一种纳米颗粒粒度分布的非接触测量方法

研究了基于高频宽带超声衰减谱非接触式方法测量纳米颗粒悬浊液中颗粒相粒度分布问题. 通过理论分析和数值计算,选择ECAH模型作为反演计算的理论模型. 以1%(j)的纳米银水悬浊液作为实验样品,采用标称中心频率为50 MHz的超声换能器和变声程脉冲回波法进行了非接触测量,获得了可利用的高频宽带(10~50 MHz)超声衰减谱,结合理论模型和最优正则化算法反演出纳米颗粒的粒度分布. 实验结果与透射电子显微镜法和高速离心沉降法的测定结果吻合较好,表明该方法可测量悬浊液中纳米颗粒粒度分布.     

水力旋流器内固体颗粒的沉降

水力旋流器内固体颗粒的离心沉降是一种复杂的两相流行为。从分析固液体系的相互作用，分别讨论了颗粒的自由沉降、干涉沉降问题，提出了高浓度下水力旋流器内颗粒之间的几种碰撞模式，阐述了旋流器内颗粒沉降的特殊性及其与使流器工作和旋流器结构间的可能联系，并指出了离心沉降本身有待深入研究的若干问题。     

关于沉降分离问题的计算方法

对于沉降分离的计算,本文提出了一种利用无因次数群(计算因子Q_u和Q_d)进行计算的方法,该法能简捷算出微粒在重力沉降或离心沉降两种情况下的沉降速度和沉降粒子的临界直径,避免了试差法的繁琐运算。它适用于非均一系的分离、流态化和借流体的流动输送固体颗粒作业等的计算。     

金属化凝胶推进剂沉降稳定性预测方法研究

为快速评价金属化凝胶推进剂中含能颗粒沉降稳定性,借助基于黏性流体中颗粒沉降规律理论基础的进一步推导,得到2种预测含能颗粒在凝胶推进剂体系中沉降的方法——流变性能预测法和离心加速预测法,并采用特定配方的金属化甲基肼凝胶推进剂进行实验验证。结果表明:与自然环境放置光扫描法得到样品发生沉降的时间(28 d)相比,流变性能预估法得出的时间(31.4 d)与实际值较接近,离心加速预测法得出的时间(51.1 d)与实际值误差较大。在黏性流体中颗粒沉降稳定性预测方面,流变性能预测法比离心加速预估法更适合于金属化凝胶推进剂体系。     

酸及磁化处理对污泥沉降与脱水性能影响研究

研究酸处理及磁化对污水处理厂活性污泥沉降性能的影响。通过对不同pH值下污泥沉降性能曲线的分析、微观照片的观察、离心脱水性能的考察,得出pH值为4时污泥沉降性能最佳、2000r/min下10min的离心效果最好;比较两组不同MLSS污泥在不同磁感应强度、不同磁场位型下污泥沉降曲线和磁化前后的颗粒微观照片,得出磁场的确能够改善污泥的沉降性能。     

旋风分离器的选型计算

旋风分离器是指采用离心沉降的原理对气流中所含固体颗粒或液滴进行分离的设备,工业中一般采用标准旋风分离器的结构比例参数进行旋风分离器的设计,通过实际项目中选用的旋风分离器的具体数据,总结出进行旋风分离器选型计算所需要的参数、所采用的具体计算方法和步骤。     

高频宽带超声衰减谱表征纳米颗粒粒度的方法

为研究纳米颗粒粒度的表征,在"长波长"条件下,通过提高超声波频率、增加频带宽度以及提高纳米颗粒悬浊液中超声波检测的稳定性等技术手段,实现了纳米级颗粒粒度分布的准确测量。实验中,采用中心频率50MHz宽频超声换能器,通过缓冲块内一次回波校验和变声程方法,以体积分数0.5%的纳米银-水悬浊液为验证性测量对象,获得了频率为25～62MHz的宽带声衰减谱。粒度反演过程中,采用McClementsBLBL理论模型结合最优正则化算法,将实测声衰减谱进行反演计算获得了纳米银颗粒的粒度分布,并证实了在50MHz频率下的理论测量下限可以达到5nm。与CPS离心沉降纳米颗粒测量仪、TEM图像等结果相比较,表明超声衰减谱法测量纳米颗粒的结果是可信的。     

