共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
Minxian Liu Suyu Wang Jiasu Wang Guangtong Ma 《Journal of Low Temperature Physics》2009,155(3-4):169-176
In the present High Temperature Superconducting (HTS) maglev vehicle system, the nonuniformity of the magnetic field along the movement direction above the NdFeB guideway is inevitable due to the assembly error and inhomogeneous of the material property of the NdFeB magnet. In order to investigate the influence of the nonuniformity on the levitation performance of the HTS bulk, an electromagnet supplied by AC current is used to simulate the nonuniformity of the external magnetic field. The levitation force of the HTS bulk is measured when applying AC currents to the electromagnet coils. Experimental results indicate that the levitation force changes abruptly and then oscillates after applying AC external magnetic field, and the levitation force is attenuated by the AC magnetic field after withdrawing the AC field. Moreover, the oscillation amplitude and the attenuation rate of the levitation force increase with the amplitude of the AC external magnetic field. 相似文献
3.
磁性微混合器混合性能的实验研究 总被引:4,自引:0,他引:4
自装配磁性微混合器是利用聚合的磁流体在旋转磁场作用下的运动,来破坏流体的层流状态,产生混沌对流而加强流体间的混合.利用Micro-PIV对不同磁场强度、旋转频率和流量下的混合效率进行了实验研究,结果表明:在保证外磁场能带动磁流体聚合链运动的前提下,磁场强度对混合效率的影响不大;而外磁场的旋转频率对混合效果有较大的影响,当旋转频率较低时混合效率随旋转频率升高而提高,而当旋转频率超过临界频率时,由于粘性拖曳力克服了磁场力,磁性颗粒的聚合被破坏,使混合效率反而下降.为磁性微混合器的设计提供基础. 相似文献
4.
Minxian Liu Yiyun Lu Guangtong Ma Suyu Wang 《Journal of Superconductivity and Novel Magnetism》2011,24(4):1339-1344
In the present High Temperature Superconducting (HTS) maglev vehicle system, the nonuniformity of the magnetic field along
the movement direction above the NdFeB guideway is inevitable due to the assembly error and inhomogeneity of the material
property of the NdFeB magnet. In order to investigate the influence of the nonuniformity on the levitation performance of
the HTS bulk, the experiment involved an electromagnet, which is supplying AC current to simulate the nonuniformity of the
external magnetic field. The levitation force of the HTS bulk is measured when applying AC current on the electromagnet coils.
The results indicate that the levitation force abruptly changes and oscillates after applying AC external magnetic field.
The effect of the amplitude of the AC magnetic field on the levitation force is studied; the result shows that the oscillation
amplitude of the levitation force increases with the amplitude of the AC external magnetic field and is independent of the
Field Cooling Height (FCH) of the bulk. 相似文献
5.
The superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the nonuniformity of the magnetic field along the movement direction above the NdFeB guideway is inevitable due to the assembly error and inhomogeneity of the material property of the NdFeB magnet. So it is required to study the characteristics of levitation force of the bulks affected by the non-uniform applied magnetic fields along the moving direction. In this paper, we will study the characteristics of the levitation force relaxation between the HTS bulk and the NdFeB guideway by an experiment in which AC external magnetic field generated by an electromagnet is used to simulate the time-varying external magnetic field caused by the inhomogeneity of the guideway. From the experimental results, it has found that the levitation force is decreasing with the application of the AC external magnetic field, and the decay increasing with the amplitude of the applied magnetic field and is almost independent of the frequency. 相似文献
6.
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
7.
Superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the HTS bulks are always exposed to AC external magnetic field, which is generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, we studied the guidance force decay of the YBCO bulk over the NdFdB guideway used in the High-temperature superconducting maglev vehicle system with the application of the AC external magnetic field, and calculated the guidance force decay as a function of time based on an analytic model. In this paper, we investigated the influence of the critical current density on the guidance force decay of HTS bulk exposed to AC field perturbation in the maglev vehicle system and try to adopt a method to suppress the decay. From the results, it was found that the guidance force decay rate was higher for the bulk with lower critical current density. Therefore, we could suppress the guidance force decay of HTS bulk exposed to AC external magnetic field perturbation in the maglev vehicle system by improving critical current density of the bulk. 相似文献
8.
