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Heat transfer augmentation in nanofluids via nanofins.

Vadasz P - Nanoscale Res Lett (2011)

Bottom Line: Theoretical results derived in this article are combined with experimental data to conclude that, while there is no improvement in the effective thermal conductivity of nanofluids beyond the Maxwell's effective medium theory (J.C.Maxwell, Treatise on Electricity and Magnetism, 1891), there is substantial heat transfer augmentation via nanofins.The latter are formed as attachments on the hot wire surface by yet an unknown mechanism, which could be related to electrophoresis, but there is no conclusive evidence yet to prove this proposed mechanism.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical Engineering, Northern Arizona University, P, O, Box 15600, Flagstaff, AZ 86011-5600, USA. peter.vadasz@nau.edu.

ABSTRACT
Theoretical results derived in this article are combined with experimental data to conclude that, while there is no improvement in the effective thermal conductivity of nanofluids beyond the Maxwell's effective medium theory (J.C. Maxwell, Treatise on Electricity and Magnetism, 1891), there is substantial heat transfer augmentation via nanofins. The latter are formed as attachments on the hot wire surface by yet an unknown mechanism, which could be related to electrophoresis, but there is no conclusive evidence yet to prove this proposed mechanism.

No MeSH data available.


Related in: MedlinePlus

Dimensionless wire temperature. Comparison between the Fourier and Dual-Phase-Lagging solutions for the following dimensionless parameters values Foq = 1.1 × 10-2 and as = 0.55.
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Figure 2: Dimensionless wire temperature. Comparison between the Fourier and Dual-Phase-Lagging solutions for the following dimensionless parameters values Foq = 1.1 × 10-2 and as = 0.55.

Mentions: The results for the solid and fluid phases' temperature at r = rw as a function of time obtained from the solutions (62) and (63) are presented in Figures 1, 2 and 3 in comparison with the single-phase Fourier solution (69) for three different combinations of values of Foq and as, and plotted on a logarithmic time scale. While the quantitative results differ amongst the three figures, there are some similar qualitative features that are important to mention. First, it is evident from these figures that the fluid phase temperature is almost the same as the temperature obtained from the single-phase Fourier solution. Second, it is also evident that the solid phase temperature lags behind the fluid phase temperature by a substantial difference. They become closer as steady-state conditions approach. It is therefore imperative to conclude that the only way, an excessively higher effective thermal conductivity of the nanofluid suspension as obtained by Eastman et al. [1], Lee et al. [2] and Choi et al. [3] could have been obtained even in an apparent form, is if the wire was excessively exposed to the solid phase temperature. The latter could have occurred if the electric current passing through the wire created electric fields that activated a possible mechanism of electrophoresis that attracted the suspended nanoparticles towards the wire. Note that such a mechanism does not cause agglomeration in the usual sense of the word, because as soon as the electric field ceases, the agglomeration does not have to persist and the particles can move freely from the wire's surface. Therefore, testing the wire's surface after such an experiment for evidence of agglomeration on the wire's surface may not necessarily produce the required evidence for the latter.


Heat transfer augmentation in nanofluids via nanofins.

Vadasz P - Nanoscale Res Lett (2011)

Dimensionless wire temperature. Comparison between the Fourier and Dual-Phase-Lagging solutions for the following dimensionless parameters values Foq = 1.1 × 10-2 and as = 0.55.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211205&req=5

Figure 2: Dimensionless wire temperature. Comparison between the Fourier and Dual-Phase-Lagging solutions for the following dimensionless parameters values Foq = 1.1 × 10-2 and as = 0.55.
Mentions: The results for the solid and fluid phases' temperature at r = rw as a function of time obtained from the solutions (62) and (63) are presented in Figures 1, 2 and 3 in comparison with the single-phase Fourier solution (69) for three different combinations of values of Foq and as, and plotted on a logarithmic time scale. While the quantitative results differ amongst the three figures, there are some similar qualitative features that are important to mention. First, it is evident from these figures that the fluid phase temperature is almost the same as the temperature obtained from the single-phase Fourier solution. Second, it is also evident that the solid phase temperature lags behind the fluid phase temperature by a substantial difference. They become closer as steady-state conditions approach. It is therefore imperative to conclude that the only way, an excessively higher effective thermal conductivity of the nanofluid suspension as obtained by Eastman et al. [1], Lee et al. [2] and Choi et al. [3] could have been obtained even in an apparent form, is if the wire was excessively exposed to the solid phase temperature. The latter could have occurred if the electric current passing through the wire created electric fields that activated a possible mechanism of electrophoresis that attracted the suspended nanoparticles towards the wire. Note that such a mechanism does not cause agglomeration in the usual sense of the word, because as soon as the electric field ceases, the agglomeration does not have to persist and the particles can move freely from the wire's surface. Therefore, testing the wire's surface after such an experiment for evidence of agglomeration on the wire's surface may not necessarily produce the required evidence for the latter.

Bottom Line: Theoretical results derived in this article are combined with experimental data to conclude that, while there is no improvement in the effective thermal conductivity of nanofluids beyond the Maxwell's effective medium theory (J.C.Maxwell, Treatise on Electricity and Magnetism, 1891), there is substantial heat transfer augmentation via nanofins.The latter are formed as attachments on the hot wire surface by yet an unknown mechanism, which could be related to electrophoresis, but there is no conclusive evidence yet to prove this proposed mechanism.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical Engineering, Northern Arizona University, P, O, Box 15600, Flagstaff, AZ 86011-5600, USA. peter.vadasz@nau.edu.

ABSTRACT
Theoretical results derived in this article are combined with experimental data to conclude that, while there is no improvement in the effective thermal conductivity of nanofluids beyond the Maxwell's effective medium theory (J.C. Maxwell, Treatise on Electricity and Magnetism, 1891), there is substantial heat transfer augmentation via nanofins. The latter are formed as attachments on the hot wire surface by yet an unknown mechanism, which could be related to electrophoresis, but there is no conclusive evidence yet to prove this proposed mechanism.

No MeSH data available.


Related in: MedlinePlus