The Effect of Particle Sedimentation on Gravity Filtration

ABSTRACT

Simulation of cake formation of mono-sized and dual-sized particles under gravitational sedimentation and filtration is presented. The dynamic analysis proposed by Lu and Hwang in 1993 is applied to examine the local cake properties formed under a falling head by considering the hindered settling effect of particles in the slurry and the variation of the pressure drop across the filter septum. Results of this study show that, at a given position in a cake, the solid compressive pressure reaches a maximum value and then decreases for a gravity filtration due to the decrease in the driving head. A cake constructed with dual-sized particles has a more compact structure than does one with mono-sized particles, and larger particles will form looser packing than will smaller ones for mono-sized particles. A dual-dispersed suspension with a lower fraction of large particles will result in the lowest cake porosity and the highest specific filtration resistance of cake. Comparison of the porosity distribution in filter cake formed by means of gravity filtration and constant head filtration shows that the porosity near the filter septum of gravity filtration has a convex behavior while that of constant head filtration has a tendency toward concavity. This discrepancy is mainly due to the change in the driving head during the filtration process. Both theoretical and experimental results show that the uniformity of particle size distributions in the filter cake will be much better when the relative settling velocity between large and fine particles is reduced.     

磷酸一铵料浆固液分离特性研究

研究了磷酸-铵(MAP)再溶解除杂生产工业级磷铵。把肥料级MAP溶解在水中,加入化学药剂使磷铵中的杂质结晶沉淀并进行溶液的澄清分离,但生成的颗粒细小,溶液黏稠,极难分离。针对这一难题,采用粉状MAP配成浓度为20％的料浆,在20℃,65℃,90℃对其重力沉降特性、离心沉降特性及微孔膜过滤特性进行了实验研究。结果表明,温度对其分离特性有较大影响,温度越高,溶液越易分离。     

纤维过滤介质过滤压力损失理论计算

为便于计算纤维过滤介质过滤压力损失,对目前各种纤维过滤介质过滤压力损失理论计算公式及半经验公式进行分析计算,将理论计算结果与实验测试结果进行对比分析发现各种理论计算结果普遍相偏大,需要对纤维的非均匀分布进行修正,修正后的大部分计算结果与实验结果基本吻合,同时对理论计算公式的鲁棒性进行了分析。计算结果准确性和鲁棒性兼顾的理论计算公式,较适宜于实际过滤材料压力损失的预测。     

聚丙烯酰胺对赤泥沉降和过滤的影响

研究了阴离子型、阳离子型和非离子型聚丙烯酰胺对赤泥沉降和过滤的影响。结果表明 :三种型式的聚丙烯酰胺均可作为赤泥的沉降助剂 ,但阴离子和非离子型不宜用作赤泥的过滤助剂 ,阳离子型则在赤泥的过滤过程中表现出了一定的助滤作用。     

Effects of Particle Packing Characteristics on Solid-State Sintering

Alumina compacts fabricated with different green densities and different pore size distributions were characterized and the changes of the pore characteristics during solid-state sintering were studied. A critical ratio of pore size to mean particle size for pore shrinkage was determined. Porosity in the compact could be classified into two classes: the first class contains pores smaller than the critical ratio, and the second class contains pores larger than the critical ratio. Pores belonging to a different class of porosity behaved differently during sintering. Pores larger than the critical ratio were not totally eliminated during sintering. The first class of porosity controlled the ultimate sintering shrinkage, and the second class of porosity controlled the final sintered density.     

Packing and Sintering of Two-Dimensional Structures Made fro Bimodal Particle Size Distributions

Binary mixtures of spheres were used to prepare a variety of two-dimensional structures ranging from ordered to disordered. The extent of particle order was influenced by the size ratio and the concentration of the bimodal constituents. If either the sizes or the concentrations were very different, the structures became phase separated into ordered regions of small spheres and ordered regions of large spheres. Disordered structures were produced when particles were present in equal concentrations and when sizes differed by about 30%. The sintering behavior of these two-dimensional structures was also examined. The domain boundaries in the ordered samples were found to develop into cracks during sintering if the domain size was large. In contrast the disordered structures sintered homogeneously, without the formation of large processing defects.     

过滤方式及压力对速率影响的研究

介绍了相关过滤方式的优缺点,自主建立了过滤实验流程,设计出相应的膜滤器,通过实验,研究了横向终端过滤、竖向终端过滤、横向错流过滤和竖向错流过滤及过滤压力对过滤速率的影响等。结果表明:采用竖向流动错流过滤方式膜过滤速率大于其它方式的过滤速率,衰减最为缓慢,且一段时间后,速率趋于一定值;压力增大可以提高竖向流动错流过滤速率,但也加快了膜污染,使膜速率衰减加快。     

Colloidal Filtration and (Simultaneous) Sedimentation of Alumina and Silica Suspensions: Influence of Aggregates

Colloidal filtration and (simultaneous) sedimentation is studied for suspensions of alumina particles and monodisperse silica spheres. A comparison is made between stable suspensions and systems which are aggregated due to salt addition (silica) or absence of a deflocculant (alumina). From separate sedimentation experiments we conclude that the stable silica settles as an ordered particle array, that the unstable silica sediments as separate aggregates, and that aggregated aluina behaves as a densifying network. The filtration results show that settling of aggregates during filtration changes the filtration kinetics in accordance with our model for simultaneous filtration and sedimentation. Further, aggregates in suspension are shown to have little influence on the silica compact microstructure, whereas they clearly increase porosity and permeability of the alumina compact. We also find that for all suspensions porosities of compacts prepared by sedimentation are clearly larger then porosities of filter compacts.     

