b Habibnezhad-Ledari - Department of Mechanical and Aerospace Engineering, Science and Research Branch, Islamic Azad University
m Khayat - Department of Mechanical and Aerospace Engineering, Science and Research Branch, Islamic Azad University

In this study, the steady state laminar convective heat transfer characteristics of CuO (40 nm)-Base oil nanofluid flow inside a vertical circular U-tube under constant heat flux were investigated experimentally. The stable CuO-base oil nanofluid with different particle weight concentrations of 0.5%, 1% and 2% was produced by means of ultrasonic device in two steps method. The effects of the weight concentration and Reynolds number were determined under constant heat flux. The results of the heat transfer characteristics with respect to appropriate variables were presented. It was observed that the heat transfer increased with the increase of Reynolds number. The heat transfer decreased with an increase in the weight concentration. It was found that The concentrations of CuO particles higher than 0.5 wt% in the base liquid were not suitable for heat transfer enhancement. The highest heat transfer enhancement was achieved at Re=307 and p=0.005. Finally, an empirical correlation is developed for predicting the Nusselt number of nanofluid flow inside vertical Utubes.

Convective heat transfer, Nanofluid, Vertical U-tube, Constant heat flux