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1.
高频感应热等离子体中粉末颗粒的运动行为研究 总被引:1,自引:1,他引:0
建立了高频电感耦合等离子体炬的二维轴对称模型,利用商用软件FLUENT对钛粉颗粒在纯氩热等离子体内的运动轨迹进行了模拟,研究了前驱体粒径及载气流量的变化对粉末颗粒受力过程的影响。研究结果表明,粒径小的颗粒受炬内回流作用的影响较大,颗粒运动轨迹杂乱,而粒径大的颗粒受回流的影响则很小;降低载气流量可以使钛粉的受热更加充分,使得更多的颗粒被加热至熔化,可提高粉末的球化率。 相似文献
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本文设计出一种应用于熔融沉积成型技术的螺杆挤出装置的进料段、挤压段结构,并基于离散单元法对挤出装置中颗粒流动特性进行了数值模拟研究。模拟中研究了螺纹形状、螺杆竖直位置、颗粒间静摩擦系数对颗粒流动特性的影响,并总结得出三种参数的变化对颗粒质量流量及相对速度标准偏差的影响规律。模拟结果表明,采用梯形螺纹时颗粒质量流量变化范围最宽,效果最理想;螺杆在进料漏斗中的竖直位置对出口颗粒质量流量无明显影响;挤出颗粒质量流量随颗粒间静摩擦系数增大而减小,出口处颗粒速度随颗粒间静摩擦系数变大而分布更加均匀。 相似文献
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建立了高频电感耦合等离子体炬的二维轴对称模型,利用商用软件FLUENT对钛粉颗粒在纯氩热等离子体内的运动轨迹进行了模拟,研究了前驱体粒径及载气流量的变化对粉末颗粒受力过程的影响。研究结果表明,粒径小的颗粒受炬内回流作用的影响较大,颗粒运动轨迹杂乱,而粒径大的颗粒受回流的影响则很小;降低载气流量可以使钛粉的受热更加充分,使得更多的颗粒被加热至熔化,可提高粉末的球化率。 相似文献
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以往的实验研究中,已经知道粗糙边界条件下,二维颗粒流的颗粒流量是以通道中心横向对称分布的,颗粒流横向分布既受通道宽度的影响,同时也受通道斜面倾斜角的影响,而且颗粒在通道两侧的分布明显少于通道中间. 主要研究粗糙边界附近颗粒分布随通道宽度以及通道斜面倾斜角的变化规律. 在稀疏流状态以及保持边界墙体的粗糙度不变的条件下,对应不同通道宽度,粗糙边界附近10d范围内的颗粒流量密度(ξ=ρv)随斜面倾斜角的增大而减小,颗粒流量密度随通道宽度的变化存在一临界宽度Wc;在通道宽度小于Wc时,粗糙墙体附近10d范围内颗粒流量密度ξ随sinθ呈指数衰减,通道宽度大于Wc时,颗粒流量密度ξ_sinθ曲线随θ增大几乎呈线性减小.
关键词:
二维颗粒流
颗粒物质
颗粒流量密度 相似文献
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用计算机模拟的方法研究了开口角度对二维颗粒流稀疏流—密集流转变的影响.在固定入口流量和固定颗粒数两种条件下,均发现当开口角度大于零时,开口角度的增大可以提高颗粒流由稀疏流向密集流转变的最大出口流量.在稀疏流状态下,出口流量与开口角度无关;而在密集流状态下,出口流量随开口角度的增大而增大.进一步的计算还发现增加开口角度可以提高颗粒流出开口的流动速度,且最大出口流量与颗粒的流动速度呈线性关系.
关键词:
颗粒物质
颗粒流
分子动力学模拟 相似文献
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在此之前已经报道了二维斜面颗粒流在通道中的分布规律以及二维斜面粗糙边界附近的颗粒 流量密度(ξ=ρ·ν)分布.本文则主要研究通道宽度W对边界附近颗粒流量密度(ξ=ρ· ν)分布的影响.结果表明,颗粒流量密度随通道宽度的变化(ξ W)存在一临界通道宽度W c.在本实验条件下临界通道宽度Wc=70d.当通道宽度小于临界宽度Wc时 ,通道中距边界20d—30d区间内的相对颗粒流量密度随斜面倾斜角的变化可描述为ξ∝( sinθ)α,α是与通道宽度W有关的参数,其数值在032至085之间.
