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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 nanofluids as a function of volume concentration (after re-ultrasonication).
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Figure 4: Relative viscosity of Al2O3 nanofluids as a function of volume concentration (after re-ultrasonication).

Mentions: Re-ultrasonication process was conducted on the 2-week Al2O3-water nanofluids in order to disperse the aggregated nanoparticles before the viscosity was measured again. Figure 3 demonstrates that the viscosity increases with the shear rate roughly linearly at the beginning before it reaches a constant value for each fluid. The nanofluids resume Newtonian. The nanofluid at 5 vol% has the largest viscosity while the value is the lowest in the 1 vol% nanofluid. Distinctively, it is seen that the relative viscosity is much lower than the relative nanofluid before re-ultrasonication, as illustrated in Figure 4. After re-ultrasonication, the effective viscosity gets back the values in the freshly prepared nanofluids [20]. The relative viscosity increases as the volume concentration increases. It supports the hypothesis that a high viscosity might be due to nanoparticle agglomeration. The results reported by Masoumi et al. [4] show a similar trend, too. From these experimental results, the measured relative viscosity of Al2O3-water nanofluids is significantly 60% higher than those of the base fluid in the nanofluids after the non-Newtonian fluids were ultrasonically agitated again. The measures of Masoumi et al. and this research are much higher than those of the predicted values given by the Einstein and Graham equations [6,11]. Clearly, the Einstein formula and the others have underestimated the nanofluid viscosities [6-11]. For higher particle concentrations, the deviation of conventional models from the present experimental data is considerable. Even the Batchelor formula that considers the Brownian effects performs poorly [10]. Chandrasekar et al. [21] suggested that the significant difference between the experimental results and the predicted values might be because of the conventional models neglecting the hydrodynamic interactions between particles which become important, as the other disturbances of the fluid around one particle might interact with the surrounding particles at higher volume concentrations. The nanoparticle aggregation in the fluids would reinforce the effects.


Viscosity affected by nanoparticle aggregation in Al2O3-water nanofluids.

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

Relative viscosity of Al2O3 nanofluids as a function of volume concentration (after re-ultrasonication).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Relative viscosity of Al2O3 nanofluids as a function of volume concentration (after re-ultrasonication).
Mentions: Re-ultrasonication process was conducted on the 2-week Al2O3-water nanofluids in order to disperse the aggregated nanoparticles before the viscosity was measured again. Figure 3 demonstrates that the viscosity increases with the shear rate roughly linearly at the beginning before it reaches a constant value for each fluid. The nanofluids resume Newtonian. The nanofluid at 5 vol% has the largest viscosity while the value is the lowest in the 1 vol% nanofluid. Distinctively, it is seen that the relative viscosity is much lower than the relative nanofluid before re-ultrasonication, as illustrated in Figure 4. After re-ultrasonication, the effective viscosity gets back the values in the freshly prepared nanofluids [20]. The relative viscosity increases as the volume concentration increases. It supports the hypothesis that a high viscosity might be due to nanoparticle agglomeration. The results reported by Masoumi et al. [4] show a similar trend, too. From these experimental results, the measured relative viscosity of Al2O3-water nanofluids is significantly 60% higher than those of the base fluid in the nanofluids after the non-Newtonian fluids were ultrasonically agitated again. The measures of Masoumi et al. and this research are much higher than those of the predicted values given by the Einstein and Graham equations [6,11]. Clearly, the Einstein formula and the others have underestimated the nanofluid viscosities [6-11]. For higher particle concentrations, the deviation of conventional models from the present experimental data is considerable. Even the Batchelor formula that considers the Brownian effects performs poorly [10]. Chandrasekar et al. [21] suggested that the significant difference between the experimental results and the predicted values might be because of the conventional models neglecting the hydrodynamic interactions between particles which become important, as the other disturbances of the fluid around one particle might interact with the surrounding particles at higher volume concentrations. The nanoparticle aggregation in the fluids would reinforce the effects.

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