QUANTITATIVE CAPACITIVE MEASUREMENTS OF VOIDAGE IN GAS-SOLID FLOWS

New capacitance probes were developed for quantitative, time-dependent measurements of voidage in gas-solid flows. Based on a unique guard circuit which nearly eliminates all stray and cable capacitances, these probes are fast (2 kHz) and they do not require in situ calibration. Two configurations were studied: small parallel plates for recording voidage profiles, and a non-intrusive design for local voidage measurements near a wall Static tests were performed using a fixed bed of known voidage and dielectric constant. The probes were also demonstrated in a two-dimensional fluidized bed of glass beads.     

PRESSURE CHANGES AT A SUDDEN EXPANSION IN GAS-SOLID FLOWS

There is a pressure recovery when a two-phase mixture passes through a pipe enlargement. This paper describes an experimental project for the determination of this pressure recovery in air-solids systems. The solids used are medium size wax and lucite particles. Two pipe diameter ratios were investigated, 0.63 and 0.76. The Reynolds numbers for the experiments varied between 45000 and 72000 and the loading ratios were low to intermediate (up to 6), it was observed that the major part of the pressure recovery in these mixtures was due to the air alone and that only a small part of it (up to 25%) was due to the deceleration of solid particles.     

LDV MEASUREMENTS IN GAS-SOLID FLOWS—A REVIEW

This paper describes the history of LDV measurements employed in research involving gas-solid flows. Much of the discussion deals with measurement techniques employed to obtain separate and simultaneous solid and gas phase velocities. Also, LDV based measurement techniques that are used to obtain particle size and concentration information in conjunction with the velocity measurements are presented.     

STABILITY OF FLOWS IN FLUIDIZED BEDS

ABSTRACT

We study the linearlized stability of the state of uniform fiuidization, within the context of the theory of mixtures. The mixture is assumed to be made up of a classical linearly viscous fluid infused with particles. In marked departure from most of the previous studies, we model the solid as a granular material and assume a constitutive relation that stems from classical motions in continuum mechanics. The linearized stability analysis of the state of uniform fiuidization, in general, for a three-dimensional disturbance leads to an eighth order equation for the characteristic whose root implies instability, when positive.     

GaAs中Si的二次离子质谱定量分析

评述砷化镓中硅SIMS定量分析的进展，讨论了相对灵敏度因子法。对此种GaAs的原始参考物质，用实验确认了其可靠性。为常规定量分析研制了二次参考物质。对一些关键实验因素，如样品装载、仪器参数以及离子选择等进行了仔细研究，并评价它们对定量重复性、精确性、检测限和基体效应的影响。Cs 源入射时GaAs中Si定量分析精度在15％内；检测AsSi二次离子时，29Si的检测限达5×1014atoms／cm3。     

收缩-扩张喷管内气固两相流运动规律研究

航空飞行器在简易跑道起飞或降落时,砂尘颗粒不可避免被发动机吸入,并与高速旋转的发动机叶片发生冲撞,导致叶片冲蚀损伤,显著降低发动机使用寿命,严重威胁飞行器的安全。试验中一般采用气动喷砂的方法将砂尘粒子加速至一定速度,并冲击试验件,以模拟发动机叶片的实际冲蚀过程。喷管是实现粒子加速的关键部件,该文通过试验和数值模拟对不同入口总压条件下收缩-扩张喷管加速砂尘颗粒的情况进行研究。实验中,通过压力传感器和双盘测速分别测量了喷管内壁静压和喷管出口处的颗粒速度;数值模拟中,采用实验入口总压条件,模拟了稀疏砂尘颗粒在喷管中的气固两相流运动,并详细分析了气流运动和颗粒的受力及加速情况。研究表明：数值模拟的气流压力分布及颗粒速度均与实验结果吻合;喷嘴出口处粒子速度随入口总压的增大而增大,且总压为0.23 MPa~0.4 MPa范围时的增长速率较大,而总压为0.4 MPa~0.56 MPa范围时的增长速率较小;粒子的加速主要发生在喷管的扩张段。     

