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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

The case of a rigid lower wall and a stress-free upper wall, Rb = 0 (no microorganisms): (a) Oscillatory and non-oscillatory instability boundaries in the (Rac, Rn) plane. (b) Critical wavenumber in the (Rac, Rn) plane. (c) Square of the oscillation frequency, ω2, versus the nanoparticle concentration Rayleigh number (for oscillatory instability to occur, ω2 must be positive so that ω remains real).
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Figure 3: The case of a rigid lower wall and a stress-free upper wall, Rb = 0 (no microorganisms): (a) Oscillatory and non-oscillatory instability boundaries in the (Rac, Rn) plane. (b) Critical wavenumber in the (Rac, Rn) plane. (c) Square of the oscillation frequency, ω2, versus the nanoparticle concentration Rayleigh number (for oscillatory instability to occur, ω2 must be positive so that ω remains real).

Mentions: For Figures 3a,b,c and 4a,b,c, which show the results for the rigid-free boundaries, the same parameter values as for Figures 1 and 2 are utilized. Figure 3a, which is computed for Rb = 0 (no microorganisms), shows boundaries of non-oscillatory and oscillatory instabilities. This figure is similar to Figure 1a, but since now the case of the rigid-free boundaries is considered, the values of the critical Rayleigh number in Figure 3a are smaller than those in Figure 1a. Again, the comparison between the non-oscillatory and oscillatory instability boundaries indicates that in order for oscillatory instability to occur Rn must be negative; in this case at the instability boundary the effect of the nanoparticle distribution is stabilizing and the effect of the temperature gradient is destabilizing; the presence of these two competing agencies makes the oscillatory instability possible.


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

Kuznetsov AV - Nanoscale Res Lett (2011)

The case of a rigid lower wall and a stress-free upper wall, Rb = 0 (no microorganisms): (a) Oscillatory and non-oscillatory instability boundaries in the (Rac, Rn) plane. (b) Critical wavenumber in the (Rac, Rn) plane. (c) Square of the oscillation frequency, ω2, versus the nanoparticle concentration Rayleigh number (for oscillatory instability to occur, ω2 must be positive so that ω remains real).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: The case of a rigid lower wall and a stress-free upper wall, Rb = 0 (no microorganisms): (a) Oscillatory and non-oscillatory instability boundaries in the (Rac, Rn) plane. (b) Critical wavenumber in the (Rac, Rn) plane. (c) Square of the oscillation frequency, ω2, versus the nanoparticle concentration Rayleigh number (for oscillatory instability to occur, ω2 must be positive so that ω remains real).
Mentions: For Figures 3a,b,c and 4a,b,c, which show the results for the rigid-free boundaries, the same parameter values as for Figures 1 and 2 are utilized. Figure 3a, which is computed for Rb = 0 (no microorganisms), shows boundaries of non-oscillatory and oscillatory instabilities. This figure is similar to Figure 1a, but since now the case of the rigid-free boundaries is considered, the values of the critical Rayleigh number in Figure 3a are smaller than those in Figure 1a. Again, the comparison between the non-oscillatory and oscillatory instability boundaries indicates that in order for oscillatory instability to occur Rn must be negative; in this case at the instability boundary the effect of the nanoparticle distribution is stabilizing and the effect of the temperature gradient is destabilizing; the presence of these two competing agencies makes the oscillatory instability possible.

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