Viscosity and Rheological properties of Nanofluids(TiO2/PG)

Nanofluids are dilute liquid suspensions of nanoparticles with at least one of their critical dimensions smaller than about 100 nm [1]. Much attention has been paid in the past decade to this new type of heat transfer materials because of their enhanced properties and behaviour associated with heat transfer, mass transfer, wetting and spreading and antibacterial activity. These enhanced properties and behaviour imply an enormous potential of nanofluids in device miniaturization and process intensification which could have an impact on many industrial sectors including chemical and process, transportation, electronics, medical and energy and environment. Most published studies on nanofluids deal with the heat transfer behaviour including thermal conduction [2], phase change (boiling) heat transfer[3], and convective heat transfer[4] , which have been reviewed recently [5]. Very few studies, however, have been reported on the rheological behaviour of nanofluids. Key requirements for nanofluids include low solids loading but with high thermal properties, favourable rheologocial properties and flow behaviour, and great stability over a wide range of temperature to meet the industrial needs. Clearly, there is a gap in the current rheological literature for this type of fluids. This forms the primary motivation of this work. Recent work has shown evidence of a relationship between the thermal and rheological behaviour of nanofluids.This forms the second motivation of carrying out this work. This work aims at understanding the rheological behaviour of nanofluids through both experimental work and theoretical analyses. The focus will be on nanofluids containing spherical particles. The experimental work uses titania (TiO2) based the propylene glycol(PG) nanofluids, whereas the theoretical analyses is based on our current understanding of the rheology of colloid suspensions. The reasons for the use of PG-based TiO2 nanofluids are: (i) TiO2 is generally regarded as a safe material for humans and animals although it is recognized that this may change in the future with more fundamental research on nano-toxicology; (ii) TiO2 nanoparticles are produced on large industrial scales so are easy to obtain; (iii) metal oxides such TiO2 nanoparticles are chemically more stable than their metallic counterparts although it is recognized that the photocatalytic effect of TiO2 may impose restrictions in selecting the base liquid