准直管磨料射流中各相介质在管内的流动机理与实验研究

介绍了准直管磨料射流的工作原理和特点,准直管磨料射流在准直管内的流动属于气（汽）、液、固多相混合介质的瞬变流动,分析了磨料在多相流体介质中的受力,推导了多相流体介质在准直管内有阻运动时的磨料运动方程式,提出了各种损失的经验计算方法,研究表明,气（汽）、液流体介质和磨料介质在准直管中的速度和密度是逐渐变化的,在０．４～３ｍ管长范围内磨料速度基本保持不变,短管时采用细磨粒,长管时长采用粗磨粒。     

流体在准直管内的高速流动及相变分析

描述了汽、液两相流在准直管内高速流动时的相变过程及有趣的物理现象,推导了准直管内高速稀疏介质的有阻运动方程式,讨论了流体介质的密度和温度变化过程。研究表明,准直管在一定长度范围内液体介质密度和速度几乎不变。     

多孔准直器性能的数值研究

在高能闪光照相中,多孔准直器法是用来扣除记录平面上照射量散射分量的技术。本文中初步研究了四种情况下多孔准直器的性能：（ａ）改变准直角θ;（ｂ）增加后保护锥到记录平面的距离;（ｃ）使用陡坡准直器;（ｄ）改变准直孔的孔径。结果表明：对全尺寸客体的闪光照相系统实施以上前三条措施之后,尽管前记录平面上的直散比ＤＳＲ与后记录平面上的照射量ＤＤ成分百分比均有所提高,但多孔准直器性能仍然不理想;也就是说,后记录     

淹没磨料射流的空泡运动分析

通过对淹没条件下磨料射流的空泡运动分析研究,建立了淹没磨料射流的空泡运动方程,揭示了淹没磨料射流中空泡的溃灭特性,数值模拟了淹没磨料射流的磨料体积浓度以及空泡所处流场压力对空泡运动及溃灭的影响规律.分析表明:淹没磨料射流中磨料的存在增大流体的粘性系数,增大空泡溃灭历时,减弱射流的空蚀破坏能力;流场压力的改变对空泡溃灭过程影响显著,压力越高,空泡溃灭历时越短.     

闪光照相多孔准直器的初步数值试验

高密度客体的闪光照相系统的散射光很强，因而常用多孔准直器方法来扣除。本文针对仅有客体的系统和既有客体、又有其它器件的系统，利用单孔准直器来研究后接收平面上总照射量的组成情况，以便论证多孔准直器方法对于各种系统的适用性。计算表明，对于仅有客体的系统，直穿分量占总照射量的９９％以上；对于既有客体、又有其它器件的系统，直穿分量占总照射量的９６％以上；对于既有客体、又有其它器件的系统，直穿分量Ｈ中总照射量     

脉冲磨料射流中球泡溃灭特性研究及数值分析

从理论上研究了脉冲磨料射流中空化球泡的溃灭特性,建立了脉冲磨料射流中空化球泡的动力学方程,数值计算分析了磨料浓度、磨料粒径、射流振荡频率和幅值以及流场压力对脉冲磨料射流中空泡溃灭过程的影响规律。研究表明,脉冲磨料射流中磨料的存在将增大空泡溃灭历时,从而减弱射流的空蚀破坏能力,其中磨料的粒径、浓度和流场压力影响幅度较大。     

基于正交实验法的淹没磨料射流冲蚀性能实验研究

简要介绍了磨料射流原理以及实现淹没磨料射流的方法和装置。影响淹没磨料射流冲蚀性能的因素很多。为了确定对冲蚀性能影响较显著的因素及其重要性次序,进而提出在淹没磨料射流实验研究中的计算方法,应用了正交实验法安排实验,同时利用正交分析的相关方法得出结论。为进一步研究和改进淹没磨料射流性能奠定了基础。     

聚四氟乙烯和超高分子量聚乙烯的磨粒磨损性能与机理研究

为了开发地面机械触土部件用高聚物基复合材料，以９６．５％（ｗｔ）石英砂（粒度４５０－９００μｍ）和３．５％（ｗｔ）膨润土（粒度７６μｍ）作磨料，在ＪＭＭ型转盘式磨粒磨损试验机上对聚四氟乙烯和超高分子量聚乙稀的耐磨粒蘑损性能与淬火回火４５＃钢的进行了对比试验研究，并且通过磨损表面形貌的扫描电子显微镜观察，探讨了这两种高聚物材料的磨损机理，在相对滑动速度为１２３．６ｍ／ｍｉｎ、滑动距离为２５７０８．８ｍ、试样摩擦面与磨粒运动的切向呈３５°角、试样在磨料中的埋入深度为４０ｍｍ的试验条件下，用重量损失和体积损失计量时，尽管超高分子量聚乙烯的耐磨性分别是聚四氟乙烯的８．４２倍和３．７６倍，但与淬火回火４５＃钢相比，其以重量损失计量时的耐磨性是后者的４．０４倍，而以体积损失计量时的耐磨性却不及４５＃钢的５０％，这说明要将超高分子量聚乙烯用于制造地面机械的触土部件，还应设法改善它的耐磨性能。研究表明，导致聚四氟乙烯磨损的重要机制是犁切，导致超高分子量聚乙烯磨损的重要机制是疲劳磨损。     

