Enhancement of thermal conductivity upon application of magnetic field to Fe3O4 nanofluids

Abstract

Enhancement of thermal conductivity of fluids upon addition of nanoparticles has been previously observed. In this study, Fe3O4 magnetite particles were used and thermal conductivity enhancements both in water and in heptane with increasing volume fraction have been shown. Upon measuring thermal conductivity under externally applied magnetic field, it has been shown experimentally that thermal conductivity can be further increased even at low concentrations and low magnetic field strengths in both fluids. Theoretical calculations are presented to support the effect of magnetic field on the thermal conductivity enhancement. This enhancement is attributed to the thermomagnetic convection which due to a temperature gradient, results in a non-uniform magnetic body force resulting in more efficient thermal conductance.

Deterioration in effective thermal conductivity of aqueous magnetic nanofluids

“…23,25,35,36 The enhancement or deterioration of thermal conductivity of magnetic nanofluids is expected to affect their applications in systems such as heat exchangers. 37 In the past decade, there has been a growing interest on the heat transfer applications of nanofluid systems and the effect of nanoparticles on the thermal conductivities of base fluids has been studied by several groups.…”

Studying thermal conductivity of magnetic nanofluids in constant magnetic field

“…3 with increasing magnetic field intensity, an increase and decrease in the thermal conductivity of a magnetic nanofluids can be observed [5,6]. It is established that the influence of magnetic field intensifies with increase of nanoparticles concentration.…”

Direct observations of field-induced assemblies in magnetite ferrofluids

“…Cryo-TEM image of zero-field sample verifies random dispersion of particles mixed with some aggregates (see page 19,Ref. 8).…”

“…7 Formation of these structures, in particular, ordered chains or columnar structures in ferrofluids as a result of an applied field, leads to a change in the macroscopic properties of the medium, 8,9 while thermodynamic properties such as effective heat capacity remain unaffected by these heterogeneous structures. 10 For instance, magnetization of ferrofluid increases with the growth of chains, 2,11-14 viscosity abruptly increases, 1,2,15 thermal conductivity is enhanced if the field direction is parallel to temperature gradient, [16][17][18][19][20] and optical properties become strongly anisotropic. 1,[21][22][23] There are several examples of successful and prospective applications of self-assembled or field-assisted magnetic nanoparticles from technical applications to medical ones: in data storage, electronic devices, sensors, rotating shaft seals, hydrostatic and hydrodynamic bearings, magnetoacoustic transducers, vibration isolation and inertia damping systems, thermal systems, medical diagnostics, therapy and drug delivery, biophysical studies, and magnetic biosensing.…”