用诺模图确定固-液系统的沉降速度

本文介绍的诺模图以经验公式为基础,用于单一颗粒和多颗粒系统,可避免在求算沉降速度时的复杂计算。对于单一颗粒和多颗粒系统,计算固体颗粒在液体介质中沉降速率的方法有许多种。此类计算具有多种应用,其中包括估算沉降槽的大小及确定流化床中颗粒的最低沉降速度。     

题录

lO.11.12.13.浓缩槽用超高速造粒沉降装置(日)产业机械、1985.4.P23—25卧式压滤机 。(日)产业机械 1985.4.P20～22离心浓缩机(日)产业机械1985.4.P14一16用膜分离没备过滤含少量带胶颗粒的悬浮物料 .(英)FiL.tration anb Separation 1985.1.P58—60分散和沉降作业所用的回水过     

聚乙烯悬浮液离心沉降分离能力的计算与评价

结合聚乙烯装置增产改造，对聚乙烯悬浮液螺沉降离心能力进行了计算和评价。确定出离心机的最大生产能力。计算结果与生产实际相符，现有螺旋沉降离心机能够满足增产的要求。     

Effect of Interparticle Potentials and Sedimentation on Particle Packing Density of Bimodal Particle Distributions During Pressure Filtration

Effect of interparticle forces, bimodal particle size distribution, and slurry viscosity on particle packing in alumina bodies consolidated by pressure filtration is presented. The requirements for packing colloidal particles to their highest density are strong repulsive interparticle forces and optimum particle size distribution. Even though these conditions are met, the high packing density in consolidated bodies may be adversely affected by particle segregation resulting from sedimentation. Therefore, the slurry during consolidation must have a sufficiently high viscosity to prevent sedimentation.     

The influence of precipitated asphaltenes on sedimentation of particles in coal liquids

Antisolvent addition to coal liquids causes the precipitation of asphaltenes on mineral particles and increases their sedimentation rate. This paper develops a mathematical model of the sedimentation rate of a single particle or agglomerate of particles. It was found that if the difference in density between the solid and the precipitate is more than twice the difference in density between the precipite and the liquid, the sedimentation rate would decrease initially upon precipitation. A simple experiment was performed to confirm the prediction. Further it was found that the agglomeration of particles had a stronger effect upon the sedimentation than the changes in particle size.     

等温条件下球形颗粒沉降的轨迹特性

采用粒子图像测速仪研究了球形颗粒在重力作用下沉降的流场特性,研究了同一雷诺数(Re)下不同释放位置、同一释放位置不同Re下的颗粒沉降的规律. 结果表明,Re≤100时,同一Re下不同释放位置,颗粒最终稳定沉降位置均在中心处. 颗粒的释放位置沿中心线对称时,颗粒沉降的轨迹线沿中心位置对称;同一释放位置不同Re下,随Re增加,颗粒最终沉降轨迹由稳定的直线下降变为稳定的周期性摆动下降.颗粒的平衡位置与颗粒的初始释放位置及Re无关,但颗粒沉降的轨迹形状与释放位置及Re有关. 模拟结果与实验结果几乎一致.     

Determination of Dispersion in Anisotropic Mica and Wollastonite Particles Using the Layer Sedimentation Method

The results of studying the dispersion composition of muscovite mica and wollastonite, whose particle shape is significantly anisometric, are described. A simple method for sedimentation analysis is proposed, which makes it possible quickly and with great accuracy to determine the particle distribution based on their sedimentation diameters. Relationships are obtained which can be used to estimate the geometrical sizes of particles for the considered materials.     

