Experimental, numerical, and theoretical investigation on the concentration-dependent Soret effect in magnetic fluids / Sprenger Lisa,Lange Adrian,Zubarev Andrey Yu.,Odenbach Stefan // PHYSICS OF FLUIDS. - 2015. - V. 27, l. 2.

ISSN/EISSN:

1070-6631 / 1089-7666

Type:

Article

Abstract:

Applying a temperature gradient to a layer of a binary fluid establishes a diffusive transport mechanism called thermophoresis or Soret effect which separates the two fluid's components and is measured by the Soret coefficient. Recent investigations carried out on concentrated magnetic fluids showed that the intensity of the Soret effect depends on the concentration of the nanoparticles transported. The present article, therefore, deals with the concentration-dependence of the Soret coefficient using five equally composed magnetic fluids only varying in the concentration of the particles from 2 vol. \% to 10 vol. \% of magnetic material. The current investigations point out that the determination of the Soret coefficient and especially its dependence on the particles' concentration is based on the determination of the thermal and particle diffusion coefficient. The article, therefore, presents a theoretical approach for the determination of the thermal diffusion coefficient and adapts a commonly used Ansatz for the particle diffusion coefficient for the present case of concentrated magnetic fluids. It is thereby possible to determine a theoretical Soret coefficient in dependence on an empirical parameter alpha. The coefficient is compared with the experimental approaches which have been previously used, these will be referred to as ``analytical approach{''} throughout the text. A second comparison is achieved with a hybrid Soret coefficient which fits the experimentally detected separation curves numerically. Within the investigations, the hydrodynamic concentration of the particles is used, assuming a surfactant layer's thickness of 2 nm per magnetic particle which leads to concentrations between approximately 11 vol. \% and 47 vol. \%. The diffusion coefficient ranges from 0.6 x 10(-11) m(2)/s to 2.5 x 10(-11) m(2)/s depending on the analytical model used. The theoretical Soret coefficient decreases with increasing particles' concentration; the experimental values derived from the analytical approach decrease from 0.06 K-1 to 0.01 K-1 for increasing particles' concentration. The numerically determined coefficient ranges from 0.11 K-1 to 0.022 K-1. The experimental values are smaller than former experimental results suggest (0.16 K-1), which is due to the fact that in formerworks, only magnetic concentrations had been considered. All three current investigations prove what could also be partly seen in former experiments that the higher the particles' concentration the weaker is thermophoresis. The particle diffusion coefficient has to be known for the determination of the Soret coefficient. It is carried out a proof of principle in the article showing that the horizontal thermophoresis cell can also be used to determine the rehomogenisation process which takes place after separating the fluid by applying a homogeneous temperature to the fluid. The diffusion coefficients that could be determined experimentally range from 1 x 10(-11) m(2)/s to 6 x 10(-11) m(2)/s. (C) 2015 AIP Publishing LLC.

Author keywords:

THERMOMAGNETIC CONVECTION; DIFFUSION-COEFFICIENTS; THERMAL-DIFFUSION; COLLOIDS; THERMODIFFUSION; FERROFLUIDS; PARTICLES; MIXTURES

DOI:

10.1063/1.4906841

Web of Science ID:

ISI:000350551300003

Соавторы в МНС:

—

Другие поля

Поле	Значение
Month	FEB
Publisher	AMER INST PHYSICS
Address	1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA
Language	English
Article-Number	022001
EISSN	1089-7666
Keywords-Plus	THERMOMAGNETIC CONVECTION; DIFFUSION-COEFFICIENTS; THERMAL-DIFFUSION; COLLOIDS; THERMODIFFUSION; FERROFLUIDS; PARTICLES; MIXTURES
Research-Areas	Mechanics; Physics
Web-of-Science-Categories	Mechanics; Physics, Fluids \& Plasmas
Author-Email	Lisa.Sprenger@tu-dresden.de
ResearcherID-Numbers	Odenbach, Stefan/D-4542-2009
Funding-Acknowledgement	Deutsche Forschungsgemeinschaft {[}LA 1182/3]; Russian Fund of Fundamental Investigations {[}12-01-00132, 13-02-91052, 13-01-96047, 14-08-00283]; Act 211 Government of the Russian Federation {[}02.A03.21.0006]; Ministry of Education of Russian Federation {[}2.1267.2011]
Funding-Text	The authors especially thank Professor Blums for very helpful discussions in the general context of the diffusion coefficient and Kuldip Raj from Ferrotec for the support with the fluid samples. The financial support by the Deutsche Forschungsgemeinschaft in project LA 1182/3, by the Russian Fund of Fundamental Investigations, Grant Nos. 12-01-00132, 13-02-91052, 13-01-96047, and 14-08-00283, by the Act 211 Government of the Russian Federation No. 02.A03.21.0006, and by the program of Ministry of Education of Russian Federation, Project No. 2.1267.2011 is gratefully acknowledged.
Number-of-Cited-References	35
Usage-Count-Last-180-days	4
Usage-Count-Since-2013	15
Journal-ISO	Phys. Fluids
Doc-Delivery-Number	CC7MG