拟,观察流体在过滤器内腔中的水流现象,分析其通过滤网时的流动状态,找到了二维数值模拟方法误差大的原因,并采集十个折褶滤芯的样本点,拟合出理论计算与数值模拟的相对误差曲线。结果表明,对于折褶滤芯而言,采用三维数值模拟方法得出来的过滤阻力误差不到5%,这对滤芯的设计和选型具有指导意义。     

基于CFD技术的多种折褶滤网数值模拟及分析

利用CFD技术研究流体通过V型折褶滤网(局部)时的流态特征,分析其在特定条件下的流场状态。并以此为契机,模拟出流体通过其他结构的折褶滤网(局部)时的流场状态,观察流体在不同结构的折褶滤网周围的速度及压力的分布情况,进一步了解折褶结构对滤芯过滤效果的影响。结果表明,V型折褶滤网虽然应用广泛,但并不是最佳结构,梯形折褶滤网的过滤效率更为突出。     

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.     

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.     

低渗油藏二氧化碳驱最小混相压力预测方法研究

向低渗油藏中注入CO2可以有效补充地层能量,显著提高采收率.最小混相压力是注气方案设计中最重要的参数,受到原油组成、注入气组成、温度等的影响.为研究不同理论方法预测注CO2最小混相压力的效果,以该油田某一油藏膨胀实验和细管实验测试的最小混相压力为基础,分别比较了经验公式、PR状态方程和系线解析法计算的二氧化碳-原油体系最小混相压力.优选了一种理论计算方法,并对该油田其他油藏的最小混相压力进行了有效预测.结果表明:系线解析方法计算的最小混相压力与细管实验测试值最接近,相对误差为2.2％,PR状态方程次之,经验公式误差最大;推荐采用系线解析方法来计算该油田低渗油藏注CO2驱最小混相压力.     

双曲肘斜排列七支点合模机构运动和力学性能分析

分析了双曲肘斜排列七支点合模机构的性能特征、行程特性及力学性能,研究了移模行程、锁模油缸活塞杆行程、锁模力、锁模油缸内径等机构关键技术参数的计算理论和工程计算准则,研究了机构的主要技术设计参数特征,提出了主要技术参数的设计准则,并通过实例验证了设计计算理论和公式的可行性。     

纤维缠绕复合管材短期爆破压力理论分析

根据一定的假设和简化构建了理论爆破压力的计算模型,并通过力学平衡法推导出纤维增强复合管材的理论短期爆破压力计算公式,然后对不同缠绕角度涤纶纤维增强高密度聚乙烯管材进行短期爆破压力测试.由实测数值与理论计算结果的偏差可知,纤维层的环向方向各层纤维受力不均不能忽略,需要对理论公式进行修正,与实测数据进行对比发现,修正公式计...     

一种简单安全的试井方法

本文从常规"一点法"试井的作业风险分析入手,利用靖边气田常规"一点法"和气体静压理论,推导出井口压力"一点法"的计算无阻流量公式,并通过5口气井实例的计算比较,验证了公式的可靠性。井口压力"一点法"计算气井无阻流量无需用试井钢丝将压力计下入气层求取地层压力和流压,只需测试时的井口套管压力和气井产量就可计算气井当前的无阻流量,有效消减了常规"一点法"试井作业的安全风险,实现了本质上的安全。     

不同操作压力下的气液过滤特性分析

根据ISO-12500标准建立了压缩空气滤芯性能检测系统,将操作压力由0.1 MPa升至0.7 MPa,分析了操作压力对亲油型和疏油型两种滤芯内的液体分布、滤材饱和度和过程压降的影响. 结果表明,操作压力对疏油型滤芯的过程压降、液体运移与饱和度有显著影响,操作压力每上升0.2 MPa,滤芯初始压降上升0.32 kPa,各操作压力下滤芯润湿压降(平衡压降与初始压降的差)为4.5~5.1 kPa,0.7 MPa时最后1层滤材饱和度比0.1 MPa时上升了71%,饱和度沿气体流动方向呈凹型分布,小面积润湿区域增多,稳态压降前出现短暂跃升阶段,可能加剧滤芯二次夹带,导致过滤器下游管道内液滴数增多,降低过滤器效率;操作压力对亲油型滤芯的初始压降影响显著,操作压力每上升0.2 MPa,初始压降上升0.39 kPa;操作压力对液体运移与饱和度影响较小,不同操作压力下各层滤材饱和度的分布规律相同,液体分布无明显差异.     

涡轮式气力分级机流场的理论分析与计算

为了设计新型高效转子超细粉体气力分级机,必须对分级机内流场进行理论分析和计算.通过分析计算得出圆柱型转子气力分级机通用的速度场公式,并且对分级机内压力的分布进行了计算.文中理论可用于指导分级机的设计和制备.     

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.     

Air flows and pressure drop modelling for different pleated industrial filters

A dimensionless model was developed to determine the pressure drop across clean pleated filters, according to filter medium type, geometric characteristics of the pleating (distance between two pleats, pleat height, etc) and air flow parameters (filtration velocity, air density, etc). The model was derived from both experimental and numerical results obtained from nuclear and automotive filters — high efficiency particulate air (HEPA) and low efficiency particulate (LE), respectively. The major findings were that a more homogeneous air flow distribution occured over the surface of the pleated HEPA filter, while geometric characteristics had a greater influence on the initial pressure drop across the LE filter. The numerical model highlighted the fundamental importance of the filter medium's air flow resistance on air flow distribution.     