为从理论上掌握有外加静磁场存在时铁催化高压歧化生成的碳纳米管中氢等离子体的微波吸收特性,根据磁离子理论和Appleton-Hartee方程,采用W.K.B近似方法,导出了碳纳米管磁化氢等离子体薄膜的微波衰减系数公式,数值计算了不同条件下碳纳米管磁化氢等离子体薄膜在0.3~30 GHz频段的微波衰减系数。研究结果表明:随着外加磁场强度的增加,Att30.00 dB/cm的频宽明显增大,吸收峰向高频方向移动.适当控制碳纳米管中等离子体的自由电子密度、电子碰撞的有效频率和外加磁场强度,能够实现碳纳米管中磁化氢等离子体薄膜对对特定微波段的强吸收.在外磁场等于0时,运用所构建的微波吸收模型得到的数值计算结果与已有的实验数据相吻合. 相似文献
9.
Minxian Liu Yiyun Lu Suyu Wang Guangtong Ma 《Journal of Superconductivity and Novel Magnetism》2011,24(5):1809-1813
In the present High-Temperature Superconducting (HTS) maglev vehicle system, the air gaps between the adjacent permanent magnets
make the magnetic fields above the NdFeB guideway non-uniform. So one is required to study the characteristics of levitation
force of the HTS bulk influenced by non-uniform fields. In this paper, we have studied the characteristics of the levitation
force relaxation by an experiment in which the AC external magnetic field generated by an electromagnet is used to simulate
the time-varying external magnetic field caused by the inhomogeneity of the NdFeB guideway. From the experiment results, it
is found that the levitation force is attenuated with the application of the AC external magnetic field, and the decay is
increased with the amplitude of the AC magnetic field, but the decay is almost independent of the frequency of the AC magnetic
field. 相似文献
10.
Minxian Liu Yiyun Lu Suyu Wang Guangtong Ma 《Journal of Superconductivity and Novel Magnetism》2011,24(5):1559-1562
The levitation force of the YBCO bulk over an NdFeB guideway used in the high-temperature superconducting (HTS) maglev vehicle
system is oscillated by the application of the AC external magnetic field. In our previous work, we interpreted that the oscillation
is due to the shielding current fluctuation caused by fluctuant external magnetic field. In this paper, based on the Bean
model, an analytical model is adopted to evaluate the levitation force. Comparing with the experimental results, the calculated
results show good matching. The model can reveal the oscillation characteristics of the levitation force of HTS bulk which
is being exposed to AC external magnetic field. Therefore, the levitation force oscillation of the HTS bulk in the maglev
vehicle system can be evaluated by this numerical method. 相似文献
11.
Longcai Zhang 《Journal of Superconductivity and Novel Magnetism》2010,23(2):205-208
Bulk superconductors have great potential for various engineering applications, especially in superconducting maglev vehicle
systems using high-temperature superconducting bulks. In such a system, the HTS bulks were always exposed to AC external magnetic
field, which was generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, it was
observed that the guidance force of the YBCO bulk over the NdFdB guideway used in the high-temperature superconducting maglev
vehicle system was decayed by the application of the AC external magnetic field. In this paper, we investigate the influence
of the work height on the guidance force decay of HTS bulk exposed to an AC field perturbation in the maglev vehicle system
and try to adopt a method to suppress the decay. From the experimental results, it was found that the decay rate of the guidance
force was smaller at higher work height in the case of the same field-cooled height. So we could suppress the guidance force
decay of HTS bulk exposed to AC external magnetic field perturbation in the maglev vehicle system by increasing the work height
of the bulk. 相似文献
12.
Bulk superconductors have great potential for various engineering applications, especially in a high-temperature superconducting (HTS) maglev vehicle system. In the vehicle system, the stable levitation can be achieved without any complex control system owed to the pinning effect of the bulks. However, the HTS bulks in the vehicle system were always exposed to the time-varying external magnetic field, which was generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, we studied the guidance force decay characteristics of the YBCO bulk over the NdFdB guideway used in the HTS maglev vehicle system by an experiment in which the AC external magnetic field generated by an electromagnet was used to simulate the time-varying external magnetic field caused by the inhomogeneity of the guideway, and calculated the guidance force decay as a function of time based on an analytic model. In this paper, we investigated the influence of thermal conductivity on the guidance force decay of HTS bulk exposed to AC field perturbation in the maglev vehicle system and tried to adopt a method to suppress the decay. From the results, it was found that the guidance force decay rate was higher for the bulk with the lower thermal conductivity. So, we could reduce the guidance force decay of the HTS bulk exposed to the AC external magnetic field perturbation in the maglev vehicle system by improving the thermal conductance of the bulks. 相似文献
13.
