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

Abstract

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.     

INTERACTION OF GRAVITY AND ELECTROSTATIC EFFECTS IN PIPE FLOW OF A GAS-PARTICLE SUSPENSION

The interaction of gravity and electrostatic effects in isothermal, fully developed, horizontal turbulent pipe flow of dilute suspensions has been examined. Experimental study has validated the fact that, in the presence of gravity, increased space charge associated with increased local concentration due to gravity accentuates the asymmetry in mass flux and particles density distributions in the vertical plane passing through the pipe centerline. The space charge effect on the particle mass flux distribution near the pipe bottom is enhanced by increased particle density. Measurements were made with air suspensions of monodispensed particles of alumina and latex with non-uniform particle charge in pipes of 51 mm and 127 mm diameters.     

INTERACTION OF GRAVITY AND ELECTROSTATIC EFFECTS IN PIPE FLOW OF A GAS-PARTICLE SUSPENSION

ABSTRACT

The interaction of gravity and electrostatic effects in isothermal, fully developed, horizontal turbulent pipe flow of dilute suspensions has been examined. Experimental study has validated the fact that, in the presence of gravity, increased space charge associated with increased local concentration due to gravity accentuates the asymmetry in mass flux and particles density distributions in the vertical plane passing through the pipe centerline. The space charge effect on the particle mass flux distribution near the pipe bottom is enhanced by increased particle density. Measurements were made with air suspensions of monodispensed particles of alumina and latex with non-uniform particle charge in pipes of 51 mm and 127 mm diameters.     

Motion of Large Particles in a Horizontal Pneumatic Pipe

The horizontal pneumatic transport of large particles with particle to pipe diameter ratio of 0.6 and particle densities of 928 kg/m³ and 2193 kg/m³ was examined experimentally and numerically. The pipe diameter and length were 10 mm and 8.8 m, respectively. The mean air velocity was between 14.2 m/s and 23.0 m/s and the number feed rate of particle was almost constant at seven per second. In this study, the method of characteristics was used for the simulation of gas flow, which considered not only the particle-particle collisions but also the particle-wall collisions. It is found that particle transport is possible even when the mean air velocity is smaller than the terminal settling velocity of particle's and that the arrival time intervals at the downstream section are not always uniform although the particles are fed uniformly. Furthermore, the velocity difference between different density particles becomes small as the mean air velocity decreases, because the particle velocities become uniform due to particle-particle collisions, and the ratio of particle velocity to the mean air velocity is almost independent of air velocity. In addition, it is shown that the particle-wall collision at the pipe joint due to pipeline misalignment can be one of the sources of bouncing motion of particles as shown by simulation results.     

Stabilization of neodymium oxide nanoparticles via soft adsorption of charged polymers

In this work, two synthetic polyelectrolytes, PSS and PAH, are employed as strong adsorbed surfactants to disperse and stabilize neodymium oxide nanoparticles. The acid-base equilibria of the oxide surfaces of the particles were investigated under different pH conditions in the absence and presence of polyelectrolytes, to optimize particle stabilization through enhancement of the effective repulsive surface charges. Surface charge amplification of a 3:5 ratio was achieved to permit improved particle transparency of 100-fold in visible wavelengths in neutral and acidic pH regimes, and a stable 10-fold surface charge amplification was achieved under basic pH conditions. The potential of polyelectrolytes as stabilizing agents for neodymium oxide NPs in large-scale particle physics experiments requiring extremely high optical transparency over long path length is evaluated based on optical absorbance and particle stability.     

