Ferrohydrodynamics in Time-Varying Magnetic Fields

2002 ◽  
Author(s):  
Carlos Rinaldi ◽  
June-Ho Lee ◽  
Adam D. Rosenthal ◽  
Thomas Franklin ◽  
Markus Zahn
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Outer Wall ◽  
Anomalous Behavior ◽  
Rotating Magnetic Fields ◽  
Free Surfaces ◽  
Couette Viscometer ◽  
Three Phase ◽  
Viscous Torque ◽  
Theoretical Analyses

Measurements of magnetic-field-induced ferrofluid flow and torque in uniform rotating magnetic fields are presented and compared to theoretical analyses in order to understand observed paradoxical behavior. The viscous torque from this fluid flow is measured using a cylindrical Couette viscometer, as a function of magnetic field amplitude, frequency, and direction of rotation. The first set of experiments measures the torque on the outer wall of a polycarbonate spindle that is attached to a viscometer, which functions as a torque meter. The spindle is immersed in the ferrofluid, which is centered in the gap of a three-phase AC 2-pole motor stator winding. Anomalous behavior, such as negative effective viscosity, is demonstrated and discussed. The second set of experiments measures the viscous torque on the inner wall of a hollow spindle attached to the torque meter and filled completely with ferrofluid so that there is no free surface. These measurements show that magnetic fluid effects arise even in the absence of free surfaces. These observations are then shown to agree with a recently derived analysis of spin-up flow in ferrofluids.

Torque Measurements in Spin-Up Flow of Ferrofluids

2004 ◽  
Vol 126 (2) ◽  
pp. 198-205 ◽  
Author(s):  
Adam D. Rosenthal ◽  
Carlos Rinaldi ◽  
Thomas Franklin ◽  
Markus Zahn
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Stator Winding ◽  
Time Varying ◽  
Rotating Magnetic Fields ◽  
Free Surfaces ◽  
Torque Measurements ◽  
Three Phase ◽  
Viscous Torque ◽  
Theoretical Analyses

Measurements of magnetic-field-induced torque in applied uniform rotating magnetic fields are presented and compared to theoretical analyses for water- and oil-based ferrofluids. These experiments measure the viscous torque on the inner wall of a stationary hollow polycarbonate spindle that is completely filled with ferrofluid and attached to a viscometer functioning as a torque meter. The spindle remains stationary and is centered inside a three-phase AC 2-pole motor stator winding, creating uniform time-varying rotating magnetic fields. The viscous torque is measured as a function of magnetic field amplitude, frequency, and direction of rotation. These measurements demonstrate that ferrofluid flow and torque are present even in the absence of free surfaces and agree with a recently derived analysis of the torque during spin-up flow of ferrofluids.

Rheology and Behavior of Magnetic Fluids in Alternating/Rotating Magnetic Fields

2003 ◽  
Author(s):  
Carlos Rinaldi ◽  
Xiaowei He ◽  
Adam Rosenthal ◽  
Thomas Franklin ◽  
Cory Lorenz ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Fluids ◽  
Rotating Magnetic Fields ◽  
Magnetic Field Rotation ◽  
Three Phase ◽  
Field Rotation ◽  
And Behavior ◽  
The Magnetic Field ◽  
Cylindrical Test

The rheology and behavior of magnetic fluids in the presence of time-varying magnetic fields is illustrated through three sets of experiments. The first involves measurements of ferrofluid torque on a cylindrical spindle under applied uniform rotating magnetic fields. We measure the torque required to restrain a stationary cylindrical test wall in contact with aqueous ferrofluids subjected to the rotating uniform magnetic field generated by a three-phase AC 2-pole motor stator winding. The torque is found to scale linearly with volume, and to be a function of the applied magnetic field amplitude, frequency and direction of rotation. Measurements show that for ferrofluid entirely inside the cylindrical test wall the torque points in the same direction as the magnetic field rotation pseudovector, whereas for ferrofluid entirely outside the cylindrical wall the torque points in the direction opposite to the field rotation pseudovector. The second set of experiments explores the formation of ordered ferrofluid structures in the gap of a Hele-Shaw cell subjected to simultaneous vertical DC and in-plane horizontal rotating magnetic fields. Finally, the third set of experiments illustrates the effect of applied DC fields on the shape of ferrofluid jets and sheets.

scholarly journals The hardening of metals by rotating magnetic fields

1931 ◽  
Vol 130 (814) ◽  
pp. 514-523 ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Work Hardening ◽  
Rotating Magnetic Fields ◽  
Hardening Process ◽  
Hard Steel ◽  
Steel Balls ◽  
Hardened Condition

In a previous paper by the author experiments were described in which the hardness of various metals was increased by rotating them in a magnetic field. It had been observed that metals in a work-hardened condition, and in particular hard steel which had been super-hardened by the “Cloudburst” process of bombardment with steel balls, exhibit a propensity to become still harder by a process of ageing, the spontaneous increase of hardness commencing with the termination of the work-hardening process, and contiuning during a period of several hours or days.

