INSTRUMENTATION FOR FLOW PROPERTIES OF GAS-SOLID SUSPENSIONS AND RECENT ADVANCES

Measurements of local velocity, density, and mass flow of phases of a gas-solid suspension are needed in determining transport properties, validating theoretical predictions, and formulating design procedures. Most of the available instruments are based on time averages or fluctuations with time. Primary standard for direct measurement of density of a phase such as solid particles is being developed. A laser phase Doppler device, within certain restrictions, may give local instantaneous density, while other optical methods and neutron beam remain secondary standards based on mass flow calibrations. An overall review including recent results has been made on both intrusive and non-intrusive instruments; their limitations and future possibilities are outlined and discussed. The limitations of the traditional approach utilizing the triangular relation between local averages of mass flow, velocity, and density of particles for the determination of flow properties, and higher order correlations are demonstrated.     

竖直矩形通道内不凝性气体对凝结换热特性的影响

本文以去离子水为工质,实验研究了竖直矩形窄通道内少量残余不凝性气体对蒸汽凝结换热特性的影响。采用热阻分离法得到凝结侧换热表面传热系数,分析了不凝性气体的含量、冷却水质量流速、进口温度和热流密度对蒸汽凝结侧表面传热系数的影响。结果表明:当热流密度为1.668 kW/m~2,即蒸汽质量流速较小时,2%体积分数的不凝性气体使凝结侧表面传热系数下降了33%,但当热流密度为3.887 kW/m~2,蒸汽质量流速较大时,2%体积分数的不凝性气体仅使凝结侧表面传热系数降低了14%,此外,凝结换热表面传热系数随冷水质量流速和不凝性气体分数的增加而变小,随冷水进口温度和热流密度的增加而变大。     

Study of the neutral gas flow on discharges of capacitively coupled plasma in a PECVD reactor

A two-dimensional fluid model is established to describe the argon discharges coupled with the neutral gas flow in a capacitively coupled plasma reactor. Two different configurations are designed to investigate the influence of the gas flow direction on discharges. The radial distributions of ion density and ion flux are paid for a special attention. It is found that when the gas flow is mainly axial, the ion density and ion flux increases significantly with the increase of inlet velocity, and the radial uniformity of their distributions changes little. When the gas flow is mainly radial, there are two peaks in the ion density distributions. With the increase of velocity, the left peak is weakened and the right peak is enhanced. It is also found that with the increase of the outlet pressure, both the ion density and ion flux increase greatly, but the influence of the gas flow on discharges decreases distinctly. Moreover, it is shown that the density peak moves from side to center at high pressure when the neutral gas flow is mainly in the axial direction.     

Bogoliubov Theory for a Superfluid Bose Gas Flowing in a Random Potential: Stability and Critical Velocity

We investigate the stability and critical velocity of a weakly interacting Bose gas flowing in a random potential. By applying the Bogoliubov theory to a disordered Bose system with a steady flow, the condensate density and the superfluid density are determined as functions of the disorder strength, flow velocity, and temperature. The critical velocity, at which the steady flow becomes unstable, is calculated from the spectrum of hydrodynamic excitation. We also show that in two dimensions the critical velocity strongly depends on the system size.     

粉末高速压制成形密度分布的数值模拟及影响因素分析

将研究不连续体力学行为的离散单元法应用于粉末高速压制致密化过程的研究,将粉末视为黏弹性的离散颗粒,建立粉末高速压制过程颗粒接触模型及每个颗粒的基本运动方程,推导了力与位移表达的粉末高速压制黏弹性本构关系。基于PFC软件实现了铁粉高速压制过程中粉末颗粒二维流动情况及压坯密度分布的数值模拟,模拟结果的密度分布规律与实际压制的密度分布规律较为一致;利用数值模拟结果对影响压坯密度分布的摩擦因数、高径比、双向压制因素进行了具体分析。     

时间压力下人员流动状态的观测和分析

利用数码摄像机、计数器等工具,在大学校园等处,就人员流动状态进行了大量的实际观测。总结分析了时间压力下,在平直通道、90°弯道以及下楼梯时,人员流动速度与群集人员密度的关系,提出了90°弯道以及下楼梯时人员流动速度的局部衰减系数等新概念。研究结果表明,时间压力下,90°弯道以及下楼梯时的人员流动速度分别衰减为平直通道上人员流动速度的70%和60%。     

有限元网格对RTM充模模拟的影响

本工作基于有限元控制体积法编写了模拟程序,研究了节点数量、网格密度对模拟过程的影响.以带圆孔的长方形为例,模拟比较了不同网格密度和注入口位置对充模时间、流动前沿以及干点形成区域的影响.结果表明,节点数量增加到一定程度时,只延长计算时间,对充模时间影响很小;网格疏密分布影响流动前沿的位置,根据流动前沿的形状可以确定排气口的位置和数量.     

双弯管法测量气固两相流质量流量的研究

提出了一种基于弯管单相流测量原理的气固两相流固相质量流量的测量方法——双弯管法，它无需知道被测物体的密度而直接得出两相流中固相质量流量。基于双弯管法测量原理，设计了一套实验系统，给出了测量数据、计算公式，实验证明了此测量方法的可行性。     

On the evolution of flow stress during constrained groove pressing of pure copper sheet

Using a mechanical model and dislocation density based model, the evolutions of dislocation density and flow stress of pure copper during constrained groove pressing (CGP) process are investigated. In this regard, the strain and strain rate are achieved from the mechanical model and then input into the dislocation model. To verify the predicted flow stress, the process of constrained groove pressing is performed on the sheets of pure copper from one to three passes. The predicted flow stresses are compared with the experimental data and a good agreement is observed. Also, it is found that during the straining of the copper sheet in CGP process, the dislocation density and strength dropping occur in lower strain than that in other severe plastic deformation processes.     

