共查询到20条相似文献,搜索用时 31 毫秒
1.
Cuculayev R Sanyal A Atay NZ Culha M Bucak S 《Journal of nanoscience and nanotechnology》2012,12(3):2761-2766
The self-assembly of magnetic nanoparticles into higher-order organizations upon external magnetic stimulation has critical importance for the fabrication of discrete microstructures. In this study, the tuning of self-assembly behavior of magnetic Fe3O4 nanoparticles (MNPs), with an average size of 6 nm, under the enhanced magnetic force upon changing the applied field strength and direction is explored. Upon evaporation of the solvent where the MNPs are suspended, formation of particular micrometer sized structures is achieved with a surface constructed from sub-micrometer size magnetic beads in between the applied magnetic field and MNPs. In this study, three different surfaces fabricated using sub-micrometer size magnetic beads in between the applied magnetic field and MNPs are used and the effect of the template pattern, applied field strength and direction are explored. 相似文献
2.
I. A. Krinberg 《Technical Physics Letters》2003,29(6):504-506
When an external axial magnetic field is applied to a vacuum arc, the radial expansion of plasma from cathode spots transforms
into a plasma flow along the magnetic field, provided that the electron-ion collision frequency is smaller than the Larmor
frequency. As the magnetic field strength increases, the diameter of the resulting cylindrical channel decreases. This leads
to an increase in the electron temperature and the ion charge due to enhanced Joule heating of the plasma. Unlike the intrinsic
azimuthal magnetic field, the external axial field only restricts expansion of the plasma, rather than compressing the plasma
jet. 相似文献
3.
《International Journal of Engineering Science》1986,24(5):649-673
The flow of an incompressible, viscous, electrically conducting fluid with a suspension of inert particles over a rotating disk in the presence of a circular magnetic field is investigated. The governing equations of motion are reduced to a set of nonlinear ordinary differential equations by similarity transformations, and solved numerically by using least squares finite element method. The radial velocity of the panicles attains its maximum on the surface of the disk and the particles slip in the tangential direction. The flow boundary layer is thickened and the axial flow field is reduced as a result of the magnetic field. The particle density is maximum near the surface of the disk. 相似文献
4.
研究了频率为20 kHz的超声作用在圆柱形料腔中出现声流现象时超声空化效应的空间分布特性。结合大振幅声源条件下的声辐射力,对声场内的声流现象进行了仿真分析,获取了不同超声功率和液位高度下的声流速度场分布,初步探究了声流条件下空化气泡的运动分布规律。采用超声空化效应的声致化学发光实验,对比研究了有、无声流条件时超声空化效应的空间分布特性。结果表明:功放电流高于80 mA(电功率为17.6 W)时,超声场可形成稳定的声致流动现象且可有效提高其声能辐射效率,大大增加了空化效应的作用区域,进而提高了声化学反应效率;声流条件下料腔内超声空化效应的分布区域与超声功率(振幅)、料腔液位高度相关,功放电流从40 mA(电功率为8.8 W)增加至120 mA(电功率为26.4 W)时,空化面积占比提高了100.86%,液位高度为60 mm时的空化面积占比较50 mm和70 mm时分别提高了13.11%和73.91%,提高超声功率及选择合理的料腔液位高度,可有效提高空化气泡扩散距离,增大空化分布面积;对于固定形状及尺寸料腔中的声场,声流速度达到一定阈值时,会出现空化效应增强,空化效应增强区域位于大于声流速... 相似文献
5.
目的选择蔬菜复合纸覆膜成型过程中的最优喷涂条件。方法利用PIV(粒子图像测速)技术测量不同喷涂参数下大豆蛋白液喷涂雾化粒子的速度场分布,并通过数据分析软件Tecplot处理分析喷涂参数对大豆蛋白液喷涂雾化粒子速度场的影响,最终得出喷雾速度场中心轴上和某一截面上速度的变化规律。结果当喷涂气压一定时,喷涂粒子速度随着喷涂液压的增大呈增大趋势,但不是很明显。当喷涂液压不变时,喷涂粒子速度随着喷涂气压的增大呈先减小后增大的趋势。在喷雾场喷嘴中轴线方向上雾化粒子速度从喷口喷出后先急剧增大,随着距喷嘴越来越远逐渐呈现波动变化的趋势,最后趋于稳定。在距离喷嘴300 mm的截面处,粒子速度以轴心处最大,向外沿径向逐渐减小,大体呈对称趋势。结论用PIV技术对大豆蛋白液喷涂粒子速度场进行研究,可为后期蔬菜复合纸覆膜成型提供一个有力的试验数据参考。 相似文献
6.
