Abstract: In this study, Al2O3/EG and TiO2/EG nanofluids as coolants have been used in the double-tube heat exchanger. The hot solvent inlet heat exchanger must be cooled down with a specified amount. We can use nanofluids as coolants in the heat exchanger for optimization of the heat transfer area. Therefore, the efficacy of nanofluids as coolants is verified. Furthermore, flow rate of coolant is optimized by using the Al2O3/EG and TiO2/EG nanofluids in the heat exchanger. Thus with decreasing the heat transfer area and flow rate of the coolant, we can reduce the costs such as pumping power, fouling costs, etc in a double-tube heat exchanger. The heat transfer relations between hot solvent and nanofluids as coolants in the heat exchanger have been investigated. The results showed that the overall heat transfer coefficient was high, when the probability of collision between nanoparticles and the wall of the heat exchanger was increased under higher concentration. Consequently, we calculated the heat transfer coefficient, overall heat transfer coefficient, friction factor, pressure drop and pumping power for Al2O3/EG and TiO2/EG nanofluids used as coolants in a double-tube heat exchanger.