Dresden 2003 – wissenschaftliches Programm

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DY: Dynamik und Statistische Physik

DY 23: Ferrofluids / Liquid crystals

DY 23.3: Vortrag

Dienstag, 25. März 2003, 12:15–12:30, G\"OR/229

Thermodiffusion in magnetic fluids: Magnetic field induced variation in the Soret coefficient — •Adrian Lange — Max-Planck-Institut für Physik komplexer Systeme, Dresden, Germany

In many studies magnetic fluids have been considered as a homogeneous fluid with effective properties assembled from those of the dispersed material (ferromagnetic nanoparticles) and the carrier liquid (oil or water). Contrarily, in thermomagnetic experiments a behaviour typical for a binary mixture can be expected, i.e. phenomena as thermal diffusion (Soret effect) will occur. Due to the sensitivity to external magnetic fields, the size and the sign of the Soret effect will depend on the strength of the magnetic field and on the relative orientation between temperature gradient and magnetic field. Recent measurements show that known microscopic theories [1] are not able to explain the observed drastic effects [2].

Therefore a novel macroscopic theory, called ferrofluid dynamics [3], will be applied and tested in a thermodiffusion problem. Assuming that anisotropic effects might be relevant for any nonzero magnetic field in thermally driven systems, a longitudinal and transversal mass flow with respect to the direction of the magnetic field is taken into account. Considering a horizontal layer of magnetic fluid cooled from below and heated from above, the effective Soret coefficient is determined and compared with known experimental results.

[1] E. Blums et al., Phys. Fluids 10, 2155 (1998)

[2] T. Völker, PhD thesis, Univ. Bremen (2002)

[3] H. W. Müller and M. Liu, Phys. Rev. E 64, 061405 (2001)