Particle Transport and Deposition in a Duct Flow with a Rectangular Obstruction

The airflow field and particle trajectory and deposition in a duct with a rectangular obstruction were studied. The governing conservation equations of mass and momentum were discretized using a finite volume method, and the corresponding velocity vector and pressure fields were evaluated. The particle trajectories were evaluated by solving the Lagrangian equation of motion that included the drag, Saffman's lift, and gravity forces. Effects of different forces as well as the blockage and the obstruction aspect ratios on particle trajectory and deposition were analyzed for a Reynolds number of 200. The simulation results showed that with the increase of Stokes number, particle deposition efficiency on the front side of the obstruction increased and also the presence of the gravitational force in the span-wise direction caused the particles to be deposited on the channel lower wall. The presence of gravity in the stream-wise direction increased the deposition efficiency and in the counter-stream-wise direction decreased the deposition efficiency. Changing the obstruction aspect ratio had no noticeable effect on the deposition but increasing the blockage ratio increased the deposition efficiency. The presence of a lift force had different effects for different blockage ratios and Stokes numbers. But the lift force generally increased the deposition rate, especially at large Stokes numbers and large blockage ratios.     

玻璃熔窑中窑坎位置变化对液流温度场和速度场的影响

本文通过建立具有实用意义的浮法玻璃熔窑内物料运动和传热过程的三维数学模型，对在熔化部中放置窑坎进行了研究。通过实例计算，系统地研究了窑坎位置变化对玻璃液流温度场和速度场的影响，认为窑坎放置在５号、６号小炉中间为实例计算时的最佳位置，可使卡脖处的回流耗热为最小。     

Some Applications of Acoustic Emission in Particle Science and Technology

Acoustic emission (AE) has been used in many applications in the field of particle science and technology. AE sensors have been used in particle concentration measurements both in gas-continuous and oil-continuous flows in the oil and gas industry. To avoid formation sand flowing into pipelines, leading to erosion of valves and in many cases even to complete blockage of the flow of oil and gas, AE sensors are almost exclusively used in sand monitoring and control. These are very often among standard sensors stipulated by the operators of oil and gas production facilities in offshore, on shore, and subsea applications. Special types of sensor design have led to easy mounting of these AE sensors, which are very often clamp-on devices. This article presents a brief overview of AE-based particle monitoring in general and focuses on flange-mounted sensors in the monitoring of particle flow. By using two or more AE sensors located suitably in the process line, the particle velocity can also be evaluated, as is shown in examples using correlation in this article. The AE sensors can easily be adapted to detect malfunctioning of the process line, whether pneumatic lines or silos, just by analyzing the time series of signals from strategically based AE sensors along the process lines. Some examples are given based on recent measurement data. Finally, the article presents an overview of possibilities for improved particle flow monitoring using a multisensor suite incorporating AE sensors with other sensors/detectors such as those derived from capacitance, resistance, gamma ray, microwave, and optical devices. Artificial intelligence (AI) techniques, such as fuzzy logic and neural network algorithms, used in handling the data from these sensors lead to faster and more reliable control. Some of these topics are addressed also.     

Some Applications of Acoustic Emission in Particle Science and Technology

Acoustic emission (AE) has been used in many applications in the field of particle science and technology. AE sensors have been used in particle concentration measurements both in gas-continuous and oil-continuous flows in the oil and gas industry. To avoid formation sand flowing into pipelines, leading to erosion of valves and in many cases even to complete blockage of the flow of oil and gas, AE sensors are almost exclusively used in sand monitoring and control. These are very often among standard sensors stipulated by the operators of oil and gas production facilities in offshore, on shore, and subsea applications. Special types of sensor design have led to easy mounting of these AE sensors, which are very often clamp-on devices. This article presents a brief overview of AE-based particle monitoring in general and focuses on flange-mounted sensors in the monitoring of particle flow. By using two or more AE sensors located suitably in the process line, the particle velocity can also be evaluated, as is shown in examples using correlation in this article. The AE sensors can easily be adapted to detect malfunctioning of the process line, whether pneumatic lines or silos, just by analyzing the time series of signals from strategically based AE sensors along the process lines. Some examples are given based on recent measurement data. Finally, the article presents an overview of possibilities for improved particle flow monitoring using a multisensor suite incorporating AE sensors with other sensors/detectors such as those derived from capacitance, resistance, gamma ray, microwave, and optical devices. Artificial intelligence (AI) techniques, such as fuzzy logic and neural network algorithms, used in handling the data from these sensors lead to faster and more reliable control. Some of these topics are addressed also.     

