Deep bed filtration model for cake filtration and erosion

Many phenomena in nature and technology are associated with the filtration of suspensions and colloids in porous media. Two main types of particle deposition,namely, cake filtration at the inlet and deep bed filtration throughout the entire porous medium, are studied by different models. A unified approach for the transport and deposition of particles based on the deep bed filtration model is proposed. A variable suspension flow rate, proportional to the number of free pores at the inlet of the porous medium, is considered. To model cake filtration, this flow rate is introduced into the mass balance equation of deep bed filtration. For the cake filtration without deposit erosion,the suspension flow rate decreases to zero, and the suspension does not penetrate deep into the porous medium. In the case of the cake filtration with erosion, the suspension flow rate is nonzero, and the deposit is distributed throughout the entire porous medium. An exact solution is obtained for a constant filtration function. The method of characteristics is used to construct the asymptotics of the concentration front of suspended and retained particles for a filtration function in a general form. Explicit formulae are obtained for a linear filtration function. The properties of these solutions are studied in detail.

Experimental study on large wood filtration performance by herringbone water-sediment separation structure

A herringbone water-sediment separation structure(hereinafter referred to as "herringbone structure") has been shown to be effective in separating coarse inorganic debris; however, less is known regarding the large wood(LW) filtration effect in this structure. This paper presents preliminary research on the wood filtration effect of the herringbone structure based on physical model tests.The results show that the herringbone structure exhibited effective performance in large wood size segregation, with a 100% component filtration rate for LW that diameter(D) larger than ribbed beam opening width(a). The total filtration rate also exceeded 80% when the Fraud number(Fr) is larger than 2.64 and increased with the increase of Fr. After exceeding Frmax, total filtration rate would be decreased due to overflow. Beside flow condition,structure parameters influence significantly on LW filtration rate. We attempt to explain the filtration process via particle contact trajectory and particle movement trajectory. The inclined angle of ribbed beam(γ) contributed the most variation to the filtration rate via influencing the coincidence with particle contact trajectory and particle movement trajectory. The high sensitivity coefficient of ribbed beam(θ) under relatively low Fr conditions implies remarkable influences on LW filtration effects by causing clogging problem. The ribbed beam opening width(a) together with LW diameter(D) influenced the size segregation performance.

Ba^(2+)/Ca^(2+)co-crosslinked alginate hydrogel filtration membrane with high strength,high flux and stability for dye/salt separation

Alginate is a natural polysaccharide polymer.Hydrogel filtration membranes prepared from alginate show excellent fouling resistance and controllable separation performance,but poor mechanical properties limit the use of algae hydrogels.In this study,Ba^(2+)/Ca^(2+)co-crosslinked alginate(Ba/CaAlg)hydrogel membrane was prepared by cross-linking sodium alginate with a blend aqueous solution of barium ions and calcium ions,and the membrane was applied to the separation of dyes/salts from dyeing wastewater.Compared with the CaAlg membrane,the Ba/CaAlg hydrogel membrane exhibited more stable structure,and the mechanical properties and salt tolerance of the membrane were significantly improved.The flux of Ba/CaAlg membrane for methyl blue/sodium chloride mixed solution reached 43.5 L m^(−2) h^(−1),which was significantly higher than that of CaAlg membrane.Besides,the Ba/CaAlg membrane showed higher dye rejection(>99.6%)and lower salt rejection(<8.2%).The structure of Ba/CaAlg membrane was preliminarily simulated by molecular dynamics,and the pore size and distribution of the membrane were calculated.The Ba/CaAlg membrane has a broad application prospect in dyes/salts separation.

Analysis of the Medium Resistance for Constant Pressure Filtration

A mathematical model for constant pressure filtration is established. The distribution of hydraulic pressure within the cake and the medium resistance are measured. The medium resistance Rm is calculated from the suppositional filtration time Ore. It is demonstrated that Rm is nearly a constant for a given filter cloth.

