Duan et al. Nanoscale Research Letters 2011, 6:248 NANO EXPRESS Open Access Viscosity affected by nanoparticle aggregation in Al2O3-water nanofluids Fei Duan*, Dingtian Kwek, Alexandru Crivoi 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 reultrasonication nanofluids in comparison with the base fluid. The microstructure analysis indicates that a. | Duan et al. Nanoscale Research Letters 2011 6 248 http content 6 1 248 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access Viscosity affected by nanoparticle aggregation in Al2O3-water nanofluids Fei Duan Dingtian Kwek Alexandru Crivoi 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 reultrasonication 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. Introduction Nanofluids consisting of solid nanoparticles at about 1100 nm have drawn greater attention since they are expected to exhibit superior properties compared with conventional heat transfer fluids 1-3 . Nanoparticles which have a much larger surface area and smaller size possess a potential to further improve heat-transfer capabilities and increase the stability in the fluids. Nanofluids would have a lower viscosity than the conventional micron-sized particle-liquid suspensions thus reducing pressure drop in the flow channel and saving the pumping power. The experiments on the nanofluid viscosity 4 5 demonstrated up to 90 increment in a 5 volume fraction nanofluid compared with the base liquid. The result was far higher than the theoretical prediction from Einstein Brinkman and Batchelor models 6-11 . In addition most reported data on the thermal properties seem to be measured in the fresh well-dispersed nanofluids. A further understanding of nanofluid stability is necessary before nanofluids can be commercialized in the practical .
