Experimental Study of Natural Convection Heat Transfer of TiO2/Ethylene Glycol Nanofluids
This work conducts heat transfer experiments with natural convection in a 80 × 80 × 180 mm vertical square enclosure (width × height × length) using variable volume fractions from 0.26% to 0.78% of TiO2/ethylene glycol (EG) nanofluids prepared using a two-step method. Measurement of the thermal transport properties of the nanofluids shows that thermal conductivity and viscosity both increase as the volume fraction of the nanofluid increases. Furthermore, the viscosity of the nanofluids decrease as temperature increases, but the change in viscosity at a fixed temperature is almost the same regardless of volume fraction. In contrast to pure EG, there is a shear thinning non-Newtonian behavior in the low shear rate region of γ < 10 s–1, although nanofluids are still treated as a Newtonian fluid for high shear rates of γ > 10 s–1. Nusselt numbers under different Rayleigh numbers are also obtained from experimental data, and for Rayleigh numbers between 107 ≤Ra≤108 the heat transfer of TiO2/EG nanofluids is worse than pure EG. The increased viscosity due to the addition of nanoparticles has a greater negative effect than the positive effect of the increased thermal conductivity.
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Document Type: Short Communication
Publication date: April 1, 2015
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- Nanoscience and Nanotechnology Letters (NNL) is a multidisciplinary peer-reviewed journal consolidating nanoscale research activities in all disciplines of science, engineering and medicine into a single and unique reference source. NNL provides the means for scientists, engineers, medical experts and technocrats to publish original short research articles as communications/letters of important new scientific and technological findings, encompassing the fundamental and applied research in all disciplines of the physical sciences, engineering and medicine.
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