Heat and mass transfer phenomena in magnetic fluids

In this article the influence of a magnetic field on heat and mass transport phenomena in magnetic fluids (ferrofluids) will be discussed. The first section is dealing with a magnetically driven convection, the so called thermomagnetic convection while in the second section the influence of a temperature gradient on the mass transport, the Soret effect in ferrofluids, is reviewed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermophoretic separation of ultrafine particles in ferrofluids in thermal diffusion column under the effect of an MHD convection

The aim of the paper is to evaluate the Soret coeAcient ST of colloidal particles in ferrofluids from measurements of an unsteady particle separation in a flat thermodiAusion column. The column theory is modified taking into account MHD eAects of thermal convection aAected by a concentration buoyancy force. It is shown that the Hartmann eAect, not only in hydrocarbon based colloids but also in ionic magnetic fluids of relatively high electric conductivity, does not influence significantly the particle separation dynamics. From measurements, positive values of ST of surfacted particles in tetradecane based colloids are calculated. An anisotropy of the Soret eAect in the presence of a uniform…

Physikalische Chemie 2004

Die Einzelmolekulspektroskopie hat sich in den letzten Jahren methodisch stetig weiterentwickelt und damit zu neuen Erkenntnissen uber die elektronische Struktur von Halbleiternanokristallen und die elektronische Kopplung zwischen Molekulen gefuhrt. Magnetisch kontrollierbare Flussigkeiten eroffnen Einsatzmoglichkeiten in der Dampfungstechnik sowie in der lokalen Tumortherapie. Mikrochips fur die Manipulation kleinster Flussigkeitsmengen halten Einzug in Analytik und Reaktionstechnik.

Magnetic Soret effect in a hydrocarbon based colloid containing surfacted Mn–Zn ferrite particles

Abstract The Soret effect has been investigated in a hydrocarbon based magnetic fluid containing surfacted Mn 0.5 Zn 0.5 Fe 2 O 4 nanoparticles with a magnetic volume concentration of 2.3%. The magnetic fluid fills up a vertical diffusion column which consists of a flat vertical channel between two walls and two reservoirs at the ends of the channel. One wall of the channel is being heated while the another one is cooled, maintaining a temperature gradient over the channel's width that leads to separation of particles due to the Soret effect as well as the convective flow in the channel. The combination of the two mentioned effects brings up a measurable change of the concentration of magne…

Separation of Ferrocolloids in Thermodiffusion Columns: the Effect of Solute Buoyancy

Determination of the Soret coefficient of magnetic particles in a ferrofluid from the steady and unsteady part of the separation curve

Experiments on the particle separation in a vertical thermodiffusion column are used to investigate the separation (Soret effect) in ferrofluids. The use of a two-sectional column with internal walls of low thermal capacity allows analyzing the initial part of the unsteady separation curves as well as the steady state regime. The Soret coefficient calculated from the measurements of the separation dynamics agrees well with the one found from the steady separation limit reached in long-time experiments especially if the solutal buoyancy is low.

Soret coefficient of nanoparticles in ferrofluids in the presence of a magnetic field

Experiments on a nonstationary separation of nanometer-sized Mn0.5Zn0.5Fe2O particles of hydrocarbon-based ferrocolloids in a flat vertical thermal diffusion column are performed. By using a modified separation theory which accounts for a one-dimensional mixed (thermal and concentration) convection in the column, the Soret coefficient of lyophilized nanoparticles from the separation curves are calculated. It is shown that in a zero magnetic field particles are transferring toward decreasing temperatures. The thermal diffusion ratio αT reaches a value αT≈+20. A significant influence of a uniform magnetic field B on particle separation is observed. If B is oriented along the temperature gradi…