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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.

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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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Effect of particle temperature in cylindrical particles. (a) Brownian force and (b) Magnus force for water-based nanofluids.
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Figure 7: Effect of particle temperature in cylindrical particles. (a) Brownian force and (b) Magnus force for water-based nanofluids.

Mentions: The results of the scaling analysis on the particle temperature are plotted in Figures 7 and 8. The Brownian and Magnus forces are found to increase with increasing temperature. An increase in the temperature of nanofluids augments the chaotic movement of the suspended nanoparticles thereby increasing the force due to Brownian motion. Gravity force has very little impact with temperature. All other forces including drag, thermophoresis, Saffman's lift, and rotational forces are found to decrease with increasing temperature. This is because for a fixed temperature gradient, the thermophoresis force is inversely proportional to the temperature of the nanofluid as given by Equations 17 and 18.


Scaling analysis for the investigation of slip mechanisms in nanofluids.

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

Effect of particle temperature in cylindrical particles. (a) Brownian force and (b) Magnus force for water-based nanofluids.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: Effect of particle temperature in cylindrical particles. (a) Brownian force and (b) Magnus force for water-based nanofluids.
Mentions: The results of the scaling analysis on the particle temperature are plotted in Figures 7 and 8. The Brownian and Magnus forces are found to increase with increasing temperature. An increase in the temperature of nanofluids augments the chaotic movement of the suspended nanoparticles thereby increasing the force due to Brownian motion. Gravity force has very little impact with temperature. All other forces including drag, thermophoresis, Saffman's lift, and rotational forces are found to decrease with increasing temperature. This is because for a fixed temperature gradient, the thermophoresis force is inversely proportional to the temperature of the nanofluid as given by Equations 17 and 18.

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