The Onset of Double-Diffusive Nanofluid Convection in a Layer of a Saturated Porous Medium |
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Authors: | A V Kuznetsov D A Nield |
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Institution: | (1) Dept. of Mechanical and Aerospace Engineering, North Carolina State University, Campus Box 7910, Raleigh, NC 27695-7910, USA |
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Abstract: | 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. For the porous medium, the Brinkman
model is employed. Three cases of free–free, rigid–rigid, and rigid–free boundaries are considered. 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, whereas the contribution of nanoparticles to the thermal energy equation is 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. |
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