Surfactant effect on titanium oxide water nanofluid thermophysical properties: experimental investigation of density, thermal conductivity and viscosity

This article presents a comprehensive experimental investigation into the stability and thermophysical behavior of a 2 mass% TiO₂–water nanofluid. To ensure long-term dispersion and mitigate agglomeration, the nanofluids were stabilized using two chemically distinct surfactants: Sodium Dodecyl Sulfate (SDS), an anionic agent, and Cetyltrimethylammonium Bromide (CTAB), a cationic agent. These surfactants are among the most widespread additives for enhancing fluid stability, as emphasized in previous literature. The primary objective of this research was to quantify the influence of surfactant type and concentration on the resulting thermophysical properties and the secondary effect of foaming. Systematic measurements were conducted to evaluate density, thermal conductivity, and dynamic viscosity across varying surfactant concentrations of the 2 mass% TiO₂–water nanofluid. Experimental results indicate that while surfactants successfully enhance the suspension’s stability, they introduce complex variations in the fluid’s transport properties. Density remained relatively stable; however, thermal conductivity showed a nuanced dependency on the surfactant-to-nanoparticle ratio. Notably, the study highlights a critical trade-off between stability and thermophysical properties, as increased surfactant concentrations significantly influenced viscosity and triggered foaming, which can impede heat transfer efficiency in practical applications. These findings contribute to a larger research framework, performed by this group, focused on adjusting surfactant nanofluid ratios for thermal engineering applications. By identifying the performance thresholds of SDS and CTAB, this study provides essential data for the development of high-efficiency, stable heat transfer fluids.