Studies of the effect of tracer activity on time-averaged positron emission particle tracking measurements on tumbling mills at PEPT Cape Town

The statistical uncertainties associated with time-averaged positron emission particle tracking (PEPT) measurements of the position, velocity and acceleration of a small tracer particle have been investigated. Experiments were undertaken using the ECAT ‘EXACT3D’ PET scanner recently installed at the facilities of PEPT Cape Town at iThemba LABS, South Africa. Small “button” sources of ⁶⁸Ga were attached to the outer shell of a small mill and PEPT data were recorded over several half-lives, for the cases of the mill being empty and entirely filled with steel balls. The effect of tracer activity on the statistical uncertainties in the positions, velocities and accelerations derived from the measurements was investigated, as a first step towards fully quantifying the uncertainties associated with tracking particles via PEPT in laboratory-scale tumbling mills.     

Towards a mechanistic model for slurry transport in tumbling mills

A new modelling approach to slurry transport in dynamic beds based upon combining space and time-averaged Navier–Stokes equations with a new type of cell model is described. The resulting Ergun-like equation is used to correlate pressure drop with time-averaged distributions of the porosity, superficial fluid velocity and solids velocity for data derived from positron-emission-particle-tracking (PEPT) experiments in a scaled industrial tumbling mill fitted with lifter bars, pulp lifters and a discharge grate and run with particles and re-circulating slurry.     

Combining Positron Emission Particle Tracking and image analysis to interpret particle motion in froths

Previous research into particle motion in the froth zone has focussed on constructing detailed CFD models that describe the behaviour of particle classes with different properties; density, size and hydrophobicity. These models have been reasonably successful in predicting trends in the separation behaviour and how it can be manipulated. Models of separation sub-processes cannot readily be verified experimentally due to the opacity and fragility of froth systems.Positron Emission Particle Tracking (PEPT) can be applied to particles in froth flotation systems to observe the behaviour of individual particles in a mixed particle–liquid–gas system. However, measuring the particle position alone is not adequate as its behaviour is also affected by instantaneous froth events such as bubble coalescence. To link the observed particle behaviour to the froth behaviour requires multi-modal measurements. Video footage of a rising foam column was recorded simultaneously with PEPT data, so that the PEPT tracer trajectory could be explained in terms of foam structure and events. A time weighting function of cubic splines with kernel width 200 ms was used to remove the effects of signal noise. An ascending 70 μm hydrophilic tracer accelerated within vertical Plateau borders and decelerated in Plateau borders angled away from vertical. The tracer trajectory showed velocity peaks and troughs when it was contained in nodes in a rising foam. When the tracer descended within a foam showing convective roll, coalescence events and subsequent foam deformation directly influenced the tracer trajectory.     

Circulation rate modelling of mill charge using position emission particle tracking

A model linking the circulation rate of charge particles with physical mill parameters (load fraction, shoulder angle and friction) has been developed and tested using experimental data derived from positron emission particle tracking (PEPT). The model parameters are obtained directly from the in situ flow field of the PEPT tracer particles. The model formulation, methodology for model parameter correlations and comparison of circulation rate model with direct measurement from PEPT forms the focus of this paper.     

Tracking the motion of media particles inside an IsaMill™ using PEPT

Stirred milling is continually gaining acceptance in the mineral processing industry. The IsaMill? is a high intensity stirred mill with a horizontal configuration and internal classification. The present work describes the use of Positron Emission Particle Tracking (PEPT) to trace the motion of a media bead in a simplified IsaMill? rig. The rig has the same inner dimensions and disc sizes as the real M20 IsaMill? but is a closed unit without any flow through, no product separator and only three discs. The PEPT system has the advantage of being able to obtain detailed charge motion measurements in opaque and aggressive environments such as those encountered in grinding processes. Glass beads (3 mm) and ceramic media (3.5 mm) were tracked over a range of volumetric fillings and rotational speeds. An analysis of the resultant trajectory fields in terms of media location (occupancy), velocity, and acceleration is presented.     

煤粉浆液十字流微滤试验研究

以三种粒径等级的煤粉悬浮液为滤浆,研究了煤粉滤浆十字流微滤的特性,滤浆流速对滤液流速的影响,剪切力作用与滤液流速的关系,以及滤液流速随过滤时间的变化规律。试验结果表明,滤液流速随滤浆流速增加而增大,但存在一个临界最大值;剪切力的增加会使滤液流速显著增大,继续增大剪切力对滤液流速影响却不大;获得平稳的滤液流速大概需要50min左右。     

应用剪切波速判别饱和砂土振动液化的研究现状

介绍了应用剪切波速判别饱和砂土振动液化的原理；从临界剪应变取值、砂土的抗液化能力与剪切波速相关关系的研究方法与设备、用剪切波速进行扰动评价、建立适用于不同土类的统一判别式四方面总结了国内外学者在该领域的一些研究成果及存在问题；针对以上问题提出一些看法。     