关键词:
二维颗粒流
颗粒物质
颗粒流量密度 相似文献
11.
Mints RG Papiashvili I Kirtley JR Hilgenkamp H Hammerl G Mannhart J 《Physical review letters》2002,89(6):067004
We have directly observed well-separated Josephson vortex splinters with unquantized magnetic flux at asymmetric 45 degrees grain boundaries in YBa(2)Cu(3)O(7-delta) films by imaging magnetic flux with scanning SQUID microscopy. The existence of these splinter vortices has been predicted and is well described by a model based on dx(2)(-y(2)) pairing symmetry and facetting of the grain boundary on a length scale shorter than the Josephson penetration depth. 相似文献
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The dust emission models to date cannot describe the relation between the transport rate of different sized grains and their
grain size composition in soil surface, so Aeolian grain transport on a soil-like bed composed of fine sand and silt powder
was measured in a wind tunnel. Six types of soil-like beds with different silt fractions have been tested in this experiment.
The mass flux profiles of silt dust and sand grains are much different due to their different motion modes. Analysis of the
vertical distribution of the powder and sand grains reveals that for a given soil bed, the ratio of the horizontal dust flux
to the horizontal sand flux is directly proportional to their mass ratio in the bed. The dust flux is closely linked to the
sand flux by the bombardment mechanism. For a given wind velocity and grain size of the bed, the slopes of the vertical mass
flux profiles of sand grains larger than 100 μm are nearly equal in a log-linear plot and the ratio between the fraction of
transport rate of each size group to the whole transport rate and the mass fraction of each size group in the bed is a constant
only dependent on grain size. With this law, the transport rate of dust and different sized grains can be related with the
grain size composition in the soil surface.
Supported by the National Natural Science Foundation of China (Grant No. 50706031) and the Natural Science Foundation of Shanxi
Province of China (Grant No. 2008021005) 相似文献
14.
《Physics letters. A》2005,343(6):454-461
We present a theoretical prediction of the new effects for critical currents across single grain boundaries in polycrystalline superconductors being under an applied magnetic field. It was shown that Josephson oscillation should be observed not only in the case of the increasing of the magnetic flux through the junction but also when vortex penetrates inside grain. In the intergrain Josephson junction the critical transport current is strongly dependent on the normalized grain size ratio, grain anisotropy ratio and grain coupling strength. These results imply that achieving a high degree of texture along these parameters is important for the obtaining of very high critical currents in pure polycrystalline samples. Also, it is shown that in contrast to the well-known Fraunhofer dependence, the period of oscillations corresponds to adding flux quantums per two grains. 相似文献
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D.H. Kim Jun-Ki Chung T.J. Hwang W.N. Kang Kook Chae Chung 《Physica C: Superconductivity and its Applications》2009,469(21):1950-1953
We measured the transport properties of MgB2 films having columnar grain structure with their axis normal to the substrate. When an external magnetic field was applied parallel to the grain axis, an enhanced critical current density has been observed, and this result has been ascribed to flux pinning induced by grain boundaries. The shape of the angular dependence of critical current density and its magnetic field dependence showed a quite similar resemblance to those of YBa2Cu3Ox films containing columnar defects, implying a possible existence of linear defects in MgB2 films of columnar structure. We propose that the amorphous regions at the vertex points of three or more grain boundaries observed in microstructural studies correspond to the linear defects and these linear defects anchor the end points of the flux line dislocations of Frank-Read sources, by which the shear in the flux line lattice is actuated. This assumed mechanism is found to reasonably explain the magnetic field dependence of the flux pinning force density of MgB2 films with columnar grain structure. 相似文献
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Durrell JH Hogg MJ Kahlmann F Barber ZH Blamire MG Evetts JE 《Physical review letters》2003,90(24):247006
Transport critical current measurements have been performed on 5 degrees [001]-tilt thin film YBa(2)Cu(3)O(7-delta) single grain boundaries with the magnetic field rotated in the plane of the film, phi. The variation of the critical current has been determined as a function of the angle between the magnetic field and the grain boundary plane. In applied fields above 1 T the critical current j(c) is found to be strongly suppressed only when the magnetic field is within an angle phi(k) of the grain boundary. Outside this angular range the behavior of the artificial grain boundary is dominated by the critical current of the grains. We show that the phi dependence of j(c) in the suppressed region is well described by a flux cutting model. 相似文献
