A comparative study on thermal conductivity of TiO2/ethylene glycol–water and TiO2/propylene glycol–water nanofluids

In the present study, TiO2 nanoparticles (NPs) have been synthesized by the sol–gel method. As synthesized, TiO2 NPs have been characterized by X-ray diffraction, high-resolution scanning electron microscopy (HR-SEM), Fourier transformation of Raman spectroscopy and UV–visible spectroscopic techniques. The different percentage of low mass concentration of TiO2 NPs have been dispersed into the mixture of ethylene glycol (EG) + water (W) and propylene glycol (PG) + water (W) in two different volume ratios (20:80 and 70:30%). The thermal and ultrasonic properties were analysed on the prepared nanofluids at the various temperature ranges from 298.15 to 323.15 K with an interval of 5 K. The 20:80% EG/W-based fluid of TiO2 nanofluids possess a higher thermal conductivity enhancement than other TiO2 nanofluids (20:80% PG/W, 70:30% EG/W and 70:30% PG/W). These results revealed that the thermal conductivity of nanofluids depends not only on nanoparticle concentrations and temperature, but also in the types of base fluids. The inter-particle interaction of nanoparticles and cluster formation have been analysed through the variation in ultrasonic parameters. Also, the thermal conductivities of nanofluids have been calculated through ultrasonic method and the results were compared with the flash laser technique method, obtained experimentally.