MEASUREMENT OF PARTICLE VELOCITY IN PNEUMATIC TRANSPORT OF COAL USING CROSS-CORRELATION TECHNIQUE

ABSTRACT

Particle velocity has been determined experimentally in a solid-gas flow using the cross-correlation technique. Signals from two flow-monitoring devices, one based on the measurement of the dielectric constant of coal/air and the other based on the rate of static charge transfer technique, have been utilized to determine the cross-correlation function and hence the time delays between the signals. Other pertinent fluid dynamic parameters have been evaluated using experimentally determined particle velocities.     

PREDICTION OF PRESSURE DROP IN PNEUMATIC TRANSPORT SYSTEMS AT VARIOUS PIPE ORIENTATIONS USING AN EMPIRICAL CORRELATION FOR THE PARTICLE VELOCITY

A new empirical correlation for the particle velocity which incorporates the angle of inclination is proposed here. This correlation coupled with the expression for the solids friction factor obtained from the force balance on the particle was used to predict the pressure drops in the 0.0266 m and 0.0504 m systems held at various angles of inclination. Particles used in these systems included glass particles of 67, 450, and 900 µm weight mean diameter. The existence of minimum points in the predicted pressure drop curves as a function of gas velocity was corroborated by these two expressions.     

PREDICTION OF PRESSURE DROP IN PNEUMATIC TRANSPORT SYSTEMS AT VARIOUS PIPE ORIENTATIONS USING AN EMPIRICAL CORRELATION FOR THE PARTICLE VELOCITY

ABSTRACT

A new empirical correlation for the particle velocity which incorporates the angle of inclination is proposed here. This correlation coupled with the expression for the solids friction factor obtained from the force balance on the particle was used to predict the pressure drops in the 0.0266 m and 0.0504 m systems held at various angles of inclination. Particles used in these systems included glass particles of 67, 450, and 900 µm weight mean diameter. The existence of minimum points in the predicted pressure drop curves as a function of gas velocity was corroborated by these two expressions.     

天然混合沙运动速度特征的风洞PIV实验

采用PIV（Particle Image Velocimetry）系统测量了天然混合沙风沙两相流中沙粒的速度分布特征,得到了沙粒入射以及起跳的速度分布情况,并且分析了沙波纹对风沙运动的影响。结果表明：沙粒运动过程中的速度分布与沙粒起跳速度的分布可以应用对数正态分布来表明;当有沙波纹存在时,沙粒总体速度分布与平坦沙床面差...     

MEASUREMENT AND CONTROL OF ELECTROSTATIC CHARGES ON PULVERIZED COAL IN A PNEUMATIC PIPELINE*

Pulverized coal particles flowing in a pneumatic pipeline are naturally charged to a detectable level due to collisions with pipe walls. Systematic charge measurements of Anthracite (AN) coals, Medium Volatile Bituminous (MVB) coals and Lignite A (LIGA) coals in a grounded copper pipe have been made with an upgraded charge measuring system. The net particle charges were found to be positive, although both negative and positive charges were detected in all experiments. Effects of air humidity and conveying velocity on particle charges were examined. The mean particle charge was found in the order of 10^-12 Coulomb and the charge-to-mass ratio in the order of 10^-5 C/kg. Charge elimination techniques by strict humidity control and by introducing neutralizing charge carriers, such as minus 1 μm activated charcoal fines, ammonia, and piezoelectric ionized gas were explored. Effective reduction of 70 % to 85 % of particle charges was achieved. A charge neutralization mechanism was proposed to interpretate the measured results.     

MEASUREMENT OF PARTICLE SIZE IN THE DENSE SUSPENSION USING THE EXTINCTION METHOD

All light scattering based instrumentation should be arranged and used under condition of the absence of multiple scattering. Using the extinction method, experimental studies have been performed to investigate the effect of multiple scattering on the measurement of size. Monodisperse polystyrene latex spheres and polydisperse industrial samples are used for size measurements at different particulate concentrations. However, experimental data show that even for the very dense suspensions, whose optical path τL may be as large as 2.5-2.7 or the extinction I/I₀ as low as 0.06-0.07, the measured diameters agree well with the nominal values of the polystyrene latex spheres.     

MEASUREMENT OF PARTICLE SIZE DISTRIBUTION IN COAL OIL WATER FUELS BY FOUR METHODS

ABSTRACT

Four methods were used to measure the solids particle size distribution in coal-ol1-water fuel. Both dry and wet screening were utilized for the coarser particles while four different instrumental methods were used to measure the finer particles in diluted liquid suspension. The wet stages of the analyses included both solvent-diluted organic suspensions and measurement after inversion to an aqueous system.

Consistent differences in the absolute values of particle size were observed between the four procedures. Possible reasons for these differences are discussed.     

用超声波技术测量螺栓轴向紧固应力

超声波速度会因材料中加载应力而产生微小的变化，这一现象特别适用于测量螺栓的轴向应力。根据螺栓的轴向应力与超声波传播时间变化率的关系，作者研究了一种可直接测量螺栓轴同应力的仪器。实验结果显示，本项技术十分适合现场的实际应用。     

MEASUREMENT OF PARTICLE SIZE DISTRIBUTION IN COAL OIL WATER FUELS BY FOUR METHODS

Four methods were used to measure the solids particle size distribution in coal-ol1-water fuel. Both dry and wet screening were utilized for the coarser particles while four different instrumental methods were used to measure the finer particles in diluted liquid suspension. The wet stages of the analyses included both solvent-diluted organic suspensions and measurement after inversion to an aqueous system.

Consistent differences in the absolute values of particle size were observed between the four procedures. Possible reasons for these differences are discussed.     

