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Thermal instability in a porous medium layer saturated by a nanofluid. (English) Zbl 1177.80047
Summary: The onset of convection in a horizontal layer of a porous medium saturated by a nanofluid is studied analytically. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The analysis reveals that for a typical nanofluid (with large Lewis number) the prime effect of the nanofluids is via a buoyancy effect coupled with the conservation of nanoparticles, the contribution of nanoparticles to the thermal energy equation being a second-order effect. It is found that the critical thermal Rayleigh number can be reduced or increased by a substantial amount, depending on whether the basic nanoparticle distribution is top-heavy or bottom-heavy, by the presence of the nanoparticles. Oscillatory instability is possible in the case of a bottom-heavy nanoparticle distribution.

MSC:
80A20 Heat and mass transfer, heat flow (MSC2010)
76S05 Flows in porous media; filtration; seepage
60J65 Brownian motion
76R10 Free convection
82D80 Statistical mechanics of nanostructures and nanoparticles
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