Asymptotics for filtration of polydisperse suspension with small impurities

A model for deep bed filtration of a polydisperse suspension with small impurities in a porous medium is considered.Different suspended particles move with the same velocity as the carrier water and get blocked in the pore throats due to the size-exclusion mechanism of particle retention.A solution of the model in the form of a traveling wave is obtained.The global exact solution for a multiparticle filtration with one high concentration and several low concentrations of suspended particles is obtained in an explicit form.The analytic solutions for a bidisperse suspension with large and small particles are constructed.The profiles of the retained small particles change monotony with time.The global asymptotics for the filtration of a polydisperse suspension with small kinetic rates is constructed in the whole filtration zone.

Pretreatment of highly turbid coal mine drainage by a chemical agent free filtration system

A filtration system used without chemical agents for the pretreatment of turbid coal mine drainage is described in this paper.The influence of different aperture sizes and different motor speeds was investigated during the study.The experimental results show that for aperture diameters of 0.4,0.6,or 0.8 mm smaller apertures provide more complete filtration.Rotations of 12,20,28,or 40 r/min show that higher speeds give more efficient filtration.Suspended solids decreased in both particle size and concentration after the filtration.The separated slime can be directly reused as a fuel.Efficient filtration pretreatment systems for coal mine drainage were investigated and the economic feasibility is analyzed in this article.

Morphology and fractal characteristic of deposits formed during fiber bundle media filtration

The scanning electronic microscope and automated image analyzer are adopted to investigate the morphology of deposits formed during fiber bundle media filtration, which results in the discovery of the self—similarity of the deposits. Then in this paper it is proposed that the deposits are a fractal structure. Moreover, the fractal dimension value is related to the filter performance. The higher the fractal dimension value, the higher the filtration efficiency, and the longer filtration cycle, but the development of the head loss is also faster.

Evaluation of gas-liquid separation performance of natural gas filters

Fibrous filters are often used to remove contaminants including both dusts and liquid droplets from natural gas. This paper aims to evaluate the gas-liquid separation performance of three types of cartridge filters used in the West-East natural gas transmission project. The comparison of the original pressure drop of clean filters and the evolution of pressure drop as liquid droplets deposited in the filter media are described. The original pressure drops of these filters were similar but the pressure drops at a steady state were different. Fractional efficiency was used to study the separation performance of cartridge filters. Droplets at the outlet of the filters had small diameters, no more than 3 μm, but were very numerous. The effect of filtration velocity on gas-liquid separation performance was analyzed. Higher filtration velocity indicated better gas-liquid separation performance. Finally the quality factor related to pressure drop and filtration efficiency was applied to evaluate the gas-liquid separation performance.

One-step fabrication superhydrophobic sand filter for capillary-driven separation of water-in-oil emulsions

The efficient separation of water-in-oil emulsion is of significance in environment and energy filed,and it has become a world-wide challenge.Herein,we have presented a one-step,facile and low-cost approach to prepare superhydrophobic sands for efficient separation of water-in-oil emulsion.The as-prepared sand layers possessed a water contact angle higher than 151°,demonstrating their superior superhydrophobic property.Besides,the as-prepared sand layers could separate water-in-emulsions with separation efficiency up to 99.7%,which is superior to both traditional and superwettable filtration membranes.The effect of thickness of sand layer on separation performance was also investigated.The results showed that the filtration flux decreased with the increased of filtration thickness while the separation efficiency increased.The as-prepared sand layer proposed by this study is a processing candidate for separating water-in-oil emulsion in practical industry.Additionally,the as-prepared superhydrophobic sand fabrication method also provides an alternative for desert water storage.

Study on Optimizing High-Gradient Magnetic Separation—Part 2: Experimental Evaluation of the Performance of a New Designed Magnetic Filter

The introduction of functionalized magnetizable particles and high-gradient magnetic separation represents a time and money saving alternative to conventional purification and separation unit operations in the biotechnical sector. This technique has some advantages especially for the recycling of immobilized enzymes. A new magnetic filter with sight glasses was constructed and produced to study the performance of high-gradient magnetic separation at varied parameters. By optical analysis the buildup of a clogging was identified as the major parameter which affected the separation performance. For the cleaning procedure, a two-phase flow of water with highly dispersed air bubbles was tested which led to a nearly complete cleaning of the filter chamber.