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.     

褶型纤维过滤介质压力损失的多尺寸模拟

统筹考虑纤维结构特性、纤维排布及纤维层数等因素,基于MATLAB编写控制程序,建立褶型纤维过滤介质微观尺寸模型,并计算过滤介质固体体积分数?,采用数值模拟方法获取微观尺寸下过滤风速v与压力损失Δp之间的数学关联式,进而获取介质的粘性阻力系数C1。在此基础上,建立褶型纤维过滤介质宏观尺寸模型,基于微观尺寸模拟得到的?及C1,采用数值模拟的方法得到宏观尺寸下迎面风速u与Δp之间的数学关联式,并将数学关联式与多个经验公式进行对比。结果表明,褶型纤维过滤介质内纤维排列方式及介质厚度对Δp有影响,但对C1等性质参数影响不大;微观尺寸研究得到的参数可以为宏观尺寸研究提供指导,微观结构与宏观结构性质参数可以沿用。本研究结果对拓展纤维过滤介质的研究方法及优化其结构具有重要理论及实际意义。     

A semi-analytical model for gas flow in pleated filters

A semi-analytical model of gas flow in pleated fibrous filters is developed for large filtration velocities. This case presents two main new and distinguishing features compared to the low filtration velocity situations studied in previous works: the velocity profiles are not parabolic within the pleat channels and the filtration velocity is not uniform along the pleated filter element and this has a great impact on the filter loading. The model relies on similarity solutions to the Navier–Stokes equations in the channels formed by pleating the filter medium. After validation by comparison with direct CFD simulations and experimental data, the model is used to determine the optimal pleat density, i.e. the pleat density minimizing the overall pressure drop across the filter for given flow rate, pleat length and given filter medium properties. As illustrated in the paper, this model greatly facilitates the study of flow within the pleated filter compared to a standard CFD approach. It represents an excellent basis for the more involved problem of filter loading computation. In particular, no remeshing across the width of the pleated filter entrance channels is needed when a filtration cake forms at the channel walls.     

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.     

NUMERICAL ANALYSIS OF MEDIUM COMPRESSION AND LOSSES IN FILTRATION AREA IN PLEATED MEMBRANE CARTRIDGE FILTERS

A computer model has been developed to simulate the fluid flow in pleated filter cartridges. This model has been used to evaluate the performance and design of pleated cartridge membrane filters. The effects of medium compression, pleat deformation, and pleat crowding are analyzed. At higher flow rates due to the exerted fluid pressure the medium is deformed, which leads to a reduction in the material permeability. Further, due to pleating and bending there is a loss in effective filtration area. The combined effects of compression and reduction in filtration area cause deviations from Darcy's law. To interpret such deviations, permeability models based on the data obtained from the flat sheets of the filter material used in cartridge fabrication have been developed. The incorporation of the permeability model within the main hydrodynamic model determines the percentage loss in filtration area, percentage medium compression, and the pressure drop across the filters. Results of this study have been presented for fiberglass medium. The simulated results have been compared against experimental industrial data for purposes of model validation. The developed simulation tool offers a robust, cost-effective, and user-friendly design and analysis tool for pleated cartridge membrane filters, which can be easily used by engineers in industry.     

HDPE装置新线粉料输送系统的技术改造

分析了高密度聚乙烯装置新建生产线粉料输送系统出现的袋式过滤器压差增大、输送风机进出口压差及电流较高等异常情况,其主要原因是该系统袋式过滤器过滤面积不足及粉料输送风机的进出口管线较长等。采用将袋式过滤器的滤袋换成褶皱袋,适当改造粉料输送风机的进出口管线等措施,提高了系统的高负荷稳定运行能力。     

Numerical study of pleated fabric cartridges during pulse-jet cleaning

We established a numerical model and used computational fluid dynamics (CFD) analysis to observe transient flow behavior across pleated filter cartridges in a dust collector during pulse-jet cleaning. The numerical results were in good agreement with the filter-testing data during important periods including during pressure ramp-up and valve opening. Larger errors for predicting overpressure occurred during the pressure ramp-down period likely due to the uniformity of the filters' permeability. This confirmed that the numerical model demonstrated the cleaning efficiency and the local cleaning quality of three different filter cartridges with different filter dimensions and pleat ratios. Data calculated from the average static pressure on the filters' surfaces were more closely correlated to cleaning efficiency than overpressure. The surface static pressure distribution along all filter cartridges showed that the top area of the filter cartridge is difficult to clean because of the lower surface pressure generated by the pulse jet. Filter cartridges with higher pleat ratios were found to have greater instances of incomplete cleaning due to the large variation of static pressure distribution along the filter cartridges. Our results showed that although information such as average pressure and pressure distribution on the filter surface is difficult to obtain by physical measurement, this data is tractable using CFD analysis and is useful for filter design and system optimization.