THE MEASUREMENT OF STRAIN IN TUNNEL LININGS USING THE VIBRATING-WIRE TECHNIQUE

The article shows how the innate qualities of the vibrating-wire strain gauge: cheapness, long term stability and tolerance to electrical troubles make it particularly suitable for experiments in tunnels. A basic type of gauge is described and its working explained. Its application is then extended to use in concrete, wet situations, the use of large numbers of gauges and the measurement of bending. Finally, practical advice is given on the assembly and tuning of this kind of gauge.     

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.     

PARTICLE VELOCITY MEASUREMENTS THROUGH ELECTROSTATIC FIELD FLUCTUATIONS USING EXTERNAL PROBES

Two new probes for measuring particle velocity and flowrate based on the elctrostatic field nature of a pneumatic transport system are Introduced. The first probe is based on the current of charged particles inducing a current in a coil placed perpendicular to the flow. The magnitude of the current induced appears to be related to the amount of charged particles passing through the coil and the velocity of the particles. The second probe utilizes fluctuations in the electrostatic field which are picked up by two probes placed a fixed distance along the axis of the flow. The signals from these two probes are identical in waveform but of set in time; therefore, the particle velocity can be obtained by cross-correlation techniques. Both probes are non-intrusive and realtively inexpensive.     

PARTICLE VELOCITY MEASUREMENTS THROUGH ELECTROSTATIC FIELD FLUCTUATIONS USING EXTERNAL PROBES

ABSTRACT

Two new probes for measuring particle velocity and flowrate based on the elctrostatic field nature of a pneumatic transport system are Introduced. The first probe is based on the current of charged particles inducing a current in a coil placed perpendicular to the flow. The magnitude of the current induced appears to be related to the amount of charged particles passing through the coil and the velocity of the particles. The second probe utilizes fluctuations in the electrostatic field which are picked up by two probes placed a fixed distance along the axis of the flow. The signals from these two probes are identical in waveform but of set in time; therefore, the particle velocity can be obtained by cross-correlation techniques. Both probes are non-intrusive and realtively inexpensive.     

孔内炸药连续爆速测试新技术

对目前炸药爆速测试技术进行了简要分析,认为常规测试手段难以满足炸药连续爆速测定、特别是孔内及水下炸药连续爆速测定的要求。本文介绍了一种便携式HandiTrapⅡ VOD爆速测试系统,并通过两个测试实例说明该测试系统在孔内及水下炸药连续爆速的测试方面,具有简便、快捷、直观、可靠等优势。     

A COMPUTER SIMULATION OF PIPE BEND EROSION IN A DILUTE PNEUMATIC TRANSPORT OF GRANULAR MATERIALS

A computational investigation of the dilute pneumatic transport of solid particles in the pipe bend is presented. The cause and effect relation among the flow velocity of the carrying fluid, the pipe bend curvature, and the rate of erosion is investigated. KIVA-3 code developed at the Los Alamos National Laboratory is utilized on the MAUI super computer to facilitate this study.     

用局部点振动数据重构系统物理参数

本文提出用系统的局部振动测量来识别其物理参数的一种方法。文章首先运用微分方程的算子解法，将描述结构振动的动力学方程转化为由测量点信号表示的输入输出系统参数模型，并建立该模型参数─—系统参数与物理参数间的对应关系，然后运用系统辨识技术识别出该系统参数，最后利用系统参数与物理参数间的映射关系，反推出待识别系统的物理参数。     

AIR FLOW AND PARTICLE TRANSPORT IN A TRIBOELECTRIC COAL/ASH CLEANING SYSTEM-COUNTER FLOWING STRAIGHT DUCT DESIGN

ABSTRACT

The process of triboelectric coal/ash cleaning is outlined and a new design for scale-up to industrial systems is described. A straight rectangular duct forms the mixing chamber and the main body of this triboelectric separator. To improve mixing and to generate a uniform concentration in the main electrostatic separator duct, the mixture enters the mixing box in the form of two opposing jets. The stress transport model of the FLUENT code is used for simulating the mean gas flow and to guide the overall design of the electrostatic coal/ash separator. The three-dimensional computational grid covers the mixing chamber with the opposing inlets and the upper part of the main separator duct. The gas flow field conditions including the directional intensities of turbulence are evaluated. The instantaneous fluctuating velocity field was simulated by a Gaussian filtered white noise model. A recently developed computational model for Lagrangian particle tracking is used to study the transport of particles from the inlets to the main body of the separator duct. The model accounts for the drag and lift forces acting on the particle, in addition to the Brownian motion and gravitational sedimentation effects. The particles are also dispersed by the action of the high level of turbulence that is generated in the mixing chamber. The computational results show that the new design generates roughly uniform flow conditions in the triboelectric separator duct. Furthermore, the larger 100 µm particles will have a more uniform distribution when compared with the smaller (40 µm) particles.

The effect of the presence of an electric field perpendicular to the flow direction is also studied. It is shown that the charged particles are significantly deflected by the action of the electrostatic forces. As a result, the system could separate coal and ash particles that carry different charges. The simplicity and effectiveness of the straight duct separator makes it a prime candidate for scale-up for use in industrial applications for online coal beneficiation and separation of minerals from ash in combustion product.     

DCPD法在蠕变局部损伤测量中的应用

论述了一种测量材料蠕变变形损伤的方法,即直流电位法（ＣＤＰＤ）,该法设计设备简单且精度高,克服了传统弹性模量法的不足,能有效测量整体及Ｖ型帛口根部的局部损伤。同时给出了代表应力式,用来描述多轴应力下的局部损伤。最后估算了１０ＣｒＭｏ９１０钢的蠕变损伤值。