Fluid flow induced by a rapidly alternating or rotating magnetic field

1979 ◽  
Vol 92 (1) ◽  
pp. 35-51 ◽  
Author(s):  
A. D. Sneyd
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Magnetic Reynolds Number ◽  
Rotating Magnetic Field ◽  
Complex Flows ◽  
Rotating Magnetic Fields ◽  
Constant Rate ◽  
Axis Parallel ◽  
Uniform Cross Section ◽  
Vorticity Generation

This paper studies the effect of alternating or rotating magnetic fields on containers of conducting fluid. The magnetic Reynolds number is assumed small. The frequency of alternation or rotation is rapid so the magnetic field is confined to a thin layer on the surface of the container. A boundary-layer analysis is used to find the rate of vorticity generation due to the Lorentz force. When the container is an infinitely long cylinder of uniform cross-section, alternating fields normal to the generators or fields rotating about an axis parallel to the generators generate vorticity at a constant rate. For containers of any other shape the rate of vorticity generation includes both constant and oscillatory terms. A perturbation analysis is used to study the flow induced in a slightly distorted circular cylinder by a rotating field. Complex flows develop in the viscous-magnetic boundary layer which may be unstable.

Flow induced in a cylindrical column by a uniformly rotating magnetic field

1967 ◽  
Vol 297 (1451) ◽  
pp. 558-563
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Reynolds Number ◽  
High Frequency ◽  
Fourier Transforms ◽  
Reynolds Numbers ◽  
Magnetic Reynolds Number ◽  
Rotating Magnetic Field ◽  
Cylindrical Column ◽  
Field Lines

Under laboratory conditions, the magnetic Reynolds number is quite small in a conductor, but can be made appreciable if a high frequency rotating field is applied. Moffatt investigated this problem for high magnetic Reynolds numbers and concluded that there existed a magnetic boundary layer due to spiralling of field lines. Applying Fourier transforms and solving the corrected equations, we find that at low magnetic Reynolds numbers the field lines uniformly penetrate the cylindrical column and do not exhibit any appreciable spiralling. The rotation opposes the drift due to conductivity which is evened out as one proceeds from the centre to the surface. This uniform behaviour persists for small magnetic Reynolds number inside and outside. When the magnetic Reynolds number becomes large, of the order of 100 (say), the field lines passing through the axis of the cylinder exhibit spiralling as suggested by Moffatt since the diffusion is unable to counterbalance the rotational effects.

An experimental investigation of current production by means of rotating magnetic fields

1981 ◽  
Vol 26 (3) ◽  
pp. 465-480 ◽  
Author(s):  
W. N. Hugrass ◽  
I. R. Jones ◽  
M. G. R. Phillips
Keyword(s):  
Magnetic Field ◽  
Experimental Investigation ◽  
Threshold Value ◽  
Rotating Magnetic Field ◽  
Electron Current ◽  
Rotating Magnetic Fields ◽  
Theta Pinch ◽  
Current Production ◽  
Made In ◽  
Rotating Field

An investigation of current production by means of a rotating magnetic field is made in an experiment in which the technique is used to generate a theta-pinch- like distribution of field and plasma. Detailed measurements are made of both the generated unidirectional azimuthal electron current and the penetration of the rotating field into the plasma. The experimental results support the theoretical prediction that a threshold value of the amplitude of the applied rotating field exists for setting the electrons into rotation.

Frequency-dependent conversion of the torque of a rotating magnetic field on a ferrofluid confined in a spherical cavity

Soft Matter ◽  
2019 ◽  
Vol 15 (44) ◽  
pp. 9018-9030
Author(s):  
Klaus D. Usadel ◽  
Anastasiya Storozhenko ◽  
Igor Arefyev ◽  
Hajnalka Nádasi ◽  
Torsten Trittel ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Nanoparticles ◽  
Magnetic Fields ◽  
Spherical Cavity ◽  
Rotating Magnetic Field ◽  
Rotating Magnetic Fields ◽  
Frequency Dependent

The dynamics of magnetic nanoparticles in rotating magnetic fields is studied both experimentally and theoretically.

