Thermal conductivity of a diamond magnetite composite fluid under the effect of a uniform magnetic field

• Magnetic fields induce chain-like structuring of diamond magnetite composite fluid.
• A thermal conductivity enhancement is observed when the magnetic field is applied.
• Thermal enhancement due to magnetic fields strongly depends on diamond concentration.

We study the thermal diffusion through a fluid made of diamond microparticles immersed in a ferrofluid. A thermal conductivity enhancement is observed when a magnetic field is applied to the fluid; this phenomenon is due to a better heat propagation through a tridimensional chain-like structuring formed by the diamond particles in the direction of the field; additionally the thermal conductivity of the material could be controlled in a switchable way and moreover with the intensity and direction of the field. This thermal improvement shows a strong dependence on the diamond volume fraction, presenting a maximum of 76% when the diamond volume concentration is 15% and as the concentration increases, the relative thermal conductivity enlargement decreases, becoming zero at the maximum diamond volume fraction. This complex behavior could be modeled with the use of the Lewis–Nielsen effective thermal conductivity model, with a form factor that depends on the diamond particle concentration.