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Stability and rheology of dilute TiO2-water nanofluids.

Penkavova V, Tihon J, Wein O - Nanoscale Res Lett (2011)

Bottom Line: In this study, a series of dilute TiO2 aqueous dispersions were prepared and tested for the possible presence of the AWS effect by means of a novel viscometric technique.The resulting stable nanofluid samples were dilute, below 0.7 vol.%.No case of important slip contribution was detected: the Navier slip coefficient of approximately 2 mm Pa-1 s-1 would affect the apparent fluidity data in a 100-μm gap by less than 1%.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Rozvojova 135, 165 02 Prague 6, Czech Republic. wein@icpf.cas.cz.

ABSTRACT
The apparent wall slip (AWS) effect, accompanying the flow of colloidal dispersions in confined geometries, can be an important factor for the applications of nanofluids in heat transfer and microfluidics. In this study, a series of dilute TiO2 aqueous dispersions were prepared and tested for the possible presence of the AWS effect by means of a novel viscometric technique. The nanofluids, prepared from TiO2 rutile or anatase nanopowders by ultrasonic dispersing in water, were stabilized by adjusting the pH to the maximum zeta potential. The resulting stable nanofluid samples were dilute, below 0.7 vol.%. All the samples manifest Newtonian behavior with the fluidities almost unaffected by the presence of the dispersed phase. No case of important slip contribution was detected: the Navier slip coefficient of approximately 2 mm Pa-1 s-1 would affect the apparent fluidity data in a 100-μm gap by less than 1%.

No MeSH data available.


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Scheme of a shear flow with the AWS effect. Dotted line - actual non-linear velocity profile observed at the constant shear stress σ due to the effect of a depletion layer of dispersion at the wall; Broken solid line - approximation of the actual velocity profile, introduced by the concept of AWS [18]. U = γh + 2u - macroscopic sliding velocity, m s-1; h - gap thickness, m; u - AWS velocity, m s-1; γ - bulk shear rate, s-1.
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Figure 4: Scheme of a shear flow with the AWS effect. Dotted line - actual non-linear velocity profile observed at the constant shear stress σ due to the effect of a depletion layer of dispersion at the wall; Broken solid line - approximation of the actual velocity profile, introduced by the concept of AWS [18]. U = γh + 2u - macroscopic sliding velocity, m s-1; h - gap thickness, m; u - AWS velocity, m s-1; γ - bulk shear rate, s-1.

Mentions: The concept of AWS effect from the viscometric viewpoint [17-19] is illustrated in Figure 4 for the simple shear flow between two mutually sliding parallel plates. A possible near-wall flow anomaly, resulting in a non-linear velocity profile under constant shear stress σ, is represented by the apparent slip velocity u. The only experimentally available kinematic quantity, the sliding velocity U, determines the apparent shear rate γapp ≡ U/h (or γapp = ΩR/h for the Couette flow in a narrow gap h between two coaxial cylinders), which is expressed as a sum of the bulk flow and wall slip contributions, as follows:(1)


Stability and rheology of dilute TiO2-water nanofluids.

Penkavova V, Tihon J, Wein O - Nanoscale Res Lett (2011)

Scheme of a shear flow with the AWS effect. Dotted line - actual non-linear velocity profile observed at the constant shear stress σ due to the effect of a depletion layer of dispersion at the wall; Broken solid line - approximation of the actual velocity profile, introduced by the concept of AWS [18]. U = γh + 2u - macroscopic sliding velocity, m s-1; h - gap thickness, m; u - AWS velocity, m s-1; γ - bulk shear rate, s-1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211337&req=5

Figure 4: Scheme of a shear flow with the AWS effect. Dotted line - actual non-linear velocity profile observed at the constant shear stress σ due to the effect of a depletion layer of dispersion at the wall; Broken solid line - approximation of the actual velocity profile, introduced by the concept of AWS [18]. U = γh + 2u - macroscopic sliding velocity, m s-1; h - gap thickness, m; u - AWS velocity, m s-1; γ - bulk shear rate, s-1.
Mentions: The concept of AWS effect from the viscometric viewpoint [17-19] is illustrated in Figure 4 for the simple shear flow between two mutually sliding parallel plates. A possible near-wall flow anomaly, resulting in a non-linear velocity profile under constant shear stress σ, is represented by the apparent slip velocity u. The only experimentally available kinematic quantity, the sliding velocity U, determines the apparent shear rate γapp ≡ U/h (or γapp = ΩR/h for the Couette flow in a narrow gap h between two coaxial cylinders), which is expressed as a sum of the bulk flow and wall slip contributions, as follows:(1)

Bottom Line: In this study, a series of dilute TiO2 aqueous dispersions were prepared and tested for the possible presence of the AWS effect by means of a novel viscometric technique.The resulting stable nanofluid samples were dilute, below 0.7 vol.%.No case of important slip contribution was detected: the Navier slip coefficient of approximately 2 mm Pa-1 s-1 would affect the apparent fluidity data in a 100-μm gap by less than 1%.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Rozvojova 135, 165 02 Prague 6, Czech Republic. wein@icpf.cas.cz.

ABSTRACT
The apparent wall slip (AWS) effect, accompanying the flow of colloidal dispersions in confined geometries, can be an important factor for the applications of nanofluids in heat transfer and microfluidics. In this study, a series of dilute TiO2 aqueous dispersions were prepared and tested for the possible presence of the AWS effect by means of a novel viscometric technique. The nanofluids, prepared from TiO2 rutile or anatase nanopowders by ultrasonic dispersing in water, were stabilized by adjusting the pH to the maximum zeta potential. The resulting stable nanofluid samples were dilute, below 0.7 vol.%. All the samples manifest Newtonian behavior with the fluidities almost unaffected by the presence of the dispersed phase. No case of important slip contribution was detected: the Navier slip coefficient of approximately 2 mm Pa-1 s-1 would affect the apparent fluidity data in a 100-μm gap by less than 1%.

No MeSH data available.


Related in: MedlinePlus