The thermal conductivity of water base ferrofluids under magnetic field

► Without magnetic field, no enhancement was observed in thermal conductivity. ► Applying a magnetic field on the ferrofluid increases the thermal conductivity. ► Increasing the magnetic field intensity enhances the thermal conductivity more. ► The thermal conductivity does not immediately return to its starting value. ► Under magnetic field thermal conductivity decreases with temperature increase. In this manuscript, the thermal conductivity of ferrofluid’s containing Fe3O4 nanoparticles suspended in de-ionized water under magnetic field was experimentally investigated. Magnetic field was created by Helmholtz coils while its intensity was controlled by the electric current. The saturation time and the reversibility of thermal conductivity were also examined after the magnetic field was turned off. Furthermore the variation of thermal conductivity with temperature was shown. According to our results a ferrofluid with 5.0% volume fraction of nanoparticles with an average diameter of 10nm enhanced the thermal conductivity more than 200% at maximum value.