PARTICULATE MOTION AND CONCENTRATION FIELDS IN CENTRIFUGAL SLURRY PUMPS

ABSTRACT

Erosion wear of centrifugal slurry pumps is primarily governed by the particulate motion and concentration as well as their physical properties. This paper presents a quasi-3D approach to predict particulate phase motion and concentration in an arbitrary radial section of a centrifugal slurry pump. A brief discussion of the fully developed turbulent flow solution of the carrier fluid is followed by a computation of the particulate phase velocity resulting from a force balance between the pressure, gravity, viscous and inertial effects. The concentration distribution is obtained by invoking the convection-diffusion equation. The governing partial differential equation is cast into a weak Galerkin finite element form. The system of algebraic equations is solved by a Newton-Raphson scheme via a frontal solver. An iterative solution scheme is employed to alternate between the fields of particle motion and concentration. Numerical solutions are examined in light of their applicability to the solution of the pump wear problem.     

PARTICULATE MOTION AND CONCENTRATION FIELDS IN CENTRIFUGAL SLURRY PUMPS

Erosion wear of centrifugal slurry pumps is primarily governed by the particulate motion and concentration as well as their physical properties. This paper presents a quasi-3D approach to predict particulate phase motion and concentration in an arbitrary radial section of a centrifugal slurry pump. A brief discussion of the fully developed turbulent flow solution of the carrier fluid is followed by a computation of the particulate phase velocity resulting from a force balance between the pressure, gravity, viscous and inertial effects. The concentration distribution is obtained by invoking the convection-diffusion equation. The governing partial differential equation is cast into a weak Galerkin finite element form. The system of algebraic equations is solved by a Newton-Raphson scheme via a frontal solver. An iterative solution scheme is employed to alternate between the fields of particle motion and concentration. Numerical solutions are examined in light of their applicability to the solution of the pump wear problem.     

颗粒增强复合材料中的界面层

本文对氧化铝(Al₂O₃)、氟化钙(CaF₂)和玻璃微珠颗粒填充环氧基(E51环氧—胺固化体系)复合材料的密度和动态力学性能进行了研究。结果发现由于颗粒填料表面和环氧基体的相互作用,从填料表面开始形成了一层致密的聚合物界面层。它的性质与本体树脂有明显的差别。把填充复合材料看成由填料、界面层和树脂本体组成的三元体系,从“临界填料含量”概念出发,求得了界面层的密度,界面层的厚度和界面层的体积分数。     

PARTICULATE MATTER EXPOSURES TO COMMUTERS IN HONG KONG

ABSTRACT

Measurements of panicle number concentrations in different vehicles (tram, Mass Transit Railway, and air-conditioned and non air-conditioned franchisee) buses) were carried out from July 1 to November 1, 1994, in Hong Kong. A total of 320 samples in 14 days were collected for four count median diameters (0.3, 0,5, 5.0, and 10.0 um). The total particle number concentrations of airborne paniculate matter exposed to commuters varied from 3.61E6 to 7.68E7 ft for particle diameter 0.3 um or greater. The concentrations were much higher, from 4 to 16 times, than those (8.02E5 to 4.60E6 ft ) in rural areas (at the seaside near Hong Kong University of Science Technology), but the concentrations in non air-conditioned transportation (trams and franchised buses) were closer to those in the streets. It was found that the number concentrations of fine particles (0.3 to 5 mm) were relatively constant, and the fine particles could not be filtered by the air-conditioners used.     

PARTICULATE MATTER EXPOSURES TO COMMUTERS IN HONG KONG

Measurements of panicle number concentrations in different vehicles (tram, Mass Transit Railway, and air-conditioned and non air-conditioned franchisee) buses) were carried out from July 1 to November 1, 1994, in Hong Kong. A total of 320 samples in 14 days were collected for four count median diameters (0.3, 0,5, 5.0, and 10.0 um). The total particle number concentrations of airborne paniculate matter exposed to commuters varied from 3.61E6 to 7.68E7 ft for particle diameter 0.3 um or greater. The concentrations were much higher, from 4 to 16 times, than those (8.02E5 to 4.60E6 ft ) in rural areas (at the seaside near Hong Kong University of Science Technology), but the concentrations in non air-conditioned transportation (trams and franchised buses) were closer to those in the streets. It was found that the number concentrations of fine particles (0.3 to 5 mm) were relatively constant, and the fine particles could not be filtered by the air-conditioners used.     

汽车发动机缸体材料质量分析

在加工不同厂家生产的同型号汽车发动机缸体过程中发现刀具使用寿命相差较大。对两种缸体的分析对比结果表明,两种缸体的化学成分和硬度指标无明显差别,都符合标准规定的要求。不同的是加工性能好的一种缸体在铸造时采用了添加锆的孕育剂,从而使得铸件的夹杂物颗粒和珠光体的片间距细化,导致铸件切削性能明显改善。     

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.     

