A NOVEL QUICK-CLOSING PROBE FOR MEASURING LOCAL PARTICULATE PHASE DENSITY IN GAS-PARTICLE SUSPENSIONS

ABSTRACT

An innovative quick-closing probe system was designed, built, and tested for measuring the local particulate phase density of gas-particle suspensions. Experiments with glass beads and powder coals were conducted in a horizontal channel with an aspect ratio of 11 to 1, and also in a 0·25 m I.D. bench-scale vortex chamber. Results of particle density distributions in these two systems indicated the ability of the probe to perform in highly turbulent, swirling, dilute and intermediate phase gas-particle suspension flows. The probe was connected with a microcomputer-assisted particle weighing system for data collection and reduction. Comparison of measured data by this probe with calculated results was assessed. Since this probe requires no calibration curve nor empirical equation, it serves as a primary standard for particle density measurements. The design features, working principle, component characteristics, overall performance, and test results are discussed in this paper.     

AN ELECTROSTATIC INDUCTION PROBE FOR MEASURING PARTICLE VELOCITY IN SUSPENSION FLOW

A probe for measuring particle velocity in pipe flow of a gas-solid suspension has been developed. A solid particle such as a 100 µm latex particle in suspension typically carries an electrostatic charge of say 10^-13 Coulomb via charge separation by surface contacts in normal handling. The tubular cylindrical probe makes use of the principle of electrostatic induction by a charged solid particle during its passage. This probe, which is insulated from ground by a teflon sleeve, converts the induced charge to voltage signals of sharp rise as the charged particle enters and a steep dip in voltage as it departs from the cylinder. Between the entering peak and the later dip at departure, the time of flight of the particle through the probe can be accurately measured and hence the particle velocity.     

SHEAR-FLOW AND MATERIAL INSTABILITIES IN PARTICULATE SUSPENSIONS AND GRANULAR MEDIA

ABSTRACT

This article is a review of recent theoretical work on shear flow instabilities of particulate suspensions and dry granular medium. Attention is devoted largely to steady homogeneous unbounded simple shearing flows, as a generalization of the classical Kelvin problem for Newtonian fluids, with a view towards identifying material or constitutive instabilities arising from the coupling of stress to particulate concentration and temperature fields. After reviewing the most common constitutive models, a unified linear-stability treatment is given for suspensions and granular media, based on an assumed ‘short-memory’ response of stress and various fluxes to perturbations on materially steady and uniform base states. A two-dimensional stability analysis of inertialess suspension flow indicates the possibility of particle-depleted shear bands. A comprehensive three-dimensional analysis of rapid granular flow reveals transverse ‘layering and spanwise ’corrugations’ as possible modes of instability. The latter appear to result from a kind of material instability, although not the simple short-wavelength instability found for suspensions. Based on the current theoretical treatments, several new studies are recommended, including the effects of granular dilatancy and yield stress, three-dimensional disturbances in suspensions and the effects of gravity in granular now.     

SHEAR-FLOW AND MATERIAL INSTABILITIES IN PARTICULATE SUSPENSIONS AND GRANULAR MEDIA

This article is a review of recent theoretical work on shear flow instabilities of particulate suspensions and dry granular medium. Attention is devoted largely to steady homogeneous unbounded simple shearing flows, as a generalization of the classical Kelvin problem for Newtonian fluids, with a view towards identifying material or constitutive instabilities arising from the coupling of stress to particulate concentration and temperature fields. After reviewing the most common constitutive models, a unified linear-stability treatment is given for suspensions and granular media, based on an assumed 'short-memory' response of stress and various fluxes to perturbations on materially steady and uniform base states. A two-dimensional stability analysis of inertialess suspension flow indicates the possibility of particle-depleted shear bands. A comprehensive three-dimensional analysis of rapid granular flow reveals transverse 'layering and spanwise 'corrugations' as possible modes of instability. The latter appear to result from a kind of material instability, although not the simple short-wavelength instability found for suspensions. Based on the current theoretical treatments, several new studies are recommended, including the effects of granular dilatancy and yield stress, three-dimensional disturbances in suspensions and the effects of gravity in granular now.     

液氧密度标准计量装置

研制了一种液氧密度标准计量装置,介绍了其测量原理、装置流程及性能实验结果。分析了该装置的不确定度,并与国际水平进行了比较。     

MEASUREMENT OF AGGLOMERATE DENSITY IN FLOCCULATED FINE PARTICLE SUSPENSIONS

An experimental procedure has been developed for estimating agglomerate densities in flocculated suspensions. The basic technique involves simultaneous measurement of floe size and free-settling velocity in the suspending fluid. Floc density is calculated using standard expressions for free settling under the appropriate flow conditions. Experiments have been carried out using a variety of solids flocculated with commercial, polymeric flocculants. The results indicate that floc density generally decreases with increasing floc size and is limited at the smallest sizes by the density of the solid particles and at the coarsest sizes by the solids concentration in the original suspension. The experimental data have been evaluated statistically in order to establish confidence limits on the observed density-size relationships. The results are compared with previously reported experimental measurements and floc simulation studies and a simple model is proposed in which it is postulated that large flocs consist of random aggregates of relatively dense floe nuclei.     

