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Nanofluid bioconvection in water-based suspensions containing nanoparticles and oxytactic microorganisms: oscillatory instability.

Kuznetsov AV - Nanoscale Res Lett (2011)

Bottom Line: Physical mechanisms responsible for the slip velocity between the nanoparticles and the base fluid, such as Brownian motion and thermophoresis, are accounted for in the model.An approximate analytical solution of the eigenvalue problem is obtained using the Galerkin method.The obtained solution provides important physical insights into the behavior of this system; it also explains when the oscillatory mode of instability is possible in such system.

View Article: PubMed Central - HTML - PubMed

Affiliation: Dept, of Mechanical and Aerospace Engineering, North Carolina State University, Campus Box 7910, Raleigh, NC 27695-7910, USA. avkuznet@eos.ncsu.edu.

ABSTRACT
The aim of this article is to propose a novel type of a nanofluid that contains both nanoparticles and motile (oxytactic) microorganisms. The benefits of adding motile microorganisms to the suspension include enhanced mass transfer, microscale mixing, and anticipated improved stability of the nanofluid. In order to understand the behavior of such a suspension at the fundamental level, this article investigates its stability when it occupies a shallow horizontal layer. The oscillatory mode of nanofluid bioconvection may be induced by the interaction of three competing agencies: oxytactic microorganisms, heating or cooling from the bottom, and top or bottom-heavy nanoparticle distribution. The model includes equations expressing conservation of total mass, momentum, thermal energy, nanoparticles, microorganisms, and oxygen. Physical mechanisms responsible for the slip velocity between the nanoparticles and the base fluid, such as Brownian motion and thermophoresis, are accounted for in the model. An approximate analytical solution of the eigenvalue problem is obtained using the Galerkin method. The obtained solution provides important physical insights into the behavior of this system; it also explains when the oscillatory mode of instability is possible in such system.

No MeSH data available.


Related in: MedlinePlus

Similar to Figure 1, but now with Rb = 120000.
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Figure 2: Similar to Figure 1, but now with Rb = 120000.

Mentions: Figure 2a,b,c is computed for the same parameter values as Figure 1a,b,c, but now with Rb = 120000. Figure 2a,b,c thus shows the effect of microorganisms. By comparing Figure 2a with 1a, it is evident that the presence of microorganisms produces the destabilizing effect and reduces the critical value of Ra. For example, at (NA + Ln) Rn = -5000 in Figure 1a the value of Rac corresponding to the non-oscillatory instability boundary is 6750 and in Figure 2a the corresponding value of Rac is 6437. At (NA + Ln) Rn = 5000 in Figure 1a the value of Rac corresponding to the non-oscillatory instability boundary is -3250 and in Figure 2a the corresponding value of Rac is -3563. The destabilizing effect of oxytactic microorganisms is explained as follows. These microorganisms are heavier than water and on average they swim in the upward direction. Therefore, the presence of microorganisms produces a top-heavy density stratification and contributes to destabilizing the suspension.


Nanofluid bioconvection in water-based suspensions containing nanoparticles and oxytactic microorganisms: oscillatory instability.

Kuznetsov AV - Nanoscale Res Lett (2011)

Similar to Figure 1, but now with Rb = 120000.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211144&req=5

Figure 2: Similar to Figure 1, but now with Rb = 120000.
Mentions: Figure 2a,b,c is computed for the same parameter values as Figure 1a,b,c, but now with Rb = 120000. Figure 2a,b,c thus shows the effect of microorganisms. By comparing Figure 2a with 1a, it is evident that the presence of microorganisms produces the destabilizing effect and reduces the critical value of Ra. For example, at (NA + Ln) Rn = -5000 in Figure 1a the value of Rac corresponding to the non-oscillatory instability boundary is 6750 and in Figure 2a the corresponding value of Rac is 6437. At (NA + Ln) Rn = 5000 in Figure 1a the value of Rac corresponding to the non-oscillatory instability boundary is -3250 and in Figure 2a the corresponding value of Rac is -3563. The destabilizing effect of oxytactic microorganisms is explained as follows. These microorganisms are heavier than water and on average they swim in the upward direction. Therefore, the presence of microorganisms produces a top-heavy density stratification and contributes to destabilizing the suspension.

Bottom Line: Physical mechanisms responsible for the slip velocity between the nanoparticles and the base fluid, such as Brownian motion and thermophoresis, are accounted for in the model.An approximate analytical solution of the eigenvalue problem is obtained using the Galerkin method.The obtained solution provides important physical insights into the behavior of this system; it also explains when the oscillatory mode of instability is possible in such system.

View Article: PubMed Central - HTML - PubMed

Affiliation: Dept, of Mechanical and Aerospace Engineering, North Carolina State University, Campus Box 7910, Raleigh, NC 27695-7910, USA. avkuznet@eos.ncsu.edu.

ABSTRACT
The aim of this article is to propose a novel type of a nanofluid that contains both nanoparticles and motile (oxytactic) microorganisms. The benefits of adding motile microorganisms to the suspension include enhanced mass transfer, microscale mixing, and anticipated improved stability of the nanofluid. In order to understand the behavior of such a suspension at the fundamental level, this article investigates its stability when it occupies a shallow horizontal layer. The oscillatory mode of nanofluid bioconvection may be induced by the interaction of three competing agencies: oxytactic microorganisms, heating or cooling from the bottom, and top or bottom-heavy nanoparticle distribution. The model includes equations expressing conservation of total mass, momentum, thermal energy, nanoparticles, microorganisms, and oxygen. Physical mechanisms responsible for the slip velocity between the nanoparticles and the base fluid, such as Brownian motion and thermophoresis, are accounted for in the model. An approximate analytical solution of the eigenvalue problem is obtained using the Galerkin method. The obtained solution provides important physical insights into the behavior of this system; it also explains when the oscillatory mode of instability is possible in such system.

No MeSH data available.


Related in: MedlinePlus