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A new heat propagation velocity prevails over Brownian particle velocities in determining the thermal conductivities of nanofluids.

Kihm KD, Chon CH, Lee JS, Choi SU - Nanoscale Res Lett (2011)

Bottom Line: An alternative insight is presented concerning heat propagation velocity scales in predicting the effective thermal conductivities of nanofluids.The widely applied Brownian particle velocities in published literature are often found too slow to describe the relatively higher nanofluid conductivities.This novel model of effective thermal conductivities of nanofluids agrees well with an extended range of experimental data.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical, Aerospace, and Biomedical Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA. kkihm@utk.edu.

ABSTRACT
An alternative insight is presented concerning heat propagation velocity scales in predicting the effective thermal conductivities of nanofluids. The widely applied Brownian particle velocities in published literature are often found too slow to describe the relatively higher nanofluid conductivities. In contrast, the present model proposes a faster heat transfer velocity at the same order as the speed of sound, rooted in a modified kinetic principle. In addition, this model accounts for both nanoparticle heat dissipation as well as coagulation effects. This novel model of effective thermal conductivities of nanofluids agrees well with an extended range of experimental data.

No MeSH data available.


Related in: MedlinePlus

Comparison of the present model (the solid curves) with published models [25-29]for the thermal conductivities of nanofluids. The symbols represent the presently (CuO nanofluids) and previously (Al2O3 nanofluids [23]) measured conductivities from the University of Tennessee laboratory: (a) 1 vol. % Al2O3 nanofluid [13], (b) 1 vol. % CuO nanofluid [present experiment], and (3) 4 vol. % Al2O3 nanofluid [13].
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Figure 2: Comparison of the present model (the solid curves) with published models [25-29]for the thermal conductivities of nanofluids. The symbols represent the presently (CuO nanofluids) and previously (Al2O3 nanofluids [23]) measured conductivities from the University of Tennessee laboratory: (a) 1 vol. % Al2O3 nanofluid [13], (b) 1 vol. % CuO nanofluid [present experiment], and (3) 4 vol. % Al2O3 nanofluid [13].

Mentions: Figure 2a-c shows the present model for thermal conductivities of water-based nanofluids, Equation 7, in comparison with five published models [25-30], for the three different nanofluids. The symbols represent the corresponding experimental data for Al2O3 [24] and CuO [present work]. For all three nanofluids with 47-nm Al2O3 at 1 and 4%, and 30-nm CuO at 1%, Xuan et al. [25] overestimated the Maxwell's model [2] for nanofluids. Jang and Choi's model [26] shows proximity with experimental data for up to about 50°C for 1 vol.% Al2O3 and 40°C for 4 vol.% Al2O3, but substantially deviates thereafter. This deviation beyond a certain temperature is believed to be attributed to their incorrect postulation implied in determining the Nusselt number, as previously noted. For the CuO nanofluid, their model shows large discrepancies throughout the tested temperature range. Additionally, the model by Kumar et al. [27] wrongly postulates the mean free path of the base fluid, as pointed out by Keblinski et al. [32], and completely fails to predict nanofuidic thermal conductivities for all presently tested conditions.


A new heat propagation velocity prevails over Brownian particle velocities in determining the thermal conductivities of nanofluids.

Kihm KD, Chon CH, Lee JS, Choi SU - Nanoscale Res Lett (2011)

Comparison of the present model (the solid curves) with published models [25-29]for the thermal conductivities of nanofluids. The symbols represent the presently (CuO nanofluids) and previously (Al2O3 nanofluids [23]) measured conductivities from the University of Tennessee laboratory: (a) 1 vol. % Al2O3 nanofluid [13], (b) 1 vol. % CuO nanofluid [present experiment], and (3) 4 vol. % Al2O3 nanofluid [13].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211451&req=5

Figure 2: Comparison of the present model (the solid curves) with published models [25-29]for the thermal conductivities of nanofluids. The symbols represent the presently (CuO nanofluids) and previously (Al2O3 nanofluids [23]) measured conductivities from the University of Tennessee laboratory: (a) 1 vol. % Al2O3 nanofluid [13], (b) 1 vol. % CuO nanofluid [present experiment], and (3) 4 vol. % Al2O3 nanofluid [13].
Mentions: Figure 2a-c shows the present model for thermal conductivities of water-based nanofluids, Equation 7, in comparison with five published models [25-30], for the three different nanofluids. The symbols represent the corresponding experimental data for Al2O3 [24] and CuO [present work]. For all three nanofluids with 47-nm Al2O3 at 1 and 4%, and 30-nm CuO at 1%, Xuan et al. [25] overestimated the Maxwell's model [2] for nanofluids. Jang and Choi's model [26] shows proximity with experimental data for up to about 50°C for 1 vol.% Al2O3 and 40°C for 4 vol.% Al2O3, but substantially deviates thereafter. This deviation beyond a certain temperature is believed to be attributed to their incorrect postulation implied in determining the Nusselt number, as previously noted. For the CuO nanofluid, their model shows large discrepancies throughout the tested temperature range. Additionally, the model by Kumar et al. [27] wrongly postulates the mean free path of the base fluid, as pointed out by Keblinski et al. [32], and completely fails to predict nanofuidic thermal conductivities for all presently tested conditions.

Bottom Line: An alternative insight is presented concerning heat propagation velocity scales in predicting the effective thermal conductivities of nanofluids.The widely applied Brownian particle velocities in published literature are often found too slow to describe the relatively higher nanofluid conductivities.This novel model of effective thermal conductivities of nanofluids agrees well with an extended range of experimental data.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical, Aerospace, and Biomedical Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA. kkihm@utk.edu.

ABSTRACT
An alternative insight is presented concerning heat propagation velocity scales in predicting the effective thermal conductivities of nanofluids. The widely applied Brownian particle velocities in published literature are often found too slow to describe the relatively higher nanofluid conductivities. In contrast, the present model proposes a faster heat transfer velocity at the same order as the speed of sound, rooted in a modified kinetic principle. In addition, this model accounts for both nanoparticle heat dissipation as well as coagulation effects. This novel model of effective thermal conductivities of nanofluids agrees well with an extended range of experimental data.

No MeSH data available.


Related in: MedlinePlus