Thermal performance of MWCNTs-Al2O3 hybrid nanofluid flow in heated tubes, entropy production, and environmental assessment

The surge in electricity generation demand has led to heightened CO₂ emissions and climate change; thus, the emphasis on transitioning to renewable energy (solar energy) and enhancing energy efficiency (hybrid nanofluids) is emerged as the most significant solutions. The investigation examines MWCNTs-Al₂O₃-water hybrid nanofluid laminar forced convection in a circular duct subject to a uniform heat flux. The effect of MWCNTs nanoparticles percentage ratio (0 to 100%), total nanoparticles volume fraction (1 to 4%), and Reynolds number (100 to 2100) on thermal and hydraulic performance, entropy generation, and CO₂ emissions, embodied energy, and water saving is investigated numerically. ANSYS Fluent was employed to solve this issue using the finite volume method; validation of the current work demonstrates strong concordance with experimental, numerical, and theoretical investigations. Outcomes show that increasing Reynolds number, total nanoparticles volume fraction, and percentage ratio of MWCNT in hybrid nanofluid significantly affects the hydrodynamic and thermal entry region in terms of average velocity, outlet temperature, and the temperature gap in the system. The heat transfer coefficient enhances by up to 50.96%. However, the maximum pressure drop, Nusselt number, and thermal efficiency increased by 769.97%, 24.75%, and 24.75%, respectively. Moreover, the entropy production due to the thermal irreversibility was reduced by 32.65% compared with water showed for 4% of (100%:0) MWCNTs-Al₂O₃–water at Reynolds number about 2100. Furthermore, the embodied energy and water consumption, tube mass, and CO₂ emissions are reduced by 1.81041 MJ, 9.00691 m³, 0.00831 kg, and 1.09892 kg, respectively.