Abstract
Nanofluids offer the exciting new possibilities to enhance heat transfer performance. In this paper, experimental and theoretical investigations have been conducted to determine the effect of CuO nanowires on the thermal conductivity and viscosity of dimethicone based nanofluids. The CuO nanowires were prepared through a thermal oxidation method, and the analysis indicated that the as-prepared CuO nanowires had high purity, monocrystalline with a monoclinic structure and large aspect ratio compared to CuO nanospheres. The experimental data show that the thermal conductivity of the nanofluids increases with the volume fraction of CuO nanowires or nanospheres, with a nearly linear relationship. For the nanofluid with the addition of 0.75 vol.% CuO nanowires, the thermal conductivity enhancement is up to 60.78%, which is much higher than that with spherical CuO nanoparticles. The nanofluids exhibit typical Newtonian behavior, and the measured viscosity of CuO nanowires contained nanofluids were found only 6.41% increment at the volume fraction of 0.75%. It is attractive in enhanced heat transfer for application. The thermal conductivity and viscosity of CuO nanofluids were further calculated and discussed by comparing our experimental results with the classic theoretical models. The mechanisms of thermal conductivity and viscosity about nanofluids were also discussed in detail.
Highlights
The concept of “nanofluid” was proposed by Choi[1]
Water is a perfect fluid for heat transfer applications because of its favorable thermophysical properties, but the boiling point of water is low, which means that it cannot be applied to higher temperatures
The results of average viscosity increase with the volume concentrations of CuO nanofluid are shown in Fig. 9(a), and our measured viscosity of CuO based nanofluids are found to maximal increase by nearly 6.41% at the volume fraction of 0.75%
Summary
The concept of “nanofluid” was proposed by Choi[1]. Nanofluids are the suspensions of solid nanoparticles, which are made of mixing the nanoparticles in various base liquids such as water, thermal oils, dimethicone or ethylene glycol. Metal oxides are commonly used as thermal additives in nanofluids, due to their outstanding properties such as high thermal conductivity, electrical insulation, excellent compatibility with base fluid and high cost performance ratio[6]. Nanofluids containing metal oxides have exhibited special potentials in heat transfer applications These advantages may be applied in some areas. The nano-CuO material has great potential applications in heterogeneous catalyst, battery anode material, photothermal, photoconductive materials and other fields because of its attractive characteristics such as light[13], electricity, magnetism and catalysis[14,15,16] When it is used as a nanofluid additive, it will show excellent performance, and can be used for heat transfer applications due to its enhancement in thermal conductivity. The effects of the particle volume fraction, shape of the additive, mechanisms and theoretical model on the thermal conductivity were further investigated
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