Experimental Insights into Influence of Surfactants on Thermophysical Properties of a Titanium Oxide Water Nanofluid

Nanofluid development is facing the challenge of instability despite the significant body of research dedicated to developing new nanoparticle-enhanced fluids. Numerous combinations of fluids and particles have been studied; however, the research on surfactants is rather limited, and the results are scattered. This paper is dedicated to the study of two regular polymeric surfactants (PVP and PSS) as well as two polyethylene glycols and one ionic liquid as possible alternatives. The results of a coordinated experiment are followed by a discussion of the density, thermal conductivity, thermal effusivity and viscosity of several samples with the same amount of titanium oxide nanoparticles dispersed in water and different mass concentrations of surfactants (2, 4 and 6%wt.). The results indicated that both the thermal properties and viscosity are negatively affected by the addition of surfactant, which is a drawback. The viscosity remains within a reasonable variation (i.e., between a 0.7 and 1.5% increase) for concentrations of PEG 200, PEG 400 and PSS up to 2%wt. Also, the addition of titania nanoparticles increases the water thermal conductivity by 1.8%, while the addition of surfactant decreases the overall values by around 5%. This disadvantage is amplified when also considering the foam creation, characteristic of all regular surfactants, that limits their real-life applications in turbulent flow.