| Summary: | The natural convection heat transfer characteristics of Al 2 O 3 / water nanofluids comprised of 47 nm, Al 2 O 3 and water, with volume fractions ranging from 0.5% through 6%, has been investigated through a set of experimental measurements. The temperature of the heated surface and the Nusselt number of different volume fractions of Al 2 O 3 / water nanofluids natural convection tests clearly demonstrated a deviation from that of pure base fluids (distilled water). In the investigation, a deterioration of the natural convection heat transfer coefficient was observed with increases of the volume fraction of the nanoparticles in the nanofluids. The deterioration phenomenon was further investigated through a visualization study on a 850 nm diameter polystyrene particle/water suspension in a bottom heating rectangular enclosure. The influence of particle movements on the heat transfer and natural flow of the polystyrene particle/DI water suspension were filmed, and the temperature changes on the heating and cooling surfaces were recorded. The results were analyzed in an effort to explain the causes of the natural convection heat transfer deterioration of the 47 nm Al 2 O 3 / water nanofluids observed in the experiments. The visualization results confirmed the natural convective heat transfer deterioration, and further explained the causes of the deterioration of the nanofluids natural convective heat transfer.
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