Convective heat transfer efficacy of an experimentally observed non-Newtonian MWCNT-Fe3O4-EG hybrid nanofluid in a driven enclosure with a heated cylinder

• Published in: International journal of thermal sciences 2024-10, Vol.204, Article 109203
• Main Authors: Mahmud, Tawsif, Nag, Preetom, Molla, Md. Mamun, Saha, Suvash C.
• Format: Article
• Language: English
• Subjects: Entropy generation; Heat transfer; Heated cylinder; Hybrid nanofluid; Non-Newtonian rheology; Nusselt number
• ISSN: 1290-0729; 1778-4166
• DOI: 10.1016/j.ijthermalsci.2024.109203

This study provides an in-depth analysis of the heat transfer (HT) characteristics of a hybrid nanofluid (HNF) composed of Multi-walled carbon nanotubes (MWCNT), Iron oxide (Fe3O4), and Ethylene glycol (EG), which is loaded in an enclosure with a heated cylinder. As per the exploratory report, this HNF exhibits Newtonian and non-Newtonian behavior depending on the percentage of nano-constituents suspended in the base fluid EG. The governing equations describing the convective HNF flow associated with the boundary conditions are numerically solved using the finite volume method. The study explores the HT performance of a loaded HNF by varying the volume fractions (ϕ), the driving condition of the vertical sides, and the aspect ratio (W∗) of the enclosure. The study investigates the variation of the Richardson number (Ri=0.01∼100) concerning the interactions between shear and buoyancy forces executed on the HNF. The study finds that the combination of the lower aspect ratio W∗=2.1 filled with non-Newtonian HNF with ϕ=1.8% in the forced convection regime (Ri=0.01) and the condition of both aiding and opposing forces applied to the side walls shows superior HT performance. The non-Newtonian HNF with ϕ=1.8% shows HT enhancement of 9.27% for aiding forces and 39.63% for opposing forces when Ri=0.01, revealing ultimate enhancement in the average Nusselt number (Nuavg). The study also investigates entropy production (Savg) from a thermodynamics perspective to assess the system’s thermal performance. The value of Savg is about 11.54 for ϕ=1.8% and Ri=0.01, and that value is comparable for both aiding and opposing force conditions. Results conclude that HT consistently enhances with nanoparticle addition in the forced convection regime. However, HT enhancement is only observed for non-Newtonian cases of HNF in the natural convection regime, suggesting the limitation of the HNF usage in the HT study. Additionally, the study discusses and compares different simulation results to comprehensively evaluate the HT characteristics and the system’s thermal performance, guiding the best benefit of the studied hybrid nanofluids in a thermal engineering system.