气液两相流阶跃脉冲瞬变过程数值计算

构建了气液两相流动的半经验波动模型，用特征线法对绝热管中初始空泡分布为阶跃脉冲的气液两相流动过程进行数值计算，研究脉冲空泡分布的流动稳定性。计算表明，脉冲空泡场具有色散波特征，存在不稳定的行波解。阶跃稳定域由阶跃初始值、终了值以及漂移通量特性决定。     

MODELING OF SALTATION AND TURBULENCE EFFECTS IN A HORIZONTAL GAS-SOLID BOUNDARY LAYER

This work is devoted to the study of the behavior of solid particles in a horizontal air boundary layer. A two-fluid model is selected to analyze the particle motion in the mixed regime where both saltation and turbulence effects are important. Boundary layer approximations are applied to the solid phase equations, using conventional space/time averaging. Resulting equations are shown to be in agreement with the phase averaged equations generally used in two-fluid models. Closure is achieved by means of a gradient law, however the particle diffusion and momentum transfer coefficients are distinguished using a variable particle Schmidt number. Turbulent particle diffusion is modeled using an available analytical model, which is modified to take the saltation effect into account in the particle r.m.s. velocity. Comparison between experimental and numerical results shows that the following analysis is acceptable within the experimental and numerical error. The model slightly underestimates the particle mean velocity in the outer region of the boundary layer, but yields satisfactory values of mass fluxes. The present simple approach adequately describes the particle behavior in a horizontal turbulent boundary layer, with the main originality being the realistic dependence of the particle Schmidt number upon the saltation phenomenon.     

银薄膜织构变化的定量研究

利用X射线衍射(XRD)织构分析技术研究了未退火及在400℃温度条件下经4h真空退火处理后的银薄膜织构。结果表明，银薄膜主要存在(111)和(100)面织构组份。银沉积薄膜(未退火)中(111)取向的晶粒多于(100)取向的晶粒。经退火处理后的硅基银薄膜表现更强的(111)和(100)面织构，而且(111)和(100)取向的晶粒数量基本相当。用表面能和应变能各向异性驱动晶粒生长的机理对此给予了解释。     

微机械电容式加速度计的开环工作模式

在微机械电容式加速度计中利用静电力反馈使加速度计处于闭环力平衡模式工作,能提高加速度计的线性度。本文阐述了静电力在开环工作模式中的作用,导出了相关的灵敏度公式,报导了实验结果和成功地将原闭环工作的±１ｇ 量程加速度计直接变为低量程的微机械电容式加速度计的实例,其量程为±０．０１ｇ,线性度优于０－２ ％ 。     

同心圆桶内电流变液瞬态屈服边界的数值模拟

运用带有调整因子的修正Bingham模型,通过数值方法对圆桶电流变离合器在突加电场情况下的动力学特性进行分析。研究表明电流变液屈服应力公式中参数b对离合器动力学特性具有很大影响,b以0.2为界,当0.2>b时未屈服区粘附于内桶壁,屈服边界始于内桶壁,并逐渐向外桶壁方向移动;当0.2相似文献   

PREDICTION OF HEAT TRANSFER IN A TURBULENT GAS-SOLID PIPE FLOW USING A TWO-FLUID MODEL

The dynamic and thermal behaviour of a turbulent gas-solid flow in a vertical pipe has been numerically studied by means of an original two-fluid approach which includes the effects of particle-particle and particle-wall collisions as well as particle-turbulence interactions. A k-ε-k_p model for the flow dynamics has been combined with the energy balances of each phase. Comparisons have been carried out with available experimental data, first for the dynamic validation, and then for the thermal portion of the problem, in the case of rather large panicles (200 to 500 µm). Heat transfer from wall to suspension is seen to be strongly affected by particles. As a consequence, a suspension Nusselt number decrease of 20% may be observed at loading ratio smaller than two. Further increase is possible if more panicles are injected. Predictions had excellent agreement with experimental data for 500 µm particles. Slight discrepancies appear for smaller particles, probably due to more complex, partially understood panicle-turbulence interactions.     

