On viscosity measurements of nanofluids in micro and mini tube flow

This study presents measurements on the relative viscosity of Al2O3 nanofluids, obtained using capillary and rotational viscometers. Suspension volume concentrations between 0.3% and 6.3% were considered and all exhibited Newtonian behaviour. This paper questions previously published data (Jang et al 2007 Appl. Phys. Lett. 91 243112) which show effective viscosity measurements of nanofluids to be strongly dependent on the tube dimension used in a microscale capillary viscometer. Hence, tubes of diameter 337 mu m and 1017 mu m were employed but no effect on relative viscosity was observed as all measurements compared favourably. Additionally, all viscosity measurements were found to correlate well using classical models when aggregate size was considered in calculating volume concentration.