MEASUREMENT OF AGGLOMERATE DENSITY IN FLOCCULATED FINE PARTICLE SUSPENSIONS

An experimental procedure has been developed for estimating agglomerate densities in flocculated suspensions. The basic technique involves simultaneous measurement of floe size and free-settling velocity in the suspending fluid. Floc density is calculated using standard expressions for free settling under the appropriate flow conditions. Experiments have been carried out using a variety of solids flocculated with commercial, polymeric flocculants. The results indicate that floc density generally decreases with increasing floc size and is limited at the smallest sizes by the density of the solid particles and at the coarsest sizes by the solids concentration in the original suspension. The experimental data have been evaluated statistically in order to establish confidence limits on the observed density-size relationships. The results are compared with previously reported experimental measurements and floc simulation studies and a simple model is proposed in which it is postulated that large flocs consist of random aggregates of relatively dense floe nuclei.     

测定陶瓷材料密度及其气孔率的方法

提出了利用电子天平测量陶瓷材料密度及其气孔率的方法。这种方法是利用电子天平的清零技术，可减少传统方法的实验步骤。结果表明，利用电子天平测定陶瓷材料密度及其气孔率可提高工作效率，并保证了实验的精确度。     

测量系统中的DSP的开发环境

数字信号处理器(DSP)用于实现被测量重构,成为测量系统的组成部分。本文介绍了被测量重构的意义及算法,介绍了一个测量系统中的DSP的开发环境,并对这个环境的主要部分作了说明。     

0.1 Hz～50 kHz直线振动幅值和相位国家计量基准系统的研究

描述中国计量科学院在直线振动幅值和相位测量的理论研究和技术实现方面取得的最新进展。简要介绍了国家高、中、低频振动基(副基)准幅相特性测量装置的系统构建、测量原理和技术实现,以及装置达到的主要技术指标。提出振动基(副基)准优化提升中关键的技术创新点,如自主提出了改进的外差正弦逼近法和基于波峰波谷的外差时间间隔法,在压电高频(2kHz～50kHz)振动台上,首次在国内外实现了(1nm～500nm)振幅范围内的纳米级振动传感器灵敏度幅值和相移的测量。中国计量科学研究院(NIM)与德国物理技术研究院(PTB)在10Hz～10kHz范围内开展的标准加速度计灵敏度幅相特性国际双边比对验证了国家基准的测量不确定度。     

双相不锈钢高温组织相含量的测定

采用共聚焦激光扫描显微镜原位分析和淬火热处理试验两种方法并结合Mivnt显微图像分析系统对双相不锈钢高温组织中的奥氏体相含量（体积分数,下同）进行了测定。两种方法所测定的奥氏体相含量随温度的变化趋势基本一致。与热处理试验方法相比,共聚焦激光扫描显微镜原位分析方法的效率较高、测量结果较精确。根据两种分析方法测定的结果,得出了奥氏体相含量与温度的线性回归关系式。     

自由表面对夹杂材料应力分布的影响

本文利用Eshelby 夹杂理论, 给出了定量分析自由表面对单球形夹杂材料应力分布影响的一种解析模型, 并利用所得的结果进一步讨论了自由表面对夹杂材料残余应力分布及表面裂纹形成的影响。      

弹塑性杆非线性断裂问题的新型增强有限元法

针对一维弹塑性材料杆件的非线性断裂,该文提出了一种新型弹塑性增强有限元。该单元采用von Mises屈服准则和线性等向硬化模型描述开裂前的材料弹塑性变形,而结合利用内聚力关系来描述随后的裂纹萌生和非线性断裂过程。引入内部节点来描述单元内由于裂纹引起的位移不连续,通过单元凝聚获得含裂纹单元的刚度矩阵,并对数值稳定性问题进行了分析。通过与基于材料力学方法推导得到的解析解的对比验证了该新型弹塑性增强有限单元法在列式上的正确性和在数值上的高效性与精确性。     

异质外延错向角的X射线精确测量方法

通过分析外延层与衬底之间存在错向角时的衍射圆锥，利用简明的衍射几何关系提出了一个测量外延层在衬底之间错向角的方法及相应的计算错向角的公式，同时提出了检验办法，设计了一个有两外延层的ＩｎＧａＡｓ／ＩｎＡｌＡｓ／ＩｎＰ样品，用高精度ｘ射线四晶衍射仪，对样品进行了衍射测量，并应用提出的方法精确地测出两个外延层各自与衬底之间的错向角以及两个外延层之间的错向角，所得结果和理论预期值完全一致，本文也指出，采用     

