Enhanced convective heat transfer in a circular tube by passive techniques has been a subject of interest for scientists and researchers in the past decades. Numerical and experimental studies have been reported in order to increase the amount of heat transferred by these techniques. The high thermal conductivity of metallic nanoparticles (gold, copper, aluminum, silver) etc. to the base fluid. This resulting in increasing the thermal conductivity of mixtures and provided new fluids which are called Nanofluids, such as, Alumina (Al2O3), copper oxide (CuO), silicon dioxide (SiO2), zinc oxide (ZnO). Nanofluids are prepared by dispersing less than 100 nanometer-sized particles in a base fluid such as water, ethylene glycol, oil and other conventional heat transfer fluids and these types of fluids have high thermal conductivity