电子墨水的组成及制备方法

电子墨水是一种新型的柔性显示材料，是由具有化学相容性的多相材料组成的。本文在介绍电子墨水显示原理的基础上，着重介绍了各组成部分，即电泳颗粒、分散介质、染料、电荷控制剂和稳定剂的作用及材料的选择，论述了电子墨水微胶囊的制备方法及存在的问题。并评述了电子墨水的研究进展。     

The role of interstitial gas in the Brazil Nut effect

We have studied the Brazil Nut effect – the rise of a large intruder particle within a vertically vibrated bed of smaller particles. In our study both intruder and bed particles were spherical and the vibration was such that bed convection was negligible. The rise of the intruder was found to be influenced by humidity of the air within the interstices of the particle bed and on the electrostatic charge developed on the bed particles during preparation and vibration. High relative humidity and high electrostatic charge each had the effect of slowing the rise of the intruder. Because increasing relative humidity of the interstitial air caused the electrostatic charge to diminish, the rise rate of the intruder achieved a maximum at a relative humidity of around 55%. Under controlled humidity and charge conditions, the time for the intruder to rise through the bed was found to decrease with increase in intruder diameter. As intruder density was varied under controlled humidity and charge conditions, the intruder rise time was found to exhibit a maximum when the intruder density of approximately one half of the bulk density of the bed of particles. This interesting trend was modelled by taking account of the pressure gradient that is generated across a bed of particles vertically vibrated within a gas. The tentative model suggests that the gas flows associated with this pressure gradient restrict the motion of the bed more than that of the intruder and that it is this difference that accounts for the rise of the intruder. Also incorporated in the model is the buoyancy force on the intruder that results from the pressure gradient across the bed. KeywordsBrazil nut effect, Vibration, Granular solids, Humidity, Electrostatics, Interstitial air Dr. Shintaro Takeuchi is a Research Fellow of the Japan Society for the Promotion of Science (JSPS). Ms. Muniandy received financial support from CSIRO grant CZ-25.     

Numerical Model for Heat Transfer in Dilute Turbulent Gas-Particle Flows

The heat transfer between a vertical pipe wall and turbulent gas-particle flow is numerically investigated according to the Eulerian-Lagrangian approach and the k-ε turbulence model. The particles are introduced homogeneously into the simulation volume by a unique technique referred to as an artificial feeding volume. The numerical code using additional computer programs is validated with available experimental results for the constant heat flux boundary condition. An average deviation of about 4% and a maximum deviation of about 7% were attained from the numerical predictions for various particle and pipe diameters. The effect of the geometrical parameters and the flow parameters on the gas/particle temperature, the convection heat transfer coefficient between the wall and the gas-particle mixture, and the thermal entry length were studied. An increase in particle diameter (loading ratio ≈ 0.5) extended the thermal entry length and decreased the bulk mixed temperature, particle temperature, and convection heat transfer coefficient. Increasing the pipe diameter led to a significant reduction in bulk mixed temperature and thermal entry length, in addition to a decrease in particle temperature and Nusselt number. Increasing the loading ratio up to 2.36 led to a reduction in wall temperature and bulk mixed temperature, in addition to an increase in the convective heat transfer coefficient and thermal entry length.     

Numerical Model for Heat Transfer in Dilute Turbulent Gas-Particle Flows

The heat transfer between a vertical pipe wall and turbulent gas-particle flow is numerically investigated according to the Eulerian-Lagrangian approach and the k-ε turbulence model. The particles are introduced homogeneously into the simulation volume by a unique technique referred to as an artificial feeding volume. The numerical code using additional computer programs is validated with available experimental results for the constant heat flux boundary condition. An average deviation of about 4% and a maximum deviation of about 7% were attained from the numerical predictions for various particle and pipe diameters. The effect of the geometrical parameters and the flow parameters on the gas/particle temperature, the convection heat transfer coefficient between the wall and the gas-particle mixture, and the thermal entry length were studied. An increase in particle diameter (loading ratio ≈ 0.5) extended the thermal entry length and decreased the bulk mixed temperature, particle temperature, and convection heat transfer coefficient. Increasing the pipe diameter led to a significant reduction in bulk mixed temperature and thermal entry length, in addition to a decrease in particle temperature and Nusselt number. Increasing the loading ratio up to 2.36 led to a reduction in wall temperature and bulk mixed temperature, in addition to an increase in the convective heat transfer coefficient and thermal entry length.     

