Experimental comparison and development of thermal conductivity correlations for three types of ternary hybrid nanofluids containing CuO, Al2O3, TiO₂, SiO₂ and MWCNT nanoparticles

Ternary hybrid nanofluids (THNFs) remain less studied than mono- and binary nanofluids, and comparative data across multiple THNF formulations under a consistent framework are scarce. In this study, three THNFs, TiO 2 (75)-MWCNT(15)-SiO 2 (10)/EG-Water(15–85), TiO 2 (70)-MWCNT(15)-CuO(15)/EG-Water(10–90), and TiO 2 (80)-MWCNT(10)-Al 2 O 3 (10)/EG-Water(20–80) were synthesized via a two-step method. XRD, SEM, and TEM confirmed the crystalline structure, phase purity, and morphology of each nanoparticle, while 21-day sedimentation, density, and zeta-potential measurements verified colloidal stability. Relative thermal conductivity was measured at 26–50 °C and 0.04–1.1%. The TiO 2 (70)-MWCNT(15)-CuO(15)/EG-Water (10–90) formulation showed the highest enhancement, reaching a relative thermal conductivity of 1.42 at 50 °C and 1.1%. A cubic Response Surface Methodology correlation developed for this formulation achieved R 2 = 0.9977, with a maximum deviation below 0.9%. Price-Performance Factor (PPF) analysis identified the TiO 2 (70)-MWCNT(15)-CuO(15)/EG-Water (10–90) formulation as the most cost-effective option. These results provide new comparative thermophysical and economic data for TiO 2 –MWCNT-based THNFs.