Thermal and rheological properties of carbon nanotubes-oil nanofluid

As a novel heat transfer medium, nanofluid is effective to strengthen heat transfer. We prepared carbon nanotubes-oil nanofluid with two-step method, and analyzed the influence of the nanotube length, volume fraction, temperature, rotate speed, SN ratio (the mass ratio of surfactant and nanoparticles) and other factors on the thermal and rheological properties. The results show that, thermal conductivity and viscosity of nanofluid increase with the increasing of volume fraction of the nanotubes while decrease with the rising of temperature. The thermal conductivity of long carbon nanotubes-oil nanofluid is relatively high and the viscosity of short carbon nanotubes-oil nanofluid is relatively low. The nanofluids prepared are pseudoplastic fluid, and at low rotational speed, viscosity decreases with SN ratio increasing firstly but increases latterly, and there exists the optimum SN ratio of 0.4, which makes the viscosity least. In the experiment, the thermal conductivity was increased by 50% at maximum with 7%(vol) carbon nanotubes and the result fits well with model of H-C when the shape factor n is taken to be 7.