Effect of SDS surfactant-to-nanoparticle ratio on the stability and thermophysical properties of CuO-DI water nanofluid

Nanofluids having enhanced thermophysical properties, faces long-term stability challenges due to agglomeration and sedimentation. To address these limitations, this study focused on the investigation of nanofluids to enhance the stability and thermophysical properties of four distinct samples, varying the SDS surfactant-to-CuO nanoparticle weight ratios at 1:5, 1:2.5, 1:1, and 2.5:1 (named as sample 1, 2, 3, and 4 respectively). The novelty of this study lies in systematically evaluating the impact of different SDS-to-CuO nanoparticle ratios on both the long-term stability and thermophysical properties of CuO/DI (w/v %) water nanofluids, a combination that has limited comprehensive studies in the literature. Initial zeta potential values (60–70 mV) confirmed excellent stability for all samples, with a notable decrease in zeta potential over 40 days observed in samples with lower SDS content. Moreover, viscosity remained stable across all samples, with no significant variation (maintaining values around 0.896 mPa·s) observed after 40 days of storage. Thermal conductivity increased with temperature, reaching a maximum at 70 °C, where the thermal conductivity was measured as 0.768 W/m·K for sample 1, 0.742 W/m·K for sample 2, 0.705 W/m·K for sample 3, and 0.690 W/m·K for sample 4. Ultimately, considering enhanced stability and thermal conductivity, the nanofluid sample 2 with a surfactant-to-nanoparticle ratio of 1:2.5 emerged as the most suitable for potential use in diverse thermal engineering applications, particularly in PVT systems for enhanced performance.