Particle Characteristics and Analysis Using a Laser-Based Phase Doppler Particle Analyzer (PDPA) and Statistical Method

Particle characterization is an important component in product research and development, manufacturing, and quality control of particulate materials. In this study a laser-based phase Doppler particle analyzer (PDPA) was used to measure particle size and velocity. Two different particles including humid particles and fog particles were tested using the PDPA. Several tests were conducted under different conditions and all data were analyzed using the statistical method and analysis of variance (ANOVA) to see which factor affects particle performance. The humid particle flow rate has a significant effect on both the particle mean diameter and the particle mean velocity with 90% confidence. The type of oil particles has a significant effect on the particle mean velocity with 90% confidence.     

Analysis of triboelectric charging of particles due to aerodynamic dispersion by a pulse of pressurised air jet

Triboelectric charging of powders causes nuisance and electrostatic discharge hazards. It is highly desirable to develop a simple method for assessing the triboelectric charging tendency of powders using a very small quantity. We explore the use of aerodynamic dispersion by a pulse of pressurised air using the disperser of Morphologi G3 as a novel application. In this device particles are dispersed by injection of a pulse of pressurised air, the dispersed particles are then analysed for size and shape analysis. The high transient air velocity inside the disperser causes collisions of sample particles with the walls, resulting in dispersion, but at the same time it could cause triboelectric charging of the particles. In this study, we analyse this process by evaluating the influence of the transient turbulent pulsed-air flow on particle impact on the walls and the resulting charge transfer. Computational Fluid Dynamics is used to calculate particle trajectory and impact velocity as a function of the inlet air pressure and particle size. Particle tracking is done using the Lagrangian approach and transient conditions. The charge transfer to particles is predicted as a function of impact velocity and number of collisions based on a charge transfer model established previously for several model particle materials. Particles experience around ten collisions at different velocities as they are dispersed and thereby acquire charges, the value of which approaches the equilibrium charge level. The number of collisions is found to be rather insensitive to particle size and pressure pulse, except for fine particles, smaller than about 30 µm. As the particle size is increased, the impact velocity decreases, but the average charge transfer per particle increases, both very rapidly. Aerodynamic dispersion by a gas pressure pulse provides an easy and quick assessment of triboelectric charging tendency of powders.     

Particle Characteristics and Analysis Using the Laser-Based Phase Doppler Particle Analyzer (PDPA) and Statistical Method

Particle characterization is an important component in product research and development, manufacturing, and quality control of particulate materials. In this article a laser-based phase Doppler particle analyzer (PDPA) was used to measure particle size and velocity. Two different particles, humid particles and fog particles, were tested using the PDPA. Several tests were conducted under different conditions and all data were analyzed using the statistical method and analysis of variance (ANOVA) to see which factor affects particle performance. The humid particle flow rate has a significant effect on both the particle mean diameter and the particle mean velocity with 90% confidence. The type of oil particle has a significant effect on the particle mean velocity with 90% confidence.     