CFD–DEM modelling of particle flow in IsaMills – Comparison between simulations and PEPT measurements

The IsaMill? is a high speed stirred mill with a horizontal configuration that offers advantages such as energy efficiency and an inert grinding environment. A combined computational fluid dynamics (CFD) and discrete element method (DEM) approach was developed to investigate the particle and fluid flows inside a simplified IsaMill?. The configuration of the mill was simpler than that of an actual IsaMill? and no feed flow or rotor was considered. The CFD–DEM model is a progression from earlier DEM only models of “dry” systems which did not account for the fluid phase. The properties of flows at a macroscopically steady state, such as velocity field, distributions of particle velocity and acceleration in the radial direction and power draw, were analysed. Detailed comparisons were carried out between the simulation results and Positron Emission Particle Tracking (PEPT) measurements under similar conditions. The comparisons showed reasonable agreements, confirming that both techniques can capture the key features of the flow. The discrepancies between simulated and measured results were discussed. The findings indicated that the proposed model can be used to generate microdynamic information that is useful in leading to a better understanding of the underpinning physics of flow inside mills.     

利用综合地脉动法测定剪切波速度

本文提出了一种既观测地脉动垂直于地面的运动,又观测强迫振动垂直于地面运动的综合地脉动法测定剪切波速度V_s。其传感器组合采用五个垂直传感器组成二维扩展圆形组合和三个垂直传感器组成线性排列组合。该方法不需要钻孔、即能测定地下数十米深范围内以至更深处的V_s地层剖面,是一种经济方便的观测方法。     

粘土剪切波速的现场和室内试验研究

利用安装在动三轴仪上的剪切波速测试装置，测试了天津地区粘土的剪切波速。并在此基础上将室内测试结果与现场测试值进行了比较。研究发现二者的差值≤16％，并与土样埋深有直接关系。     

饱和松散粉土剪切波速对其抗液化强度影响的研究

采用剪切波速与振动三轴联合试验装置,分析了原状和重塑饱和松散粉土的抗液化强度与剪切波速之间的相关性。结果表明,当采用的液化判别标准超过7%时,不论原状还是重塑粉土,只要在相同围压下具有相同的剪切波速,其抗液化强度仍具有较强的相关性,并且实验样本的相关系数均在0.82以上。这为用剪切波速评价松散粉土的抗液化强度奠定了基础。     

土样现场和室内剪切波速的试验研究

利用安装在动三轴仪上的剪切波速测试装置 ,测试了天津某地区土的剪切波速 ,并在此基础上将室内测试结果与现场测试值进行了比较。研究发现二者的差值与土层埋深、粘粒含量等因素有直接关系     

煤岩特性对超声波速影响的试验研究

超声波测试技术广泛应用材料内部缺陷与表面裂缝检测和描述,然而其声学参数同煤岩物理特性与结构特征的关系,成为该技术在地下采矿工程中应用的瓶颈问题之一。在大同煤矿集团塔山矿8212工作面采集煤块及顶板岩芯,采用美国Tektronix公司生产的超声波仪,开展不同层理方向煤岩及不同岩性岩石的超声波室内测试试验,并结合CT扫描、磨片分析等微观测试手段和覆压渗透试验获得煤岩内部物质含量组成形态及渗透特性,系统研究密度、层理方向、孔隙度、渗透率、矿物颗粒成分及大小等因素对超声波传播速度的影响。试验表明：纵波与横波波速均表现出随密度增大而增大的趋势;煤岩的超声波速有明显的层理效应,试验发现轴向与层理的夹角由小变大,其纵波和横波波速呈减小趋势,轴向平行层理煤岩的纵波、横波波速分别约为轴向垂直层理的1.22,1.23倍;纵波波速随孔隙率与渗透率的增大而减小,且煤的渗透率亦呈现明显的层理效应,轴向平行层理煤岩的渗透率约为轴向垂直层理的57.1倍;岩石矿物颗粒越细纵波波速越大,岩样纵波波速依次以细砂岩、中粗粒砂岩、含粗砂细砾岩和粗粒砂岩由大到小排列。     

山东东营城区剪切波速回归分析及应用

剪切波速是当前工程场地地震安全性评价和地震小区划工作中必备的参数之一,是土层地震反应分析中一个重要参数.然而受到实际情况的制约,测试不能达到工作要求的深度或是测试结果未满足要求,这时必须对剪切波速进行估计.该文通过对东营城区46个钻孔土体剪切波速测试结果的统计回归分析,提出了线性函数、幂函数相结合的土体剪切波速推算公式...     

