Nanotechnology is a promising field in sustainable energy to reduce the energy consumption for optimum design of heat exchangers. Nanofluid provides significant improvement of thermo-physical properties and augmentation of heat transfer coefficients as well as reduces the pumping power if properly selected. In this chapter a CFD simulation using a finite volume method is presented for investigation of the hydrodynamic and thermal behavior of nanofluid flowing through a circular tube of heat exchanger with constant heat flux under single-phase turbulent flow condition for Reynolds number from 4000 to 20,000. Three different nanoparticles (Al2O3, CuO, and TiO2) with different volume fractions (1–5%) dispersed in water are analyzed. The heat transfer coefficient and pumping power increase with the increase in both the Reynolds number and volume fraction. The maximum saving of pumping power at a particular heat transfer coefficient has been obtained at 2% volume fraction for Al2O3–water and TiO2–water nanofluid and at 3% volume fraction for CuO–water nanofluid.