目的 研究外加纵向磁场对倾斜电极TIG焊接的电弧温度分布、流动模式和工件所受热力作用的影响.方法 建立磁场-电弧复合焊接热、电、磁、流动的三维数学模型.通过数值模拟和高速摄像实验,揭示倾斜电极电弧在外加磁场作用下的流动、形貌及温度演化机制.结果 外加纵向磁场后,电弧流动速度明显增加,流动模式由沿电极方向喷射变为近似沿竖直方向旋转向下的流动模式;电弧对工件的热作用均匀性提高,热作用中心向电极正下方靠近,但在焊接横向方向上存在偏离;工件受到表面的电弧旋转拖拽力和内部的旋转洛伦兹力作用,最大洛伦兹力可达50000 N/m3.结论 基于所建立数学模型的模拟结果与实验电弧形貌吻合良好,结果表明,外加纵向磁场能够显著改变电弧的形态及流动模式,提高电弧热流密度的均匀性,并能够对熔池产生有效的搅拌作用. 相似文献
7.
Egon Krause 《Acta Mechanica》2008,201(1-4):23-30
Inviscid compressible flow in a slender longitudinal vortex with the axis parallel to the main flow direction is discussed. The Euler equations for steady, axially symmetric flow are simplified for the neighbourhood of the axis of the vortex. The resulting relations, expressing the angular velocity in terms of the axial mass flow, when recast and integrated, represent an analogy to the area–velocity and the area-Mach number relation of one-dimensional gasdynamics. By restricting the analysis to the flow in a Rankine vortex with constant stagnation enthalpy, the static pressure on the axis can be related to the free-stream pressure far away from the axis and the maximum value of the azimuthal velocity. The influence of a radial wake-like distribution of the axial velocity component on the axial pressure is discussed. Its dependence on variable external boundary conditions is given. A condition is formulated, which has to be satisfied for the formation of a free stagnation point on the axis. 相似文献
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9.
A mathematical model is presented to analyze the unsteady peristaltic flow of magnetized viscoelastic fluids through a deformable curved channel. The study simulates the bio-inspired pumping of electroconductive rheological polymers which possess both electroconductive and viscoelastic properties. The Jeffrey viscoelastic model is utilized which features both relaxation and retardation terms of relevance to real polymers. A magnetic body force is incorporated for the influence of static radial magnetic field. The mass and momentum conservation equations are formulated in an intrinsic coordinate system and transformed with appropriate variables into a nondimensional system between the wave and the laboratory frames, under lubrication (i.e., low Reynolds number and long wavelength) approximations. Kinematic and no-slip boundary conditions are imposed at the channel walls. A magnetic body force is incorporated for the influence of static radial magnetic field in the primary momentum equation. An analytic approach is employed to determine closed-form solutions for stream function, axial pressure gradient, and volumetric flow rate. Spatiotemporal plots for pressure distribution along the channel (passage) length are presented to study the influences of curvature parameter, relaxation-to-retardation time ratio (Jeffrey first viscoelastic parameter) and Hartmann number (magnetic field parameter). The effects of these parameters on radial velocity distributions are also visualized. Cases of trapping and reflux in a curved channel are discussed. Streamline distributions are included to study trapping phenomena and to investigate more closely the impact of curvature, magnetic field, and viscoelastic properties on bolus evolution. The reflux or retrograde motion of the particles is studied by particle advection based on Lagrangian viewpoint. The simulations provide new insight into the mechanisms of pumping of electroconductive non-Newtonian liquids in realistic geometries. 相似文献
10.
