Chen, Haisheng, Yang, Wei, He, Yurong, Ding, Yulong, Zhang, Lingling, Tan, Chunqing, Lapkin, Alexei A. and Bavykin, Dmitry V.
Heat transfer and flow behaviour of aqueous suspensions of titanate nanotubes (nanofluids)
Powder Technology, 183, (1), . (doi:10.1016/j.powtec.2007.11.014).
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Titanate nanotubes of an aspect ratio of ~10 are synthesized, characterised and dispersed in water to form stable nanofluids containing 0.5, 1.0
and 2.5 wt.% of the nanotubes. Experiments are then carried out to investigate the effective thermal conductivity, rheological behaviour and forced
convective heat transfer of the nanofluids. The results show a small thermal conductivity enhancement of ~3% at 25 °C and ~5% at 40 °C for the
2.5 wt.% nanofluid. The nanofluids are found to be non-Newtonian with obvious shear thinning behaviour with the shear viscosity decreasing with
increasing shear rate at low shear rates. The shear viscosity approaches constant at a shear rate higher than ~100–1000 s?1 depending nanoparticle
concentration. The high shear viscosity is found to be much higher than that predicted by the conventional viscosity models for dilute suspensions.
Despite the small thermal conduction enhancement, an excellent enhancement is observed on the convective heat transfer coefficient, which is
much higher than that of the thermal conductivity enhancement. In comparison with nanofluids containing spherical titania nanoparticles under
similar conditions, the enhancement of both thermal conductivity and convective heat transfer coefficient of the titanate nanotube nanofluids is
considerably higher indicating the important role of particle shape in the heat transfer enhancement. Possible mechanisms are also proposed for the
observed enhancement of the convective heat transfer coefficient.
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