定量分析中NiAl3标准K值的一种测定方法

利用平衡凝固方法制备了NiAl3相和α-Al相(质量比，1：1)的混合标准试样，利用该试样对NiAl3相X射线定量分析用的K值进行了实验测定。分析表明，平衡凝固工艺可直接获得NiAl3相K值测定用标准试样，所测定的NiAl3相K值可应用于Ni-A1合金相组成的准确测定。     

APPLICATION OF LIAPUNOV'S SECOND METHOD OF STABILITY TO GAS-SOLID TRANSPORT

Liapunov's second method of stability was applied to two basic equations describing particle and gas velocities during horizontal gas-solid transport. System parameters were then varied to determine which, if any, had a significant effect on the conditions at which the transport system borders between stability and Instability. The regions of asymptotic stability (RAS) increase with an increase in particle diameter, particle density and linear pressure drop but decreases with an increase in fluid density. The line diameter is not a significant parameter for changing the RAS. Actual experimental data must be tested to evaluate the usefulness of the analysis.     

温州滨海平坦地貌近地台风特性实测研究

为研究温州滨海平坦地貌近地台风特性,在温州滨海建立了风工程实测基地（塔高10 m）,并利用台风\     

MODELING OF SOLID FLOWS IN A FLUIDIZED BED WITH SECONDARY TANGENTIAL AIR INJECTION IN THE FREEBOARD

Abstract

The Vortexing Fluidized-Bed Combustion (VFBC) technique was recently developed for small- and medium-scale coal-burning boiler applications. Experimental observations showed that the general solid flows in the freeboard of a vortexing fluidized bed consisted of three successive stages: (1) spirally ascending motion before colliding the freeboard wall, (2) bouncing on the wall, and (3) sliding on the wall and exiting the freeboard. This study attempts to model these three stages of solid flows. The dimensionless governing equations for particle motion in the swirling field were presented taking into account the interactions of particle inertia, centrifugal force, viscous fluid drag, and gravity. Numerical solutions of particle velocities and trajectories were pursued, and effects of particle momentum transfer number, Froude number, and particle-wall restitution coefficient were delineated. The experimental validation of solid flows in the swirling freeboard was furnished with an 18 cm ID laboratory fluidized bed.     

MODELING OF SOLID FLOWS IN A FLUIDIZED BED WITH SECONDARY TANGENTIAL AIR INJECTION IN THE FREEBOARD

The Vortexing Fluidized-Bed Combustion (VFBC) technique was recently developed for small- and medium-scale coal-burning boiler applications. Experimental observations showed that the general solid flows in the freeboard of a vortexing fluidized bed consisted of three successive stages: (1) spirally ascending motion before colliding the freeboard wall, (2) bouncing on the wall, and (3) sliding on the wall and exiting the freeboard. This study attempts to model these three stages of solid flows. The dimensionless governing equations for particle motion in the swirling field were presented taking into account the interactions of particle inertia, centrifugal force, viscous fluid drag, and gravity. Numerical solutions of particle velocities and trajectories were pursued, and effects of particle momentum transfer number, Froude number, and particle-wall restitution coefficient were delineated. The experimental validation of solid flows in the swirling freeboard was furnished with an 18 cm ID laboratory fluidized bed.     

MAGNETOSTRICTION EFFECTS IN CRACK LENGTH MEASUREMENTS

Abstract— Fatigue crack lengths were measured in a ferromagnetic material (a low alloy steel) using the d.c. potential drop technique. Significant cyclic fluctuations in potential were observed. Using discriminatory tests it has been established that the fluctuations may be attributed to inverse magnetostriction known as the Villari effect. The strain rate dependence of the fluctuations was investigated using sinusoidal, square and sawtooth waveforms, and the amplitude of the fluctuations was shown to be proportional to strain rate. In some cases the amplitude of the fluctuations was of similar magnitude to the crack length measurement potential.