将封有聚α-烯烃合成油基磁性液体的两玻璃管放置于磁场中,为消除磁场力、重力所引起的磁性液体自然对流的影响,消除端部效应,研制了磁性液体在均匀磁场中瞬态双热线导热系数的实验测量系统,经与蒸馏水、乙醇标准样品的导热系数测量比较,实验装置有较高的测量精度。实验测量了不同方向的均匀磁场对不同体积浓度的磁性液体导热系数的影响。结果显示,当磁场方向与热通量方向一致时,磁场显著强化磁性液体的导热系数,其导热系数随磁场强度的增加而近似线性增加,且体积浓度越大增加量越大;当磁场方向与热通量方向垂直时,磁性液体的导热系数随磁场强度的变化不明显。 相似文献
11.
An experimental investigation is made of the effect of axisymmetric two-dimensional magnetic field on the forming of plasma and on the configuration of cathode spots in a vacuum-arc discharge. It is demonstrated that a magnetic field with a transverse (relative to the discharge axis) component has a significant effect on the shape of plasma column and on the rate of expansion of the cathode spot region. In a magnetic field, arc plasma has the form of truncated cone expanding toward the anode. The cathode spots take up a part of the cathode area which decreases with increasing magnetic field. Arguments are given in support of the assumption that the arrangement of cathode spots and the form of arc plasma are defined by the minimum principle similar to the Steinbeck principle. In so doing, the displacement of spots is caused by their emergence in a new region corresponding to a lower arc voltage. Also discussed is the mechanism associated with retrograde motion of cathode spot in view of the effect of azimuthal magnetic field on the axial component of current and of the effect of axial magnetic field on the azimuthal component of current. 相似文献
12.
利用CFD软件Fluent,基于颗粒动力学理论的双流体模型对循环流化床锅炉的3种二次风送风结构对炉膛内气-固两相流宏观流动特性的影响进行数值模拟,将3种结构下的计算结果进行对比分析。结果表明:二次风通常采用90°垂直入射的情况下,炉膛内颗粒的环-核分布结构及上稀下浓的分布不均匀性达到最大;二次风进口入射角为与轴向方向成60°向上入射情况下,炉膛内颗粒主要分布在炉膛中上部区域,不均匀程度减小,最有利于炉膛内的燃烧和提高传热效率,同时得到二次风的射流深度最大;二次风送入结构为渐缩型入射口的情况时,二次风射流深度最小,炉膛内偏流现象明显,在本文的操作条件下,并没有达到喷射的设计效果,还有待于进一步的研究。 相似文献
13.
The boundary element method was applied to study the motion of magnetic particles in fluid flow under the action of external nonuniform magnetic field. The derived formulation combines the velocity-vorticity resolved Navier–Stokes equations with the Lagrange based particle tracking model, where the one-way coupling with fluid phase was considered. The derived algorithm was used to test a possible design of high gradient magnetic separation in a narrow channel by computing particles trajectories in channel flow under the influence of hydrodynamic and magnetic forces. Magnetic field gradient was obtained by magnetization wires placed outside of the channel. Simulations with varying external magnetic field and flow rate were preformed in order to asses the collection efficiency of the proposed device. We found that the collection efficiency decreases linearly with increasing flow rate. Also, the collection efficiency was found to increase with magnetic field strength only up a saturation point. Furthermore, we found that high collection efficiently is not feasible at high flow velocity and/or at weak magnetic field. Recommendation for optimal choice of external magnetic field and flow rate is discussed. 相似文献
14.