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.

Solidification of AlSi Alloys in the ARTEMIS and ARTEX Facilities Including Rotating Magnetic Fields – A Combined Experimental and Numerical Analysis

2006 ◽  
Vol 508 ◽  
pp. 199-204 ◽  
Author(s):  
Marc Hainke ◽  
Sonja Steinbach ◽  
Johannes Dagner ◽  
Lorenz Ratke ◽  
Georg Müller
Keyword(s):  
Magnetic Field ◽  
Numerical Modeling ◽  
Numerical Analysis ◽  
Temperature Gradient ◽  
Magnetic Fields ◽  
Time Dependent ◽  
Flow Conditions ◽  
Rotating Magnetic Fields ◽  
Microstructural Parameters ◽  
Wide Range

The solidification microstructure is the consequence of a wide range of process parameters, like the growth velocity, the temperature gradient and the composition. Although the influence of these parameters is nowadays considerably well understood, an overall theory of the influence of convection on microstructural features is still lacking. The application of time dependent magnetic fields during directional solidification offers the possibility to create defined solidification and flow conditions. In this work, we report about solidification experiments in the ARTEMIS and ARTEX facilities including rotating magnetic fields (RMF). The effect of the forced melt flow on microstructural parameters like the primary and secondary dendrite arm spacing is analyzed for a wide range of magnetic field parameters. The experimental analysis is supported by a rigorous application of numerical modeling. An important issue is hereby the prediction of the resulting macrosegregation, i.e., differences in the composition on the scale of the sample (macroscale) due to the RMF. For the considered configuration and parameters an axial enrichment of Si is found beyond a certain magnetic field strength. The results are compared to available theories and their applicability is discussed.

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.

scholarly journals Магнитоструктурные особенности фазовых переходов в системе Mn-=SUB=-1-x-=/SUB=-Co-=SUB=-x-=/SUB=-NiGe Часть 1. Экспериментальные результаты

2021 ◽  
Vol 63 (12) ◽  
pp. 2073
Author(s):  
В.И. Митюк ◽  
Г.С. Римский ◽  
К.И. Янушкевич ◽  
В.В. Коледов ◽  
А.В. Маширов ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Phase ◽  
Experimental Studies ◽  
Anomalous Behavior ◽  
Magnetic Phase Transitions ◽  
Strong Magnetic Fields ◽  
Weak Magnetic Fields ◽  
Wide Range ◽  
Co Concentrations

Experimental studies of the magnetic and structural properties of solid solutions of the Mn1-xCoxNiGe system in a wide range of Co concentrations (0.05≤ x≤ 0.8), temperatures (5 K≤ x≤600 K) and magnetic fields (0.016 T≤ x≤ 13.5 T) have revealed a number of nontrivial magnetic and magnetocaloric features of this system. The latter include: 1) a change in the nature of magnetic phase transitions from magnetostructural transitions of the 1st order paramagnetism-antiferromagnetism (0.05≤ x≤ 0.15) to isostructural transitions of the 2nd order paramagnetism-ferromagnetism (0.15≤ x≤0.8) with a change in the concentration of Co ; 2) anomalous behavior of low-temperature regions of magnetization in weak magnetic fields; 3) a change in the saturation magnetization and the appearance of irreversible magnetic field-induced transitions at helium temperatures in strong magnetic fields.

Galvanomagnetic Properties of Cd3As2- MnAs (MnAs - 20%) System in Transverse Magnetic Field at Hydrostatic Pressure up to 9 Gpa

2020 ◽  
Vol 28 ◽  
pp. 3-8
Author(s):  
Louisa A. Saypulaeva ◽  
Shapiullah B. Abdulvagidov ◽  
Magomed M. Gadjialiev ◽  
Abdulabek G. Alibekov ◽  
Naida S. Abakarova ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Hydrostatic Pressure ◽  
Magnetic Fields ◽  
Transverse Magnetic Field ◽  
Magnetic Moment ◽  
Transverse Magnetic ◽  
Anomalous Behavior ◽  
Structural Transitions ◽  
Galvanomagnetic Properties ◽  
Magnetic Resistance

The Cd3As2+MnAs composite with 20 mole % of MnAs has been studied complexly in a wide ranges of temperatures, pressures and magnetic fields. Negative magnetic resistance has been found in the sample. This anomalous behavior is considered as a result of changes in tunneling processes due to reduce of distance between magnetic moment of ferromagnetic and structural transitions caused by pressure.

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