Ferrofluid Phenomena

Ferrofluids spontaneously flow toward regions of strong magnetic fields and then stubbornly remain there, even in the presence of other forces. Quantitative predictions of how this occurs can be made using the appropriate ferrofluid constitutive equation, the equation of motion, and the boundary conditions for ferrofluids. These are presented and discussed in detail in Rosenzweig (1985). The equation of motion is (Rosenzweig 1985) 

To give the reader a flavor of the kinds of phenomena that can be predicted, we consider the simple case of a pool of ferrofluid, a portion of which is subjected to a weak magnetic field, at static equilibrium (see Fig. 8-14a). Thus, we drop the time derivative and the flow terms from Eq. (8-33), yielding 

If the magnetic field at point 2 is normal to the interface and the field strength does not Jump when the interface is crossed, and if the interface curvature is negligible (so that the capillary pressure term can be dropped), then p — p = p, the pressure in the air. The difference A/i = h2 h n the height of the interface is therefore 

For a strong enough field, the magnetic fluid fills the gap between the poles of the magnet. 

Ferrofluids have recently been combined with other complex fluids to produce fluids with very interesting behavior. When ionic ferrofluids are doped into nematic liquid crystals (Brochard and de Gennes 1970), the resulting nematic liquid orients under a magnetic field 10 times lower than that required in the absenceof the dopant (Chen and Amer 1983 Bacri 

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In what follows the magnetoviscosity phenomenon is analyzed by formulating the local ferrohydrodynamic model, the upscaled volume-average model in porous media with the closure problem, and solution and discussion of a simplified zero-order steady-state isothermal incompressible axisymmetric model for non-Darcy-Forchheimer flow of a Newtonian ferrofluid in a porous medium of the... 

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