Thermal conductivity measurements on ferrofluids with special reference to measuring arrangement

Material properties like viscosity and sound propagation in colloidal suspensions of magnetic nanoparticles, so-called ferrofluids, are known to depend on external magnetic fields due to structure formation of the magnetic particles. In this experimental study we investigate the effect of magnetically driven structure formation on heat flux in ferrofluids on the basis of thermal conductivity measurements in variation of an external magnetic field. Therefore an improved measuring device based on the plane heat source instead of the standard hot wire method is used to enable both parallel and perpendicular orientation of magnetic field and heat flux. Thermal conductivity measurements are carried out in variation of strength and direction of an external magnetic field relative to heat flux. Unlike former experimental investigations for the first time the results show qualitative consistency with theoretical predictions for both orientations. (C) 2012 Elsevier B.V. All rights reserved.