天津软土剪切波速影响因素的灰色关联分析

剪切波速是评价场地土动力特性的重要指标。很多地区基于已有勘察资料 ,取得了剪切波速与深度及土性指标之间的统计关系。但影响剪切波速的诸多因素的主次关系难以确定 ,致使在工程中难以找出影响剪切波速的主要因素 ,从而难以确定具有代表性的统计关系。该文引入灰色系统中灰色关联理论 ,对天津地区剪切波速及相应土性指标进行了灰色关联分析 ,得到了该地区影响剪切波速因素的主次关系。     

煤矿井下巷道槽波的频散特性研究

为了分析实际接收的槽波信息,真实反演地质条件,采用Matlab数学模拟软件,对影响煤矿井下槽波频散特性影响因素,底板岩层横波速度、煤层横波速度、煤的密度、顶底板岩层密度、煤层厚度等对频散曲线的影响程度进行了研究。研究得出:煤层的横波速度对煤矿井下槽波频散特性的影响最大,埃里相位的速度与煤层的横波速度密切相关,煤层的横波速度越高,埃里相位的速度也越高;围岩和煤层密度对勒夫型槽波的频散特性影响最低,因此在实际探测时,可以忽略围岩和煤层密度对频散特性的影响,为煤矿安全掘进回采提供科学依据,确保矿井的安全生产。     

钻孔灌注桩泥浆流变性能评价方法探讨

粘度是评价钻孔灌注桩泥浆性能的重要参数之一.由于钻孔灌注桩桩径大,泥浆循环速度低,剪切速率低,评价石油钻井和地质勘探泥浆流变性能的方法不适合评价钻孔灌注桩泥浆粘度.首先分析了钻孔灌注桩循环速度,推出其剪切速率分布;然后分析了旋转粘度计的剪切速率,提出了低转速的粘度计更适合评价钻孔灌注桩泥浆;最后推导出了塑性粘度、有效粘度和动切力的计算公式,对准确评价钻孔灌注桩泥浆具有重要理论和实践意义.     

原位应力下裂缝性致密砂岩各向异性地震波速及其渗透率关联特征

超深层裂缝性非常规天然气藏的开发在能源领域所占比重越来越大,但目前关于该类型储层在原位应力下各向异性地震波速及渗透率的基础研究仍鲜有报道,一定程度上制约了其高效开发策略的制定进程。以塔里木油田克深2号裂缝性致密砂岩天然气储层为工程背景,利用先进的地球物理成像真三轴测试系统,开展了储层衰竭期间原位应力下完整砂岩与不同倾角裂缝岩样的各向异性地震波速以及各向异性渗透率演化规律实验研究,探讨了压缩波、剪切波、纵横波速比、3个主应力方向渗透率各向异性特性与内在机制,研究了地震波速与渗透率的内在关联特征。研究结果表明：首先,裂缝引起的结构非均质性以及三向不等应力作用下岩石各主应力方向微观结构的变形差异导致了地震波速的各向异性;储层衰竭期间地震波速度均随有效应力的增大近似线性增加,压缩波速度明显大于剪切波速度;纵横波速比随有效应力增大而单调减小,表明剪切波对外部荷载敏感性更强;通过压缩波速和纵横波波速比数据对比,发现剪切波S2速度对裂缝倾角更为敏感。其次,原位应力下各主方向渗透率均表现出显著的应力敏感性和结构（裂缝）敏感性,早期应力大小对储层衰竭中后期渗透率变化具有重要影响,渗透率各向异性随裂缝倾角...     

乳胶基质体系分散相粒度分布研究

乳胶基质分散相的粒径对乳化炸药的稳定性,爆轰性能都有很大的影响。本文利用两种测试手段分析乳胶基质的粒径分布与乳化搅拌剪切速度的关系,实验结果表明:乳胶基质分散相粒径大小,随着搅拌剪切速度的增加而减小;乳胶基质乳化搅拌的临界剪切速度为1500 r/min;剪切速度越高,乳胶基质分散相粒径平均值越小,分布越均匀。     

PEPT studies of heavy particle flow within a spiral concentrator

Future improvements of gravity concentrators require an increased knowledge of the mechanics behind the separation, including the motion of the particles. This work details the investigation of particle motion through a spiral concentrator. The results of tracking the motion of individual particles using the positron emission particle tracking (PEPT) technique are described. Tracer particles of different sizes and density were tracked along the trough of a laboratory scale spiral. Multiple passes of one tracer through the spiral are combined to represent the bulk of flow of this particle type and size, with the position and time recorded to allow for the particle trajectory and speed to be determined. Finally, the use of PEPT will be shown to be a powerful method to visualise the behaviour of particles during the concentration process, providing data that will be used for the validation of new models of spiral concentrator performance.