Study on Optimizing High-Gradient Magnetic Separation—Part 1: Improvement of Magnetic Particle Retention Based on CFD Simulations

The introduction of functionalized magnetizable particles for the purification of enzymes or for the multi-use of pre-immobilized biocatalysts offers a great potential for time and cost savings in biotechnological process design. The selective separation of the magnetizable particles is performed for example by a high-gradient magnetic separator. In this study FEM and CFD simulations of the magnetic field and the fluid flow field within a filter chamber of a magnetic separator were carried out, to find an optimal separator design. The motion of virtual magnetizable particles was calculated with a one-way coupled Lagrangian approach in order to test many geometric and parametric variations in reduced time. It was found that a flow homogenisator smoothed the fluid flow, so that the linear velocity became nearly equal over the cross section in the direction of flow. Furthermore the retention of magnetizable particles increases with a high total edge length within the filter matrix.

Electrospinning of ABS nanofibers and their high filtration performance

Acrylonitrile-butadiene-styrene(ABS)is a commercial polymer for widely industrial applications due to its good mechanical and physical properties.However,there are only countable reports regarding its fibers from electrospinning.Comprehensive investigation on its optimized electrospinning parameters is missing.Herein,ABS fibers with different fiber diameters were produced by electrospinning.The electrospinning conditions,including the solvents,solution concentrations and amounts of different salt additives,have been comprehensively investigated.The morphologies of electrospun ABS fibers are studied by scanning electron microscopy and Raman spectroscopy.Different fiber diameters and coating densities are applied for filtration applications,which showed excellent filtration performance.The filtration efficiency of up to 99%,low pressure drop of<30 Pa,and high filtration quality factor of up to 0.477 are achieved from the electrospun ABS fibers coated on microfibrous polypropylene substrates.In addition,the electrospun ABS fibers also shows good thermal stability and other applications such as oil/water separation.

Recovery of zinc from Zn-Al-Fe alloys by gas pressure filtration

The recovery of zinc from galvanizing dross and the removal of iron contained dross particles by gas pressure filtration were investigated using the model of Zn-Fe-Al alloys.The majority of molten zinc was separated after filtration,and the residue intercepted by the filter consisting mostly of dross particles.The effects of the pressure differential(p),separation temperature(T)and alloy composition on the zinc recovery and iron removal were investigated.At p=0.30 MPa and T=723 K,86.2 wt.%zinc was recovered from the Zn-4Al-2Fe alloy,and up to 99.9 wt.%of the iron was concentrated in the residue.Applying a higher pressure differential led to the improved filtration efficiency,and the desired separation temperature was about 723 K.The aluminum content in the Zn-Al-Fe alloy had little effect on separation efficiency,whereas increasing the iron content led to a decrease in the separation efficiency.Our findings demonstrate the potential of the gas pressure filtration method for the recovery of zinc from galvanizing dross.

Semigroup Solution for Layered Filtration

This paper deals with a simple case of filtration in a layered porous media. A new kind of PDE (partial differential equntion) problem is proposed to explain such phenomena as the transition of fluid in layered porous media. The characteristic of these problems is that across the interface between the two layers, the flux is conserved, but the fluid content in general is different. This situation is very different from the model of filtration in homogeneous porous media, in which the primary objective is to maintain fluid continuity.

ONE DIMENSIONAL FILTRATION PROBLEM IN PARTIALLY SATURATED LAYERED POROUS MEDIA

We study in this paper the first boundary value problem of one dimensional degenerate quasilinear elliptic-parabolic equation with discontinuous coefficients (layered media). The uniquenessof the weak solutions is proved under natural conditions.