Magnetohydrodynamics Nanofluid Flow Containing Gyrotactic Microorganisms Propagating Over a Stretching Surface by Successive Taylor Series Linearization Method

Nanofluid dynamics with magnetohydrodynamics has tremendously contributed in industrial applications recently since presence of nanoparticle in base fluids enhances the specific chemical and physical properties. Owing to the relevance of nanofluid dynamics, we analyze the nanofluid flow in the presence of gyrotactic microorganism and magnetohydrodynamics through a stretching/shrinking plate. The impacts of chemical reaction and thermal radiation on flow characteristics are also studied. To simplify the governing equations of microorganisms, velocity, concentration and temperature, the similarity transformations are employed. The couple governing equations are numerically solved using Successive Taylor Series Linearization Method (STSLM). The velocity profile, motile microorganism density profile, concentration profile, temperature profile as well as Nusselt number, skin friction coefficient, Sherwood number and density number of motile microorganisms are discussed using tables and graphs against all the sundry parameters. A numerical comparison is also given for Nusselt number, Sherwood number, skin friction, and density number of motile microorganisms with previously published results to validate the present model. The results show that Nusselt number, Sherwood number and density number diminish with increasing the magnetic field effects.     

Maximum likelihood segmentation of ultrasound images with Rayleigh distribution

This study presents a geometric model and a computational algorithm for segmentation of ultrasound images. A partial differential equation (PDE)-based flow is designed in order to achieve a maximum likelihood segmentation of the target in the scene. The flow is derived as the steepest descent of an energy functional taking into account the density probability distribution of the gray levels of the image as well as smoothness constraints. To model gray level behavior of ultrasound images, the classic Rayleigh probability distribution is considered. The steady state of the flow presents a maximum likelihood segmentation of the target. A finite difference approximation of the flow is derived, and numerical experiments are provided. Results are presented on ultrasound medical images as fetal echography and echocardiography.     

常压下超音速等离子体射流的数值模拟

数值模拟研究了在二维轴对称情形下,超音速等离子体射流喷射于常压环境中的湍流流动,其中考虑了等离子体物性随温度的大幅度变化,还考虑了粘性耗散。等离子体射流的数学模型采用了Navier-Stockes方程,对湍流的模拟采用了ek-方程。计算方法以SIMPLER方法为基础,引入密度修正,得到适用于可压缩流体的p方程和p方程。p方程用来更新现有压力场和密度场,p方程用来修正速度场以保证质量守恒。计算结果对常压下超音速等离子体射流的进一步研究有重要的参考价值     

Thermal flow permeametry – A rapid method for finding local changes in flow channels

Solid bodies with flow channels can have very heterogeneous structure, whose local variations are difficult to analyze. Yet, this can play an important role affecting characteristics, such as, fluid flow property, strength and heat conductivity. This article presents a method named thermal flow permeametry (TFP) that is applicable for a quick analysis of variations in flow channels, even in meter-sized structures. For illustrating the method, we analyzed the local permeability levels of a large and extremely complex fiber structure. In TFP, hot air is ejected through a structure, while thermal camera measures local surface temperature variations during heating. Gray values of the thermal image are then plotted versus the structures local thickness, density and permeability. We showed that gray values link with local permeability, affected by thickness, density and flow channel tortuousness. We also found out that TFP is very sensitive to local changes in flow channels.     

Method of Measuring the Mass Flow Rate of a Substance by Using Restricting Apertures

A new method is considered for measuring the mass flow rate of a substance in pipelines using restricting apertures, without the use of instruments for measuring the density and temperature of the flow. A structural measurement scheme is given and analytical expressions are obtained for determining the mass flow rate and the density of the substance under working conditions. A calculation is given of the errors of the flow parameters.     

Current–voltage characteristics of a flat probe in a rarified plasma flow

Mathematical and numerical models of a collision-free plasma flow about the flat probe are developed. The current–voltage characteristics of flat probes located along and transverse across the flow, as well as the distributions of the current density over the probe width, are obtained. The numerical simulation results might be applied in probe diagnostics of plasma flows.     

Characterization of atmospheric aerosols from infrared measurements: simulations, testing, and applications

An inversion method for the characterization of atmospheric condensed phases from infrared (IR) spectra is described. The method is tested with both synthetic IR spectra and the spectra of particles that flow in a cryogenic flow tube. The method is applied to the IR spectra recorded by the Atmospheric Trace Molecule Spectroscopy instrument carried by the Space Shuttle during three missions in 1992, 1993, and 1994. The volume density and particle size distribution for sulfate aerosol are obtained as a function of altitude. The density and size distribution of ice particles in several cirrus clouds are also retrieved. The probable radius of the ice particles in the high-altitude (10-15-km) cirrus clouds is found to be approximately 6-7 microm.     

新型气固两相流亚微米级粉体浓度及浓度分布测量方法

提出了一种新型的基于激光散射原理的气固两相流亚微米级粉体浓度及浓度分布测量方法, 适合流场的物质组成及其浓度分布等气固两相流特性分析。以烟气烟尘浓度检测为例, 介绍了基于上述测量原理的烟尘浓度监测装置的设计及其工程实现方法, 可望推广到石油、医药等其它化学工业的气固两相流浓度分析。