Tuning of Thermal Conductivity and Rheology of Nanofluids Using an External Stimulus

We discuss a new methodology to tune the thermal properties of magnetic nanofluids from low to very high values by varying the magnetic field strength and its orientation. This is achieved by varying the mode of conduction of heat, through nanoparticles and base fluid, from a series to parallel mode. Because the parallel mode has a geometric configuration that allows the most efficient means of heat propagation through nanoparticle paths, very large thermal conductivity enhancement is achieved with parallel fields. With the increase in nanoparticle size, the field-induced k enhancement also increases because of enhanced dipole–dipole interactions. Furthermore, we also demonstrate that the thermal and rheological properties of such response stimuli fluids are reversibly switchable and may find applications in miniature devices such as micro- and nano-electromechanical systems.