共查询到19条相似文献,搜索用时 156 毫秒
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通过分析现有的层流、湍流及过渡状态下非球形颗粒及颗粒群阻力系数的实验与理论研究结果,给出了非球形颗粒及颗粒群自由沉降速度的理论计算公式,并对各种单一非球形颗粒及非球形颗粒群沉降速度的计算结果与现有的实验结果进行了比较.比较结果表明,所得到的非球形颗粒及颗粒群自由沉降速度的理论计算公式与实验结果符合的很好. 相似文献
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本文从理论上对散式流态化中流化颗粒所受作用罚进行了探讨。表明广泛应用的拟均相模型的不合理性,提出了应采用分离流模型来分析散式流态化中颗粒的受力情况,证明了流化颗粒所受浮力符合陈基米德原理。 相似文献
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衍射法测量柱形颗粒群尺寸分布的数值计算方法 总被引:2,自引:0,他引:2
以柱形颗粒的衍射理论为基础,提出了适用于非球形颗粒衍射模型的数值计算方法。应用结果证明这种计算方法的数值计算时间满足在线测量的需要,并特别适合于测量颗粒尺寸分布空窄时的数值计算。 相似文献
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该文提出一种基于概率接触算法,并嵌入到球形颗粒离散元程序中,在保持原有颗粒接触检索效率的基础上,实现了非球形颗粒模拟。以椭球颗粒为例给出了算法推导过程,进行了球形西米、椭球形绿豆和长米的料仓卸料过程模拟,对颗粒体系的流态和流量进行了研究,并开展了相应的试验加以验证。结果表明:基于概率接触算法的非球形颗粒离散元法适用于在椭球颗粒流动特性方面的研究,可以较精确的模拟卸料过程,且计算效率较高。 相似文献
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以低成本工业级硅酸钠为原料,采用离子交换法制备了非球形纳米二氧化硅颗粒。在制备过程中,采用控制无机碱催化剂1%(质量分数)氢氧化钠水溶液滴加到活性硅酸速度的方法来控制二氧化硅晶核成核的形貌,进而控制二氧化硅颗粒的形貌,避免了传统方法(通过引入有机碱或者引入二价或三价阳离子)制备非球形二氧化硅颗粒的不足。扫描电镜显示所制备的二氧化硅颗粒为非球形(呈花生、哑铃或枣状),轴向粒径为10~20nm,径向粒径为45~80nm。激光粒度分析仪测试表明非球形颗粒高斯分布平均粒径为39.0nm,多分散指数高达0.261。该方法制备非球形二氧化硅颗粒步骤简单、环境友好,非常有利于工业化生产与应用。 相似文献
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《Advanced Powder Technology》2003,14(1):17-31
In order to prepare standard reference particles, experimental and theoretical studies have been conducted on particle size measurement of two kinds of spherical glass beads. The sheath flow- type electrical sensing zone method and the revised sedimentation balance method were used for the measurement. The data were compared with those obtained by the microscopic method with a sample size greater than 10 000. The particle size distributions obtained by use of the sheath flow- type electrical sensing zone method and microscopic method are nearly equal for the two kinds of glass beads. However, deviations of less than 5% were observed between the improved sedimentation balance and microscopic methods. The experimental data of the microscopic method are within the 95% reliability region of the sheath flow-type electrical sensing zone method. 相似文献
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Simon Vanmaercke Engelbert Tijskens Gert Van den Eynde Yann Bartosiewicz 《Granular Matter》2011,13(6):713-721
The paper aims at developing a validated model that can accurately predict the flow of a particulate material. This model
will serve as a virtual design tool for the design of a novel passive safety system for nuclear reactors. Therefore an experimental
setup consisting of a vertical glass tube is filled with 500±30 μm spherical glass particles. The experiment is then placed in a vacuum and the particles are released by opening a valve.
The velocity of the particles is recorded during their fall at three different heights using a non invasive optical tracking
technique with an original implementation. The same experiment is then simulated using the Discrete Element Method and results
are compared. A good agreement between the simulation and the experiment was found. The sensitivity of the simulation to a
change in the contact stiffness, dynamic Coulomb coefficient of friction and tangential contact force model was investigated.
