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Viscosity affected by nanoparticle aggregation in Al2O3-water nanofluids.

Duan F, Kwek D, Crivoi A - Nanoscale Res Lett (2011)

Bottom Line: The shear stress was observed with a non-Newtonian behavior.On further ultrasonic agitation treatment, the nanofluids resumed as a Newtonian fluids.The microstructure analysis indicates that a higher nanoparticle aggregation had been observed in the nanofluids before re-ultrasonication.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Singapore. feiduan@ntu.edu.sg.

ABSTRACT
An investigation on viscosity was conducted 2 weeks after the Al2O3-water nanofluids having dispersants were prepared at the volume concentration of 1-5%. The shear stress was observed with a non-Newtonian behavior. On further ultrasonic agitation treatment, the nanofluids resumed as a Newtonian fluids. The relative viscosity increases as the volume concentrations increases. At 5% volume concentration, an increment was about 60% in the re-ultrasonication nanofluids in comparison with the base fluid. The microstructure analysis indicates that a higher nanoparticle aggregation had been observed in the nanofluids before re-ultrasonication.

No MeSH data available.


Related in: MedlinePlus

Relative viscosity of Al2O3-water nanofluids as a function of volume con-centration (after 2 weeks).
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Figure 2: Relative viscosity of Al2O3-water nanofluids as a function of volume con-centration (after 2 weeks).

Mentions: The viscosity measurement was taken 2 weeks after the nanofluid preparation. As seen in Figure 1, the viscosity decreases as the shear rate increases. At a certain shear rate, the nanofluid at 5 vol% has the largest viscosity while the viscosity value is the lowest in the 1 vol% nanofluid. The nanofluids behaved as non-Newtonian fluids. The effective viscosity, μeff, of nanofluids increases up to about 38 × 10-3 Pa·S for the 5 vol% nanofluid. Figure 2 shows that the relative viscosity, μeff/μf (μf is the viscosity of the base fluid) increases from the above value for the 1 vol% nanofluid to about 43 for the 5 vol% nanofluid. However, the values are much higher than the those predicted from the conventional Einstein model, and those of the modified models by Brinkman, Batchelor, and Graham [6,7,10,11]. The data of Xie et al. [18] show a similar phenomenon also as shown in Figure 2. The nanoparticles were indicated to be prone to form agglomeration in a nanofluid suspension. The high viscosity observed is probably as a result of agglomeration that had occurred in the nanofluids after 2 weeks. Once agglomeration is formed, a larger stress is necessary to break the ligand structure among particles when shearing takes place; therefore, a high relative viscosity would be observed in the fluids as shown in Figures 1 and 2. Zhou et al. [19] also highlighted that the shear thinning behavior at high shear rate is likely due to aggregates being destroyed under shear. This can also explain that the non-Newtonian characteristics of nanofluids are more obvious at a higher volume fraction and a longer holding time since the chance of aggregation is higher. The aggregates are also verified in the following SEM images.


Viscosity affected by nanoparticle aggregation in Al2O3-water nanofluids.

Duan F, Kwek D, Crivoi A - Nanoscale Res Lett (2011)

Relative viscosity of Al2O3-water nanofluids as a function of volume con-centration (after 2 weeks).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211309&req=5

Figure 2: Relative viscosity of Al2O3-water nanofluids as a function of volume con-centration (after 2 weeks).
Mentions: The viscosity measurement was taken 2 weeks after the nanofluid preparation. As seen in Figure 1, the viscosity decreases as the shear rate increases. At a certain shear rate, the nanofluid at 5 vol% has the largest viscosity while the viscosity value is the lowest in the 1 vol% nanofluid. The nanofluids behaved as non-Newtonian fluids. The effective viscosity, μeff, of nanofluids increases up to about 38 × 10-3 Pa·S for the 5 vol% nanofluid. Figure 2 shows that the relative viscosity, μeff/μf (μf is the viscosity of the base fluid) increases from the above value for the 1 vol% nanofluid to about 43 for the 5 vol% nanofluid. However, the values are much higher than the those predicted from the conventional Einstein model, and those of the modified models by Brinkman, Batchelor, and Graham [6,7,10,11]. The data of Xie et al. [18] show a similar phenomenon also as shown in Figure 2. The nanoparticles were indicated to be prone to form agglomeration in a nanofluid suspension. The high viscosity observed is probably as a result of agglomeration that had occurred in the nanofluids after 2 weeks. Once agglomeration is formed, a larger stress is necessary to break the ligand structure among particles when shearing takes place; therefore, a high relative viscosity would be observed in the fluids as shown in Figures 1 and 2. Zhou et al. [19] also highlighted that the shear thinning behavior at high shear rate is likely due to aggregates being destroyed under shear. This can also explain that the non-Newtonian characteristics of nanofluids are more obvious at a higher volume fraction and a longer holding time since the chance of aggregation is higher. The aggregates are also verified in the following SEM images.

Bottom Line: The shear stress was observed with a non-Newtonian behavior.On further ultrasonic agitation treatment, the nanofluids resumed as a Newtonian fluids.The microstructure analysis indicates that a higher nanoparticle aggregation had been observed in the nanofluids before re-ultrasonication.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 639798, Singapore. feiduan@ntu.edu.sg.

ABSTRACT
An investigation on viscosity was conducted 2 weeks after the Al2O3-water nanofluids having dispersants were prepared at the volume concentration of 1-5%. The shear stress was observed with a non-Newtonian behavior. On further ultrasonic agitation treatment, the nanofluids resumed as a Newtonian fluids. The relative viscosity increases as the volume concentrations increases. At 5% volume concentration, an increment was about 60% in the re-ultrasonication nanofluids in comparison with the base fluid. The microstructure analysis indicates that a higher nanoparticle aggregation had been observed in the nanofluids before re-ultrasonication.

No MeSH data available.


Related in: MedlinePlus