Control of the Macrosegregations during Solidification of a Binary Alloy by Means of a AC Magnetic Field

2006 ◽  
Vol 508 ◽  
pp. 163-168 ◽  
Author(s):  
Xiao Dong Wang ◽  
A. Ciobanas ◽  
Florin Baltaretu ◽  
Anne Marie Bianchi ◽  
Yves Fautrelle
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Mushy Zone ◽  
Binary Alloy ◽  
Solidification Front ◽  
Laminar Flows ◽  
Rotating Magnetic Field ◽  
Moderate Intensity ◽  
Mushy Region ◽  
Rotating Magnetic Fields

A numerical model aimed at simulating the segregations during the columnar solidification of a binary alloy is used to investigate the effects of a forced convection. Our objective is to study how the segregation characteristics in the mushy zone are influenced by laminar flows driven both by buoyancy and by AC fields of moderate intensity. Various types of magnetic fields have been tested, namely travelling, rotating magnetic field and slowly modulated electromagnetic forces. The calculations have been achieved on two types of alloys, namely tin-lead and aluminiumsilicon. It is shown that the flow configuration changes the segregation pattern. The change comes from the coupling between the liquid flow and the top of the mushy zone via the pressure distribution along the solidification front. The pressure difference along the front drives a mush flow, which transports the solute in the mushy region. Another interesting type of travelling magnetic field has been tested. It consists of a slowly modulated travelling magnetic field. It is shown that in a certain range of values of the modulation period, the channels are almost suppressed. The normal macrosegregation remains, but the averaged segregation in the mushy zone is weaker than in the natural convection case. The optimal period depends on the electromagnetic force strength as well as the cooling rate. The latter phenomenon cannot occur in the case of rotating magnetic fields, since in that configuration the sign of the pressure gradient along the solidification front remains unchanged. Recent solidification experiments with electromagnetic stirring confirm the predicted macrosegregation patterns.

Semiconductor Crystal Growth by the Vertical Bridgman Process With Transverse Rotating Magnetic Fields

2006 ◽  
Vol 129 (2) ◽  
pp. 241-243 ◽  
Author(s):  
X. Wang ◽  
N. Ma
Keyword(s):  
Magnetic Field ◽  
Crystal Growth ◽  
Magnetic Fields ◽  
Applied Magnetic Field ◽  
Rotating Magnetic Field ◽  
Semiconductor Crystal ◽  
Rotating Magnetic Fields ◽  
Electrically Conducting ◽  
Vertical Bridgman ◽  
Bridgman Process

During the vertical Bridgman process, a single semiconductor crystal is grown by the solidification of an initially molten semiconductor contained in an ampoule. The motion of the electrically conducting molten semiconductor can be controlled with an externally applied magnetic field. This paper treats the flow of a molten semiconductor and the dopant transport during the vertical Bridgman process with a periodic transverse or rotating magnetic field. The frequency of the externally applied magnetic field is sufficiently low that this field penetrates throughout the molten semiconductor. Dopant distributions in the crystal are presented.

scholarly journals Dynamics of superparamagnetic nanoparticles in viscous liquids in rotating magnetic fields

2019 ◽  
Vol 10 ◽  
pp. 2294-2303
Author(s):  
Nikolai A Usov ◽  
Ruslan A Rytov ◽  
Vasiliy A Bautin
Keyword(s):  
Magnetic Field ◽  
Absorption Rate ◽  
Specific Absorption Rate ◽  
Stochastic Equation ◽  
Magnetization Vector ◽  
Optimal Choice ◽  
Superparamagnetic Nanoparticles ◽  
Rotating Magnetic Field ◽  
Rotating Magnetic Fields ◽  
Specific Absorption

The dynamics of magnetic nanoparticles in a viscous liquid in a rotating magnetic field has been studied by means of numerical simulations and analytical calculations. In the magneto-dynamics approximation three different modes of motion of the unit magnetization vector and particle director are distinguished depending on frequency and amplitude of the rotating magnetic field. The specific absorption rate of a dilute assembly of superparamagnetic nanoparticles in rotating magnetic field is calculated by solving the Landau–Lifshitz stochastic equation for the unit magnetization vector and the stochastic equation for the particle director. At elevated frequencies an optimal range of particle diameters is found where the specific absorption rate of an assembly in a rotating magnetic field has a maximum. It is shown that with an optimal choice of the particle sizes sufficiently large SAR values of the order of 400–500 W/g can be obtained in a rotating magnetic field with a frequency f = 400 kHz and a moderate magnetic field amplitude H 0 = 100 Oe.