烟草中甲霜灵的手性分离方法差异研究

对比反相液相色谱-串联质谱(RPLC-MS/MS)和超临界流体色谱-串联质谱(SFC-MS/MS)手性分离烟草中甲霜灵的差异。烟草样品经乙腈提取、盐析分层、快速滤过型净化(multi-Plug Filtration Cleanup,m-PFC)柱净化后,分别采用RPLC-MS/MS和SFC-MS/MS进行手性分离。从多个性能参数(分离效率、线性、选择性、回收率、重复性、灵敏度、基质效应等)对两种方法进行了全面比较。采用不同的分离方法,在10~500 ng/mL范围内,甲霜灵的不同异构体均可呈现良好的线性关系(R^(2)≥0.9993)。在各异构体加标浓度为0.1、0.5、2.0 mg/kg水平下,采用不同的分离方法均可获得满意的回收率(88.7%~96.2%)和良好的重复性(RSD<7.0%)。结果表明:RPLC-MS/MS和SFC-MS/MS具有互补性,均适用于手性分离和测定烟草基质中的甲霜灵。

油液多层过滤去固分离及特性分析

针对油-固体系中单层滤网无法同时满足过滤精度高与使用寿命长的问题,采用多层过滤器并对其去固分离特性展开分析。通过耦合流场控制方程、颗粒运动方程、颗粒-壁面碰撞模型方程,建立了适用油-固体系的多层过滤数值分析模型,探究了油-固体系中多层过滤器的去固分离特性,分析了入口流速和滤网层数对流场特性及过滤比(β)的影响。结果表明:多层过滤器可有效过滤孔径与粒径比(k_(d))大于15的固体颗粒;增加滤网层数,d_(5)和d_(20)(β分别为5和20时对应的颗粒粒径)显著降低;增大入口流速,d_(5)和d_(20)变化较小;当β<5时,颗粒粒径的变化对过滤比的影响较小;当β>5时,颗粒粒径的小幅增大可能导致过滤比显著提高。

聚醚砜基过滤膜制备与应用研究进展

为了探究聚醚砜作为有机膜材料的性能及应用潜力,总结了聚醚砜基过滤膜的制备工艺及应用情况。介绍了聚醚砜材料的特点和性能,分析了聚醚砜过滤膜各类制备方法的优缺点,包括相转化法、静电纺丝法和涂覆法,总结了聚醚砜基过滤膜在生物医用领域、水处理领域、电池领域及其他领域应用进展。认为:尽管已有研究表明聚醚砜基过滤膜制备方法多元、应用领域广泛,但高功能化、高性能化方面仍是聚醚砜过滤膜研究和产业化发展需要攻克的重点。

高通量-高截留率时间维度膜法水处理机理研究

传统固液两相流膜分离技术利用尺寸效应易受到渗透性-选择性权衡的制约、膜污染与浓差极化等挑战。通过引入旋转剪切动态膜技术与施加固液滑移边界条件,利用膜表面颗粒径向穿透膜孔的时间大于切向划过孔径的时间——时间维度选择性,可有效同步提升渗透性和选择性。通过建立滑移边界旋转剪切动态膜过滤模型,对稀悬浮液微滤过程进行有限元模拟仿真,并结合理论分析揭示了滑移速度、膜厚度与孔隙率等关键参数对膜分离性能的影响规律。结果表明,对于比颗粒直径大1~10倍的膜孔径,在时间维度选择性与流体剪切诱导颗粒迁移的协同作用下,可获取95%以上的微颗粒截留率和350 L(/m^(2)·h)以上的有效水通量。该研究结果进一步验证并拓展了时间维度选择性机理在微米尺度的适用性,并为高通量-高截留率动态膜法水处理技术提供了新思路。

熔喷非织造材料制备及其应用研究进展

为了解熔喷非织造材料在制造工艺、结构设计和应用等方面的研究进展,文章介绍了聚乳酸、聚丙烯等常用高聚物原料的特性,分析了以其为原料所制备熔喷非织造材料的性能特点,总结了熔喷非织造材料在空气过滤、液体过滤、医用抗菌、智能电子纺织品等领域的应用现状,提出了未来熔喷非织造材料的发展方向,以期为熔喷非织造材料的研究提供一定参考,拓展熔喷非织造材料应用领域。