Papers by Keyword: Particle

Abstract: The research on the relationship between vortex evolution and diffusion of aerosol in human upper respiratory tract can deepen understanding of the characteristics of the particle deposition pattern in human upper respiratory tract and plays a very important role in analyzing the transition of aerosol in human upper respiratory tract. Large eddy simulation and an efficient Lagrangian particle tracking module were used to simulate relationship between vortex evolution and diffusion of aerosol in mouth-throat model in the conditions of the low intensive respiratory, and the vortex evolution and the mechanism of aerosol transition in human mouth-throat model were discussed. The results show that the diffusion of small aerosol particles follow the vortex structure very closely; the capabilities of the vortex for carrying aerosol particle increase with increase in vorticity, which can affect the diffuseness and deposition of the particles.

Abstract: Mg doped BaAl₁₂O₁₉:Mn²⁺ phosphor is one of the most efficient green phosphors for PDP. It is difficult to prepare the phosphor both have small particle size (< 3μm) and high luminescence. In the present work, a BaAl₁₂O₁₉:Mn²⁺ phosphor with small particle size was synthesized by the chemical co-precipitation method. Phase transformation and particle growth process during calcining process were investigated. The nucleation process was also discussed. The results show that, the phase transformation is complicated, the transition phases include BaCO₃, γ-Al₂O₃, BaF₂, BaAl₂O₄ and two phases contain Mn; The BaAl₁₂O₁₉ phase is formed from the reaction between BaAl₂O₄ phase and γ-Al₂O₃ phase, no a-Al₂O₃ phase appears during the entire process; The formation temperature of pure BaAl₁₂O₁₉ phase is 1200°C, which is lower than that in the high-temperature solid state reaction method. High efficiency BaAl₁₂O₁₉:Mn²⁺ phosphor with small particle size (< 2μm) and hexagonal flaky shape can be prepared by this method.

Abstract: In order to settle the influence of measuring results of particles with its shape-variety, the scattering pulse width and peak distribution and the relation of particles’ size and shape characters are systems analyzed based on the Mie theory and perturbation ameliorating method. In addition, a theorem of equivalence probability area is setup and a method of obtaining the probability distribution function of shape particles in real time is built. At last, the theories are validated in the experiments. The effect of the particles’ shape is modified and the accuracy of measurement of the particles’ size is improved effectively.

Abstract: The relationships among the n, ap , and f of the SiCp /Cu composite material produced by powder metallurgy and extrusion have been investigated. The cutting force F of this material is also discussed in this paper by the measuring of the three cutting factors of n, ap, and f, applying the dislocation theory and the electron microscope analysis of the cutting surface and sub-surface. The differences are analyzed between the SiCp/Cu composite materials, QSn6-6-3. H59-1and the copper cutting surface and the sub-surface. The forming of mechanism, the function of SiCp in the cutting process and the influence on the cutting surface quality are also analyzed. This research has shown: because the SiCp particles prevent the dislocation moving, the dislocation groups are formed on the SiC/Cu interface, and the stress concentration is produced, the typical brittle separation appears in the SiC/Cu composite material cutting process. In addition, the cutting force increases with the depth of cut and feed increasing and decreases while the cutting speed increases.

Abstract: The role of ceramic particles, calcium and rare earth elements on magnesium alloys during solidification from the melt and after hot rolling has been studied by microstructural investigations, texture measurements and mechanical tests. Different ceramic inoculants like silicon carbide or zirconium diboride and two different rare earth elements (cerium and lanthanum) forming intermetallic compounds were used. Both, ceramic particles and intermetallic phases, modify the texture evolution during hot forming. The rolled alloys exhibited a basal fibre texture which is weakened by ceramic particles and intermetallic phases respectively. This weakening of the basal texture is capable of lowering the anisotropy of the yield stress and improving the formability of sheet material. Influences of the alloying contents on microstructure, texture evolution and mechanical properties will be discussed.