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D.H. Kim T.J. Hwang Y.J. Cha W.K. Seong W.N. Kang 《Physica C: Superconductivity and its Applications》2009,469(15-20):1059-1062
We studied the flux pinning properties by grain boundaries in MgB2 films prepared by using a hybrid physical chemical vapor deposition method on the c-axis oriented sapphire substrates. All the films we report here had the columnar grains with the growth direction perpendicular to the substrates and the grain sizes in the range of a few hundred nanometers. At very low magnetic fields, no discernable grain-boundary (GB) pinning effect was observed in all measuring temperatures, but above those fields, the effect of GB flux pinning was observed as enhanced critical current densities (Jcs) and reduced resistances when an external magnetic field (B) was aligned parallel to the c-axis. We interpret the B dependence of Jc in the terms of flux line lattice shear inside the columnar grains activated by dislocations of Frank–Read source while the flux lines pinned by GB act as anchors for dislocations. Magnetic field dependence of flux pinning force density for B parallel to the c-axis was reasonably explained by the above model. 相似文献
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建立了梯度磁场下金属熔体中晶粒迁移的一般动力学模型,导出了磁场对导电熔体黏度的影响规律,得到了迁移速度的解析解和迁移距离的分析解.导电熔体的有效黏度随磁场强度的平方成线性递增关系.迁移速度达到终极速度的时间为10-3s数量级.终极速度随着磁场强度的增加而迅速减小,表明强磁场对晶粒迁移有抑制作用.迁移距离和迁移率与磁场分布密切相关.为观察初晶硅的迁移状况,将Al-18wt%Si合金在650℃保温60min后,施加强梯度磁场(Bz=5 T,BzdBz/dz=-224T2·m-1)对熔体作用不同时间并淬火,结果表明,晶粒半径大于等于40μm的初晶硅在120s内大部分完成迁移,与理论计算符合.
关键词:
强梯度磁场
析出相
迁移
刚体动力学 相似文献
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We study the percolation aspects of diffusional "Coble" creep on heterogeneous grain boundary networks, assuming free grain boundary sliding. A novel percolation threshold is obtained for the honeycomb lattice when two representative types of grain boundaries are randomly distributed, p(cc)=0.5416+/-0.0036. The creep viscosity diverges near the percolation threshold with power-law exponents t=1.69+/-0.09 and s=1.88+/-0.12, different from the standard conduction and rigidity percolation exponents. The moments of both the force and flux distributions all conform to finite-size scaling at p(cc), but with new exponents. These new scaling behaviors seen in the creeping system are proposed to arise from the unique coupling of both force and flux balances in the network. 相似文献
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Previous considerations of dust acoustic waves is demonstrated to be inconsistent ‐ the required equilibrium state for perturbations was not defined since balance of plasma fluxes was neglecting. The self‐consistent treatment shows that plasma flux perturbations are accompanying any collective waves propagating in dusty plasmas and can play an important role in wave dispersion, wave damping and can create instabilities. This is illustrated by the derivation of dispersion relation for dust acoustic modes taking into account the plasma flux balances and plasma flux perturbations by waves. The result of this approach shows that the dust acoustic waves with linear dependence of wave frequency on the wave number exist only in restricted range of the wave numbers. Only for wave numbers larger than some critical wave number for low frequency modes the frequency can be have approximately a linear dependence on wave number and can be called as dust acoustic wave but the phase velocity of these waves is different from that which can be obtained neglecting the flux balance and depends on grain charge variations which are determined by the balance of fluxes. The presence of plasma fluxes previously neglected is the main typical feature of dusty plasmas. The dispersion relation in the range of small wave numbers is found to be mainly determined by the change of the plasma fluxes and is quite different from that of dust acoustic type, namely it is found to have the same form as the well known dispersion relation for the gravitational instability. This result proves in general way the existence of the collective grain attractions of negatively charged grains for for large distances between them and for any source of ionization. The attraction of grains found from dispersion relation of the dust acoustic branch coincides with that found previously for pair grain interactions using some models for the ionization source. For the existing experiments the effective Jeans length for such attraction is estimated to be about 8 – 10 times larger than the ion Debye length and the effective gravitational constant for the grain attraction is estimated to be several orders of magnitude larger than the usual gravitational constant. The grain attraction at large inter‐grain distances described by the gravitationlike grain instability is considered as the simplest explanation for observed dust cloud clustering, formation of dust structures including the plasma crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献