H. A. Attia 《Acta Mechanica》2001,151(1-2):89-101
Summary This paper studies the effect of variable viscosity on the transient flow of dusty fluid with heat transfer. The fluid is acted upon by a constant pressure gradient, and an external uniform magnetic field is applied perpendieular to the plates. The governing nonlinear partial differential equations are solved numerically, and some important effects for the variable viscosity and the uniform magnetic field on the transient flow and heat transfer of both the fluid and dust particles are indicated. 相似文献
14.
The behavior of macroparticles that form a near-wall dust in tokamaks is described with allowance for the force of gravity,
force of entrainment by plasma ion flux, and Lorentz force acting on the motion of charged macroparticles in an inhomogeneous
magnetic field. It is shown that, in some cases, the effect of induced currents that arise in the particles during this motion
must in some cases be taken into account. 相似文献
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17.
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
18.
The non-similar boundary layer flow of a viscous incompressible electrically conducting fluid over a moving surface in a rotating fluid, in the presence of a magnetic field, Hall currents and the free stream velocity has been studied. The parabolic partial differential equations governing the flow are solved numerically using an implicit finite-difference scheme. The Coriolis force induces overshoot in the velocity profile of the primary flow and the magnetic field reduces/removes the velocity overshoot. The local skin friction coefficient for the primary flow increases with the magnetic field, but the skin friction coefficient for the secondary flow reduces it. Also the local skin friction coefficients for the primary and secondary flows are reduced due to the Hall currents. The effects of the magnetic field, Hall currents and the wall velocity, on the skin friction coefficients for the primary and secondary flows increase with the Coriolis force. The wall velocity strongly affects the flow field. When the wall velocity is equal to the free stream velocity, the skin friction coefficients for the primary and secondary flows vanish, but this does not imply separation. 相似文献
19.
M. S. Zakharov B. M. Smolyak G. V. Ermakov 《Journal of Superconductivity and Novel Magnetism》2013,26(5):2013-2016
The effect of an external nonuniform magnetic field on the flux creep rate in a high-temperature superconductor with trapped magnetic flux was studied. The magnetic relaxation was suppressed when the superconductor was put into a field of permanent magnets or when it approached a ferromagnet. The effect arises when the field sources (being magnetized, the ferromagnet produces its own field) are placed near the superconductor surface, where the flux line ends are located. For these cases, we carried out the calculations of vortex and current density distributions, which demonstrate that reverse currents flow in the near-surface regions of the sample. This verifies the hypothesis suggested earlier about the influence of counter Lorentz forces retarding the creep of the vortices. In the interpretation of the results, we also take into consideration the magnetic force acting on the vortex ends in the external nonuniform magnetic field that allows us to explain the experimental results, in which the current structure in the sample is unipolar. 相似文献
20.
Computational modeling of magnetic nanoparticle targeting to stent surface under high gradient field
Shunqiang Wang Yihua Zhou Jifu Tan Jiang Xu Jie Yang Yaling Liu 《Computational Mechanics》2014,53(3):403-412
A multi-physics model was developed to study the delivery of magnetic nanoparticles (MNPs) to the stent-implanted region under an external magnetic field. The model is firstly validated by experimental work in literature. Then, effects of external magnetic field strength, magnetic particle size, and flow velocity on MNPs’ targeting and binding have been analyzed through a parametric study. Two new dimensionless numbers were introduced to characterize relative effects of Brownian motion, magnetic force induced particle motion, and convective blood flow on MNPs motion. It was found that larger magnetic field strength, bigger MNP size, and slower flow velocity increase the capture efficiency of MNPs. The distribution of captured MNPs on the vessel along axial and azimuthal directions was also discussed. Results showed that the MNPs density decreased exponentially along axial direction after one-dose injection while it was uniform along azimuthal direction in the whole stented region (averaged over all sections). For the beginning section of the stented region, the density ratio distribution of captured MNPs along azimuthal direction is center-symmetrical, corresponding to the center-symmetrical distribution of magnetic force in that section. Two different generation mechanisms are revealed to form four main attraction regions. These results could serve as guidelines to design a better magnetic drug delivery system. 相似文献