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Heterogeneous nanofluids: natural convection heat transfer enhancement.

Oueslati FS, Bennacer R - Nanoscale Res Lett (2011)

Bottom Line: Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection.The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach.The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N.

View Article: PubMed Central - HTML - PubMed

Affiliation: ENS-Cachan Dpt GC/LMT, 61, Av du Président Wilson 94235 Cachan Cedex, France. rachid.bennacer@dgc.ens-cachan.fr.

ABSTRACT
Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case.

No MeSH data available.


Related in: MedlinePlus

Dynamic, thermal and concentration fields for homogeneous (plotted by dashed lines) and heterogeneous (plotted by solid lines) cases (RT = 104, Pr = 6.2, Le = 3, Sr = 0.5%, φ = 2%, N = 1.75).
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Figure 6: Dynamic, thermal and concentration fields for homogeneous (plotted by dashed lines) and heterogeneous (plotted by solid lines) cases (RT = 104, Pr = 6.2, Le = 3, Sr = 0.5%, φ = 2%, N = 1.75).

Mentions: Figure 6 shows a comparison between homogeneous (plotted by dashed lines) and heterogeneous (plotted by solid lines) cases on streamlines (on the left), isotherms (at the middle) and isoconcentrations (on the right) using the same nanoparticles Al2O3. The figure demonstrates that a single circulation cell is formed in the clockwise direction for all values of Rayleigh numbers. One can observe that the separation caused by the Soret effect clearly shows the importance of the heterogeneity of the nanoparticle concentration in the cavity. Such a spatial heterogeneity causes, in turn, a relatively important modification of the thermal field, which can modify the heat transfer rate by as much as 10%. It is worth noting that many previous results do not take into account the buoyancy forces effect caused by this heterogeneous distribution of particle concentration. Our results from Figure 6 obviously show that such heterogeneity of nanoparticle concentration induces extra buoyancy forces and would modify the momentum equilibrium. Also, Figure 6 illustrates an example of the resulting dynamic, thermal and species fields as well as the important changes related to the adding temperature and concentration effects.


Heterogeneous nanofluids: natural convection heat transfer enhancement.

Oueslati FS, Bennacer R - Nanoscale Res Lett (2011)

Dynamic, thermal and concentration fields for homogeneous (plotted by dashed lines) and heterogeneous (plotted by solid lines) cases (RT = 104, Pr = 6.2, Le = 3, Sr = 0.5%, φ = 2%, N = 1.75).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211280&req=5

Figure 6: Dynamic, thermal and concentration fields for homogeneous (plotted by dashed lines) and heterogeneous (plotted by solid lines) cases (RT = 104, Pr = 6.2, Le = 3, Sr = 0.5%, φ = 2%, N = 1.75).
Mentions: Figure 6 shows a comparison between homogeneous (plotted by dashed lines) and heterogeneous (plotted by solid lines) cases on streamlines (on the left), isotherms (at the middle) and isoconcentrations (on the right) using the same nanoparticles Al2O3. The figure demonstrates that a single circulation cell is formed in the clockwise direction for all values of Rayleigh numbers. One can observe that the separation caused by the Soret effect clearly shows the importance of the heterogeneity of the nanoparticle concentration in the cavity. Such a spatial heterogeneity causes, in turn, a relatively important modification of the thermal field, which can modify the heat transfer rate by as much as 10%. It is worth noting that many previous results do not take into account the buoyancy forces effect caused by this heterogeneous distribution of particle concentration. Our results from Figure 6 obviously show that such heterogeneity of nanoparticle concentration induces extra buoyancy forces and would modify the momentum equilibrium. Also, Figure 6 illustrates an example of the resulting dynamic, thermal and species fields as well as the important changes related to the adding temperature and concentration effects.

Bottom Line: Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection.The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach.The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N.

View Article: PubMed Central - HTML - PubMed

Affiliation: ENS-Cachan Dpt GC/LMT, 61, Av du Président Wilson 94235 Cachan Cedex, France. rachid.bennacer@dgc.ens-cachan.fr.

ABSTRACT
Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case.

No MeSH data available.


Related in: MedlinePlus