ABSTRACT A numerical simulation for swirling and axial flow pneumatic conveying in a horizontal pipe was carried out with a Eulerian approach for the gas phase and a stochastic Lagrangian approach for particle phase, where particle-particle and particle-wall collisions were taken into consideration. The k-? turbulence model is used to characterize the time and length scales of the gas-phase turbulence. Models are proposed for predicting the particle source and additional pressure loss. The numerical results are presented for polyethylene pellets of 3.1 mm diameter conveyed through a pipeline of 13 m in length with an inner diameter of 80 mm, solid mass flow rate was 0.084 kg/s, and gas velocity was varied from 10 m/s to 18 m/s. The particle flow patterns, the particle concentration and the particle velocity, and additional pressure loss were obtained. It is found that the particle velocity and concentration has almost same value along flow direction in swirling flow pneumatic conveying. The profile of particle concentration for swirling flow pneumatic conveying exhibits symmetric distribution towards the centerline and the higher particle concentration appears in neighbor of wall in the acceleration region. At downstream, the uniform profile of particle concentration is observed. The particle velocity profile, on the other hand, is uniform for both swirling and axial flow pneumatic conveying. A comparison of the calculations with the measured data shows a good agreement within an average error of less than 15 percent. 相似文献
15.
A NUMERICAL SIMULATION OF SWIRLING FLOW PNEUMATIC CONVEYING IN A HORIZONTAL PIPELINE 总被引:4,自引:0,他引:4
A numerical simulation for swirling and axial flow pneumatic conveying in a horizontal pipe was carried out with a Eulerian approach for the gas phase and a stochastic Lagrangian approach for particle phase, where particle-particle and particle-wall collisions were taken into consideration. The k-ε turbulence model is used to characterize the time and length scales of the gas-phase turbulence. Models are proposed for predicting the particle source and additional pressure loss. The numerical results are presented for polyethylene pellets of 3.1 mm diameter conveyed through a pipeline of 13 m in length with an inner diameter of 80 mm, solid mass flow rate was 0.084 kg/s, and gas velocity was varied from 10 m/s to 18 m/s. The particle flow patterns, the particle concentration and the particle velocity, and additional pressure loss were obtained. It is found that the particle velocity and concentration has almost same value along flow direction in swirling flow pneumatic conveying. The profile of particle concentration for swirling flow pneumatic conveying exhibits symmetric distribution towards the centerline and the higher particle concentration appears in neighbor of wall in the acceleration region. At downstream, the uniform profile of particle concentration is observed. The particle velocity profile, on the other hand, is uniform for both swirling and axial flow pneumatic conveying. A comparison of the calculations with the measured data shows a good agreement within an average error of less than 15 percent. 相似文献
16.
The effect of a transverse magnetic field on the characteristics of planar diffusion positive column of electric discharge has been studied. It is shown that, as the magnetic induction increases, the distributions of plasma density and particle fluxes to walls become asymmetric; the density maximum shifts in the direction of Ampere’s force action, and the ion flux in this force direction can significantly exceed the reverse flux. It is established that there is a maximum value of magnetic induction, which bounds from above the region of magnetic fields in which a stationary state of the positive column is possible. In the region where a stationary state of the positive column is possible, each value of the magnetic induction corresponds to two positive-column regimes with different values of the electron energy, drift velocity, and electric field strength. 相似文献
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18.
《Materials Science & Technology》2013,29(11):994-999
AbstractIn this paper the turbulent flow generated in a cylindrical container by a low-frequency rotating magnetic field is considered. The rotational part of the electromagnetic body force is steady and axisymmetric, driving an azimuthal swirl flow. It is shown that curvature effects are negligible near the wall of the containing vessel and consequently the velocity profile in that region has the standard logarithmic form. Extrapolating this profile to the core allows an estimate of the core angular velocity to be made. This estimate is consistent with published experimental data and with the results of a more complex two-parameter closure model.MST/207 相似文献
19.
The distribution of pressure on the surface of a cylinder is obtained as a result of experimental investigation; this distribution significantly varies with increasing magnetic induction compared to the flow past a cylinder in the absence of magnetic field. In so doing, the pressure drag coefficient of the cylinder significantly increases. The measurements of velocity profiles reveal that the extent of the region of stagnant flow before the cylinder (the so-called “leading” wake) increases with magnetic induction. The dependence of axial defect of velocity on the MHD interaction parameter is obtained; this dependence under conditions of flow in a strong magnetic field is unaffected by the shape of the body subjected to flow, as is confirmed by the results of experiment involving the flow past a plate. 相似文献