Abstract
In this study, the flow and heat transfer of non-Newtonian Al2O3-water nanofluid in Rayleigh-Bénard cavity are numerically studied. Power-law model is used to describe the non-Newtonian effect of nanofluids in which the flow behavior index depends on the nanoparticle volume fraction. We present a systematic study of the Al2O3-water nanofluid for Rayleigh number of 1000 ≤ Ra ≤ 500000, cavity aspect ratio of 0.25 ≤ AR ≤ 4.0 and nanoparticle volume fraction of 0% ≤ϕ≤ 3%. The flow pattern inside the cavity changes complicatedly as Ra increases and the heat transfer performance of the system is strongly affected by the flow pattern. The convectional structure is influenced by both of the shear-thinning effect and the variation of effective viscosity. The average Nusselt number changes non-monotonically because of the flow pattern change under the variation of Ra and n. The consideration of Brownian motion and thermophoresis could bring about 3% increase of average Nusselt number, and the value varies slightly with different AR and ϕ. The comparison between non-Newtonian and Newtonian models shows that noticeable underestimation of heat transfer performance could be resulted by Newtonian model. The average Nusselt number of non-Newtonian model is approximately 1.5 times to that of Newtonian model, and the deviation is more pronounced with the increase of particle volume fraction.
Published Version
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