Carbon nanotube glycol nanofluids: Photo-thermal properties, thermal conductivities and rheological behavior

The efficiency and effectiveness of solar energy capture and storage are to a large extent functions of the heat transfer and storage capacity of the medium used. This paper investigates the potential of using carbon nanotube (CNT)-glycol nanosuspension as such a medium, prepared by freeze drying-ultrasonic dispersing after oxidation treatment with HNO3. The influences of the mass fraction of CNTs glycol nanofluids and temperatures on photo-thermal properties, thermal conductivities and rheological behavior were investigated. The results show that CNTs with oxidation treatment exhibited good dispersing performance. Strong optical absorption of the CNTs glycol nanofluids was detected in the range of 200–2500 nm. At room temperature, 18% enhancement was found in the photo-thermal conversion efficiency of the 0.5% mass fraction CNTs glycol nanofluids in comparison to the basic fluids, without significant increase in viscosity. At 55 °C, CNTs glycol nanofluids with 4.0% mass fraction exhibited much lower viscosity and 25.4% higher thermal conductivity in comparison to that of pure glycol at room temperature.

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► CNTs glycol nanofluid, prepared by supersonic dispersing after oxidation treatment with HNO3, had strong absorption for sunlight.
► Enhancement of photo-thermal conversion was 18% for 0.5 wt% nanofluid at 25 °C.
► Nanofluids with 4.0 wt% CNTs exhibited lower viscosity and 25.4% higher thermal conductivity at 55 °C compared to that of pure glycol at 25 °C.