Effect of surfactant type on the stability and thermophysical performance of ZnO–ethylene glycol nano fluids

This work reports a systematic experimental study of preparation, stability, and thermophysical properties of ZnO–ethylene glycol nano fluids stabilized with three surfactants: namely, Eriochrome Black T (EBT), sodium dodecyl sulphate (SDS), and polyvinylpyrrolidone (PVP). Nano fluids of 0.5%, 1.0%, and 1.5% ZnO concentration by weight were prepared, and their thermal conductivity, viscosity, density, and FTIR-based chemical stability were measured. Maximum thermal conductivity enhancements up to 1.399 W m−1 K−1 (5.6 × hat of pure ethylene glycol) were achieved in EBT-stabilized nano fluids at 1.5% loading, while base fluid values were 0.25 W m−1 K−1. Viscosities increased modestly in the range from 2.8 × 10−3 to 4.3 × 10−3 Pa s (base fluid: 2.87 × 10−3 Pa s), with density increasing from 1.078 g/ml (base fluid) up to 1.9 g/ml at the highest particle loadings. EBT fared best among SDS and PVP in balancing high thermal conductivity with minimum viscosity rise and ensured strong molecular stabilization, as confirmed by persistent O–H, Zn–O, and surfactant-characteristic FTIR peaks. No new or unanticipated bands were detected in the FTIR spectra, which shows strong dispersion and no chemical degradation. These results indicates to the importance of the kind and optimal weight concentration of surfactant for optimizing thermal and flow properties of ZnO and ethylene glycol based nano fluids and offer practical design guidelines for their positioning in advanced heat exchangers, cooling, and energy components.