Synergistic mechanism of enhanced thermal conductivity and the corresponding economic analysis are analyzed to select a reasonable nanofluid. To this end, effects of nanoparticles (NP) and base fluids (BF) mixture ratios on thermal conductivity enhancement (Al2O3-TiO2/EG-W, Al2O3-CuO/EG-W and Al2O3-Cu/EG-W) are carried out at 1.0 vol% and temperature of 20 degrees C to 60 degrees C. Results show that the maximum thermal conductivity for Al2O3-TiO2/EG-W nanofluid increases from 0.482 (20 degrees C) to 0543 W/(nrK) (60 degrees C). Moreover, synergistic mechanism of thermal conductivity enhancement is caused by dispersing different sizes of nanopartides to form order arrangement of liquid molecules around nanoparticles, results in more compact solid-liquid interface and reasonable heat transfer network. Then, sensitivity analysis indicates that NP mixture ratio is a more important factor to determine the alignment of nanoparticles. Finally, Al2O3-CuO/EG-W nanofluid is an efficient fluid in laminar flow, while Al2O3-EG/W single nanofluid is the best choice for turbulent flow from economic analysis. (C) 2020 Elsevier B.V. All rights reserved.