淹没磨料射流研究进展及冲击特性试验研究

本文简要回顾了非淹没磨料射流技术与人工淹没环境条件理论的发展与应用，认为将磨料射流引入水下加工领域是一种新的尝试，通过介绍国内外的一些相关研究，充分显示了淹没磨料射流的潜在优势，在此基础上，提出一套淹没磨料射流的模拟装置，实现了在实验室进行模拟大水深环境的淹没磨料射流性能试验。     

苜蓿草粉对金属材料磨损性能的影响

采用正交试验法在磨料磨损试验机上考察了不同粒度苜蓿草粉对45#钢和HT200灰铸铁磨损性能的影响,研究了不同载荷和转速等条件下的磨料磨损行为,采用扫描电子显微镜对其磨损表面形貌进行观察.结果表明:影响材料磨损性能的因素由大到小依次为转速、磨粒粒度和载荷;苜蓿草粉磨粒对金属材料表面的磨损为硬、软磨粒共同作用的结果;45#钢在硬磨料磨损条件下以显微切削为主要磨损机制,在软磨粒磨损条件下以多次塑性变形和低周期疲劳为主要磨损机制;HT200灰铸铁以塑性变形而产生的脆化剥落为主要磨损机制.     

Particle behavior in a turbulent pipe flow with a flat bed

Particle behavior in a turbulent flow in a circular pipe with a bed height h = 0.5R is studied at Re_b = 40,000 and for two sizes of particles (5 μm and 50 μm) using large eddy simulation, one-way coupled with a Lagrangian particle tracking technique. Turbulent secondary flows are found within the pipe, with the curved upper wall affecting the secondary flow formation giving rise to a pair of large upper vortices above two smaller vortices close to the pipe floor. The behavior of the two sizes of particle is found to be quite different. The 50 μm particles deposit forming irregular elongated particle streaks close to the pipe floor, particularly at the center of the flow and the pipe corners due to the impact of the secondary flows. The deposition and resuspension rate of the 5 μm particles is high near the center of the floor and at the pipe corners, while values for the 50 μm particles are greatest near the corners. Near the curved upper wall of the pipe, the deposition rate of the 5 μm particles increases in moving from the wall center to the corners, and is greater than that for the larger particles due to the effects of the secondary flow. The maximum resuspension rate of the smaller particles occurs above the pipe corners, with the 50 μm particles showing their highest resuspension rate above and at the corners of the pipe.     

Particle motion and turbulence in dense two-phase flows

Measurements of particle mean and r.m.s. velocity were obtained by laser-Doppler anemometry in a descending solid-liquid turbulent flow in a vertical pipe with volumetric concentrations of suspended spherical particles of 270 μm mean diameter in the range 0.1–14%. Similar measurements were obtained in the flow downstream of an axisymmetric baffle of 50% area blockage placed in the pipe with volumetric concentrations of 310 μm particles up to 8% and of 665 μm particles up to 2%. In order to enable measurements in high particle concentrations without blockage of the laser beams the refractive index of the particles was matched to that of the carrier fluid.

The results show that the particle mean velocity profiles become more uniform and the particle r.m.s. velocity decreases with increasing concentration in both flow cases. The particle mean velocity in the pipe flow also decreases with concentration and the relative velocity, the difference between the particle velocity and the fluid velocity in single-phase flow, decreases with increasing Reynolds number. The length of the recirculation region downstream of the baffle was shorter than in single-phase flow by 11 and 24% for particle concentrations of 4 and 8%, respectively. The particle mean velocities were hardly affected by size for concentrations up fo 2%, but the r.m.s. velocities were lower with the larger particles.     

A Modelling Study of Evolving Particle-laden Turbulent Pipe-flow

An Eulerian turbulent two phase flow model using kinetic theory of granular flows for the particle phase was developed in order to study evolving upward turbulent gas particle flows in a pipe. The model takes the feedback of the particles into account and its results agree well with experiments. Simulations show that the pipe length required for particle laden turbulent flow to become fully developed is up to five times longer than an unladen flow. To increase the understanding of the dependence of the development length on particle diameter a simple model for the expected development length was derived. It shows that the development length becomes shorter for increasing particle diameters, which agrees with simulations up to a particle diameter of 100 ??m. Thereafter the development length becomes longer again for increasing particle diameters because larger particles need a longer time to adjust to the velocity of the carrier phase.     