Flow Control Using Alternating Magnetic Fields During Crystal Growth From a Melt

2012 ◽  
Author(s):  
Yue Huang ◽  
Kenneth E. Davis ◽  
Brent C. Houchens
Keyword(s):  
Magnetic Field ◽  
Crystal Growth ◽  
Magnetic Fields ◽  
Flow Control ◽  
Body Force ◽  
Stokes Equations ◽  
Magnetic Reynolds Number ◽  
Rotating Magnetic Field ◽  
Bandgap Energy ◽  
Alternating Magnetic Fields

Flow control during bulk melt crystal growth is desirable for producing ternary alloy semiconductors with tunable lattice parameters and bandgap energy, providing custom materials for specific electro-optical applications. Segregation between constituent elements in the melt, be it through preferential rejection at the growth front or density variations, limits the growth rate and the uniformity in the crystal. External alternating magnetic fields are employed to stir the electrically conducting melt. While mixing is desired, turbulent flow is generally not. Precise control is required to maintain a laminar melt flow while providing sufficient mixing. Stirring via a rotating magnetic field (RMF) and a three-coil traveling magnetic field (TMF) is modeled and compared for a cylindrical melt confined in an ampule. The RMF imposes a body force in the azimuthal direction while the TMF induces primarily radial and axial body forces. The magnetic fields are effectively decoupled from the flow fields due to the small magnetic Reynolds number. Therefore, the magnetic fields are first determined using a finite element solver. The flows are then solved by a spectral element model of the Navier-Stokes equations including an electromagnetic body force term.

Tuning mass transport in magnetic nanoparticle-filled viscoelastic hydrogels using low-frequency rotating magnetic fields

Soft Matter ◽  
2017 ◽  
Vol 13 (36) ◽  
pp. 6259-6269 ◽  
Author(s):  
Shahab Boroun ◽  
Faïçal Larachi
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Mass Transport ◽  
Magnetic Nanoparticle ◽  
Low Frequency ◽  
Rotating Magnetic Field ◽  
Rotating Magnetic Fields ◽  
Rotational Movement

Rotational movement of MNPs in ferrogels in an external rotating magnetic field for tuning mass transport.

scholarly journals Power and Momentum Relations in Rotating Magnetic Field Current Drive

1984 ◽  
Vol 37 (5) ◽  
pp. 509 ◽  
Author(s):  
WN Hugrass
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Magnetic Fields ◽  
Phase Velocity ◽  
Current Drive ◽  
Rotating Magnetic Field ◽  
Plasma Current ◽  
Rotating Magnetic Fields ◽  
Frequency Source ◽  
Rotating Field

The use of rotating magnetic fields (RMF) to drive steady currents in plasmas involves a transfer of energy and angular momentum from the radio frequency source feeding the rotating field coils to the plasma. The. power-torque relationships in RMF systems are discussed and the analogy between RMF current drive and the polyphase induction motor is explained. The general relationship between the energy and angular momentum transfer is utilized to calculate the efficiency of the RMF plasma current drive. It is found that relatively high efficiencies can be achieved in RMF current drive because of the low phase velocity and small slip between the rotating field and the electron fluid.

The Momentum Integral Approximation for Compressible Magnetogasdynamic Boundary-Layer Flow

1963 ◽  
Vol 30 (2) ◽  
pp. 269-274 ◽  
Author(s):  
J. J. Kauzlarich ◽  
A. B. Cambel
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Magnetic Reynolds Number ◽  
Viscous Drag ◽  
Adiabatic Wall ◽  
Integral Approximation ◽  
Two Dimensional Flow ◽  
Layer Flow ◽  
Momentum Integral ◽  
The Magnetic Field

The drag of an adiabatic flat plate in an ionized gas for a constant magnetic field applied to the boundary layer on the plate is found by a momentum integral approximation of von Karman. Laminar, two-dimensional flow, zero pressure gradient, small magnetic Reynolds number, and negligible electrical conductivity outside the boundary layer are assumed. The solution is valid in particular to a continuous, perfect-gas plasma, of unitary Prandtl number, and for conditions when the interaction parameter is very small. The solution shows the following effects: The adiabatic wall temperature is independent of the magnetic field; there is an increase in the boundary-layer thickness as the magnetic-field strength is increased; and the viscous drag coefficient decreases whereas the coefficient of total drag increases.

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