ORIGINAL Morphology and thermophysical properties of non-aqueous titania nanofluids S. M. S. Murshed 1,2 & F. J. V. Santos 1 & C. A. Nieto de Castro 1 & V. S. Patil 3 & K. R. Patil 3 Received: 20 November 2015 /Accepted: 10 February 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract This work deals with the experimental investigation on thermophysical properties of TiO 2 -nanofluids and characterization of morphology and structure of TiO 2 nanoparticles. Non-aqueous liquids like silicone oil and ethylene glycol are used as base fluids to prepare the nanofluids. Thermophysical properties including viscosity and thermal conductivity of these nanofluids are measured at different concentrations and temperatures. Results showed that silicone oil-based TiO 2 nanofluid is Newtonian and the viscosity of this nanofluid increases with the loading of nanoparticles but it decreases nonlinearly with increasing temperature. Existing viscosity models are found unable to predict the viscosity of nanofluids. Although the effective thermal conductivities of both the silicone oil and ethylene glycol-based nanofluids increased with the TiO 2 concentration, their enhanced thermal conductivity was found to decrease with increasing temperature. 1 Introduction Nanofluids, which are the suspensions of nanoparticles (typically 1 to 100 nm) in conventional heat transfer fluids, exhibit superior heat transfer capabilities and have potential applications in nu- merous important fields such as microelectronics, micro- electromechanical systems, microfluidics, transportation, manufacturing, instrumentation, medical, and HVAC systems [1–4]. Since coining the concept of nanofluids by Steve Choi in 1995 [5], extensive research works have been conducted par- ticularly on thermal conductivity of numerous types of nanofluids [2, 3, 6–13]. However, results obtained from various laboratories are not consistent and there are also controversies on the heat transfer mechanisms of nanofluids [1–3, 14]. On the other hand, comparatively less efforts have been devoted on the viscosity of nanofluids, which is as crucial as thermal conductiv- ity in any systems that employs fluids flow. Though nanofluids showed substantially higher viscosity compared to their base fluids, significantly enhanced thermal properties make these new fluids a strong candidate for the next generation heat transfer fluids or coolants. Available viscosity data in the literature are also scattered and most of the reported studies are mainly on aqueous-based nanofluids [2, 3, 15]. Studies on identifying the influences of temperature and nanoparticles concentration on the thermal conductivity and viscosity of non-aqueous nanofluids are very limited and results are not consistent as well [3, 15, 16]. Among various types of nanoparticles used in nanofluids preparation, TiO 2 (also known as Titania) nanoparticles are very popular. This is mainly because of its comparatively low cost, mass scale availability, and good dispersion nature in most of the base fluids. Although the moderately viscous silicone oil (SO), which has potential in many applications such as heat exchangers and other thermal management systems could be used as a base fluid for nanofluids, only a couple of research efforts was made to investigate the thermophysical properties of SO-based nanofluids. Among the very limited number of studies on SO-nanofluids, Kolade et al. [17] measured the ther- mal conductivity of SO-based multiwall carbon nanotubes (MWCNT)-nanofluids and found about 10% increase in the thermal conductivity of silicone oil by dispersing 0.2 vol.% MWCNT in it. Chen and Xie [18] studied thermal conductivity and viscosity of a silicone oil-based MWCNT-nanofluid. They reported that the thermal conductivity of their nanofluid in- creased substantially with increasing temperature and nanofluid exhibited Newtonian nature at all volume fractions and * S. M. S. Murshed smmurshed@ciencias.ulisboa.pt 1 Centro de Química Estrutural, Faculdade de Ciências, Universidade de Lisboa, Lisboa 1749-016, Portugal 2 Center for Innovation,Technology and Policy Research, Instituto Superior Técnico, Universidade de Lisboa, Lisboa 1049-001, Portugal 3 NCL, Pune, India Heat and Mass Transfer https://doi.org/10.1007/s00231-018-2308-4