Numerical prediction of particle erosion of pipe bends

In the present study the Euler/Lagrange approach in combination with a proper turbulence model and full two-way coupling is applied for erosion estimation due to particle conveying along a horizontal to vertical pipe bend. Particle tracking considers both particle translational and rotational motion and all relevant forces such as drag, gravity/buoyancy and transverse lift due to shear and particle rotation were accounted for Laín and Sommerfeld (2012). Moreover, models for turbulent transport of the particles, collisions with rough walls and inter-particle collisions using a stochastic approach are considered Sommerfeld and Laín (2009). In this work, the different transport effects on spherical solid particle erosion in a pipe bend of a pneumatic conveying system are analysed. For describing the combined effect of cutting and deformation erosion the model of Oka et al. (2005) is used. Erosion depth was calculated for two- and four-way coupling and for mono-sized spherical glass beads as well as a size distribution of particles with the same number mean diameter (i.e. 40?μm). Additionally, particle mass loading was varied in the range from 0.3 to 1.0. The erosion model was validated on the basis of experiments by Mazumder et al. (2008) for a narrow vertical to horizontal pipe system with high conveying velocity. Then a 150?mm pipe system with 5?m horizontal pipe, pipe bend and 5?m vertical pipe with a bulk velocity of 27?m/s was considered for further analysis. As a result inter-particle collisions reduce erosion although the wall collision frequency is enhanced Sommerfeld and Laín (2015); additionally, considering a particle size distribution with the same number mean diameter as mono-sized particles yields much higher erosion depth. Finally, when particle mass loading is increased, bend erosion is reduced due to modifications of particle impact velocity and angle, although wall collision frequency grows.     

Advanced materials for drug delivery and biosensors based on magnetic label detection

Many traditional magnetic materials are not suitable for the increasing demands of microsensors for environmental control, biomedical applications, drug delivery, and homeland security. The design of magnetic biosensors can be based on different types of magnetic effects. The detection principles are measurements of the resistance, impedance, etc. in the absence and presence of magnetic nanoparticles. Variations in the measured parameters can be associated with either many individual molecular recognition events or with a specific uptake. Magnetic materials which could be used in magnetoimpedance based biosensors have been studied both for the sensitive element and for magnetic label. The self-assembling processes were observed in perpendicular field for different concentrations of the Dynabeads® M-480. Magnetic field controlled assembly is proposed for designing new composite materials which can be also useful to study the properties of the separate particles. The morphology of the particle agglomerates and dipolar chains in the external field can be controlled by using simultaneously two different suspensions of magnetic particles. A new concept is to define synergetic combinations of two or more nanostructures for the best performance.     

Design and modelling of a self-dispersing twisted pipe to mitigate settling in coal water suspension

The hydrotransport of the industrial powders and bulk solids such as minerals, mineral tailings, coal and ash is considered to be an efficient mode of transportation. The pipelines ranging from a few meters to few kilometers in length are used for such transportation purposes. If not well addressed, the issue of particle settling in such pipelines can lead to blockage and even bursting of the pipeline due to the continued deposition of the solids. The present study proposes the introduction of a twisted pipe section of a suitable length and geometry, that produces enough turbulence in the flow, sufficient for the re-dispersion of the already settled particles and check their further deposition. To achieve this objective, 5 different geometries (each having 4 different lengths) of twisted pipes are designed and used to model the dynamics of the particles’ flow through them and in their downstream region. A low influx velocity (where particle settling is expected) of 0.5 m/s is selected for all the cases and the influx solids’ mass concentration ranges from 40 to 60%. The results generated by the commercial CFD software are in good agreement with the experimental data. The parameters viz. mixing index, pressure loss, and specific energy consumption are evaluated to choose the best design of the twisted pipe section. The 0.2 m long 3 lobes twisted pipe section is found to deliver the suspension of highest homogeneity at the cost of a slight increase in pressure loss and specific energy consumption. The present solution ensures the mitigation of particles’ settling and the other related issues.     

Continuous-flow lithography for high-throughput microparticle synthesis

Precisely shaped polymeric particles and structures are widely used for applications in photonic materials, MEMS, biomaterials and self-assembly. Current approaches for particle synthesis are either batch processes or flow-through microfluidic schemes that are based on two-phase systems, limiting the throughput, shape and functionality of the particles. We report a one-phase method that combines the advantages of microscope projection photolithography and microfluidics to continuously form morphologically complex or multifunctional particles down to the colloidal length scale. Exploiting the inhibition of free-radical polymerization near PDMS surfaces, we are able to repeatedly pattern and flow rows of particles in less than 0.1 s, affording a throughput of near 100 particles per second using the simplest of device designs. Polymerization was also carried out across laminar, co-flowing streams to generate Janus particles containing different chemistries, whose relative proportions could be easily tuned. This new high-throughput technique offers unprecedented control over particle size, shape and anisotropy.     