Simulation of Particle Deposition Behavior in Cold-Sprayed Mg Anticorrosion Coating

In this work, finite-element analysis method is adopted to simulate Al particle deposition behavior on Mg substrate by cold spray. The effects of particle parameters such as incident velocities and angles, particle sizes, and number and types of incident particles on impacting character are analyzed. The particle energy, effective plastic strain, and its temperature distribution are discussed. Results reveal that increasing the particle incident velocity can intensify the deformation of both particle and substrate. The bonding will also be strengthened. Incident angles will also affect the bonding between particles and substrate. In multiple particle deposition process, the compaction effect of subsequent particles can promote the deformation of former particles and its bonding with substrate. Temperature distribution and the effective plastic strain distribution are consistent: temperature is higher in the area where the plastic deformation and stress is higher. Local melting may occur in that area at high temperature.     

Formation and Transport of Atomic Hydrogen in Hot-Filament Chemical Vapor Deposition Reactors

In this paper we focus on diamond film hot-filament chemical vapor deposition reactors where the only reactant is hydrogen so as to study the formation and transport of hydrogen atoms. Analysis of dimensionless numbers for heat and mass transfer reveals that thermal conduction and diffusion are the dominant mechanisms for gas-phase heat and mass transfer, respectively. A simplified model has been established to simulate gas-phase temperature and H concentration distributions between the filament and the substrate. Examination of the relative importance of homogeneous and heterogeneous production of H atoms indicates that filament-surface decomposition of molecular hydrogen is the dominant source of H and gas-phase reaction plays a negligible role. The filament-surface dissociation rates of H2 for various filament temperatures were calculated to match H-atom concentrations observed in the literature or derived from power consumption by filaments. Arrhenius plots of the filament-surface hydrogen dissociation rates suggest that dissociation of H2 at refractory filament surface is a catalytic process, which has a rather lower effective activation energy than homogeneous thermal dissociation. Atomic hydrogen, acting as an important heat transfer medium to heat the substrate, can freely diffuse from the filament to the substrate without recombination.     

Efficient Simulation of Gas Flow in Blast Furnace

Simulation of gas flow in a multilayered non-isothermal packed bed is useful for blast furnace operators in deciding appropriate charging strategy. While using an anisotropic form of Ergun equation to simulate gas flow through such systems, a new solution methodology for non-isothermal gas with varying density flowing through a layered burden has been proposed. This involves handling non-linearity due to gas density variation with pressure and temperature by solving for the square of pressure instead of pressure directly and handling the non-linearity due to |v| term in the Ergun equation by solving linearized form of Ergun equation and updating |v| iteratively. The proposed scheme is capable of predicting the effect of layer structure on gas flow with economy in number of grid points as well as computation time.     

Evolution of Charging Programs for Achieving Required Gas Temperature Profile in a Blast Furnace

This article presents an approach by which charging programs in the blast furnace can be evolved. The core of the method is a mathematical model, which on the basis of a given charging program estimates the two-dimensional distribution of burden layers in the shaft. A gas flow model uses this information to estimate the gas distribution, applying a simplified treatment of the conditions in the upper shaft. The aim is to find the charging program that gives a state of the furnace shaft matching a target for the radial temperature profile at the level of an in-burden probe. This is accomplished by applying a genetic algorithm (GA) that makes an efficient search among the huge number of potential charging programs, executing the burden and gas flow models in the function evaluations. The method is illustrated by six cases, where targets for the gas temperature distribution are given and the GA evolves the charging sequence and the chute settings for the dumps. It is demonstrated that the algorithm efficiently can evolve charging programs which yield temperatures in agreement with the targets, which holds promise for a practical application of the method in the steel plant.     

MFC在单晶炉上控制氩气流量的应用

目前单晶炉设备全自动控制技术日趋成熟。单晶硅炉拉晶生长过程中,炉体内的真空度稳定性是一个重要的环节。质量流量控制器MFC对于维持单晶炉内真空值起着极其重要的作用。     

Geometry Effect on Deposition and Residence Time of Polydisperse Fine Drops in Mini-Risers Under Developing Flow Condition

Mini-riser geometry effect on the transport, dispersion and deposition of fine water drops in the three-dimensional laminar developing flow was investigated numerically and experimentally. Circular, triangular and rectangular cross-section risers with a hydraulic diameter of 14 mm were examined. Microscopic high-speed particle shadow velocimetry (PSV) technique was employed for planar velocity measurement of droplets. The experimental data were used to validate the simulation results obtained with an Eulerian–Lagrangian computational code. In addition, simulation results of the penetration were compared with the existing theoretical model, and a close agreement was found. In these simulations the polydispersed fine droplets were randomly distributed at the inlet of the risers in a size range of 0.01 to 10 µm. For comparison of the effect of riser shapes, the airflow rate was assumed to be constant. Simulation results indicated significantly more droplets were deposited on the walls of the triangular and high aspect ratio rectangular risers. Brownian diffusion tends to increase the residence time especially for risers with a corner. Employing the riser shapes with sharper corners and higher aspect ratio was found to be more beneficial for increasing the droplet size moving in a supersaturated carrier gas, especially at high flow rates, due to higher residence time.     

