عنوان مقاله [English]
نویسندگان [English]چکیده [English]
An experimental study for the convection heat transfer coefficient in a region of nanofluid containing Al2O3 oxide nanoparticles of 20 nanometer diameter in water as a base fluid through circular annular tube in the cosine thermal flux boundary condition was carried out. The primary purpose of this investigation was accomplished on the surface temperature of the heat source (inner pipe) determined at the maximum upper than the middle of pipe for the whole entry temperatures and surface temperature for nanofluid which was less than that of the base fluid. However, the nanofluid did not have any effect on the location point on the maximum temperature surface. Then, the convection heat transfer coefficient and Nusselt number were scrutinized showing that both of them increase by increasing of the volume fraction and Reynolds number. The maximum value of the heat transfer coefficient of nanofluid belongs to the volume fraction of 1.5% and the Reynolds number near 2100 which is 19%, compared to that of the base-fluid. The effect of entrance temperature and pressure of nanofluid on the heat transfer coefficient was also studied. The experimental data have shown that by increasing the entrance temperature, the heat transfer coefficient improves but the pressure has a negligible effect on heat transfer. The results demonstrated that the relative pressure drop of nanofluid increased remarkably by increasing the volume fraction. Furtheremore, we observed that by decreasing the Reynolds number the pressure drop increased because of more sediment of nanoparticle at lower velocities.