基于映射的拓扑优化最大尺寸控制方法

拓扑优化方法经过几十年的发展,已成功应用于机械工程、航空航天、电磁等领域的构型设计中。然而,由于制造工艺的限制,拓扑优化结果通常无法直接应用,需根据工艺要求进行修改,因此在拓扑优化模型中考虑制造约束成为重要的研究方向。其中,尺寸控制广泛存在于大部分制造工艺中,主要包括最小尺寸控制与最大尺寸控制。该文提出了一种基于映射的拓扑优化最大尺寸控制方法,构造了一种新的映射模型,对结构中不满足最大尺寸约束的中心单元密度进行惩罚,在不引入任何约束条件的情况下实现了对结构最大尺寸的控制。此外,该文将该方法中的惩罚转变为一个全局约束条件后与具有最小尺寸控制功能的拓扑优化鲁棒列式相结合,实现了对构件的最大最小尺寸协同控制。数值算例表明了该方法的有效性。     

纳米氧化物的合成新方法

以草酸和醋酸盐为原料,用低热固相化学反应合成出前驱配合物ＮｉＣ２Ｏ４·２Ｈ２Ｏ,ＣｕＣ２Ｏ４ 和ＺｎＣ２Ｏ４·２Ｈ２Ｏ,再分别在３５０℃,３００ ℃和４６０℃热分解２ｈ,得到纳米ＮｉＯ,ＣｕＯ和ＺｎＯ。用Ｘ－ 射线粉末衍射、透射电镜对产物的组成、大小、形貌进行表征。结果表明,纳米ＮｉＯ为球形立方晶系结构,平均粒径约为４０ｎｍ 左右;纳米ＣｕＯ为球形单斜晶系结构,平均粒径约为３０ｎｍ 左右;ＺｎＯ为粒度分布均匀的球形六角晶系结构,平均粒径约为２０ｎｍ 。     

A NEW APPROACH TO HYDRODYNAMIC INTERACTIONS IN POLYDISPERSE SUSPENSIONS

A general approach is presented for the computation of hydro dynamic interactions between spheres of disparate sizes in a polydisperse suspension of rigid spheres in a Newtonian solvent. The theory applies when the particle-based Reynolds number is small ( usually valid for colloidal suspensions ). The cornerstone of the method consists of a new class of image solutions for singularities near a rigid sphere. The new approach facilitates analytical [ see equations (12) and (13)] and numerical computations as well as physical interpretation of the velocity fields induced by the particles. The applications in particle aggregation and aerosol deposition are discussed. In addition, the solution methodology can be extended to more general situations, such as interactions between viscous drops.     

SOME NOVEL DEVELOPMENTS IN FINITE ELEMENT PROCEDURES FOR GRADIENT-DEPENDENT PLASTICITY

Improved algorithms are proposed for a gradient plasticity theory in which the Laplacian of an invariant plastic strain measure enters the yield function. Particular attention is given to the type of finite elements that can be used within the format of gradient-dependent plasticity. Assuming a weak satisfaction of the yield function, mixed finite elements are developed, in which the invariant plastic strain measure and the displacements are discretized. Two families of finite elements are developed: one in which the invariant plastic strain measure is interpolated using C¹-continuous polynomials, and one in which penalty-enhanced C⁰-continuous interpolants are used. The performance of both families of finite elements is assessed numerically in one-dimensional and two-dimensional boundary value problems. The regularizing effect of the used gradient enhancement in computations of elastoplastic solids is demonstrated, both for mesh refinement and for the directional bias of the grid lines.     

CLUSTER THEORY FOR THE CONCENTRATION DEPENDENT TRANSLATIONAL SELF-FRICTION COEFFICIENT OF ROD-LIKE MACROMOLECULES IN SUSPENSIONS

A general theory of the concentration dependence of the self-friction coefficient of rod-like macromoiecules is presented based on multiple scattering ideas.Using the Riseman-Kirkweed model for Dolvmer, exdHEit farmyls are derived by taking both the hydrodynamic and the direct potential interactions between the solute molecules into account. Ana1vtical resullts are obdantned For the leading concentration dependence of the translational self-friction coefficient under theta conditions.     

A NUMERICAL MODEL FOR THE TURBULENT FLUCTUATION AND DIFFUSION OF GAS-PARTICLE FLOWS AND ITS APPLICATION IN THE FREEBOARD OF A FLUIDIZED BED

A numerical model for the turbulent fluctuation and diffusion of gas-particle flows is presented. This model is based on the idea of treating a turbulent gas flow field as a set of k-ε equations, and of modeling the turbulent fluctuation velocity of gas flow as a random Fourier series based on the fluctuation frequency and spectrum. The particle properties (trajectory and velocity) are described by a Lagrangian approach. Hence this model is known as the fluctuation-spectrum-random-trajectory () model. Finally, particle movements in the freeboard of a fluidized bed and in a turbulent gas-particle-laden jet are analyzed to illustrate the applicability of the model.