Drying regime maps for particulate coatings

Key microstructural properties of particulate coatings such as porosity and particle order are established during drying. Therefore, understanding the evolution of particulate distributions during drying is useful for designing coating properties. Here, a 1D model is proposed for the particle distribution through the coating thickness at different drying times and conditions, including Brownian diffusion, sedimentation, and evaporation. Effects of particle concentration on diffusion and sedimentation rates are included. Results are condensed onto a drying regime map which predicts the presence of particle surface accumulation or sediment based on two dimensionless numbers: the Peclet number and the sedimentation number. Cryogenic scanning electron microscopy (cryoSEM) is used to image the transient particulate distributions during the drying of a model system comprised of monodisperse silica particles in water. Particle size and evaporation rates are altered to access various domains of the drying map. There is good agreement between cryoSEM observations and model predictions. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

A new method for the control of dilute suspension sedimentation by horizontal movement

This research addresses some factors that control the stability of dilute suspensions in sedimentation processes under a dynamic environment. Experimental and numerical studies were conducted about the sedimentation velocity control of dilute suspensions by horizontal movement for particle concentrations up to 8 wt.%. Nearly monodispersed particles were used as test particles. The effects of horizontal movement speed and amplitude on particle sedimentation process were investigated. Under stationary conditions, particles settle in only one vertical direction because of gravitational force. However, complicated particle motions arise under moving conditions due to circulation flow in horizontal moving conditions. The results show that horizontal movement can reduce the particle settling velocity or maintain the stability of the suspension.     

离心沉降法粒度分析──固液分离设备选型依据之一

应用离心沉降粒度分析仪进行粒度分析时，准确、合理地选择沉降介质及圆盘转速等测试条件是获得正确测试结果的关键。粒度分析结果为固液分离设备及分离介质的选型提供了依据。     

The Sedimentation of Bimodal Distributions of Unflocculated Microspheres

Abstract

An improved analysis for sedimentation of binary mixtures (two particle sizes) is proposed and tested with data that include differences in both the particle sizes and densities and sedimentation in both the viscous region and the transitions region, between viscous and turbulent (inertial flow). The new analysis can be used for any ratio of particle sizes even when the particle sizes are relatively close. It has been successfully tested beyond the viscous region and with variations in particle density as well as particle size. Although one previous analysis has been successful in predicting most earlier binary data with particles of different size, the new analysis is believed to be better supported by physical principles and thus more reliably extrapolated to different conditions.     

EFFECTS OF INTERPARTICLE INTERACTIONS ON STABILITY, AGGREGATION AND SEDIMENTATION IN COLLOIDAL SUSPENSIONS

Relations between interparticle effective interactions, structure formation, stability and sedimentation for a colloidal system are presented in this paper. For a binary mixture of large and small particles, the potential of the mean forces between large particles is obtained from the Ornstein-Zernike equation. We incorporated the small particles in our numerical simulations by using this potential of the mean force as the interparticle effective interaction. Our numerical results reveal the phenomenon of strong particle aggregation due to the attractive depletion force exerted by small particles. In the absence of the effect of gravity, this aggregation can result in flocculation and the formation of particle clusters thereby forming “void” structures, while under the influence of gravity, the aggregation can greatly affect the sedimentation rates. An analytical expression relating the aggregation number to the sedimentation velocity is presented. Our sedimentation experiments with a bidisperse latex suspension as well as clay particle dispersions show both the destabilizing and stabilizing effects of small particles, which are in qualitative agreement with our theoretical predictions.     

Large-scale calculation of hydrodynamic transport properties for random suspensions of hard-sphere particles

A numerical method based on fast multipole summation scheme is used to calculate hydrodynamic interactions in random suspensions of non-colloidal hard-sphere particles. The calculation is carried out for suspensions of 1,024 particles randomly placed in periodic unit cell to determine hydrodynamic transport properties such as permeability of a viscous flow through porous medium, effective viscosity of suspension, and sedimentation velocity of the suspended particles. The particle volume fraction ø ranges from 0.01 to 0.25. Effect of particle number N on the transport properties was examined through the numerical calculations with N=64-1,024. It is shown that sedimentation velocity increases with N approaching an estimate for infinite N, and the finite N effect is negligible in effective viscosity and permeability problems. The present scheme is quite useful for obtaining a statistically-averaged quantity for random suspensions. As an example, ensemble-averaged velocity when position of one particle is fixed is numerically obtained in sedimentation problem. The numerical results are shown to be in excellent agreement with theoretical prediction.