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Scaling analysis for the investigation of slip mechanisms in nanofluids.

Savithiri S, Pattamatta A, Das SK - Nanoscale Res Lett (2011)

Bottom Line: From the scaling analysis, it is found that all of the slip mechanisms are dominant in particles of cylindrical shape as compared to that of spherical and sheet particles.The effect of thermophoresis and Magnus forces is found to increase with the particle size and concentration.The drag and gravity forces tend to reduce the Nusselt number of the nanofluid while the other forces tend to enhance it.

View Article: PubMed Central - HTML - PubMed

Affiliation: Heat Transfer and Thermal Power Laboratory, Department of Mechanical Engineering, Indian Institute of Technology - Madras, Chennai 600 036, India. skdas@iitm.ac.in.

ABSTRACT
The primary objective of this study is to investigate the effect of slip mechanisms in nanofluids through scaling analysis. The role of nanoparticle slip mechanisms in both water- and ethylene glycol-based nanofluids is analyzed by considering shape, size, concentration, and temperature of the nanoparticles. From the scaling analysis, it is found that all of the slip mechanisms are dominant in particles of cylindrical shape as compared to that of spherical and sheet particles. The magnitudes of slip mechanisms are found to be higher for particles of size between 10 and 80 nm. The Brownian force is found to dominate in smaller particles below 10 nm and also at smaller volume fraction. However, the drag force is found to dominate in smaller particles below 10 nm and at higher volume fraction. The effect of thermophoresis and Magnus forces is found to increase with the particle size and concentration. In terms of time scales, the Brownian and gravity forces act considerably over a longer duration than the other forces. For copper-water-based nanofluid, the effective contribution of slip mechanisms leads to a heat transfer augmentation which is approximately 36% over that of the base fluid. The drag and gravity forces tend to reduce the Nusselt number of the nanofluid while the other forces tend to enhance it.

No MeSH data available.


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Time scales of slip mechanisms for ethylene glycol-based nanofluids.
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Figure 10: Time scales of slip mechanisms for ethylene glycol-based nanofluids.

Mentions: Time scale is defined as the ratio of the particle size to the velocity of each mechanism (Section 4). Time scale is an important parameter for the comparison of different slip mechanisms in scaling analysis [5]. The results of the time scale analysis for both water- and ethylene glycol-based nanofluids are plotted in Figures 9 and 10. From these figures, it is observed that for water- and ethylene glycol-based nanofluids, the time scales associated with rotational and lift forces are smaller than that of the other forces. It is also found that drag, rotational, and lift forces in both the nanofluids occur within a very short duration of the order of 10-7 to 10-10 s, whereas the time scales of Magnus and thermophoresis forces are in the range between 10-4 and 10-8 s. The time scale of Brownian and gravity forces are in the range of 10-2 to 10-1 and 1 to 100 s, respectively. Hence, the Brownian and gravity tend to act upon for a considerably longer duration than the other forces.


Scaling analysis for the investigation of slip mechanisms in nanofluids.

Savithiri S, Pattamatta A, Das SK - Nanoscale Res Lett (2011)

Time scales of slip mechanisms for ethylene glycol-based nanofluids.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211984&req=5

Figure 10: Time scales of slip mechanisms for ethylene glycol-based nanofluids.
Mentions: Time scale is defined as the ratio of the particle size to the velocity of each mechanism (Section 4). Time scale is an important parameter for the comparison of different slip mechanisms in scaling analysis [5]. The results of the time scale analysis for both water- and ethylene glycol-based nanofluids are plotted in Figures 9 and 10. From these figures, it is observed that for water- and ethylene glycol-based nanofluids, the time scales associated with rotational and lift forces are smaller than that of the other forces. It is also found that drag, rotational, and lift forces in both the nanofluids occur within a very short duration of the order of 10-7 to 10-10 s, whereas the time scales of Magnus and thermophoresis forces are in the range between 10-4 and 10-8 s. The time scale of Brownian and gravity forces are in the range of 10-2 to 10-1 and 1 to 100 s, respectively. Hence, the Brownian and gravity tend to act upon for a considerably longer duration than the other forces.

Bottom Line: From the scaling analysis, it is found that all of the slip mechanisms are dominant in particles of cylindrical shape as compared to that of spherical and sheet particles.The effect of thermophoresis and Magnus forces is found to increase with the particle size and concentration.The drag and gravity forces tend to reduce the Nusselt number of the nanofluid while the other forces tend to enhance it.

View Article: PubMed Central - HTML - PubMed

Affiliation: Heat Transfer and Thermal Power Laboratory, Department of Mechanical Engineering, Indian Institute of Technology - Madras, Chennai 600 036, India. skdas@iitm.ac.in.

ABSTRACT
The primary objective of this study is to investigate the effect of slip mechanisms in nanofluids through scaling analysis. The role of nanoparticle slip mechanisms in both water- and ethylene glycol-based nanofluids is analyzed by considering shape, size, concentration, and temperature of the nanoparticles. From the scaling analysis, it is found that all of the slip mechanisms are dominant in particles of cylindrical shape as compared to that of spherical and sheet particles. The magnitudes of slip mechanisms are found to be higher for particles of size between 10 and 80 nm. The Brownian force is found to dominate in smaller particles below 10 nm and also at smaller volume fraction. However, the drag force is found to dominate in smaller particles below 10 nm and at higher volume fraction. The effect of thermophoresis and Magnus forces is found to increase with the particle size and concentration. In terms of time scales, the Brownian and gravity forces act considerably over a longer duration than the other forces. For copper-water-based nanofluid, the effective contribution of slip mechanisms leads to a heat transfer augmentation which is approximately 36% over that of the base fluid. The drag and gravity forces tend to reduce the Nusselt number of the nanofluid while the other forces tend to enhance it.

No MeSH data available.


Related in: MedlinePlus