Aalikhani, R.Toghraie, D.Mehmandoust, B.Salahshour, S.2025-06-152025-06-1520252590-123010.1016/j.rineng.2025.1052952-s2.0-105005087720https://doi.org/10.1016/j.rineng.2025.105295This study is focused on the viscosity of mono-nanofluids (MNFs) composed of CeO<inf>2</inf>/water, MWCNT/water, and MgO/water, as well as hybrid nanofluids (HNFs) namely MgO-MWCNT/water, MgO[sbnd]CeO<inf>2</inf>/water, and CeO<inf>2</inf>−MWCNT/water. Additionally, a ternary hybrid nanofluid (THNF) of MgO[sbnd]CeO<inf>2</inf>−MWCNT/water was examined. The study encompassed temperatures ranging from 20 to 60 ℃ and solid volume fractions (SVFs) of 0.1 % and 0.3 % for MNFs and HNFs, while THNF was studied at SVFs of 0.1 %, 0.2 %, 0.3 %, 0.4 %, and 0.5 %. Post-nanofluid preparation, zeta potential and dynamic light scattering (DLS) tests were performed to confirm stability, with tests conducted at the highest SVF (SVF = 0.5 %), indicating favorable nanofluid quality. Brookfield viscometer measurements were employed to assess nanofluid viscosity. The experimental findings revealed that viscosity decreases with rising temperature at a constant SVF, while it increases with rising SVF at a constant temperature. Notably, at SVF = 0.1 % and 0.3 %, the most significant viscosity increase occurred in the water/MWCNT MNF, reaching 2.7 times that of the base fluid (BF) at SVF = 0.3 % and T = 40 ℃. For THNF, the highest viscosity increase was observed at SVF = 0.5 % and T = 50 ℃, growing approximately 1.3 times that of BF. Subsequently, a mathematical model was proposed to predict THNF viscosity, demonstrating high consistency with laboratory results. © 2025 The Author(s)eninfo:eu-repo/semantics/openAccessCeO2Dynamic ViscosityMgOMWCNTNanofluidArticle