The influence of the initial position of the simulated particles on the packing factor was shown to be very important. Finally
the experiment proved to be extremely sensitive to a perturbation of the outflow section of the tube, something that was predicted
by the simulations. 相似文献
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《Advanced Powder Technology》2014,25(3):847-852
The aim of this study is to apply the inkjet technique to liquid–liquid interfacial crystallization. Instillation with an inkjet nozzle was compared with the batch process in order to evaluate the effectiveness of the inkjet technique for controlling particle morphology. The effects of amino acid solution concentration and organic solvent type on particle properties were investigated for instillation with an inkjet nozzle. The morphology of alanine and glycine particles was observed by scanning electron microscopy and X-ray powder diffraction. The inner structure of alanine and glycine particles was investigated by cutting particles with an ion milling machine. Controlling particle size by adjusting the droplet size in the instillation with an inkjet nozzle was found to be feasible. Most alanine and glycine particles produced by instillation were spherical, whereas most particles produced by the batch process were non-spherical. A higher concentration of amino acid in the solution may lead to the generation of solute particles at the spherical interface. It was found that the surface structure of alanine particles changed when using two kinds of organic solvents as anti-solvents. In addition, instillation allowed for β-glycine to be identified and the crystal polymorph of the particles to be controlled. 相似文献
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The behavior of spherical particles with various geometric and physical parameters is experimentally investigated at the stimulated longitudinal gas oscillations in closed and opened tubes as well as in the external wave field near subharmonic resonances. The temporal dependences of the oscillating particle coordinate are obtained for different tube lengths and excitement frequencies. It is shown that, inside the tube, a particle moves, performing the longitudinal oscillations, from the opened end to the piston. Outside the tube, a particle moves from the opened end to the external wave field, without oscillations and with nonlinear coordinate increase in time. Also investigated is the influence of the particle weight and diameter and of the gas excitement frequency on the oscillation amplitude of the particle and its average velocity. The nonmonotone character revealed the dependence of the average velocity of the spherical particle on the gaseous column oscillation frequency at passing through the subharmonic resonance frequencies. 相似文献
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Abstract Transverse trapping force in laser tweezers is investigated in the presence of spherical aberration caused by the refractive-index mismatch between a cover slip and the water solution where particles are suspended. The transverse trapping efficiency is characterized in terms of the numerical aperture of a microscope objective and the thickness of a sample cell. It has been experimentally demonstrated that the spherical aberration can be compensated for by changing the effective tube length of an objective used for trapping. As a result, the transverse trapping efficiency can be improved by up to 20%. In principle, a further improvement in the trapping efficiency is possible if an objective of an infinitely-long tube length is used. 相似文献
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Takumasa Muraoka 《Thin solid films》2009,518(3):1012-1015
We have observed for the first time a deposition of MgO microparticles with spherical shape. Experiment has been carried out in a small coaxial electrode system for an impulse discharge, consisting of an inner Mg-rod electrode of 1.7 mm in diameter, and an outer ring electrode, between which a small-diameter glass tube substrate is placed. From the SEM and Raman analyses, we have observed a formation of MgO particles with size less than several 500 nm. Most of the particles are spherical in shape, and distributed on the glass surface near the electrodes. The formation processes of the spherical particles are discussed. 相似文献
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《Advanced Powder Technology》2019,30(10):2330-2337
In the present research, the characteristics and atomization behavior of Ti-6Al-4V powders produced by plasma rotating electrode process (PREP) with different rotation speeds were investigated. Three kinds of particles in the as-PREPed powders are observed: spherical particles, satellite particles and irregular particles. The mean particle size of the PREP powder decreases and its distribution becomes narrower gradually with increasing rotation speed. PREP powder at higher rotation speed demonstrates lower fractions of both satellite particles and irregular particles. By observing the residual electrode tip, it is considered that the irregular particles with corner or flat shape are possibly caused by the tearing of liquid film under the action of centrifugal force and shear force during the atomization process. 相似文献
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《Advanced Powder Technology》2023,34(1):103887
The properties of elastic wave propagation in granular assemblies have become a subject of immense interest in recent years, however, the influence of different confinements on the sound velocity is seldom investigated. This study provides a method to determine the contact point between spherical, super-ellipsoidal particles and complex boundaries, in order to investigate how the anisotropy induced by particle shape or boundary affects velocity. Taking cylinder and spiral tube confinements as examples, the falling process of spherical and super-ellipsoidal assemblies are simulated to verify the validation by the discrete element method (DEM). The convergence of the kinetic energy during the falling process and the equilibrium state with zero residual kinetic energy guarantees the stability and correctness. On the basis, elastic wave propagation of spherical and super-ellipsoidal systems in spiral tube and cylindrical confinements under different pressures are modelled, and sound velocities are calculated. The effective medium theory (EMT), granular solid hydrodynamics (GSH), and elastic stiffness are used to interpret the relationship between velocity and stress in cylindrical confinement. However, the results in the spiral tube deviate from EMT and GSH, which means the boundary affects velocity significantly. The difference of velocity between spiral tube and cylinder is qualitatively explained from the perspective of anisotropy of contact force distribution in the system. The simulation results show that anisotropy introduced by the curved surface affects the acoustic properties greatly. The method used for spiral boundary is also suitable for other complicated confinements. 相似文献