عنوان مقاله [English]
In this paper, heat transfer rate from these surfaces were studied by computational fluid dynamics. The effect of nanoparticles concentrations and kinds on the rate of heat transfer were investigated numerically. Different models were used in order to access optimum results in simulations. The results of these simulations were compared with the well-known empirical relationships and showed a good adaptation.Finally, the RNG k-&epsilon model was chosen to simulate the heat transfer from spherical surface in the turbulent regimes. The results showed that with 5 times increasing in nanoparticles concentration, heat transfer rate increased 2.6 times. At low Reynolds number (Re=11.2), the enhancement of heat transfer rate in Ag nanofluids was 2.8 fold greater than that in Al2O3 nanofluids.Nanoparticles effects were negligible at high Reynolds number so that at Re=11190 heat transfer at three different kinds of nanofluids, which were contained Ag, Al2O3 and Cu nanoparticles,was equal.
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