基于流-固耦合传热的冷坩埚分瓣散热研究

针对冷坩埚真空悬浮熔炼装置散热系统的复杂性和重要性, 本文使用了一种基于整场离散的冷坩埚冷却系统和冷却水之间耦合分析的方法。首先分析了流固耦合的基本原理及关键问题, 建立了冷坩埚冷却系统流固耦合传热的物理模型及计算模型, 通过CFX仿真计算软件对其冷却系统的流-固耦合传热模型进行了求解, 得出了冷坩埚循环水套流体区域的流场、压力分布及固体区域的温度场, 并对计算结果进行了分析。实验结果表明:冷却水在水套内流动顺畅, 总体速度分布均匀, 有利于冷却水对冷坩埚分瓣结构的冷却;冷坩埚整体温度从冷坩埚中心至外端依次递增, 最高温度出现在冷坩埚最外端的边缘区域, 温度分布从低至高自然过度, 温度梯度变化缓慢, 不易产生局部高温和热应力。     

Predicting the Particle Deposition Characteristics Using a Modified Eulerian Method on a Tilted Surface in the Turbulent Flow

This study uses a v2-f turbulence model with a two phase Eulerian approach. The v2-f model can accurately calculate the near wall fluctuationsm which mainly represent the nonisotropic nature of turbulent flow near the walls. The Eulerian method was modified based on considering the most important mechanisms in the particle deposition rate when compared to the experimental data. The model performance is examined by comparing the rate of particle deposition on a vertical surface with the experimental and numerical data in a turbulent channel flow available in the literature. The model takes into account the effects of lift, turbophoretic, electrostatic, gravitational, and Brownian forces together with turbulent diffusion on the particle deposition rate. Electrostatic forces due to mirror charging and due to charged particles under the influence of an electric field were considered. The influence of the tilt angle on the particle deposition rate was investigated. The results show that, using the modified model with v2-f model predicts the rate of deposition with reasonable accuracy. It is shown that considering the turbophoretic force as the only inertia force and neglecting the lift force, leads to reasonable accuracy in predicting particle deposition rate. It is also observed that when the mirror charging and electric field are present, the electrostatic force has the dominant effect in a wider range of particles’ size. Furthermore, the results show that increasing the Reynolds number at a given tilt angle decreases the rate of particle deposition and the tilt angle has insignificant impact on the particle deposition rate in high shear velocity or high Reynolds number.     

One‐Way Particle Transport Using Oscillatory Flow in Asymmetric Traps

One challenge of integrating of passive, microparticles manipulation techniques into multifunctional microfluidic devices is coupling the continuous‐flow format of most systems with the often batch‐type operation of particle separation systems. Here, a passive fluidic technique—one‐way particle transport—that can conduct microparticle operations in a closed fluidic circuit is presented. Exploiting pass/capture interactions between microparticles and asymmetric traps, this technique accomplishes a net displacement of particles in an oscillatory flow field. One‐way particle transport is achieved through four kinds of trap–particle interactions: mechanical capture of the particle, asymmetric interactions between the trap and the particle, physical collision of the particle with an obstacle, and lateral shift of the particle into a particle–trapping stream. The critical dimensions for those four conditions are found by numerically solving analytical mass balance equations formulated using the characteristics of the flow field in periodic obstacle arrays. Visual observation of experimental trap–particle dynamics in low Reynolds number flow (<0.01) confirms the validity of the theoretical predictions. This technique can transport hundreds of microparticles across trap rows in only a few fluid oscillations (<500 ms per oscillation) and separate particles by their size differences.     

流量可调燃气发生器压力闭环模糊控制算法

为了改进流量可调燃气发生器的调节精度,引入燃气发生器压力闭环控制,针对流量可调燃气发生器压力闭环控制特点,在压力闭环中引入了模糊积分控制,此控制算法响应速度快,超调量较小,不同工况及长时间工作下系统仍然有较好的动态特性。      

气—固两相流流型检测与调节的专家系统

气－固两相流流型的检测与调节是与两相流的测量密切相关的，本文针对精确的测量往往要受众多因素影响的情况，提出了一种判断流型的新方法，通过引入领域专家的知识，改进了单纯用模糊聚类方法的不确定，建立了检测和调节的专家系统结构，进行了计算机仿真试验，运用效果良好。     

