Enhancement of thermal conductivity in water-based nanofluids employing TiO2/reduced graphene oxide composites

In this study, composites consisting of well-dispersed TiO2 nanoparticles deposited on the surface of reduced graphene oxide (designed as TiO2-G) were fabricated via a facile synthesis method, namely in situ hydrolysis of TiCl4 and subsequently immobilization on the surface of reduced graphene oxide. TiO2-G/water nanofluids with the nanoparticles loading of 0.02, 0.03, 0.05, 0.07, and 0.1 wt% were prepared by ultrasonic probe in the condition without the addition of surfactants. Furthermore, the stability, zeta potential, and thermal conductivity of the TiO2-G/water nanofluids were analyzed by using different experimental methods. With the nanoparticles loading of 0.02 wt% (0.015 vol%) and 0.05 wt% (0.038 vol%), the zeta potential value of TiO2-G/water nanofluids can reach up to −46.49 and −37.44 mV, respectively, exhibiting great stability. Compared to that of the base fluid, the thermal conductivity of TiO2-G/water nanofluids increased with the increase of the loading of TiO2-G composite and the temperature of the nanofluids, and reached a maximum enhancement of ~33 % at a composite concentration of 0.1 wt% (0.078 vol%). Therefore, TiO2-G/water nanofluids can be applied to heat exchanger systems, as they provide a good long-time dispersion stability and a significant thermal conductivity enhancement.