An unexpected phenomenon observed in particle settling: oscillating falling spheres

We have observed the phenomenon of oscillating particle settling. A particle settling in borate cross-linked hydroxy propyl guar in a pipe with a relatively large particle/pipe diameter ratio regularly accelerates and decelerates while it is settling. The phenomenon can be described by a particle that settles slower and slower until at a certain point the particle suddenly accelerates as if it is settling in a Newtonian fluid and then start slowing down again. This cycle regularly repeats itself a number of times before the bottom of the pipe is reached. The phenomenon has been reproduced a number of times with different fluids.     

Wavelet analysis on particle dynamics in a horizontal air–solid two-phase pipe flow at low air velocity

High-speed particle image velocimetry (PIV) is first used to measure two components of the fluctuating particle velocities for different particle sizes and solid mass flow rates at low air velocity in a horizontal pipe. Then, the continuous wavelet transform and orthogonal wavelet multi-resolution techniques are employed to analyze and decompose the fluctuating particle velocities to provide both quantitative and qualitative information on the particle fluctuation velocity of various frequencies. It is revealed that the fluctuating energy of axial particle velocity is mainly contributed from the wavelet components of low frequency, accounting for about 84%, near the bottom part of the pipe cross-section. However, the contribution to the fluctuating energy of vertical particle velocity accounts for about 82% from the wavelet components of high frequency. The auto-correlation analysis suggests a quasi-periodical large-scale axial particle fluctuating velocity. On the other hand, the spatial correlation analysis indicates that the low-frequency components of the axial particle velocity exhibit a large correlation near the bottom part of the pipe cross-section. From the probability density function (PDF) distribution, it is found that the low-frequency components of the axial particle velocity exhibit larger fluctuation, and this fluctuation reduces as the frequencies increase near the bottom part of the pipe cross-section. Near the top part of the pipe cross-section, however, a larger fluctuating axial particle velocity appears in the high-frequency range.     

气固两相分支管流动及流量分配特性的研究

在水平T型分支管道中,用压缩空气对平均粒径为0．5mm砂石进行气固两相流试验。试验结果表明,当压缩空气的流速大于33m／s时,T型分支接头处没有固相沉积,两个分支管路分配的流量几乎相同。当压缩空气的流速小于33m／s时,分支接头处出现沉积,并且沉积量和分支管路的流量分配与分支管路上阀门开度有关:开度相同时,分支接头两侧的固相沉积量和流量分配相同;开度不同时,阀门开度小的一侧分支接头处的沉积量少,其分配的流量也少。     

惰化剂粒径对铝粉火焰传播特性影响的实验研究

为探索惰化剂粒径对可燃工业粉尘火焰传播特性的影响,通过建立竖直粉尘燃烧管道实验平台,在碳酸氢钠质量分数为30%的惰化条件下,就碳酸氢钠粒径对铝粉燃烧火焰传播特性的影响进行了实验研究。结果表明:平均粒径为30 μm的碳酸氢钠粉体对平均粒径为15 μm的铝粉的火焰传播速度具有较好的抑制作用,惰性粉体与可燃工业粉尘应存在粒度匹配效应;碳酸氢钠粉体对铝粉火焰温度的惰化抑制效果与其粒径呈反比关系;碳酸氢钠粉体会减小铝粉火焰预热区厚度,预热区厚度随碳酸氢钠粒径的增加先减小后增大。此外,分析了碳酸氢钠粒径对铝粉火焰传播特性影响的作用机理。     

Effect of particle size on a two-phase turbulent jet

The effect of particle size on two-phase turbulent jet flow structure is studied in the present experimental investigation. Polystyrene solid particles of 210, 460, and 780 μm were used. The particles' mass loading ratios ranged from 0 to 3.6. The flow Reynolds number was 2 ‘ 10⁴, which was based on the pipe nozzle diameter and the fluid-phase centerline velocity at the nozzle exit. A two-color laser-Doppler anemometer (LDA), combined with the amplitude discrimination method and the velocity filter method, was employed for measurement. The measurement range of the jet flow was from the initial pipe exit to 90D downstream. Results are presented for the mean velocities of particle and fluid phases, the flow's turbulent intensities and the flow's Reynolds stresses. The energy spectra and the correlation functions of the two-phase jet flow were also obtained by using another one-component He-Ne LDA system.     

Pipe flow of suspensions in turbulent fluid

The general case of a fully developed pipe flow of a suspension in a turbulent fluid with electrically charged particles or with significant gravity effect, or both, and for any inclination of the pipe with the direction of gravity, is formulated. Parameters defining the state of motion are: pipe flow Reynolds number, Froude number, electro diffusion number, diffusion response number, momentum transfer number and particle Knudsen number. Comparison with experimental results is made for both gas-solid and liquid-solid suspensions. It is shown that the gravity effect becomes significant in the case of large pipe diameters and large particle concentrations.