Experimental investigation on the effect of dispersant addition on thermal and rheological characteristics of TiO₂ nanofluid

In the current work, TiO₂ nanofluid has been synthesized via two-step co-precipitation method. TEM analysis has been carried out to measure the average particle size and to check the particle distributions which confirm the formation of a suspension having an average particle size of < 100 nm. Thermogravimetric analysis of TiO₂ nanoparticle confirms its suitability for high-temperature cooling application without the concern of thermal degradation (up to 800 °C weight loss < 1%). However, the prime objective of the present study focuses on the numerous thermo-physical aspects (i.e. thermal conductivity, surface tension, and viscosity) and rheological properties of TiO₂ nanofluid at different fluid temperature. Thermal conductivity is considered as the most crucial thermo-physical properties of any nanofluid. In the present study with increasing particle concentration, the thermal conductivity value increased up to an optimum concentration then reduced. For temperature dependency study, with increasing temperature the thermal conductivity values for all particle concentration increases. Dispersant (Polyvinylpyrrolidone, Tween 20) addition in nanofluid plays a crucial role not only in terms of stability but also regarding thermal and rheological properties which have also been investigated in details in this work. Different rheological models have been fitted with experimentally obtained viscosity value to assess the flow behaviour of TiO₂ nanofluids with and without dispersants. Rheological analysis revealed that for all the temperatures, both TiO₂, TiO₂-Tween 20 nanofluid follows Carreau model whereas TiO₂-PVP nanofluid follows Cross model. Effect of dispersants addition on nanofluid stability is another key aspect of the present investigation and the study shows that TiO₂-PVP nanofluid shows the best stability.