Binary Nanoparticle Combinations in Acetone‐Based Working Fluids for Thermal Performance Enhancement of Evacuated Tube Solar Water Collectors

ABSTRACT This experimental investigation evaluates the thermal performance enhancement of evacuated tube solar water collectors through the implementation of binary nanofluid formulations using acetone as the base fluid. Three metal oxide nanoparticles, including magnesium oxide (MgO), copper oxide (CuO), and titanium dioxide (TiO₂), were systematically tested both individually at 0.25 wt% concentration and in binary combinations to assess synergistic enhancement effects. Mono‐nanofluid analysis revealed that MgO exhibited superior performance among single‐nanoparticle formulations, achieving 36.2% maximum thermal efficiency and 52.1°C maximum water temperature, representing 33.6% efficiency improvement over the pure acetone baseline. Binary combinations demonstrated synergistic enhancement exceeding individual constituent performance. The MgO‐CuO combination achieved 41.1% maximum efficiency with 51.6% improvement, while MgO‐TiO₂ exhibited favorable temperature stability during afternoon hours. Parametric investigation of MgO‐TiO₂ mixing ratios identified that 0.30 wt% MgO combined with 0.20 wt% TiO₂ achieved superior overall performance with 49.2% maximum thermal efficiency and 60.9°C maximum water temperature, representing 81.5% efficiency improvement and 38.1% temperature improvement relative to baseline. This enhancement is attributed to the synergistic combination of high thermal conductivity from MgO, enabling rapid heat absorption, and elevated specific heat capacity from TiO₂, providing improved thermal retention. The findings demonstrate that strategic binary nanoparticle combinations with appropriate mixing ratios can overcome inherent limitations of single‐component systems, offering a practical pathway for solar thermal efficiency enhancement.