Abstract: Based on experimental and computational fluid dynamics analysis, the phenomenon of particle back-mixing near the dust outlet in cyclone separator with tangential inlet was studied. The results show that particle back-mixing appears near the dust outlet geometry. Particle back-mixing can be divided into dust hopper back-mixing and discharge cone back-mixing for different generation mechanism. The upward flow coming from dust hopper, which occupies 17.7% of the inlet gas, can induce dust hopper back-mixing. The particle mass flow rate that caused by dust hopper back-mixing occupies 46.6% of total inlet particle mass flow rate. Precessing vortex core, bias flow and high turbulent intensity near the dust outlet can induce discharge cone back-mixing. For both dust hopper back-mixing and discharge cone back-mixing, particle back-mixing is serious near the dust outlet geometry, which occupies 56.8% of total inlet particle mass flow rate. Particle which is smaller than 18μm can mix backward. The axial distribution of particle concentration decreases sharply in a range of 1.5 D (cyclone diameter) height above the dust discharge port. At last, only 2.6% of back-mixing particles with diameter no bigger than 13μm escape from vortex finder. This effect on separator efficiency increases with the particle diameter decreases.

Abstract: A microfluidic chip device was developed for rapid and automatic particle sorting. The chip was made up of six individual layers. Each layer was used to implement different functions such as the sample loading, electric voltage loading, optic detection, cell sorting, and product extraction. Sheath flow was used to form single-row cells in order to let cells flow through the optic detection zone one by one. Optic fiber based detector could distinguish particles with different sizes. When a particle flowed through the light beam between two opposite optic fibers, it induced the dispersion of the incident light. The size of the particle was related with the strength of the scattering light. Thus, different particles could be distinguished. In the detection method, light path was simple and label was not required. Furthermore, optic fiber based detector was helpful to decrease the volume of the whole system. When desired particle was detected, it would be separated in the downstream by using an electric deflection method. Two types of particles with different sizes were sorted by using a prototype device. The result showed that these particles could be obviously distinguished. This microfluidic system could also be used to sort biological cells. Instantaneous electric field on the cells could prevent cells from severe injuries.

Abstract: The widespread use of metal matrix composites (MMC) is often limited due to the difficulties related to their joining by means of traditional fusion welding processes. The aim of this work was to evaluate the effect on microstructure and mechanical properties (hardness and tensile strength) of two different friction welding techniques used for joining two Al-based metal matrix composites. In particular, Friction Stir Welding was applied to a 6061 (Al-Mg-Si) alloy matrix, reinforced with 20vol.% of Al₂O₃ particles (W6A20A), while Linear Friction Welding was applied to a 2124 (Al-Cu-Mg) alloy matrix reinforced with 25vol.% of SiC particles (AMC225xe). Both the welding processes permitted to obtain substantially defect-free joints, whose microstructures was found to be dependent on both the initial microstructure of the composites and the welding processes. Hardness decrease was in the order of 40% for the FSW joint and of 10% for the LFW joint, mainly due to overaging of the matrix induced by the frictional heating, while the joint efficiency in respect to the ultimate tensile strength was 72% and 82%, respectively. Elongation to failure increased in the FSW joint due to coarsening of precipitates, whereas it decreased in the LFW joints due to the fibrosity in the thermomechanically altered zone. Fracture surface analysis showed good matrix/reinforcement interface for both composites.

Abstract: It is proposed the method based on particle movement to simulate flow in this paper. The force on particles can be obtained from N-S equations, and the calculation error caused by particles’ simulation is discussed. Results show that the method is more effective through the example of flow field affected by the cube. The advantage of this method is to solve problems of multiphase flow and fluid-structure interaction.

Abstract: The use of Al-Mg-Si-(Cu) heat treatable 6xxx alloys is steadily increasing in the automotive industry. The possibility of weight reduction of the cars in combination with the good formability and high in-service dent resistance of these alloys, make them a favorable material for body panel applications. One of the most common, environment-friendly and easy to perform processes used to join aluminum sheets, is the hemming joining operation. This operation heavily relies on the bendability of the sheets, because they are bent to an angle of 180° over of a radius equal to their thickness. Tearing or cracking of the outer bent surface are often very common. In this study we attempt to understand the relations between the microstructural features of the sheets and their hemming behavior. The hemming experiments are performed in laboratory conditions and the results are discussed together with the data obtained from crystallographic, microstructural and textural investigations. Relations between the hemming appearance, chemical composition, natural aging time and dispersoid’s density are found and discussed.