一种真空状态下的气体流量测量新方法

当空气绝对压力小于40 kPa时,目前尚无简便有效的气流质量流量测量手段,为此本文设计了一套新颖的流量标定装置,并提出一种了流量测量方法。在流量调节过程中,调节阀必不可少。真空状态下,流经调节阀的流量几乎完全由阀前、后压力、气流温度四个变量决定。本文由流量标定装置获取有效的数据样本,基于多元非线性回归方法建立了流量与四者的关系表达式。一定范围内只要测定四个变量,则能直接计算出相应流量。实验结果表明计算值与实测流量偏差小于3.0%。     

Transport and Deposition of Evaporating Droplets in a Ventilated Environment

In this study, droplet transport, dispersion, and deposition in a ventilated office with two manikins were studied using a computer-modeling approach. Different airflow distribution systems were used, and an Eulerian approach was employed for the airflow simulation. The trajectories of droplets were evaluated using the Lagrangian approach by solving the equation of droplet motion that included the inertial, viscous drag, Brownian, Saffman lift, and gravity forces. Droplet evaporation was also taken into account by solving the droplet heat and mass transfer equations, thus, allowing for the variation of the droplet size. Mixing and displacement air distribution systems were examined, and trajectories of droplets in the range of 1 to 100 microns emitted by one of the manikins were simulated under a range of conditions. The simulation results showed that the chance for small droplets to leave the room through the exhaust is relatively high. When the mixing air distribution system is used, the drop dispersion is higher than with the displacement distribution system. This in turn suggests that the chance of transmission of air borne diseases is relatively higher for the mixing ventilation system.     

Particle dynamics in a multi-staged fluidized bed: Particle transport behavior on micro-scale by discrete particle modelling

This work studies the particle exchange rates in horizontal fluidized beds equipped with different weir designs between compartments. These particle exchange rates provide information on the axial dispersion of the solid material within the process. For this purpose discrete particle modelling (DPM) was used to determine the particle exchange on microscopic level. This method uses a coupled CFD-DEM approach to observe particle dynamics in a fluid field. The model was validated against exchange rates in a lab-scale setup as determined by Particle Tracking Velocimetry (PTV) with very good quantitative agreement, showing the suitability of the method for the evaluation of weir designs. Simulations were performed for different weir designs and under variation of the hold-up mass, the feed rate and gas velocity to predict their transport behavior in a pilot-scale 3D horizontal fluidized bed. The results indicate that the solids transport behavior is strongly dependent on the used weir design and the main driving force for the particle transport that can be influenced by the process conditions. The installation of weirs between two compartments induces a transport resistance, while the base type without the installation of a weir between the two chambers represents the fastest possibility for mixing the particles of a two-compartment system. It has been observed that the general trend shows higher particle recirculation rates for the overflow weir and base configuration (no weir), whereas the underflow and sideflow weir applications improve the solids transport through the horizontal fluidized bed.     

Particle conveying under microgravity in a vibrating vessel

This paper presents a numerical study on the conveying of particles in a vibrating vessel under microgravity. Such a vessel is composed of parallel plates with sawtooth wavy surfaces, which are specifically designed to convey particles using simple vibration. The numerical model was validated by good agreement between the simulated and experimental results. Then the effects of key variables, including the vessel geometry, vibration amplitude and frequency and gravity level, were systematically investigated by a series of controlled simulations. The results confirm the optimised design from the previous experiments, and numerically demonstrate that using such a system a steady conveying operation can be achieved under microgravity. The convey rate is positively affected by the vibration amplitude and frequency in a complicated way, which cannot be simply described by the commonly used vibration intensity or velocity amplitude. The gravity level also has a significant effect on the convey rate when it is over 0.001g. The convey rate can be estimated by the product of the average solid fraction and velocity. And the effects of the variables can be better understood through the analyses on these two parameters. Finally, a predictive model is proposed to estimate the convey rate under different operational conditions. The findings are useful for the design of particle conveying techniques for outer space applications.     

Particle Trajectory in a Bidirectional Vortex Flow

In this research particle trajectory in a bidirectional vortex flow has been numerically predicted and the results experimentally validated. Scale analyses of forces show their order of magnitudes and give a criterion to recognize the order of magnitude of exerting forces on the particle. The particle has been assumed to be a rigid sphere. Initial velocity, diameter, density, and position of entering particle are assumed to be known. If the particle length scale is considered not to be comparable with the chamber length and if particle number density is low, then influence of particle on the flow field is negligible and a one-way solution is applicable. The governing equation is converted to a set of nonlinear, coupled, second-order ODE and solved by a numerical scheme. Results show that higher density, larger diameter, and higher initial axial velocity tend to move the particles further in the axial direction. Also, the maximum axial movement of the particle occurs when the initial radial velocity is zero and there is an optimum entrance position that provides a maximum traveling trajectory for particles. Increasing initial z-direction velocity component and density will result in increasing traveling trajectory.