In this paper, carbon nanotubes (CNT) particles have been dispersed into transformer oil to make a nanofluid with two volume fractions of 0.0004 and 0.0041 to measure their thermophysical properties. The effects of several parameters such as temperature and nanoparticles concentration have been investigated on thermal conductivity and viscosity of the nanofluid. The measured thermophysical properties have been used for developing the nanofluid thermophysical properties correlations that are employed in the numerical simulation. The flow and heat transfer of the CNT/transformer oil have been numerically simulated for the straight and 90° curved pipe employing the single-phase approach. The experimental results indicated that adding CNTs improves the thermal conductivity of transformer oil. Despite the thermal conductivity reduction of the base fluid with the increase in temperature, nanofluid shows slight increase in thermal conductivity at higher temperatures. In addition, the increase in temperature decreases the viscosity of nanofluid, while CNTs concentration have no significant effect on the nanofluid viscosity. The numerical results revealed that the nanofluid convective heat transfer coefficient is higher than that of the base fluid. Furthermore, curvature effects increase the convective heat transfer characteristics considerably specially at higher nanoparticle volume fractions.

Keywords