Enhanced natural convective heat transfer in a horizontal elliptic annulus using a diamond fin vortex generator and MWCNT-MgO nanofluid

Optimizing heat transfer within the annular region of concentric horizontal cylinders is critical for improving the efficiency and reliability of industrial cooling systems, particularly in waste heat recovery and thermal management applications. Conventional natural convection technologies face limitations due to the development of a stagnant conductive layer and the suppression of turbulence near the heat exchanger tube. To address this, the study introduces a novel combination of Hybrid Multi-Walled Carbon Nanotube-Magnesium Oxide (MWCNT-MgO) nanofluid with a Diamond Fin Vortex Generator, aimed at enhancing turbulence and thermal conductivity for superior convective heat transfer. Through the disruption of coolant flow, a proposed Diamond Fin Vortex Generator improves heat transfer rates by disrupting boundary layer formation and promoting turbulent mixing to prevent stagnant fluid zones. Furthermore, the cutting-edge Hybrid Multi-Walled Carbon Nanotube-magnesium oxide Nano Coolant, which combines magnesium oxide nanoparticles with multi-walled carbon nanotubes, enhances thermal conductivity and simplifies preparation by eliminating the need for surfactants, thereby reducing risks associated with corrosion and scale formation. The proposed strategy is evaluated through numerical simulations in ANSYS CFD, exploring variations in fin heights and their impact on key metrics such as heat transfer coefficient, turbulence intensity, and pressure drop. The results show that the proposed model outperforms existing designs with a 28 % higher convective heat transfer coefficient and a 10.7 % improvement over standard elliptical annuli. The Hybrid MWCNT-MgO nanofluid achieves a thermal conductivity of 0.278 kW/mK and a 15 % increase in Nusselt number. This results in a surface temperature reduction to 25.8 °C at 1000 W/m².