规整填料层压降的计算及与散装填料的比较

根据文献[6]导出的规整填料层压降关联式,由实验数据计算出9种规整填料本文关联式的压降常数,用空气-水物系和非水物系的实验数据进行了验证,并与Billet关联式计算值和实验值进行了比较;对规整填料层与散装填料的泛点和压降进行了比较。结果表明:该关联式与实验数据吻合较好,压降计算误差在±15％;规整填料力学性能优于散装填料。     

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。     

脉动压力诱导保压过程中的模腔压力响应

利用自行研制的脉动压力诱导注塑成型装置成功地将脉动变化的压力引入到塑料注塑成型的保压过程中。在该装置上用低密度聚乙烯进行实验,结果表明:保压过程中模腔压力、模腔压力差随保压时间脉动变化,模腔压力差周期性的变化并出现负压,脉动的变化有利于提高保压补缩效果,提高了制品质量。     

液力过滤与液力压密脱水的理论(一)

将滤室固定不变的板框或箱式压滤机的操作过程分成滤饼过滤阶段和液力压密脱水阶段两个过程来研究。在滤饼过滤阶段 ,应用表面过滤机理 ,采用传统的鲁思过滤基本方程和平均过滤比阻的理论进行研究。在液力压密脱水阶段 ,应用达西定律建立了液力压密基本微分方程 ,根据研究得出滤饼渗透系数与孔隙率在压密脱水阶段的线性取代关系的结论 ;滤室固定的限制条件和物料平衡条件 ,推导出液力压密的脱水方程式。分析了影响液力压密脱水的时间因素和液力压密速率的各操作参数。建立了完整的液力过滤和压密脱水理论 ,为自动压滤机的设计提供了理论指导     

液力过滤与液力压密脱水的理论(Ⅱ)

将滤室固定不变的板框或箱式压滤机的操作过程分成滤饼过滤阶段和液力压密脱水阶段两个过程来研究。在滤饼过滤阶段 ,应用表面过滤机理 ,采用传统的鲁思过滤基本方程和平均过滤比阻的理论进行研究。在液力压密脱水阶段 ,应用达西定律建立了液力压密基本微分方程 ,根据研究得出滤饼渗透系数与孔隙率在压密脱水阶段的线性取代关系的结论 ;滤室固定的限制条件和物料平衡条件 ,推导出液力压密的脱水方程式。分析了影响液力压密脱水的时间因素和液力压密速率的各操作参数。建立了完整的液力过滤和压密脱水理论 ,为自动压滤机的设计提供了理论指导     

结构陶瓷部件的压滤成型工艺

本文简要介绍了结构陶瓷部件的压滤成型工艺原理，浆料体系及性能、成型压力参数、模型材料及模型结构和坯体干燥等，讨论了影响压滤成型及成型体均匀性的一些因素，并介绍了一种提高压滤成型坯体均匀性的同步超声波辅助压滤成型。     

基于质量的注塑保压过程建模方法研究：最优保压压力曲线设定

质量控制是注塑过程控制研究的重要内容，而保压过程是决定最终制品质量的一个重要阶段。在大量实验结果的基础上探讨了最优保压压力曲线的设定。实验结果表明，递减型线性保压压力曲线有利于减小模腔压力差和制品粗糙度，而递增型保压曲线则可能加大制品粗糙度。另外，阶跃型保压曲线与线性保压曲线相比，没有任何质量优势，还可能造成熔体倒流。     

氧化精矿压滤脱水实践

介绍了一种氧化精矿压滤脱水方法 ,能使氧化精矿压滤脱水水份低 ,产量大 ,效率高。     

恒压操作下深层过滤阻力模型的研究

分析了流体在深层滤床中所受的阻力,从经典的达西公式和科泽尼——卡曼方程着手,推导出清洁滤层的过滤阻力及过滤速度表达式,在此基础上结合深层过滤物理模型,引入微元概念,得到恒压操作下截污滤层的过滤阻力和过滤速度数学模型,明确了过滤阻力随各种参数的变化关系,对恒压操作深层过滤的应用有指导意义。     

一种凹凸棒石粘土的高压过滤与分析

凹凸棒黏土其集合体呈土状、致密块体构造,土质细腻,有油脂滑感,比重轻,性脆,电化学性能稳定,由于具有较大的比表面积,使其具有较强的吸附作用。在相当低的浓度下可以形成高粘度的悬浮液,被广泛用于食品行业的脱色剂、干燥剂。凹凸棒黏土矿浆在过滤工艺过程中存在着水分较难过滤,含水率大的问题。影响选矿后续工序。根据其本身固有特性及广泛的应用前景,我们制定并分析了几种由入料压力、挤压压力等工艺来降低凹凸棒黏土水分的过滤方案     

维纶生产中凝胶粒子过滤的研究

纺丝原液中的凝胶粒子不仅影响喷丝头换头率,而且严重影响成品纤维的质量指标。而目前的熔体过滤器只是对所有的杂质进行过滤,并没有考虑针对凝胶粒子自身的特点进行过滤方法的改进与设计。通过分析凝胶粒子的性质、分类、形成机理、主要停留位置以及压差与停留时间对凝胶粒子过滤的影响,提出了凝胶粒子过滤的合理化建议。     

波纹填料层压降的新关联

导出了计算波纹填料层压降的半经验关联式,在包括泛点气速的多种气速下关联式对于波纹填料层压降的计算值与实验数据吻合较好,计算准确性优于文献公式。