SIMULATION OF FLUX DECLINE DUE TO PARTICULATE FOULING IN ULTRAFILTRATION

The flux decline in thin-channel and tubular ultrafiltration (UF) modules due to fouling by dilute suspensions is presented for a wide range of operating conditions. The dynamics of fouling is simplified by viewing the particle deposition on the membrane surface at discrete time as a steady state event and formulating the problem as an infinite series of successive events. Only inertial effects are considered and it is assumed that for a dilute system, particle-particle interactions and forces of interaction between particles and membrane walls are insignificant. Further, at such low concentration, the motion of fluid and particle may be taken independent of each other. The equations of motion for the particles are solved by Fourthorder Runge-Kutta method, where the fluid flow is obtained from the finite difference solution of Navier-Stokes equation. The present theoretical calculations of flux decline due to particulate fouling at typical UF operating conditions indicate that the inertial effects are important and under positive wall permeation flux conditions, particles are encouraged to migrate to the membrane walls.     

汽车转向机构的滑动轴套破裂分析

采用宏观观察、硬度分析与金相检验等方法对汽车转向机构的滑动轴套破裂失效原因进行了分析。结果表明：滑动轴套热处理工艺不合理导致硬度差异悬殊及材料内部存在微裂纹等缺陷,从而降低了滑动轴套承受冲击载荷的能力,且在使用过程中又保养不善,锈蚀严重,这些是转向机构发生故障的主要原因。     

新型氧敏薄膜材料

采用溶胶-凝胶工艺制备了用于汽车新型传感器的氧敏薄膜材料、包括过渡金属氧化物（MoOx、TiOx、CrOx）、钙钛矿型（SrTiO3/LaNiO3、LaNiO3、LaCrO3）和类钙钛矿型（La1-xMxNiO4）纳米粒子薄膜。结果表明,与传统氧传感器用的ZrO2、TiO2半导体材料相比,这三类材料的阻温系数小,敏感度高,响应速度快。     

THE USE OF FACTOR ANALYSIS IN SOURCE DETERMINATION OF PARTICULATE EMISSIONS

The development of multivariate statistical approaches to receptor models have focussed on factor analysis. Target transformation factor analysis (TTFA) offers the possibility of determining the number of sources and their elemental composition as well as their mass contributions. In this current work, a new approach is presented for calculating the mass contributions of each source to each sample. In addition an approach to estimating the uncertainties in the analysis is introduced. The method is applied to a subset of the Regional Air Pollution Study (RAPS) particulate composition data set for site 203 in July and August 1976. The data is divided into subsets covering the daylight (6 AM to 6 PM) or night (6 PM to 6 AM) samples. Similar source profiles are obtained for these subsets.     

STRESS CONCENTRATION FACTOR FORMULAE WIDELY USED IN JAPAN

Abstract— This report presents a brief outline of three papers on stress concentration factor formulae, which have been frequently referred to in Japanese technical literature. Most well known is a book entitled "Stress Concentration" [1] while Refs [2,3] have often been quoted for cases of fillet joints. The stress concentration factor covered in this report is the so-called theoretical, elastic stress concentration factor. A discussion on plastic stress concentration factors is not in the scope of this report.     

GROWTH OF FATIGUE CRACKS EMANATING FROM NOTCHES IN SiC PARTICULATE ALUMINUM COMPOSITE

Abstract— The initiation and growth of cracks emanating from blunt notches in 6061-Al alloy reinforced with 25% particulate Sic metal matrix composite were investigated. To elucidate the role of aging condition of the matrix on the fatigue behavior, the studies were carried out at T6 and overaged conditions. The results show that the number of cycles required for initiation of fatigue cracks are not influenced with the notch severity and the aging condition of the matrix. The overaging heat treatment resulted in slower fatigue crack growth rates. The failure of the Sic particles during the fatigue process is given as the reason for the both observed initiation and crack growth characteristics. It is also shown that the growth rate of cracks emanating from blunt notches can be accurately described by an equivalent stress intensity factor range Δ K _eq. This could provide an adequate engineering method for design against fatigue failure from various stress concentrations for this composite system.     

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

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.     

汽车用热镀锌钢板镀层的性能综述

对汽车用热镀锌钢板镀层的耐腐蚀性、成型性、焊接性和涂装性等几个重要的性能进行了介绍,同时介绍了国内外对汽车用热镀锌钢板镀层性能研究的最新进展。展望了对这些性能研究的新的方法与方向。     

DUST STRANDS IN CYCLONE SEPARATORS AT LOW DUST CONCENTRATION

State of the art in calculating a cyclone separator is the application of the equilibrium theory and taking the formation of dust strands into account as well. The latter process does not depend on particle size mainly. An ideal flow pattern for the formation of dust strands is the so called Dean-vortex: it is being realized favorably in the axial flow cyclone. A dust strand can be produced down to a raw gas concentration C₀ ≈ 10^-5. Then, it is being exhausted through one or few holes in the mantle of the axial cyclone applying bleeding of about 10 % of the volume flow Separating its dust in a bin cyclone and recirculating the binflow gas to the main, axial cyclone completes this high performance cyclone separator. Dimensional analysis shows that the clean gas concentration c₁ mainly depends on the swirl W_tan/w_ax, the raw gas concentration c₀and on Reynolds number. For usual dust conditions a clean gas concentration c₁ ≤ 50 mg/m³ is feasible.     

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.