Rotating Ferrofluid Drops

Engel, A.; Lebedev, A. V.; Morozov, Konstantin I.

doi:10.1515/zna-2003-1206

Cited by 6 publications

(5 citation statements)

References 18 publications

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“…Taking into account the various contributions two equations for Ω and ζ can be derived. The final expressions are rather long and will be published elsewhere [22]. Results for the rotation frequency Ω of the drop are shown in fig.…”

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Shape transformations in rotating ferrofluid drops

2002

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Floating drops of magnetic fluid can be brought into rotation by applying a rotating magnetic field. We report theoretical and experimental results on the transition from a spheroid equilibrium shape to non-axissymmetrical three-axes ellipsoids at certain values of the external field strength. The transitions are continuous for small values of the magnetic susceptibility and show hysteresis for larger ones. In the non-axissymmetric shape the rotational motion of the drop consists of a vortical flow inside the drop combined with a slow rotation of the shape. Nonlinear magnetization laws are crucial to obtain quantitative agreement between theory and experiment.PACS numbers: 47.20.Hw, 47.55.Dz, 75.50.Mm The equilibrium shapes of rotating fluid bodies are of importance in various fields of physics as, e.g., astrophysics [1], nuclear fission [2], plasma [3], and biological physics [4]. The famous controversy between Newton and Cassini on whether the Earth has the form of an oblate or prolate rotational ellipsoid started a series of ingenious investigations of the equilibrium shapes of heavenly bodies including work by Maupertius, MacLaurin, Jacobi, Riemann, Poincaré and others. Among the suprising results discovered are the possibility of threeaxes ellipsoids as shown by Jacobi and the emergence of pear-shaped configurations found by Poincaré. In rotating non-neutral plasmas, laser cooled in a Penning trap, a novel equilibrium state with non-axissymmetric surface has recently been observed [5]. Tank-treading elliptical membranes in a shear flow have been used as a theoretical model for the motion of human red blood cells [6].Experimental investigations of the stationary shapes of rotating bodies in the laboratory usually start with a static drop of fluid floating in another, immiscible fluid of the same density. The rotational motion of the drop is then set up by, e.g., using a rotating shaft [7] or applying an acoustic torque [8]. An elegant way to spin up drops made from polarizable fluids is to use rotating electric [5] or magnetic fields [9,10].In the present letter we report theoretical and experimental investigations of rotating ferrofluid drops and in particular perform the first quantitative study of a transition from a spheroidal to a non-axissymmetric equilibrium shape in this system. Moreover, providing an approximate solution of the hydrodynamic flow problem inside and outside the drop we are able to analyze the rotational motion of the drop shape and to separate it from the internal hydrodynamic flow.Ferrofluids are suspensions of ferromagnetic nanoparticles in suitable carrier liquids combining the hydrodynamic behaviour of a Newtonian fluid with the magnetic properties of a super-paramagnet [11]. A rotating external field induces a rotational motion of the nanoparticles which due to their viscous coupling to the surrounding liquid transfer the angular momentum to the whole drop. The system has been studied previously by Bacri et al. using microdrops with a typical radius of 10 µm, very small surfac...

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“…The remaining differences with the experiment may be due to the magnetic particle size polydispersity of the fluid resulting in a whole spectrum of relaxation times, and a small ellipticity of the external field. These questions will be dealt with in detail elsewhere [23].…”

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Shape transformations in rotating ferrofluid drops

2002

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“…The penetrant may be applied to all non-ferrous materials and ferrous materials, but for inspection of ferrous components magnetic-particle inspection is also preferred for its subsurface detection capability. The experiments presented above in full generality are a formidable task [4]. The impact of the magnetic field on the ferrofluids drop is described by the magnetic stress Where B, H and M denote the magnetic induction, the magnetic field and the magnetization respectively.…”

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On-Board Monitoring of Crack and Corrosion Using Wireless Network

NISHA.M.

2012

IJICA

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Structural health monitoring is an important safety factor in aviation that might benefit from advanced smart systems for damage sensing. This paper presents a new concept for a wireless crack and corrosion detection system for onboard health monitoring of aircraft. The sensor which is use to identify the structural damage and material loss on the surface of the aircraft by Ferrous Fluid under magnetic field. The Ferro fluid shall be applied as an emulsion on the test substrate. When a crack occurs, due to the crack there will a flux leakage. By constantly monitoring the flux on the surface of the substrate, whenever there is a flux leakage we can correlate it to a crack. The Ferro fluid shall be a ferromagnetic material and the particles should be in sub micron or nanometer region. These particles shall be mixed in suitable surfactants to get a uniformly monodispersed emulsion. This emulsion is to be applied on the test substrate and then the flux generated due to the emulsion shall be first measured. This measured flux density shall be taken as the baseline. Any deviation from the baseline shall be considered as flux leakage. It is possible to differentiate between the signals received from a crack and corrosion. One of the advantages of the present set up using Ferrous Fluid Sensor (FFS) for the generation and detection of signals can be easily processed by wireless application. The signal sensed by the FFS is transmitted to the cockpit through the wireless sensor network for monitoring of crack and corrosion on the surface of the aircraft.

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“…However, it should be fulfilled on average. It can be shown that this requirement is equivalent to the energy dissipation balance in the system stating that per time unit the energy fed into the system by the magnetic field must be equal to the energy dissipated in the viscous flows and the periodic re-magnetization of the ferrofluid [23].…”

Section: 10mentioning

confidence: 99%

“…Naturally this makes the theoretical analysis more complicated and less accessible to analytical techniques. A detailed theoretical discussion of the implications of a non-linear magnetization law on the problem at hand can be found in [23]. Here we will only mention the main points and present some of the results which can be obtained by using the complete magnetization function M = M(H ) as determined in an independent experiment.…”

Section: Non-linear Magnetization Lawmentioning

confidence: 99%

Ferrofluid drops in rotating magnetic fields

Lebedev

Engel²,

Morozov

et al. 2003

New J. Phys.

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Abstract. Drops of a ferrofluid floating in a non-magnetic liquid of the same density and spun by a rotating magnetic field are investigated experimentally and theoretically. The parameters for the experiment are chosen such that different stationary drop shapes including non-axis-symmetric configurations could be observed. Within an approximate theoretical analysis the character of the occurring shape bifurcations, the different stationary drop forms, as well as the slow rotational motion of the drop is investigated. The results are in qualitative, and often quantitative agreement, with the experimental findings. It is also shown that a small eccentricity of the rotating field may have a substantial impact on the rotational motion of the drop. Contents

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Rotating Ferrofluid Drops

Cited by 6 publications

References 18 publications

Shape transformations in rotating ferrofluid drops

Shape transformations in rotating ferrofluid drops

On-Board Monitoring of Crack and Corrosion Using Wireless Network

Ferrofluid drops in rotating magnetic fields

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