Effect of particle-wall interaction on triboelectric separation of fine particles in a turbulent flow

Triboelectric separation is an effective way to separate fine powders with particle sizes and densities in the same order of magnitude. Many relevant process variables influence the charging behaviour; however, the corresponding effects on the subsequent separation of particles remain unknown. To utilize triboelectric separation as a powerful tool for fine powder separation, process parameters such as the choice of contact wall materials in the charging region have to be investigated. We report for the first time the influence of the tube’s wall material, in which particle charging took place, on triboelectric separation of fine protein-starch mixtures. Different electrically insulating materials along the triboelectric series were tested. No significant influence of the wall material on the separation selectivity and efficiency was found. In addition, particle-wall interaction was inhibited using an experimental setup which allows to control the flow boundary-layer by blowing out air through the tube wall. Also the results obtained by this novel setup showed no significant differences compared to the setup with particle-wall interactions. Additionally, CFD simulations were used to confirm the absence of particle-wall interactions in the boundary-layer control setup. A variation of the boundary-layer thickness leads to a constriction of the particle-containing flow region in the centre of the pipe. Experiments show that this compression of the particle flow zone results in no further increase in selectivity and efficiency of separation. Thus, particle-particle interaction is the prevalent triboelectric charging mechanism of fine powders charged in a turbulent flow regime.     

Design and characterisation of poly(lactide-co-glycolide) small particulate systems for the delivery of immunostimulant CpG oligonucleotide

The aim of this study was to develop and characterize biodegradable small particles of poly(lactide-co-glycolide) (PLGA) as oral vehicle for immunostimulatory oligonucleotide (ODN-CpG). Three different polymers were used as surface stabilizing agents (SSA): polyvinyl alcohol (PVA), hydrophobically modified hydroxyethylcellulose (HMHEC), or polyethylenimine (PEI). Particle surface was characterized as well as ODN-CpG release kinetics. All particles were found to be around 1 microm. Particles of PLGA-PVA and PLGA-HMHEC were spherical in shape with a smooth surface whereas PLGA-PEI particles were porous. The presence of ODN-CpG within the particle matrix was confirmed in all particle type using scanning laser confocal microscopy. Particle surface assayed by XPS, zeta potential analysis, and evaluation of particle surface hydrophobicity suggested that a significant amount of SSA remains associated onto particle surface. Release profiles evidenced that ODN-CpG release was strongly dependent on particle surface properties. 100% of encapsulated ODN-CpG was released from PLGA-PVA and PLGA-HMHEC particles 37 days after incubation in a buffer solution, whereas only 25% were released from PLGA-PEI particles. ODN-CpG can therefore be nicely entrapped in several types of small particles displaying a prolonged and controlled release upon time. In addition, particle surface is not modified by the presence of ODN-CpG.     

机械合金化法制备锂离子电池Si基负极材料及其电化学性能研究

Si具有高的储锂容量,但是其循环性能很差。采用机械合金化方法,对纯Si进行处理。同时以石墨、炭黑对纯Si进行掺杂以改善Si的循环特性。对于纯Si,随着球磨时间的延长,材料的非晶化程度增加;经过球磨后材料的平均粒径由原来的29μm变成0.2μm;由大的块状变为小的圆形颗粒。充放电结果表明未经球磨处理的纯Si的首次放电比容量较高,但放电比容量损失较大,循环性能差,而经过球磨的纯Si能增加首次放电比容量,循环性能变化不大;对纯Si采用石墨、炭黑掺杂后材料的首次放电比容量下降,循环性能有所提高;球磨和掺杂没有改变Si储锂的电位。经过阻抗分析发现,球磨后纯Si材料中Li的扩散系数增大。